THE EFFECT OF BAREFOOT SHOE TECHNOLOGY ON THE PERFORMANCE OF MALE RUNNERS AT DIFFERENT GRADIENTS ROBERT JONES HONOURS RESEARCH PROJECT

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1 THE EFFECT OF BAREFOOT SHOE TECHNOLOGY ON THE PERFORMANCE OF MALE RUNNERS AT DIFFERENT GRADIENTS BY ROBERT JONES HONOURS RESEARCH PROJECT Submitted in fulfilment of the requirements for the Degree Bachelor of Science (Honours) Department of Human Kinetics and Ergonomics Rhodes University, 2010 Grahamstown, South Africa

2 ABSTRACT People all around the world are regularly involved in jogging and running activities, as a result it is becoming increasingly more important to study the short and long term effects of running on the musculoskeletal system of the body. Recent research has shown that unshod running may be beneficial in terms of improvements in performance as well as decreasing the risk of running related injuries. The possible health and performance benefits associated with an unshod lifestyle have resulted in the release of modern barefoot shoe technologies onto the market. The focus of the present study was to investigate the impact of changes in gradient (uphill, level and downhill) on the biomechanical, physiological and psychophysical responses of males, to shod running and running in the Vibram Fivefingers. Participants were required to perform six experimental conditions, while running on a treadmill at a speed of 12km.h -1 for six minutes per condition. The experimental conditions consisted of running at three different gradients (-5%, 0%, +5%) while running in either standard running shoes or in the Vibram Fivefingers, the latest in barefoot shoe technology. Foot strike patterns, heart rate, oxygen consumption, energy expenditure, minute ventilation, Ratings of Perceived Exertion and body discomfort responses were collected from 12 moderately trained male runners (age: 22.33±1.83 years, mass: 74.59±10.4 kg). The experimental conditions were performed over two, hour long sessions and adequate recovery periods between each condition were provided. When running in the Vibram Fivefingers, participants adopted flatter foot strike positions than when running in standard running shoes. Statistical significance (p<0.05) was found between the uphill, level and downhill gradients for both the shod and Vibram Fivefinger conditions for the physiological and psychophysical responses elicited. The largest responses were elicited from the uphill gradient, followed by the level gradient, and finally the downhill gradient. Although many of the physiological and psychophysical responses collected during experimental conditions were found to be lower at all three gradients during the Vibram Fivefinger conditions, these differences were not statistically significant. Due to alterations in gradient and foot i

3 strike patterns, differences in body discomfort were experienced due to altered muscle activation patterns. These findings indicate that changes in gradient have a significant effect on the various responses of male runners. It can be suggested that the habitual use of the Vibram Fivefingers results in changes to the biomechanical, physiological and psychophysical responses of male runners. These changes may be beneficial in improving running performance as well as decreasing the risk of running related injuries. Further research is required to accurately determine the extent to which these changes occur, as well as to establish the possible benefits associated with the habitual use of the Vibram Fivefingers. ii

4 ACKNOWLEDGEMENTS I would like to acknowledge and thank the following people for their encouragement and support in conducting this study: Firstly to my supervisor Mr. Andrew Todd for his tireless efforts, insight, guidance, and positive reinforcement that has continued to inspire me to strive for academic excellence. To my classmates, Kim Stephenson and David Goble for their contribution in assisting with the tireless hours of data collection. To my subjects, for so willingly and enthusiastically taking the time to participate in this project. Finally, I would like to express my love and gratitude to my parents for the support and encouragement they have given me over the last 22 years. iii

5 TABLE OF CONTENTS CHAPTER I: INTRODUCTION... 1 BACKGROUND TO THE STUDY... 1 STATEMENT OF THE PROBLEM... 2 RESEARCH HYPOTHESIS... 3 STATISTICAL HYPOTHESIS... 3 DELIMITATIONS... 4 LIMITATIONS... 5 CHAPTER II: REVIEW OF LITERATURE... 7 INTRODUCTION... 7 WALKING VERSUS RUNNING... 8 FOOT STRIKE PATTERNS ENERGY COST OF RUNNING EFFECT OF GRADIENT RUNNING RELATED INJURIES Acute injury Chronic injury THE VIBRAM FIVEFINGERS (Vibram ) UNSHOD VERSUS RUNNING IN NORMAL RUNNING SHOES UNSHOD VERSUS VIBRAM FIVEFINGERS SHOD VERSUS THE VIBRAM FIVEFINGERS INFLUENCE OF FOOTWEAR ON RUNNING KINETICS AND KINEMATICS CHAPTER III: METHODOLOGY INTRODUCTION PILOT TEST PROTOCOL Speed selection Gradient selection EXPERIMENTAL DESIGN MEASUREMENT AND EQUIPMENT iv

6 Anthropometrical measurements Physiological measurements Psychophysical measurements Other equipment EXPERIMENTAL PROCEDURES Session Session Session ETHICAL CONSIDERATIONS SUBJECT CHARACTERISTICS STATISTICAL PROCEDURES CHAPTER IV: RESULTS INTRODUCTION BIOMECHANICAL DATA Foot strike patterns PHYSIOLOGICAL DATA Heart rate Oxygen consumption (VO 2 ) Energy Expenditure Minute ventilation (V E ) PSYCHOPHYSICAL DATA Ratings of Perceived Exertion (RPE) Body discomfort CHAPTER V: DISCUSSION INTRODUCTION BIOMECHANICAL DATA Foot strike patterns PHYSIOLOGICAL DATA Heart rate Oxygen consumption (VO 2 ) and energy expenditure Minute ventilation (V E ) v

7 PSYCHOPHYSICAL DATA Ratings of Perceived Exertion (RPE) Body discomfort CHAPTER VI: SUMMARY, CONCLUSIONS AND RECOMMENDATIONS INTRODUCTION SUMMARY OF PROCEDURES SUMMARY OF RESULTS Foot strike patterns Heart rate Oxygen consumption and energy expenditure Minute Ventilation Ratings of Perceived Exertion Body discomfort HYPOTHESES CONCLUSIONS RECOMMENDATIONS REFERENCES APPENDICES APPENDIX A: GENERAL INFORMATION Letter to the subject Do s and don ts Informed consent form Administrators protocol explanation Administrator s checklist APPENDIX B: DATA COLLECTION Condition randomisation Data sheet Data sheet 2 and vi

8 LIST OF TABLES TABLE PAGE I Design matrix of experimental conditions 29 II Descriptive characteristics of participants (n=12) 40 III Observed foot strike patterns 41 IV Impact of footwear and gradient on mean heart rate 44 V Impact of footwear and gradient on mean oxygen consumption 45 VI Impact of footwear and gradient on mean energy expenditure 47 VII Impact of footwear and gradient on mean minute ventilation 47 VIII Impact of footwear and gradient on mean RPE 49 IX Impact of footwear and gradient on ratings of body discomfort 50 vii

9 LIST OF FIGURES FIGURE PAGE 1 Walking and running gait cycle (adapted from Novacheck, 1998). 8 2 The relationship between potential and kinetic energy during (adapted from Novacheck, 1998). 3 Vertical ground reaction forces and foot kinematics for three running foot strike patterns (adapted from Lieberman et al., 2010). 4 The energy expenditure during walking and running (adapted from Novacheck, 1998). 5 Vertical and parallel ground reaction forces for level running (adapted from Gottschall et al., 2004). 6 The Vibram Fivefingers. 7 The Quark b 2. 8 Ratings of Perceived Exertion Scale (adapted from Borg, 1970). 9 Body Discomfort Scale and Map (adapted from Corlett et al., 1976). 10 Foot strike patterns observed. 11 Heart rate responses measured during experimental conditions testing. 12 Energy expenditure responses measured during experimental conditions testing. 13 Minute ventilation responses measured during experimental conditions testing. 14 The observed foot strike patterns adopted by participants Mean physiological responses of participants during experimental conditions testing 56 viii

