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1 This article was downloaded by: [Karolinska Institute] On: 16 November 2010 Access details: Access Details: [subscription number ] Publisher Routledge Informa Ltd Registered in England and Wales Registered Number: Registered office: Mortimer House, Mortimer Street, London W1T 3JH, UK Sports Biomechanics Publication details, including instructions for authors and subscription information: The effect of periodized resistance training on accelerative sprint performance Gavin Moir a ; Ross Sanders b ; Chris Button c ; Mark Glaister d a Exercise Science Department, East Stroudsburg University, East Stroudsburg, Pennsylvania, USA b Department of Physical Education, Sport and Leisure Studies, University of Edinburgh, Edinburgh, UK c School of Physical Education, University of Otago, Dunedin, New Zealand d School of Human Sciences, St. Mary's College, University of Surrey, Twickenham, UK To cite this Article Moir, Gavin, Sanders, Ross, Button, Chris and Glaister, Mark(2007) 'The effect of periodized resistance training on accelerative sprint performance', Sports Biomechanics, 6: 3, To link to this Article: DOI: / URL: PLEASE SCROLL DOWN FOR ARTICLE Full terms and conditions of use: This article may be used for research, teaching and private study purposes. Any substantial or systematic reproduction, re-distribution, re-selling, loan or sub-licensing, systematic supply or distribution in any form to anyone is expressly forbidden. The publisher does not give any warranty express or implied or make any representation that the contents will be complete or accurate or up to date. The accuracy of any instructions, formulae and drug doses should be independently verified with primary sources. The publisher shall not be liable for any loss, actions, claims, proceedings, demand or costs or damages whatsoever or howsoever caused arising directly or indirectly in connection with or arising out of the use of this material.

2 Sports Biomechanics September 2007; 6(3): The effect of periodized resistance training on accelerative sprint performance GAVIN MOIR 1, ROSS SANDERS 2, CHRIS BUTTON 3, & MARK GLAISTER 4 1 Exercise Science Department, East Stroudsburg University, East Stroudsburg, Pennsylvania, USA, 2 Department of Physical Education, Sport and Leisure Studies, University of Edinburgh, Edinburgh, UK, 3 School of Physical Education, University of Otago, Dunedin, New Zealand, and 4 School of Human Sciences, St. Mary s College, University of Surrey, Twickenham, UK Abstract The purpose of this study was to assess the effect of periodized resistance training on accelerative sprint performance. Sixteen physically active men participated in a randomized controlled study. An experimental group (n ¼ 10) completed an 8-week periodized resistance training intervention, while a control group (n ¼ 6) did not train. Pre- and post-training measures of 20-m straight-line sprint time, including a 10-m split, maximum strength, and explosive strength, were recorded. Flight time, stance time, stride length, and stride frequency were quantified from digitized video recordings of the first three strides of the 20-m sprint. Resistance training resulted in significant increases in maximum strength (parallel back squat: 19%) and explosive strength (6 10%). However, both groups increased 0 10 m sprint times (experimental group ¼ 6%; control group ¼ 3%) while m times were reduced (experimental group ¼ 7%; control group ¼ 4%), highlighting the mechanical differences between the distinct sprint phases. The change during the 0 10 m interval was accompanied by a reduction in stride frequency during the first three strides. Strength coaches should be aware that the potential benefits of increased muscular strength during short sprints are likely to be affected by mechanical specificity and that improvements in sprinting performance may not occur immediately after a period of resistance training. Keywords: Acceleration, flight time, resistance training, sprinting, stride frequency Introduction Straight-line sprint running is an integral component of successful performance in many sports. Based upon the horizontal velocity of the athlete, sprint running can be regarded as comprising three distinct phases: acceleration, attainment of maximum speed, and maintenance of maximum speed (Delecluse et al., 1995a). This multidimensional structure can be generalized to athletes of differing abilities with adjustments to the duration of each phase. For example, untrained sprinters have been shown to achieve maximum speed between 10 and 36 m during a 100-m sprint (Delecluse et al., 1995a), while elite sprinters may not reach maximum speed until the 80-m point of a 100-m race (Ae, Ito, and Suzuki, 1992). Also, the roles of the active muscles and neural regulation differ across the distinct phases of sprint running (Delecluse, 1997; Mero, Komi, and Gregor, 1992) and therefore different training methods are likely to affect each phase in different ways. Correspondence: G. Moir, Exercise Science Department, East Stroudsburg University, 200 Prospect Street, East Stroudsburg, PA , USA. gmoir@po-box.esu.edu ISSN print/issn online q 2007 Taylor & Francis DOI: /