10 16 Mean running economy of participants during experimental conditions testing 58 ix

11 CHAPTER I INTRODUCTION BACKGROUND TO THE STUDY As millions of people all around the world are regularly involved in jogging and running activities, it is becoming increasingly more important to study the short and long term effects of running on the musculoskeletal system of the body (Squadrone et al., 2009). The highly repetitive nature of running and the large impact forces transferred through the soft tissues of the body lead to high incidences of injuries such as; ankle sprains, shin splints, iliotibial band syndrome, and peri patellar pain (Siff et al., 1999). According to Novacheck (1998), each year between a quarter and half of runners will sustain an injury that is severe enough to affect practice or performance. A key factor associated with running and the development of running related injuries are the ground reaction forces generated the moment the foot comes into contact with the ground (Lieberman et al., 2010). Recent research has shown that running unshod opposed to shod has an impact on the ground reaction forces generated while running (Squadrone et al., 2009; Lieberman et al., 2010). Where habitually unshod runners often land on the forefoot or midfoot, habitually shod runners tend to rear foot strike. The analysis of shod versus unshod running shows that unshod running generates smaller collision forces than shod running (Lieberman et al., 2010). Therefore, it is suggested that forefoot and midfoot running gaits protect the feet and lower limbs from some of the impact related injuries experienced by a large percentage of runners (Warburton, 2001; Lieberman et al., 2010). Various authors also suggest that an unshod lifestyle, training, as well as performing unshod in competitions may have positive effects regarding running economy and ultimately performance (Flaherty, 1994; Wallden, 2009; Squadrone et al., 2009; Lieberman et al., 2010). Over the last decade there has been a large dearth in well designed research regarding the positive and negative effects of shod and unshod running on injury and performance (Warburton, 2001). The possible health and performance benefits associated with an unshod lifestyle resulted in the release of the modern barefoot shoe technologies onto the market (Wallden, 2009). Products such as the Vibram 1

12 Fivefingers have attracted increased interest from trainers, athletes and researchers from around the world (Squadrone et al., 2009). As a result, a handful of studies aimed at testing the benefits of unshod running, as well as the claims of the product manufacturers have been carried out. The findings of these studies suggests that habitual unshod running is linked with lower injury rates and increased running economy when compared to habitual shod running (Flaherty, 1994; Wallden, 2009; Squadrone et al., 2009; Lieberman et al., 2010). However, no research has been carried out regarding the effect of different gradients on running economy and other physiological and biomechanical responses, while testing both shod and barefoot shoe technology conditions. Such research is of importance as runners typically encounter changes in gradient in most geographical locations (Gottschall et al., 2004). According to Gottschall et al. (2005), changes in gradient affect the gait patterns adopted by athletes. When running downhill runners generally adopt a rearfoot striking gait pattern, resulting in increased ground reaction forces acting on the body (Minetti et al., 1994). In contrast, runners generally adopt a midfoot or forefoot striking pattern when running at an uphill gradient (Minetti et al., 1994). Uphill running is also associated with larger metabolic costs, increased propulsive forces, decreased breaking forces, and increased muscle activity when compared to downhill running (Minetti et al., 2002). However, there is a greater risk of musculoskeletal injury associated with downhill running due to the rearfoot striking pattern adopted by runners (Gottschall et al., 2004). Therefore, the current research aims to highlight the differences between running at various gradients, as well as to determine if the physiological and mechanical differences associated with shod gradient running persist in barefoot shoe technology conditions. STATEMENT OF THE PROBLEM The majority of studies that have investigated shod and unshod conditions have focused predominantly on the comparisons of ground reaction forces between running in normal running shoes and running barefoot. The limited research regarding experimentation with the Vibram Fivefingers has focused on the energy expenditure and other physiological responses while running at a level (0%) gradient. The impact of gradient on the biomechanical, physiological and 2

13 psychophysical responses to shod and unshod conditions remains poorly understood. Therefore, the purpose of the current research was to investigate the impact of changes in gradient (uphill, level, and downhill) on the biomechanical, physiological and psychophysical responses to shod running and running in the Vibram Fivefingers. RESEARCH HYPOTHESIS Firstly, it was hypothesised that running in the Vibram Fivefingers will result in lower energy expenditure (VO 2 ), lower heart rate responses (HR), lower ratings of perceived exertion with regards to musculature (RPE) at all gradients than during the shod conditions. Secondly, it was hypothesised that running at a downhill gradient (-5%) will result in the lowest energy expenditure, lowest heart rate, and lowest ratings of perceived muscular exertion. While running at an uphill gradient (+5%) will result in the highest energy expenditure, highest heart rate, and highest ratings of perceived muscular exertion. STATISTICAL HYPOTHESIS Hypothesis 1: The null hypothesis proposed that there will be no difference in the physiological responses (oxygen consumption, heart rate, minute ventilation), and psychophysical responses (RPE) between the Vibram Fivefingers and normal running shoes at all gradients. Ho: µ Shod (-5%, level, +5%) = µ Vibram Fivefingers (-5%, level, +5%) Ha: µ Shod (-5%, level, +5%) µ Vibram Fivefingers (-5%, level, +5%) Where: µ= physiological and psychophysical responses -5%, level, +5% = percentage gradient Shod= standard running shoes 3

14 Hypothesis 2: The null hypothesis proposed that there will be no difference in the physiological responses (oxygen consumption, energy expenditure, heart rate, minute ventilation), and psychophysical responses (RPE) between the -5%, level, and +5% gradients with regards to the Vibram Fivefingers and normal running shoes. Ho: µ -5% (Vibram+ Shod) = µ Level (Vibram+ Shod) = µ 5% (Vibram+ Shod) Ha: µ -5% (Vibram+ Shod) µ Level (Vibram+ Shod) µ 5% (Vibram+ Shod) Where: µ= physiological and psychophysical responses -5%, level, +5% = percentage gradient Vibram + Shod= Vibram Fivefingers and standard running shoes DELIMITATIONS All participants who volunteered for this study were drawn from the male population of Rhodes University students. The 12 participants, aged between 18 and 25, were all habitual runners who run at least 15km per week. Prior to experimentation, self reports indicated that subjects were free from illness or injury, specifically relating to the lower limbs. Each subject attended three sessions in the Human Kinetics and Ergonomics Department, Rhodes University, Grahamstown. During the first session, the experimental procedures were explained to each subject, both verbally and in a letter of information. Once the procedures were explained and any subject queries had been dealt with, each subject was required to sign an informed consent form. The subjects were then familiarised with the necessary equipment and anthropometric data were obtained. Each subject was then fitted with a Polar Heart Rate monitor telemetry strap and a face mask, and habituated to treadmill running at downhill, uphill and level gradients. Subjects were provided with standardised instructions on how to perform each protocol, which included a self selected warm up routine, running at a speed of 12km.h -1 in either the Vibram Fivefingers or normal running shoes, and at gradients of -5%, level, and +5%. Subjects performed three conditions each in the following two sessions. Each condition lasted six minutes and was followed by a four minute rest before beginning the next condition. Experimentation occurred under controlled 4

15 laboratory conditions, negating the effect of environmental factors and allowing the standardisation of methodological parameters. Data collected from each subject was that of; foot strike patterns through the use of a Sony Handycam, heart rate through the use of a Polar Heart Rate telemetry strap and the Quark b 2, oxygen consumption through the use of a Quark b 2 ergospirometer, muscular ratings of perceived exertion through the use of a Borg scale (Borg, 1970), and Body Discomfort ratings through the use of a Body Discomfort Scale and Map (Corlett et al., 1976). LIMITATIONS Despite efforts to rigorously control extraneous variables from affecting the reliability of measures, it is impossible to control all impinging influences. Therefore, when examining the implications and conclusions from the results, one must consider the following limitations. Time restraints restricted the sample size to only 12 Rhodes University students. Studying a larger sample of people over a larger geographical area would have allowed greater generality of the findings and a stronger statistical significance. Subjects were instructed to avoid alcohol, food and drink prior to testing as these substances may alter the responses obtained during testing, thus reducing the validity of the results. During this study however, adherence to these conditions was dependant on the cooperation of the subject, and thus could not be guaranteed. The theoretical concept of rating perceived muscular exertion and body discomfort was explained to the subject during the initial session, however as this measure is subjective and a perceived rating is obtained, the value of the collected data is questionable. Although this investigation simulated the demands placed on an individual during outdoor running, experimentation occurred in a controlled laboratory setting on a treadmill. Therefore, environmental conditions such as humidity and wind resistance differed significantly from the dynamic conditions experienced outdoors, which may compromise this studies external validity. 5

16 Furthermore, the test conditions were significantly shorter in duration compared to those experienced during normal or endurance running, thereby limiting the extrapolation of the subjects responses to longer durations. The controlled speed at which the subjects were required to perform at further added to the limitations of this study. As this speed does not consider the implications of self selected speeds or pacing strategies which athletes may adopt. 6

17 CHAPTER II: REVIEW OF LITERATURE INTRODUCTION Running has evolved from an activity that was critical for day to day survival to one that is considered important for overall fitness and longevity. As a consequence, people around the world are routinely involved in jogging and running activities (Squadrone et al., 2009). Humans have engaged in running for millions of years, but the modern running shoe was only invented in the 1970s (Bramble et al., 2004). Human evolutionary history shows that runners were either unshod or wore minimal footwear with small heels and little cushioning compared to modern running shoes up until this date (Lieberman et al., 2010). According to Lieberman et al. (2010), running is most injurious at the moment the foot collides with the ground. As a result, modern running shoes are fitted with a large, cushioned heel component which attempts to reduce the impact and the subsequent forces resulting from the collision between the foot and the ground (Morio et al., 2009). The average runner s foot strikes the ground approximately 600 times per kilometre (Milner et al., 2006; van Gent et al., 2007). Due to the highly repetitive nature of running, runners are prone to numerous repetitive stress injuries (Lieberman et al., 2010). These athletes are at risk of incurring acute injuries such as ankle sprains, as well as developing chronic running injuries such as plantar fasciitis (Warburton, 2001). These chronic injuries occur as a result of continuous and long term exposure to the harmful forces associated with running on unnatural surfaces (Robbins et al., 1995). However, recent research suggests that footwear increases the risk of both acute and chronic injury (Zipfel et al., 2007). As a result, the study of the foot offers the opportunity to consider factors which are both beneficial as well as injurious to the musculoskeletal system (Warburton, 2001). Many published papers support the claims that unshod running is healthy and natural, and that footwear is entirely unnecessary and in many cases detrimental to foot health (Robbins et al., 1987; Clement et al., 1981; Siff et al., 1999). As a result, barefoot training is being used by various trainers and athletes as it is suggested that an unshod lifestyle may result in overall improvements in the musculoskeletal system 7

18 and trains the muscles of the foot (Bruggermann et al., 2005). Recent research (Flaherty, 1994; Squadrone et al., 2009; Wallden, 2009) also suggests that unshod running may also have performance benefits as it results in improvements in running economy. Unfortunately, the bare foot is at risk of injury such as cuts, bruises and puncture wounds, even when the plantar surface is thickened due to barefoot adaptation (Squadrone et al., 2009). As a result the concept of functional footwear and barefoot shoe technology has emerged as shoe manufacturers attempt to produce a product which mimics unshod running while providing a layer of protection to the foot (Wallden 2009). WALKING VERSUS RUNNING According to Novacheck (1998), the discrimination between walking and running occurs when continuous periods of double support (both feet in contact with the ground at the same time) during the stance phase of the gait cycle give way to two periods of double float (neither foot is in contact with the ground) at the beginning and the end of the swing phase of the gait cycle (Figure 1). Figure 1: Walking and running gait cycle (IC= initial contact, LR= loading response, TO= toe off, MS= mid stance, TS= terminal stance, PS= pre swing, IS= initial swing, MS= mid swing, TS= terminal swing, StR= stance phase reversal, SwR= swing phase reversal) (adapted from Novacheck, 1998:79). 8

19 When speed is increased and a running gait is adopted, initial contact with the ground changes from a position on the hindfoot to a position on the forefoot. The gait cycle begins when one foot makes contact with the ground and ends when the same foot makes contact with the ground again. This collision between the foot and the ground is referred to as initial contact (Gage, 1990). The stance phase of the gait cycle ends when the foot is no longer in contact with the ground. Toe off characterises the beginning of the swing phase of the gait cycle. When walking, the stance phase is longer than 50% of the gait cycle, therefore two periods of double support exist (Novacheck, 1998). When running, toe off occurs before 50% of the gait cycle is complete. Instead of two periods of double support, both feet are airborne twice during the gait cycle (Ounpuu, 1990; Novacheck, 1995). Novacheck (1998) states that alternate periods of acceleration and deceleration occur during running, referred to as phases of absorption and generation (Figure 1). During the period of absorption, the centre of mass of a body falls from its peak height. Following its drop in height, the centre of mass is the propelled upwards and forwards during the generation phase (Novacheck, 1995; Novacheck, 1998). Walking and running are critically different from each other in the mechanics employed during each gait (Novacheck, 1998; McArdle et al., 2007). When an individual is walking, potential and kinetic energy are out of phase with each other (Figure 2). When kinetic energy is high, potential energy is low, and vice versa (Novacheck, 1998). Walking makes use of an inverted pendulum model, effectively cycling potential and kinetic energy out of phase with each step (Lieberman et al., 2004). Within this model, the centre of mass (COM) of an individual pivots over a relatively extended leg during the stance phase (Steudel- Numbers et al., 2007). Efficiency in walking is related to the finely tuned system of storage and recovery of the energy used for motion within each stride (Carrier et al., 1984). The energy cost of human walking is represented by a U shaped curve. The optimal speed of walking for humans is approximately 1.3 m.s -1, and is largely a function of relative leg length (Steudel- Numbers et al., 2007 and Bramble et al., 2004). Typically, humans change from walking to running at ± m.s -1. At these increased speeds, running becomes far more energetically efficient than walking (Lieberman et al., 2004). When an individual is running, potential and kinetic energy are in phase with each other (Figure 2). When kinetic energy is high, potential energy is high and vice 9