3 286 G. Moir et al. Accelerative sprinting requires the body to be propelled primarily by the leg extensor muscles, a requirement that is reflected in the strong relationships between relative measures of maximum strength of the knee extensors and accelerative sprint performance (Mero, Luhtanen, Viitasalo, and Komi, 1981; Sleivert and Taingahue, 2004). Similarly, measures of explosive strength of the knee extensors are strongly related to accelerative sprint performance (Mero et al., 1981; Berthion, Dupont, Mary, and Gerbeaux, 2001). Despite the strong relationships demonstrated between accelerative sprinting and measures of maximum and explosive strength, research on the effects of resistance training on accelerative sprint time reveals conflicting results. For example, while some studies have reported a decrease in accelerative sprint time after a resistance training intervention (Delecluse et al., 1995b; Gorostiaga et al., 2004; Hennesey and Watson, 1994; Rimmer and Sleivert, 2000), others have reported either no significant change (Fry et al., 1991; McBride, Triplett-McBride, Davie, and Newton, 2002) or a significant increase (McBride et al., 2002). McBride and colleagues (2002) reported a significant increase in 5-m sprint time and a non-significant increase in 10-m sprint time after an 8-week resistance training programme using heavy loads (80% one-repetition maximum [1-RM] squat). Conversely, an improvement in sprint performance was achieved after resistance training using relatively lighter loads (30% 1-RM squat). These authors noted that, despite the large increase in 10- m time after the heavy resistance training intervention, there was only a slight (nonsignificant) increase in 20-m time, suggesting that the heavy resistance training may have affected the first and second 10-m intervals in different ways. These two distances (initial 10 m, second 10 m) could represent two distinct sprint phases for the participants used. Recently, Brown and colleagues (Brown, Vescovi, and VanHeest, 2004) differentiated between the initial acceleration ( m) and the middle acceleration ( m) phases in field-sport athletes using sprint time. Taken together, the results of these studies highlight the differing effects of strength development on the phases during straight-line sprinting. A failing of the extant research investigating the effect of resistance training on accelerative sprint performance is the reliance solely on outcome measures such as sprint time. This is particularly important when attempting to explain why the strength gained from a resistance training intervention may or may not have improved sprint performance. The analysis of sprint time or related variables does not consider the mechanisms that lead to performance changes. If the issue of the transfer of strength gains to accelerative sprinting is to be adequately explained, more in-depth analyses are required. For example, changes in the kinematics of each stride after a period of resistance training need to be examined. Sprinting speed is the product of stride length and stride frequency (Mero et al., 1992). The relative importance of stride length and stride frequency during the maximum speed phase of sprinting remains a source of debate. For example, some researchers have identified stride length as the most important variable during maximum speed sprinting (Chapman and Caldwell, 1983; Hoshikawa, Matsui, and Miyashita, 1973; Weyand, Sternlight, Bellizzi, and Wright, 2000), while others have considered stride frequency to be more important than stride length at maximal sprinting velocities (Mero et al., 1981). However, few studies have investigated the relative importance of stride length and stride frequency during the acceleration phase. In an analysis of field sport athletes, Murphy and colleagues (Murphy, Lockie, and Coutts, 2003) observed that the faster accelerators produced significantly greater stride frequencies than their slower counterparts, with no differences in stride length. Any changes in sprint running performance will result from changes in the interaction between stride length and stride frequency. Despite this, few studies have investigated the effects of resistance training on these kinematic variables. Rimmer and Sleivert (2000)