20 versa (Novacheck, 1998). Running therefore exploits a mass spring system which exchanges kinetic energy and potential energy very differently to walking. The human legs contain collagen rich soft tissues such as ligaments and tendons which store elastic energy during the initial foot strike of the support phase of running. These springs then releasee their stored energy by recoiling during propulsive phases (Lieberman et al.., 2004). The effective use of these springs relies on a more flexed, or compliant, limb than in walking (Carrier et al., 1984; Lieberman et al., 2004; Steudel- Numbers et al., 2007). During running, kinetic and potential energy peak in midswing (Novacheck, 1998). As the centre of mass falls toward the ground, potential energy is lost. Whereas, when the foot comes into contact with the ground, kinetic energy is lost. Most of the lost energy is converted into elastic potential energy and stored in the soft tissues of the body. During the generation phase the body s centre of mass accelerates upwards, causing an increase in both kinetic and potential energy. This movement in the centre of mass is facilitated by the active contraction n of muscles as welll as the releasee of stored elastic potential energy (Carrier et al., 1984; Novacheck, 1998; Lieberman et al., 2004; Steudel- Numbers et al.., 2007). Figure 2: The relationship between potential and kinetic energy during; a. walking and b. running (adapted from Novacheck, 1998:88) FOOT STRIKE PATTERNS According to Lieberman et al. (2010), running is most injurious at the moment the foot collides with the ground. The collision between the foot and the ground can occur in three ways; forefoot striking (FFS), midfoot striking (MFS) and rearfoot 10

21 striking (RFS). When an individual adopts a FFS gait pattern (Figure 3a) the ball of the foot lands before the heel lowers. This impact occurs towards the front of the foot, causing the ankle to dorsiflex as the heel lowers to the ground. The ground reaction forces therefore torque the foot around the ankle, converting the limb s translational energy into rotation (Lieberman et al., 2010). During MFS, the ball of the foot and the heel land simultaneously. During RFS (Figure 3b) the heel comes into contact with the ground first (Lieberman et al., 2010). This impact occurs just below the ankle, under the centre of mass of the foot and the leg. Due to this, the ankle converts little translational energy into rotation and most of the translational energy is lost (Lieberman et al., 2010). a c Figure 3: Vertical ground reaction forces and foot kinematics for three running foot strike patterns. a, unshod FFS; b, shod RFS; c, unshod RFS (adapted from Lieberman et al., 2010;532). 11

22 It is suggested that 75-80% of all shod runners adopt a RFS pattern (Kerr et al., 1983; Hasegawa et al., 2007). Lieberman et al. (2010) states that runners who adopt a RFS pattern must repeatedly cope with impact transients approximately times their body weight, within a collision time of 50ms. The impact transients generated when RFS running are sudden forces with high rates and magnitudes of loading which travel up the body, and through the tissues. These impact transients are thus believed to contribute to the high incidence of running related injuries (Milner et al., 2006; van Gent et al., 2007). The heel pad of the human foot attempts to cushion the impact transient but does so poorly (Ker et al., 1989; De Clercq et al., 1994; Chi et al., 2005). Therefore, modern running shoes are designed with a large cushioned heel made of elastic materials, which make RFS running less demanding and less injurious. The large heel aims to absorb some of the impact transient, allowing the force to act over a larger surface area and spreads the impulse over a longer period of contact time (Nigg et al., 1986). A study by Lieberman et al. (2010) compared foot strike kinematics among both habitually shod and habitually unshod runners. The findings from this particular study were as follows: Habitually shod runners predominantly adopt a RFS gait pattern when shod, and also adopt a RFS pattern when unshod, however, with a slightly flatter foot position. Habitually unshod runners predominantly adopt a MFS or FFS gait pattern when running both shod and unshod, and infrequently adopt a RFS pattern when running unshod. According to Lieberman et al. (2010), the major contributing factor to the predominance of the RFS pattern in shod runners is the large, cushioned heel of most modern running shoes. Running shoes with a raised and cushioned heel facilitate RFS running and making it a more comfortable foot striking pattern to adopt. Differences in foot striking patterns, namely; FFS, MFS and RFS generate different collision forces at the moment the foot comes into contact with the ground. A RFS pattern generates large impact transients in shod runners (Figure 3b) and noticeably larger impact transients in unshod runners (Figure 3c). A FFS or MFS gait pattern generates ground reaction forces that are lacking distinct impact transient (Figure 3a). At constant speeds, the magnitude of peak vertical force during the impact between the foot and the ground are approximately three times lower in habitually barefoot runners who FFS than in RFS in either the shod or unshod conditions. The average rate of loading in individuals adopting a unshod FFS 12

23 pattern is seven times lower than in habitually shod runners who RFS when unshod, and is similar to the rate of loading of shod RFS pattern runners. In the majority of unshod FFS pattern runners, the rates of loading were in the region of half those of shod RFS pattern runners. ENERGY COST OF RUNNING One of the most pertinent determining factors of the manner in which we as humans move is to minimise energy expenditure, and thus improve energy efficiency (Novacheck, 1998). The energy requirements of walking reveals a U shaped relationship between economy and speed (Figure 4). However, no such relationship occurs for running speed and economy. Oxygen consumption is said to change little over a range of selected running speeds and is represented by a linear relationship (Cavanagh et al., 1982). Factors which are said to affect running economy are; stature, mass, feet size, somatotype, leg morphology, stride length and frequency, arm movement, knee angle, and vertical centre of mass oscillations (Anderson, 1996). Figure 4: The energy expenditure during walking and running (adapted from Novacheck, 1998:90). 13

24 Burkett et al. (1985) found that oxygen consumption during running increased as the amount of mass added to the foot increased. Shoes representing 1% of body mass were said to increase oxygen consumption by approximately 3.1%. In a study by Flaherty (1994) it was found that when running at 12km.h -1, oxygen consumption was 4.7% higher in shoes of mass 700g per pair when compared to bare feet. Similarly, Wallden (2009) established that shod running is approximately 2-3% less efficient in terms of oxygen consumption, when compared to unshod running. Finally, a study by Squadrone et al. (2009) showed that unshod running decreases the oxygen consumption (VO 2 ) by 1.3% compared to shod running. The differences found by Squadrone et al. (2009) in oxygen consumption when comparing a shod to an unshod condition were not found to be statistically different, and were lower than previously found. The increase in oxygen consumption when running with shoes could have many possible causes. One possibility that must be considered is the energy cost of accelerating and decelerating the additional mass of the shoe continually while running (Warburton, 2001; Wallden, 2009). Alterations in foot strike kinematics may also have an important effect on oxygen consumption. This is as MFS and FFS gait patterns allows for the limb s translational energy to be converted into rotation, resulting in lower energy expenditure (Lieberman et al., 2010). Another possibility is the extra external work that is carried out by compressing and flexing the large sole of standard running shoes, and in rotating this sole against the ground (Warburton, 2001). In 1986, Frederick reported that oxygen consumption increased substantially as sole thickness was increased during treadmill running. This is due to the materials used to form the cushioning in shoes continually absorbing energy (Stefanyshyn et al., 2000). Lastly, Shoes compromise the ability of the lower limbs to act like a spring, returning energy stored in their soft tissues. When unshod, the limb returns ±70% of the energy stored in it, this energy return is far less when running in shoes (Yessis, 2000). An increase in oxygen consumption of approximately 4% is of little importance to a recreational runner, however to a competitive athlete a 1-2% decrease in oxygen consumption has a major effect on running speed and overall performance (Warburton, 2001). 14

25 EFFECT OF GRADIENT In most geographical locations, runners encounter changes in gradient, however there is little information available regarding ground reaction forces for running on inclines and declines (Gottschall et al., 2004). As a result the understanding of biomechanical characteristics of hill running is limited. Many researches such as Cavanagh (1980) and Munro et al. (1987) have measured and quantified ground reaction forces on a level, but limited research has been aimed at the ground reaction forces and gait patterns associated with running at different gradients (Gottschall et al., 2004). The absence of data for hill running is most likely due to difficulty in the use of a force platform runway on an angle (Iversen et al., 1992). Figure 5: The a. vertical (normal) and b. parallel ground reaction forces for level running (adapted from Gottschall et al., 2004:446). Dick et al. (1987) found that during downhill running, the vertical impact force peak increased by 14%, the vertical active force peak did not change, and the parallel breaking impulses increased by 200% when compared to level running (Figure 5). A study by Iversen et al. (1992) showed that the normal active force peak was 2% larger during downhill running and 11% smaller during uphill running, contradicting earlier research. The above studies failed to quantify both the vertical and parallel 15

26 ground reaction forces for a range of differing gradients. Furthermore, there is an element of inconsistency between the findings of the studies (Gottschall et al., 2004). A study by Gottschall et al. (2004) aimed to quantify the ground reaction forces during uphill and downhill running. From this study, it was found that when compared to level running, the normal impact force peaks were considerably larger for downhill running and smaller for uphill running. The obtained results were somewhat due to a change in the foot strike patterns which the runners chose to adopt when running at the different gradients. When running at gradients of -9º, -6º and -3º downhill, on a level, and +3º uphill, all participants adopted a RFS pattern. However, when running at an uphill gradient of +6º, 33% of subjects adopted a MFS gait pattern. Finally, at a +9º uphill gradient, all subjects adopted a MFS pattern. According to Gottschall et al. (2004), the normal impact loading rates were higher for downhill and reduced for uphill running, the normal active force peaks did not significantly change during uphill or downhill running, and the parallel breaking force peaks were larger for downhill running and smaller for uphill running. Whereas few authors have attempted to quantify the ground reaction forces while running at a range of gradients, many studies have been carried out which have focused on the physiological responses to running at various gradients. Research by Minetti et al. (1994), Minetti et al. (2002), and Lin et al. (2009) focused specifically on the physiological responses associated with gradient running. Responses such as heart rate, oxygen consumption, energy expenditure and minute ventilation were measured in order to assess the effect of changes in gradient on these physiological responses while running. From the above studies it was concluded that as running gradient is increased, the above physiological responses also increase. However it was suggested that as the downhill gradient is increased, the physiological responses also increase (Lin et al., 2009). Typically, when running uphill; runners adopt a MFS or FFS gait pattern, there is an increase in metabolic cost due to increased propulsive forces, smaller breaking forces required, an increase in stride rate and a decrease in stride length (Gottschall et al., 2004). When running downhill; runners adopt a RFS gait pattern, there is a lower metabolic cost, large impact forces due to increased breaking forces, small propulsive forces are required, an increase in stride length and a decrease in stride 16

27 rate (Gottschall et al., 2004). The normal impact force peak data suggests that there is a greater probability of musculoskeletal injury during downhill running, and a reduced chance of such injuries during uphill running (Hrelijac et al., 2000). The vertical impact forces coupled with a RFS gait pattern therefore result in a higher incidence of injury occurring during downhill running (Clement et al., 1981; Grimston et al., 1994; Gottschall et al., 2004). RUNNING RELATED INJURIES The average runner s foot strikes the ground approximately 600 times per kilometre (Milner et al., 2006; van Gent et al., 2007). Due to the highly repetitive nature of running, runners are prone to numerous repetitive stress injuries (Lieberman et al., 2010). According to Robbins et al. (1987), where shod and unshod populations coexist, injury rates of the lower extremities are substantially higher in the shod populations. In addition, running related chronic injuries to bone and soft tissues in the legs are rare in developing countries, where large portions of the population are habitually unshod (Robbins et al., 1987). When shod and unshod populations are compared, there is research confirming that in the unshod populations there is a lower prevalence of many of the common running injuries, including; ankle sprains, shin splints, Achilles tendinopathy, plantar fasciitis, iliotibial band syndrome, peri patella pain and back pain (Rao et al., 1992; Warburton, 2001; Mauch et al., 2008). This association between wearing shoes and injury is consistent with the possibility that wearing shoes increases the risk of injury (Warburton, 2001). Cushioned heeled running shoes are comfortable and make it easier for runners to adopt a RFS gait pattern. However, standard running shoes limit proprioception (Lieberman et al., 2010). Moreover, most running shoes have arch supports and stiffened soles that may lead to weaker foot muscles and reduced arch strength (Lieberman et al., 2010). Two types of running related injuries exist which effect both elite and non elite runners, namely acute and chronic injuries. Acute injury Acute running injuries result from an accident occurring during running (Warburton, 2001). According to Robbins et al. (1987), ankle sprains are the most frequently reported acute sports injury % of these ankle sprains involve inversion 17

28 injuries, causing damage to the anterior talofibular ligament and the calcaneofibular ligament (Robbins et al., 1995; Stacoff et al., 1996). Siff et al. (1999) reported that running shoes reduce proprioceptive and tactile sensitivity, effecting balance and spatial orientation detection. Footwear increases the chance of ankle sprains either by decreasing awareness of foot position provided by feedback from mechanoreceptors in contact with the ground (Robbins et al., 1995), or by increasing the leverage arm and as a result the torque around the subtalar joint during a stumble (Stacoff et al., 1996). The skin on the plantar surface of the foot is far more resistant to the injurious effects of inflammation resulting from abrasion than other parts of the human body (Robbins et al., 1993; Squadrone et al., 2009). However, the available surfaces in developed countries, and particularly developing countries, are not always suited for unshod running (Squadrone et al., 2009). Pieces of glass, nails, stones or needles can cause puncture wounds or bruising even when the plantar skin is thickened by adaptation to unshod running (Robbins et al., 1995; Warburton, 2001; Squadrone et al., 2009). Temperature extremes may also lead to discomfort, blisters or chill blains (Warburton, 2001). Therefore, running shoes offer protection to the runner on some courses and in extreme weather conditions (Warburton, 2001). Chronic injury Chronic injuries occur as a result of continual exposure to the repetitive nature of running (Warburton, 2001). According to Warburton (2001) and Lieberman et al. (2010), the most common of all chronic injuries in runners is planter fasciitis, an inflammation of the ligament running along the sole of the foot. Robbins et al. (1987) states that there is evidence that the normally unyielding plantar fascia acts as the support for the medial longitudinal arch, and that continuous strain on the proximal fascial attachment during initial contact leads to plantar fasciitis. Barefoot running may induce an adaptation that transfers the impact of initial contact with the ground to the more yielding musculature, thus reducing the strain placed on the fascia and reducing the incidence of chronic injury in the unshod populations (Robbins et al., 1987). Lieberman et al. (2010) suggests that it is the design of the shoes themselves that may lead to weaker muscles in the foot and a reduction in arch strength. These structural changes then results in excessive pronation, placing greater demands on 18