4 Resistance training and sprint performance 287 reported no significant changes in stride length or stride frequency at the 37-m mark of a 40-m sprint after an 8-week programme of sprint-specific plyometric exercises. However, there is a paucity of research investigating the effects of resistance training on the variables of stride length and stride frequency during the acceleration phase of sprint running. The purpose of this study was therefore to investigate the effect of a periodized resistance training intervention on accelerative sprint performance with particular emphasis on changes to the kinematic stride variables during the first three strides of the sprint. Methods Participants Sixteen male students volunteered to participate in the study. Participants were randomly assigned to an experimental (n ¼ 10) or a control (n ¼ 6) group before training. All participants were physically active, being involved in sports that included rugby, soccer, and basketball and all had previous experience of resistance training, although none had been involved in a programme of resistance training in the 3 months before the study. Approval to undertake the study was granted by the University of Edinburgh Ethics Committee and written informed consent was obtained from each participant. The pre-training physical characteristics of the experimental and control groups are shown in Table I. For the duration of the study, the participants in the experimental group were instructed to refrain from sprint training while the control group were instructed to refrain from strength and sprint training. Other than these restrictions both groups maintained their normal physically active lifestyles. Testing was performed on two separate occasions, before and after training. All participants completed a 4-week familiarization period before assignment to the experimental and control groups to ensure that they were familiar with the training and testing exercises and to counter the possibility of learning mechanisms contributing significantly to any gains in strength (Jones and Rutherford, 1987). During this familiarization period, the participants performed all of the training and testing exercises. Resistance training programme The 8-week resistance training programme consisted of two mesocycles of 4 weeks each. The first mesocycle emphasized strength endurance, whereas the second emphasized the development of maximum strength and power. The volumes and loads used in each mesocycle were as follows: the first mesocycle comprised 4 weeks of 3 12 repetitions at a load corresponding to a 12-repetition maximum; the second mesocycle comprised 4 weeks of 3 5 repetitions at a load corresponding to a 5-repetition maximum. Major and assistance exercises were included in the training programme (Tables II and III). The exercises used were typical of those recommended in sprint-training articles (Dintiman, Ward, and Tellez, 1998; Sheppard, 2003; Young, Benton, Duthie, and Pryor, 2001). Table I. Pre-training group means for age, height, and mass (mean ^ standard deviation). Group Age (years) Height (m) Mass (kg) Experimental (n ¼ 10) 18.9 ^ ^ ^ 15.0 Control (n ¼ 6) 19.5 ^ ^ ^ 7.5

5 288 G. Moir et al. Table II. Outline of the exercises used in the strength endurance microcycle of the resistance training programme. Exercise Day Sets Repetitions Target repetition maximum Parallel squats Mon & Fri RM (Mon) 12-RM 20% (Fri) Bench-press Mon & Fri RM (Mon) 12-RM 20% (Fri) Push-press Mon & Fri RM (Mon) 12-RM 20% (Fri) Flys Mon & Fri RM (Mon) 12-RM 20% (Fri) Sit-ups Mon & Fri Power cleans Wed RM 10% (Wed) SLDL Wed RM 10% (Wed) CGSS Wed RM 10% (Wed) THE Wed Note: Mon ¼ Monday (heavy); Wed ¼ Wednesday (moderate); Fri ¼ Friday (light); SLDL ¼ stiff-legged deadlift; CGSS ¼ clean grip shoulder shrugs; THE ¼ trunk hyperextensions. All participants had previous experience with the resistance training exercises before the study, with the exception of the power clean. For this exercise the participants were taught to perform the double-knee bend technique, following Newton (2002). This was practised by all participants during the familiarization period. Training loads during each mesocycle were determined using a target repetition maximum for each exercise as recommended by Kraemer (2002). The target repetition maximum for each participant on all exercises was determined towards the end of the 4 week familiarization period. The loads were increased by 5% to 10% in consecutive weeks during the first 3 weeks of each cycle, with a reduction in load during the final week. Training frequency was three times per week, incorporating heavy (Monday), moderate (Wednesday), and light (Friday) training days based upon each participant s predicted target repetition maximum for each exercise. This manipulation reduced the risk of overtraining (Stone, Collins, Plisk, Haff, and Stone, 2000). Variations in the loads were achieved by reducing the target repetition maximum by 10% on moderate days and 20% on light days. This variation produced a training regime that combined high force and high speed movements (Cronin, McNair, and Marshall, 2002; Stone, 1993). The volume and intensity during each session were monitored by calculating the volume load across the training period (Robinson et al., 1995). In addition to variations in volume and load, exercises were varied on moderate days to reduce the risk of overtraining (Stone et al., 2000). Table III. Outline of the exercises used in the maximum strength and power microcycle of the resistance training programme. Exercise Day Sets Repetitions Target repetition maximum Parallel squats Mon & Fri RM (Mon) 5-RM 20% (Fri) Bench-press Mon & Fri RM (Mon) 5-RM 20% (Fri) Push-press Mon & Fri RM (Mon) 5-RM 20% (Fri) Flys Mon & Fri RM (Mon) 5-RM 20% (Fri) SU (5 10 kg) Mon & Fri Power cleans Wed RM 10% (Wed) SLDL Wed RM 10% (Wed) CGSS Wed RM 10% (Wed) THE (5 10 kg) Wed Note: Mon ¼ Monday (heavy); Wed ¼ Wednesday (moderate); Fri ¼ Friday (light); SU ¼ sit-ups; SLDL ¼ stifflegged deadlift; CGSS ¼ clean grip shoulder shrugs; THE ¼ trunk hyperextensions.

6 Resistance training and sprint performance 289 The length of rest periods between sets during each training session was 2 min during the strength endurance phase and 3 min during the maximum strength and power phase (Kraemer, 2002). Each training session was supervised by an instructor to ensure that participants adhered to the programme and that the appropriate safety factors were applied (such as spotting of the participants). These instructors also ensured that correct form was used in all exercises. Before each training session, a standardized warm-up was performed by each participant consisting of 5 min of jogging, followed by various dynamic exercises. An instructor was present to ensure the appropriate warm-up exercises were performed. No sprinting exercises were performed as part of the resistance training programme. Data collection and treatment Measures of sprint time, kinematic stride variables, maximum and explosive strength were recorded during the pre- and post-training test sessions. Each of the two test sessions was performed over a 5-day period, with the assessments following the same order each time: Day 1, maximum strength; Day 2, rest; Day 3, rest; Day 4, sprint time and kinematic stride variables; Day 5, explosive strength. All testing was performed at the same time of the day for each participant. Sprint time. Sprint time was assessed using a 20-m straight-line sprint from a three-point, crouched stationary start with a split time recorded at 10 m (Moir and Glaister, 2004). Sprint times were recorded using telemetric photocells (Sprint Timer Telemetry, Cranlea & Co., UK) that were placed at the 0-m, 10-m, and 20-m marks of an indoor running track. Each participant performed three maximal sprints, with mean times for the first 10 m, second 10 m, and overall 20 m used in the subsequent analysis. All sprints were initiated voluntarily by the participants and 3 min recovery was provided between each sprint. Before the sprints, participants performed a standardized warmup consisting of jogging followed by specific static exercises, dynamic exercises, and sprint drills under the guidance of an instructor. Measures of 10-m and 20-m sprint time have been shown to have high test retest reliability and low within-participant variation without the need for familiarization using this protocol (Moir and Glaister, 2004). Stride variables. Sprint performance over the first 10 m of each 20-m trial was recorded using two stationary digital cameras (JVC, GR-DVL 9800, Japan) with sampling frequencies of 120 Hz. The cameras were set at a height of 0.85 m and were positioned 4.5 m apart and at a distance 15 m perpendicular to the line of the sprint (Figure 1). Both camera views were calibrated using metal frames of known dimensions. Each participant ran with a marker placed on the fifth metatarsophalangeal joint. The video footage provided two-dimensional kinematic data for at least the first three strides of the 20-m sprint of each participant. The metatarsophalangeal joint data were digitized using APAS software (Ariel Performance Analysis System, version 1.0, Ariel Dynamics) using the automatic digitizing function. A stride cycle was defined as the period between toe-off and the next ipsilateral toe-off. Toe-off was determined from the raw data as the frame at which the vertical displacement of the fifth metatarsophalangeal joint increased from its position during the stance period of the stride cycle (when the foot was in contact with the ground). The following kinematic variables during the first three strides of the 20-m sprint were calculated, with the mean of three trials for each variable during the separate strides used in the subsequent analysis:

7 290 G. Moir et al. Figure 1. Plan showing the camera positions relative to the line of running during the first 10 m of the 20-m sprint. 1. Flight time. The time between consecutive ipsilateral stance periods defined the flight time. Flight time began at the frame when the scaled y coordinates of the fifth metatarsophalangeal joint increased from the minimum values during each stride cycle (the stance period). The flight time ended at the frame before that when the scaled y coordinates of the fifth metatarsophalangeal joint achieved the minimum values during the stride (next ipsilateral stance). 2. Stance time. The time that each ipsilateral foot was in contact with the ground defined stance time; that is, the time between the frames corresponding to touch-down and toeoff. Touch-down occurred at the frame when the scaled y coordinates for the fifth metatarsophalangeal joint marker reached their minimum during each stride cycle. The frame before that when the scaled y coordinates exceeded the lowest point (when the fifth metatarsophalangeal joint left the ground) marked the end of the stance time. 3. Stride length. Stride length was defined as the horizontal displacement between consecutive ipsilateral toe-off events. It was calculated as the difference between the scaled x coordinates of the fifth metatarsophalangeal joint at the frames before toe-off. 4. Stride frequency. Stride frequency was calculated as the inverse of the time taken to complete one stride cycle (the addition of flight time and stance time). Measures of maximum strength. To assess any changes in sprint performance due to the resistance training intervention, the change in maximum strength of the lower-body musculature was assessed using a free-weights parallel back squat 1-RM test. For this test, a standard 20-kg Olympic barbell and Olympic disks (Eleiko, Sweden) were used. The equation proposed by Jaric (2002) was used to calculate a 1-RM relative to body mass: S n ¼ S=m 2=3

8 Resistance training and sprint performance 291 where S n ¼ normalized strength, S ¼ the load lifted (kg), and m 2/3 ¼ the body mass (kg) of the participant to the power (2/3). The 1-RM test protocol for the parallel squat exercise was based upon that proposed by Baechle and colleagues(baechle, Earle, and Wathen, 2000). A standardized warm-up consisting of 5 min of dynamic exercises was performed by all participants before the first sub-maximal repetitions of the parallel squat test. Measures of explosive strength. Changes in measures of explosive strength were assessed using vertical jumps. The participants performed static vertical jumps under three different load conditions: unloaded, with 30% of 1-RM parallel squat, and with 60% of 1-RM parallel squat as described by Moir and colleagues (Moir, Sanders, Button, and Glaister, 2005). The jumps were performed on a force platform (Kistler, type 9261A, Winterthur, Switzerland) measuring m. Peak power output was calculated by integrating the vertical force time trace during each jump. This method has been shown to produce high test retest reliability and low within-participant variation in peak power output values (Moir et al., 2005). All participants performed a practice session during the 4 week familiarization period to ensure the correct depth of descent. Statistical analysis All statistical analyses were performed using the Statistical Package for the Social Sciences (SPSS for Windows, version 11.0, SPSS Inc., Chicago, IL, USA). Measures of central tendency and spread of the data are presented as means ^ standard deviations (s). Independent t-tests were used to test for any pre-training differences between the experimental and control groups on measures of sprint time, maximum strength and explosive strength before the training period. The outcome scores for the two groups on the assessment measures (sprint times, kinematic stride variables, maximum and explosive strength) recorded before and after training were compared using a two-way analysis of variance (ANOVA: 2 groups 2 test occasions) with repeated measures on one factor (test session). Statistical significance was set at P, 0.05, allowing for Bonferroni adjustments for multiple comparisons. Results There were no significant differences between the experimental and control groups on measures of sprint time, maximum strength or explosive strength before the training period (P. 0.05). Table IV. Pre- and post-training 10-m and 20-m sprint times (mean ^ standard deviation). First 10 m (s)* Second 10 m (s)* 20 m (s) Group Pre Post Pre Post Pre Post Experimental 1.84 ^ ^ ^ ^ ^ ^ 0.21 Control 1.88 ^ ^ ^ ^ ^ ^ 0.08 *Significant main effects for test occasion (P, 0.001).