29 the plantar fascia, ultimately leading to plantar fasciitis. Other chronic injuries such as shin splints, iliotibial band syndrome and peri patella pain are associated with excessive supination, pronation, and shock loading of the limbs (Siff et al., 1999). When running unshod on hard surfaces, the runner adopts a FFS or MFS pattern in order to compensate for the lack of cushioning underfoot, thus increasing the work of the soft tissues in the lower limbs (Frederick, 1986). Thereby increasing the strength of the soft tissues in the lower limb and reducing the risk of injury (Yessis, 2000). The modern running shoe generally reduces sensory feedback, apparently without decreasing an individual s chance of injury (Robbins et al., 1991). The resulting false sense of security may contribute to an increased risk of injury (Robbins et al., 1991). The measurement of the vertical component of the ground reaction forces generated while running provide no evidence that running shoes reduce the shock waves which the body is repeatedly subjected to (Robbins et al., 1990). However, Lieberman et al. (2010) suggests that standard running shoes reduce the impact forces repeatedly generated when running with a RFS gait pattern, however not to an extent where they are completely dissipated. A lesser, thinner cushioned shoe allows for increased plantar discomfort to be sensed and moderated, termed shock setting by Robbins et al. (1987). Running shoes with larger, thicker cushioning reportedly provokes a marked reduction in shock moderating behaviour, resulting in greater impact forces (Robbins et al., 1987; Robbins et al., 1989; Robbins et al., 1990). Other common features of athletic shoes such as arch supports and orthotics may interfere with the body s natural shock moderating behaviour (Robbins et al., 1987). In addition, the above features are also said to reduce pronation and supination or provide the athlete with arch support (Warburton, 2001). Although this may be beneficial for individuals with foot pathologies, their benefit is uncertain for runners with healthy feet (Yessis, 2000). Yessis (2000) also reasoned that once the natural structures of the foot are weakened by long term shoe use, individuals must then rely on the external support provided by the footwear, but the provided support does not match the natural support of a healthy unshod foot. A study by Zipfel et al. (2007) focused on the emergence of forefoot pathologies in modern humans from both a shod and unshod populations. Their findings suggested that the unshod lifestyle was associated with a lower frequency of osteological modifications (changes to the skeletal system as a result of bone remodelling due to stress). The influence of a 19

30 modern lifestyle including the use of footwear appears to have a negative effect on overall foot functioning, potentially resulting in an increasee in pathological changes to the structure of the foot (Zipfel et al., 2007). THE VIBRAM FIVEFINGERS (Vibram ) The Vibram Fivefingers (Figure 6) are a very lightweigh shoe with a thin, durable sole and separated toe compartments, designed to mimic the experience of running barefoot while providing a layer of protection (Squadrone et al., 2009; Wallden, 2009). The idea behind the design for the Vibram Fivefingers was to create a shoe that mimicked the sensation of being barefoot on a sailing boat with the grip and protection of a Vibram sole (Wallden, 2009). However, according to Wallden (2009), when the Vibram Fivefingers were released onto the market in 2006, it became clear that they were attracting attention from areas other than the intended sailing market. Yoga and pilates instructors, physical therapists, podiatrists, strength and conditioning coaches, and running coaches showed a keen interest in the product (Wallden, 2009). Figure 6: The Vibram Fivefingers 20

31 A study by Squadrone et al. (2009) focused on comparing the biomechanical effects of two shod running conditions and an unshod condition. The subjects consisted of habitually unshod runners who were required to run on an instrumented treadmill on three separate occasions. The three conditions the subjects were required to carry out included; running in normal running shoes, running in the Vibram Fivefingers, and finally running barefoot. The results from the study are as follows: Unshod versus running in normal running shoes Contact time was significantly lower while stride frequency was significantly higher in the unshod condition when compared to the shod condition, results similar to De Wit et al. (2000) and Divert et al. (2005). Significantly lower peak vertical impact forces observed while running unshod supports the hypothesis that the above changes in stride kinematics help to limit the larger impact forces experienced in running unshod and that should be absorbed by the soft tissues of the lower limbs during running. In the study, unshod running elicited a 1.3% decrease in energy cost. The lower energy requirements were not statistically significant and were lower than previously discovered. The absence of a significant difference may be explained by changes in running behaviour such as foot strike patterns, as well as the relatively low speeds at which the tests were carried out. Unshod versus Vibram Fivefingers Step time was found to be higher, where as stride frequency was found to be lower when running with the Vibram Fivefingers compared to the unshod condition. The differences in stride time were mainly due to differences in airborne phase duration, due to contact time being very similar. In contrast, the peak vertical impact forces for the two conditions were similar. The lower limb kinematics associated with the Vibram Fivefinger condition were also similar to unshod running, adopting either a MFS or FFS gait pattern. The peak vertical thrust forces were higher for the Vibram Fivefinger condition when compared to the unshod condition. This indicated that the Vibram Fivefingers allowed users to push more forcefully than when unshod, explaining a longer stride length obtained by the specialised shoes compared to the unshod condition. According to Squadrone et al. (2009), it is probable that the sole of the Vibram Fivefingers is thin enough to permit plantar discomfort to be sensed, resulting in shock setting. 21

32 Shod versus the Vibram Fivefingers Running in the Vibram Fivefingers allowed for a significant, 2.8% decrease in oxygen requirement compared to the standard running shoe. These differences in oxygen consumption may be as a result of differing masses between the normal running shoes and the Vibram Fivefingers, or as a result of kinematic changes at the ankle as a result of the Vibram Fivefingers, resulting in flatter foot strike positions. It is also possible that the work done in flexing and compressing, as well as rotating the sole during toe off was more for the normal running shoe when compared to the Vibram Fivefingers. Though the difference in oxygen requirements between the normal running shoes and the Vibram Fivefingers was expected, the discovery that running unshod requires greater amounts of oxygen than when running in the Vibram Fivefingers was less expected. From this, it can only be speculated that the stiffness level, for which each runner has an optimum, obtained while running in the Vibram Fivefingers allowed for an increased running economy compared to both the unshod and the normal running shoe conditions. This is as Grant et al. (1998) found that performing on stiffer surfaces may result in an increased energy requirement when compared to less stiff surfaces. Squadrone et al. (2009) states that the Vibram Fivefinger model seems to be an effective in mimicking barefoot conditions while providing a small amount of protection to the skin on the plantar surface of the foot. This allows runners to push more forcefully as evidenced by a larger step length, a lower step frequency, and a peak thrust force compared to unshod running. Even though oxygen consumption was lower while running in Vibram Fivefingers when compared to an unshod condition, the cause of this finding can only be speculated. INFLUENCE OF FOOTWEAR ON RUNNING KINETICS AND KINEMATICS Research by Morio et al. (2009) attempted to highlight the influence of footwear on the restriction of foot motion, suggesting that footwear restricts the natural motion of the foot. During this study foot kinematics were assessed for both a shod condition and an unshod condition. Results from the shod condition presented restricted motion of the foot in the frontal plane (eversion and inversion) and the horizontal plane (abduction and adduction), but not the sagittal plane (plantarflexion and 22