9 292 G. Moir et al. Sprint times The mean pre- and post-training sprint times for the experimental and control groups are shown in Table IV. A significant main effect for test occasion was found for the 0 10 m sprint time (F 1,14 ¼ 20.46, P, 0.05), with both groups increasing their time from the pre-training to the post-training test session (mean difference between test sessions: 0.08 s; 95% likely range: s). There was a significant main effect for test occasion for the m sprint times (F 1,14 ¼ 24.01, P, 0.05), with both groups decreasing their time from the pretraining to the post-training test session (mean difference between test sessions: 0.08 s; 95% likely range: s). There were no other significant main effects or interactions for the sprint times. Figure 2 shows the percentage changes in sprint times for the experimental and control groups. Stride variables The pre- and post-training stride variables during the first three strides of the 20-m sprint for the experimental and control groups are shown in Table V. Flight times. Significant main effects for test occasion were found for flight time during Stride 1(F 1,14 ¼ 8.23, P ¼ 0.012), Stride 2 (F 1,14 ¼ 11.90, P ¼ 0.004), and Stride 3 (F 1,14 ¼ 7.35, P ¼ 0.017). These main effects were caused by both groups increasing flight time during Stride 1 (mean difference between test sessions: 5 ms; 95% likely range: 1 9 ms), Stride 2 (mean difference between test sessions: 5 ms: 95% likely range: 2 8 ms), and Stride 3 (mean difference between test sessions: 6 ms; 95% likely range: 1 10 ms) during the post-training test session. Figure 2. Graph showing the percentage change in sprint times for the experimental and control groups. Values are means; bars are standard deviations.

10 Table V. Pre- and post-training kinematic variables during the first three strides of the 20-m sprint (mean ^ standard deviation). Stride variable Flight time (ms) Stance time (ms) Stride length (m) Stride frequency (Hz) Stride Group Pre Post Pre Post Pre Post Pre Post Stride 1 Experimental 321 ^ ^ 28* 148 ^ ^ ^ ^ ^ ^ 0.19* Control 341 ^ ^ 34* 154 ^ ^ ^ ^ ^ ^ 0.19* Stride 2 Experimental 320 ^ ^ 28* 133 ^ ^ ^ ^ ^ ^ 0.19* Control 334 ^ ^ 29* 134 ^ ^ ^ ^ ^ ^ 0.17* Stride 3 Experimental 324 ^ ^ 31* 122 ^ ^ ^ ^ ^ ^ 0.21 Control 334 ^ ^ 24* 128 ^ ^ ^ ^ ^ ^ 0.14 *Significant main effects for test occasion (P, 0.05). Resistance training and sprint performance 293

11 294 G. Moir et al. Figure 3. Graph showing the percentage change in stride length during the first 10 m for the experimental and control groups. Values are means; bars are standard deviations. Stance times. No significant main effects or interactions were observed for stance time during the first three strides of the sprint. Stride length. No significant main effects or interactions were observed for stride length. Figure 3 shows the percentage changes in stride length during the first three strides for the experimental and control groups. Stride frequency. A significant main effect for test occasion was found for stride frequency during Stride 1 (F 1,14 ¼ 7.37, P ¼ 0.017), with both groups decreasing stride frequency (mean difference between test sessions: 3 Hz; 95% likely range: 1 6 Hz) during the posttraining test session. A significant main effect for test occasion was also observed during Stride 2 (F 1,14 ¼ 14.92, P ¼ 0.002), with both groups decreasing stride frequency during the post-training test session (mean difference between test sessions: 4 Hz; 95% likely range: 1 6 Hz). Figure 4 shows the percentage changes in stride frequency during the first three strides for the experimental and control groups. Maximum strength The maximum loads achieved for the measure of lower-body normalized maximum strength are shown in Table VI. The increase across the test sessions by the experimental group was significantly different from the change by the control group, producing a significant group test occasion interaction (F 1,14 ¼ 59.12, P, 0.05). Explosive strength The pre- and post-training group means for peak power output during the static vertical jump under the different load conditions are shown in Table VII. The experimental group increased peak power output under the unloaded jump condition across the test

12 Resistance training and sprint performance 295 Figure 4. Graph showing the percentage change in stride frequency during the first 10 m for the experimental and control groups. Values are means; bars are standard deviations. sessions, although the change was not significantly different from that by the control group (P. 0.05). During both of the loaded vertical jump conditions, the increase by the experimental group across the test sessions was significantly different from the decrease by the control group, producing significant group test occasion interactions (peak power output with 30% 1-RM: F 1,14 ¼ 17.41, P ¼ 0.001; peak power output with 60% 1-RM: F 1,14 ¼ 30.87, P, 0.05). Figure 5 shows the percentage changes in peak power output during the unloaded and loaded vertical jumps for the experimental and control groups. Table VI. Pre- and post-training measures of lower-body maximum strength (mean ^ standard deviation). Parallel squat (kg BM 22/3 ) * Group Pre-training Post-training Experimental 6.08 ^ ^ 0.93 Control 5.72 ^ ^ 0.91 Note: kg BM 22/3 ¼ kilogram load per kilogram body mass to power (2/3); *Significant group test occasion interaction (P, 0.001). Table VII. Pre- and post-training measures of explosive strength (mean ^ standard deviation). PP unloaded (W) PP 30% 1-RM (W) * PP 60% 1-RM (W) * Group Pre Post Pre Post Pre Post Experimental 4096 ^ ^ ^ ^ ^ ^ 700 Control 3903 ^ ^ ^ ^ ^ ^ 345 Note: PP¼ peak power output; 1-RM ¼ one repetition maximum parallel squat; *Significant group test occasion interactions (P # 0.001).

13 296 G. Moir et al. Figure 5. Graph showing the percentage change in peak power output during the unloaded and loaded static vertical jumps for the experimental and control groups. Values are means; bars are standard deviations. Discussion and implications The principal aim of this investigation was to assess the effect of a periodized resistance training intervention on accelerative sprint performance. We found that an 8-week period of resistance training increased measures of maximum and explosive strength while also increasing accelerative sprint time immediately after the training period. The increase in maximum squat strength was comparable to that reported in a previous study of similar training duration (Fry et al., 1991). The increases in explosive strength, although less than the increases in maximum strength, were similar to those reported by McBride et al. (2002). These authors investigated the effects of two resistance training interventions, one involving light jump squats (30% 1-RM) and the other involving heavy jump squats (80% 1-RM). The heavy jump squat intervention produced greater improvements in peak power during vertical jumps with heavy loads (80% 1-RM) than with lighter loads (30% 1-RM), an adaptation found after the resistance training programme used in the present study. Moreover, a similar increase in 10-m sprint time to that reported in the present study was found by McBride et al. (2002) after heavy jump squat training. The resistance training programme in the present study was developed to emphasize strength and power development. However, the changes in explosive strength demonstrated that the changes in power were limited to the heavy load conditions (Figure 5). This is likely to be due to the heavy loads used. McBride et al. (2002) reported improvements in 5-m and 10-m sprint times after a resistance training regime involving relatively light loads (30% 1-RM). It is possible that the use of much lower loads during the lighter days in the present study would have resulted in improvements in the initial acceleration phase of the sprint. However, given the multidimensional nature of sprinting, improvements in one phase may be offset by decrements in another phase (Delecluse, 1997). Although the changes in sprint times for the experimental group were not significantly different from the changes reported for the control group, the resistance training intervention tended to increase the time over the initial 10 m and decrease the time over the

14 Resistance training and sprint performance 297 second 10 m of the 20-m sprint (Figure 2). It is likely that the two halves of the 20-m sprint (initial 10 m, second 10 m) represent distinct phases for the participants in the present study (cf. Brown et al., 2004), demanding different mechanical and neuromuscular qualities (Delecluse, 1997; Mero et al., 1992). The large standard deviations in the changes for the experimental group (Figure 2) suggest that there were large variations in the responses to the resistance training, even within the fairly homogeneous sample used in the present study. An increase in initial 10-m time was also reported for the control group in the present investigation. It is likely that this finding was caused by the cessation of strength and sprint training for the duration of the training period by the members of the control group (i.e. a detraining effect). Although the magnitude of the change associated with the control group was less than that for the experimental group, it is possible that a proportion of the change by the experimental group was also as a consequence of refraining from sprint activity for the duration of the training period. This limits the application of the present findings to many sporting contexts. Future research should examine the influence of sustained sprint activity during a resistance training intervention to account for this potential explanation of the results. The mechanical demands are likely to differ between the 0 10 m and m sprint distances. During the initial acceleration phase, it has been proposed that athletes optimize stride length and stride frequency by using a technique whereby the centre of mass is rotated over the ground leg before the proximal-to-distal extension of the lower limb joints (Jacobs and van Ingen Schenau, 1992). Such a technique requires a specific muscle coordination pattern that controls the direction of the ground reaction force relative to the centre of mass and allows high horizontal and low vertical velocities of the centre of mass at toe-off, producing greater stride length and stride frequency during acceleration (Hunter, Marshall, and McNair, 2004). In contrast, as the athlete approaches maximum sprinting speed, flight time is maximized to allow sufficient time to reposition the swinging leg in preparation for the subsequent stance periods (Weyand et al., 2000). The flight times are achieved by applying large vertical impulse during the shorter stance durations associated with maximum sprinting speed. The ground reaction impulse applied during stance is important in both accelerative and maximum speed sprinting. However, during accelerative sprinting it is important that vertical impulse is not excessive, otherwise the vertical velocity of the centre of mass will be large at toe-off, interfering with the optimal interaction between stride length and stride frequency and therefore affecting sprint time (Hunter et al., 2004). The resistance training exercises used in the present study are likely to have increased the capacity to apply vertical impulse during stance. However, they could have interfered with the appropriate control of the ground reaction force relative to the centre of mass during each stance period, a constraint specific to the initial acceleration phase of sprinting. This would adversely affect accelerative sprinting, yet be beneficial as the athlete approached maximum speed where the application of vertical impulse may limit performance. This could explain why the experimental group was slower over 0 10 m, yet appeared to improve slightly over m. Few studies have investigated changes in kinematic stride variables as a result of resistance training. Although the changes were not significantly different from those of the control group, there was a trend for the experimental group to increase stride length during the first three strides of the sprint (Figure 3). However, these increases were offset by greater decreases in stride frequency during the three strides (Figure 4), resulting in the participants slowing over the initial 10 m. Murphy et al. (2003) reported that stride frequency was more important than stride length during accelerative sprinting. Again, however, the large standard deviations in the changes for the experimental group (Figures 3 and 4) suggest that there were large variations in the responses to the resistance training intervention. It should