33 dorsiflexion), results similar to Wolf et al. (2008). Morio et al. (2009) as well as Wolf et al. (2008) found that footwear restrained foot torsion, forefoot spreading, and foot pronation during toe off. According to Morio et al. (2009), the above suggests that not only does footwear restrict the natural motion of the barefoot, but also appears to impose a specific foot motion pattern on users during the toe off phase of the gait cycle. During energy generation, the mass spring system causes the runners leg to continually shorten and extend (Farley et al., 1993). According to Bishop et al. (2006), runners encounter a range of surfaces with differing stiffness properties. Depending on the type of terrain which the limb comes into contact with, the stiffness of the leg varies (Alexander, 1992). Williams et al. (2004) found that runners with a high arch exhibited low limb compliance (stiffer limb) and are more likely to develop injuries to the skeletal system. Whereas, runners with a low arch exhibited greater limb compliance (more flexible) and are more likely to develop injuries to the soft tissues of the limb. When footwear is worn while running, the complex system of springs must adjust in order compensate for the change in the system caused by the shoe, maintaining overall system stiffness (Bishop et al., 2006). Running shoes attempt to reduce impact forces generated while running by fitting a large, cushioned heel. If the heel of running shoes reduces impact, then the stiffness of the limb may be modified (McPoil, 2000). According to Lieberman et al. (2010), how runners strike the ground also affects leg compliance. Limb compliance is greater during FFS running than while running adopting a RFS pattern (Lieberman et al., 2010). When a runner adopts a FFS pattern, the leg is more compliant during the impact period due to ankle dorsiflexion and knee flexion, leading to a lower rate of loading. A study by Bishop et al. (2006) focused on determining the effect of running footwear on lower limb stiffness. Their findings indicated that limb stiffness increased during a shod condition when compared to an unshod condition. The authors speculate that the introduction of a shoe with a sole of relatively low stiffness reduced contact surface stiffness enough to require the subjects to increase overall limb stiffness. While shod running, runners land in more dorsiflexed ankle position and with decreased joint excursion into dorsiflexion compared to unshod running. Whereas, unshod runners land in a more plantarflexed position and moved through a greater ankle motion to dorsiflexion. At the knee however, there is an increased joint 23

34 excursion while running shod, and a decrease while running unshod. This suggests that runners absorb the impact of initial contact while running unshod, while shod running results in increased ankle stiffness (Stefanyshyn et al., 1998; Bishop et al., 2006). De Wit et al. (2000) stated that the kinematic differences between shod and unshod running occurs mainly at the ankle. 24

35 CHAPTER III METHODOLOGY INTRODUCTION Previous research regarding shod versus unshod running has focused on the effect of footwear on oxygen consumption, energy expenditure, heart rate, foot strike patterns, and ground reaction forces in long distance runners (Flaherty, 1994; De Wit et al., 2000; Wallden, 2009; Squadrone et al., 2009; Lieberman et al., 2010). During these studies it was important to control a number of variables in order to allow for standardised testing procedures as well as accurate and valid results. Within the limited available literature, variables such as running speed, shoe type, environmental conditions, and other extraneous variables were strictly controlled. The use of a small range of speeds as well as the use of similar footwear within previous studies allows for comparisons to be made between the available literature and with the outcomes of this particular study. However, the impact of changes in gradient on the above responses remains poorly understood with regards to shod and unshod conditions. Previous research on the physiological responses to changes in gradient controlled gradients between the range of 5º and 10º. Therefore within this study, the key considerations in developing an appropriate method include the strict control of; gradient, running speed, environmental conditions, and footwear. PILOT TEST PROTOCOL In order to determine the feasibility and logistical working of the proposed research, pre pilot and pilot investigations were performed in the Department of Human Kinetics and Ergonomics, Rhodes University, Grahamstown. Two volunteers participated in trial protocols during which selected conditions, namely running shod at gradients of -5%, 0%, and +5%, were performed. These preliminary simulations served to refine the testing protocols, establish the suitability of equipment, and to gain a basic overview of the expected research outcomes. The pilot testing further 25

36 allowed for familiarisation of the required equipment and enabled the researcher to establish the appropriate recovery time between protocols. Speed selection The selection of an appropriate speed was pertinent to the present study as it was important that all participants were able to run comfortably at the selected speed, allowing a natural and familiar running style to be adopted. An appropriate treadmill running speed allowed each participant to adopt a suitable and natural foot striking pattern throughout experimental condition testing. Research regarding shod versus unshod conditions have typically utilised speeds of between 10km.h -1 and 20km.h -1 (Flaherty, 1994; De Wit et al., 2000; Wallden, 2009; Squadrone et al., 2009; Lieberman et al., 2010). According to Novacheck (1998), if the selected speed was too fast, the participant would be unable to maintain a natural jogging gait pattern, and be forced to adopt a more FFS gait pattern. However, if the speed was too slow the participant would be forced to adopt a more RFS gait pattern as the centre of mass must be continually decelerated in order to maintain a reduced running speed (Novacheck, 1998). The natural running gait adopted by the participants ensured that any changes to foot strike patterns occurring during experimental conditions testing could be attributed to changes in footwear (Shod or Vibram Fingers). The selection of an appropriate running speed was also important from an energy expenditure perspective. As the duration of each condition was controlled at six minutes in order to allow a plateau in physiological responses, it was important that the subject was able to run at the selected speed for the full duration without incurring significant fatigue. This ensured that appropriate responses were elicited from each participant, and these responses were not affected by any form of fatigue experienced. Therefore, the selection of an appropriate speed of 12km.h -1 allowed subjects to adopt a comfortable and natural running style, while being able to run for the entire test duration without incurring significant levels of muscular and cardiovascular fatigue. This ensured all data collected during experimentation were reliable, accurate and valid. 26

37 Gradient selection The analysis of running has mostly been conducted by comparing different running techniques, running velocities, and shoe types (Squadrone et al., 2009). Until recently, few authors have compared shod and unshod running. Whereas, no research exists regarding the comparison of shod versus unshod conditions and the affect changes in gradient could have on biomechanical and physiological responses. Many researchers have studied the biomechanical and physiological responses for running on a level gradient (Fenn, 1930; Lafortune et al., 1980; Munro et al., 1987; Gottschall et al., 2004; Squadrone et al., 2009; Lieberman et al., 2010). However, very limited literature is available regarding the above responses for running at a range of different gradients. Studies by Minetti et al. (1994), Minetti et al. (2002), and Lin et al. (2009) focused on researching the physiological responses associated with gradient running. Where as a study by Gottschall et al, (2004) attempted to quantify a number of biomechanical responses, such as foot strike patterns, while running at both uphill and downhill gradients. The above studies required participants to run at a number of speeds while at a range of uphill and downhill gradients. Gradients between the range of -15% and +15% were used in order to assess differences in oxygen consumption, heart rate, minute ventilation and other physiological responses, as well as biomechanical responses such as ground reaction forces and foot strike patterns, between a number of running conditions. Results from these studies showed that different metabolic energy costs result from different gradients, and participant runners adopt different foot strike patterns depending on the severity of the gradient imposed. Therefore, the gradients of -5%, level, and +5% have been selected in order to maximise the variability between the conditions while ensuring that the participants do not experience significant fatigue during experimental conditions testing as a result of gradient. 27

38 EXPERIMENTAL DESIGN The objectives of this study were to compare oxygen consumption, other physiological variables, foot strike patterns and perceptual ratings of exertion and body discomfort while running in two forms of footwear at three different gradients. The footwear selected for use in the present study consists of normal running shoes (with large cushioned heel) and the Vibram Fivefinger barefoot shoe technology. The special lightweight Vibram Fivefinger shoes are designed to mimic unshod running, while providing protection to the plantar surface of the foot. This footwear provides enough protection to the feet to enable the user to run barefoot without worrying about puncture wounds, bruises and cuts (Squadrone et al., 2009). The analysis of running has mostly been conducted by comparing different running techniques, running velocities and shoe types. Recently, more and more runners around the world are discovering unshod running and the advantages associated with a barefoot lifestyle (Squadrone et al., 2009; Wallden, 2009; Lieberman et al., 2010). It is due to this current barefoot trend that products such as the Vibram Fivefingers are gaining popularity amongst both recreational and competitive runners (Wallden, 2009). With the exception of a study by Squadrone et al. (2009), no authors have focused on the comparison between normal running shoes and the Vibram Fivefingers. Therefore, this study focused on comparing two shod conditions, namely; normal running shoes (large cushioned heel) and the Vibram Fivefingers. Within the available literature regarding the effect of gradient on the biomechanical, physiological and psychophysical responses of athletes, no study has focused on the influence of footwear. Footwear alters the interaction between a runner s foot and the ground during initial contact, causing changes in foot striking patterns (Lieberman et al., 2010). In addition, running shoes add weight to the distal segments of the leg, directly affecting running economy (Flaherty, 1994; De Wit et al., 2000; Wallden, 2009; Squadrone et al., 2009; Lieberman et al., 2010). This study made use of three gradients in order to assess the influence of changes in gradient on a number of responses. It was important that the selected gradients were steep enough to ensure significantly different responses were elicited from each participant, but small enough so that to ensure each participant did not incur significant muscular or cardiovascular fatigue. The selected gradients consist of a negative (downhill) gradient, a level 28

39 gradient, and a positive (uphill) gradient. This allowed for the assessment of the selected responses to each gradient within each footwear type (shod or Vibram Fivefingers), as well as allowed the author to determine whether the differences (if any) between the shod and Vibram Fivefinger conditions persist or are altered with regards to the change in gradient, as a result of footwear. Therefore, the gradients selected consisted of; a downhill gradient of -5%, a level gradient (0%), and finally and uphill gradient of +5%. Consequently, six conditions, shown in the design matrix (Table I) were randomly performed in order to determine if significant differences existed between running shod and running in the Vibram Fivefingers, as well as between running at the selected gradients (-5%, 0%, and +5%). Table I: Design matrix of experimental conditions Gradient Downhill (-5%) Level (0%) Uphill (5%) Shod Vibram Fivefingers Where: 1, represents the six experimental conditions To facilitate controlled testing conditions and easy measurement of the selected dependent variables, each participant ran on an incremental treadmill with adjustable speed and both a positively and negatively adjustable gradient. This is because treadmill running provides the primary exercise mode to evaluate the biomechanical, physiological and psychophysical responses to running (McArdle et al., 2007). According to McArdle et al. (2007), no measurable differences emerge in the aerobic requirements of submaximal running on a treadmill and track, either on a level or at range of gradients. The experimental condition testing was carried out in a strict laboratory environment. The methodological parameters of the current study aimed to simulate the conditions associated with endurance running as accurately as possible. The employment of a strict laboratory based methodology to evaluate the respective conditions enabled the rigorous standardisation of procedures and the exclusion of extraneous variables. In effect, adopting this approach allowed for a more stringent control of experimentation, enhancing the accuracy of measures by isolating the variables of interest, thus improving the study s reliability. 29

40 Recent studies (Saunders et al., 2004; Chen et al., 2007; Chen et al., 2008) have shown that in tests of physical exercise, analysing physiological parameters such as oxygen consumption, minute ventilation, heart rate, as well as kinematic parameters such as ankle range of motion is an effective way to evaluate exercise intensity, physiological response and performance (Lin et al., 2009). Using ergospirometry, a non invasive technique for breath by breath analysis, the following physiological responses were measured and recorded; oxygen consumption, heart rate, running economy, minute ventilation, tidal volume and breathing frequency. The use of a video camera and video software allowed for the analysis of the foot striking patterns adopted by each participant during experimental condition testing. Psychophysical responses were collected from each participant during experimental conditions testing through the use of RPE scales and body discomfort map and scales. This allowed for each participant to subjectively rate fatigue and discomfort during each condition. Different areas and levels of discomfort may have arisen as a result of both the footwear and the gradients. Firstly, as footwear influences the foot striking patterns adopted by each participant, which results in different muscle activation patterns in the lower extremities. Secondly, as changes in gradient also influence the foot striking pattern adopted by each participant, the areas and ratings of exertion and fatigue to be compared between shod and Vibram Fivefinger running, as well as between the three selected gradients. Each participant was required to run for duration of six minutes per condition. This allowed for a steady state (plateau in physiological responses) to be reached. According to McArdle et al. (2007), a steady state is achieved after between three to four minutes of effort. From the collected six minutes of data, the third and fifth minutes were extracted using Microsoft Excel, and compared using Statistica 7 in order to ensure a steady state had been obtained. MEASUREMENT AND EQUIPMENT During both the habituation and the experimental condition testing sessions, it was vitally important that accurate and reliable data was continually collected from each subject. In order to ensure that each subject s elicited responses to the six conditions were representative, all equipment utilised during experimentation was properly set 30

41 up, calibrated, fitted to the subject and correctly operated. The following equipment was required in order to collect anthropometrical, physiological, biomechanical, and psychophysical responses: Anthropometrical measurements Body mass: Toledo scale The body mass of each subject was recorded in order to relativise oxygen consumption and calculate energy expenditure. The Toledo electronic scale was used to record body mass to the nearest 0.01kg. Each subject was required to remove their footwear and wore minimal clothing. The researcher requested the subject to stand still, in the centre of the scale, with body mass distributed evenly between feet. Mass was recorded once a stable recording could be obtained. In addition, the mass of each subject s running shoes were also measured and recorded. Physiological measurements The following equipment was used to measure and record the physiological responses during the six minutes of each experimental condition. The third and fifth minutes were marked using the Quark b 2 software and then extracted from the data using Microsoft Excel. The two extracted minutes were then compared and averaged allowing steady state values to be obtained. Heart Rate: Polar TM Heart Rate monitor telemetry strap Each subject s heart rate was measured as it is an accurate indicator for cardiovascular exertion. Heart rate was measured in beats per minute (bt.min -1 ) using a Polar TM Heart Rate monitor telemetry strap and the Quark b 2 ergospirometer. The Polar Coded Transmitter, which measures the heart s electrical activity, was fitted around the subject s chest with an elastic strap and aligned with the sternum at the level of the inferior border of the pectoralis muscles. The Quark b 2 recorded heart rate responses to the various conditions and protocols. Before experimentation took place, a reliable resting heart rate value was obtained as a reference heart rate. This reference heart rate was used in order to indicate when the subject had returned to rest between each testing condition, as each condition could only begin once the subject was at rest. Heart rate was measured as recent research shows that analysing heart rate during physical exercise is an effective way to evaluate an 31

42 athlete s efficiency and performance (Saunders et al., 2004; Chen et al., 2007; Chen et al., 2008). Ergospirometry: Quark b 2 (Cosmed) For the purpose of this investigation, ventilatory data such as oxygen consumption were collected. This allowed for each subject s energy expenditure to be calculated and compared with regards to each of the six experimental conditions. This nonportable, open circuit spirometer allows for breath by breath analysis of cardiorespiratory function, gas metabolism, and other physiological responses. Figure 7: The Quark b 2 A face mask which encloses the nose and mouth ensures all inhaled and exhaled air is measured on a breath by breath basis. The face mask is placed on the subject using an adjustable head harness, which is tightly secured to the subject. The various gas tubes and equipment wiring were fastened to the subject s back using masking tape to make sure that they did not interfere with the subject during testing. 32

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