15 298 G. Moir et al. be noted that some of the associated kinematic stride variables (i.e. flight time and stride frequency) of the control group also mirrored the changes shown by the experimental group, but to a lesser extent. It is likely that this trend contributed to the lack of significant group time interactions reported in this study. In the present study, sprint performance was assessed one week after completing the resistance training programme. It is possible that the slight decrements in sprint performance reported here for the experimental group reflect the time delay between an increase in strength training load and an improvement in performance (Zatsiorsky, 1995). If this is true, then it might be that improvements in sprint performance would be realized beyond the duration of the present study. Zatsiorsky (1995) proposes a positive relationship between the increment in training load and the time required to adapt. Therefore, an improvement in sprint performance for the present group of participants may occur weeks after the end of the resistance training. The fact that the experimental group showed gains in both maximum and explosive strength suggests that any delays in adaptations are likely to be associated with the coordination of the sprinting movement. It is possible that sprinting performance will not be optimized until a coordination pattern is developed that is commensurate with the increased strength capabilities of the motor system. However, further research is required to investigate this possibility. This investigation has shown that despite increases in measures of maximum and explosive strength, a period of resistance training does not improve the initial acceleration phase of sprinting (0 10 m interval) immediately after the training period. After the resistance training intervention, the specific coordination pattern that allows the production of long strides and high stride frequencies during acceleration was unlikely to have been modified to optimize performance to suit the increased capacity (muscular strength) of the motor system. It is likely that athletes require time to adapt and transfer the gains in strength accrued from a resistance training intervention to activities such as sprint running. However, the adaptations resulting from the resistance training exercises used in the present study appeared to be appropriate for performance as the participants approached maximum speed sprinting (10 20 m interval). These findings contribute to the current equivocal literature concerning the supposed benefits of resistance training. Strength and conditioning coaches responsible for improving straight-line sprint running performance should be aware of the mechanical differences between the distinct sprint phases and select appropriate resistance training exercises commensurate with the specific phase of sprinting. Coaches should also be aware that the potential benefits of increased strength during the initial acceleration phase may be delayed, possibly until the development of new patterns of coordination suited to the increased capacity for force production. It is therefore important to consider the timing of resistance training loads within the athlete s wider training regime. Acknowledgements The authors would like to thank Mark Kilgallon for his help in data collection. References Ae, M., Ito, A., and Suzuki, M. (1992). The men s 100 metres. New Studies in Athletics, 7, Baechle, T. R., Earle, R. W., and Wathen, D. (2000). Resistance training. In T. R. Baechle, and R. W. Earle (Eds.), Essentials of strength training and conditioning (pp ). Champaign: Human Kinetics.

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