The study on exercise effects by the change of elastics and angle of the Insole

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1 The study on exercise effects by the change of elastics and angle of the Insole Lee, Chang-Min, Oh, Yeon-ju, Kim, Jin-Hoon Department of Industrial and Management Engineering Dong-Eui University Gaya-Dong 24, Pusanjin-ku Pusan, Korea Abstract: Several studies on the functions of shoes have been actively progressed that functions could be maximized through the modification and change of shoes materials. The exercise effects of shoes can lead the natural heel-toe walking by changing the angle and the hardness etc., from the heel to the metatarsal. The purpose of the study is to investigate the ergonomics analysis to cause the natural heel-toe walking and to improve exercise effects of the 5 protocol insoles. The experiments are performed by measuring the Electromyography with exercise time variable under the 7.2m power-walking condition (8cm/1step). As the results, variation of the Median Frequency and Mean Power Frequency show the highest exercise effect and statistic significance in insole 3 (p <.5) at the calf. In conclusion, this paper suggests a new design insole for improvement in exercise effect by changing the hardness and shape of the insole. 1. INTRODUCTION Recent science technologies reduce the workload by automation and provide a convenient environment for people, but they restrict the physical activities of people in daily life. An automatic tool simplifies tasks and reduces physical activities which cause geriatric diseases and obesity due to the lack of exercises of the modern age. Those facts have become a motive of current studies on the various functions of shoes to increase exercise ability. Many kinds of sport shoes such as taekwondo, hiking, golf, tennis, and soccer shoes, etc., having various functions have been developed and also there are some safety shoes such as nursing, safety and cooking shoes. Most of the functional shoes were developed to achieve special purposes. For example, marathon shoes have functions of light weight and good ventilation and golf shoes are designed to prevent slipping and to increase stability while swinging. Functional shoes are designed with special objects for efficiency, however these are not necessary for daily living. The shoes usually protect the foot from impact, as well as prevent injury of the muscles, tendons, and joints in our body. These functions should be required in soles. Especially, outsole exposed to the ground surface affects to the abrasion and grounding capacity. Those basic roles can be performed by using the materials strengthening the characters of the flexibility, non-slip, and weight. Midsole and insole which are

2 parts that touch directly to the foot can strengthen the functions of the shoes by dispersing pressure and fatigue. Walking shoes like MBT (Masai Barefoot Technology) and SRD (Soft Road Diet), which lead a natural walking posture from heel to toe, give the functions of the sole using the walking mechanism of human. The front part of metatarsus and the heel part are high in walking shoes and the bottom is rounded, those shapes lead not only to increase the stability while walking, but also to relieve body tension and disperse pressure on the foot. Some papers comparing normal shoes with walking shoes presented that the load of the ankle joint due to the ground reaction is reduced by the round structure of the outsole and those factors induce adequate exercising effects to maintain stability (Choi et al., 23). The shoes having the round structure of the outsole can help people who have walking problems at articulation genu, by strengthening of lower leg muscle due to activating unused muscles (Nigg B. et al., 26). An et al. (27) showed that the shoes have roles to use muscles of the ankle and knee by correcting the instability of the body from the comparison study of walking patterns and motion characters of the lower muscles during walking on the treadmill with rounded outsole shoes. The current studies and developments related with the walking shoes focused on diet shoes. Kwak (21) presented that the hardness and weight of the shoes affect walking efficiency so the heavier the shoes the more energy consumption. Up until today the study related with the function of outsole and midsole to increase muscle activity has been performed often, but studies are few concerning insole. The studies and the developments of the functional insole can provide function respective to the type of the walking, task, and body size and provide economic and social (Lee, 25) advantages. By using the design concept of outsole and midsole in walking shoes, we develop walking insole. On the study, EMG (electromyography) measurements were performed to comprehend the level of the activity of the lower and lumber muscles during dynamic walking. 2. METHOD Six subjects with a mean age of 26.16(SD=.41) and a mean body mass of 72.5(SD=4.32) kg who have not experienced disease at the lumber and lower limbs participated in this study. All subjects checked their walking speed to measure stable steps for exercising with prototype insoles to improve exercise effects. The average walking speed of the subjects was 1.44m/s and was marked with tape on the floor. They had advance training for adaptation to the experimental environment. EMG measurement was performed to check muscle activities using the prototype insoles. The prototype insoles used for our experiment were designed so that the toe section was higher than the metatarsal to improve the exercise effects (L. Stewart, 27) and the arch was also designed higher than the metatarsal to disperse pressure on the foot. Also we applied the outsole type of the existing walking shoe to the prototype insoles. The hardness of the prototype insoles was measured from A hardness meter. The prototype insoles have two different kinds on hardness; below 15 and over 2. Each insole has been modified to a

3 specific shape. That shape has a given inclination from zero to 3 degrees at the metatarsal and has round types or stair types (Fig 1). There are 5 items in the prototype insoles and they are defined as insole 1, insole 2, insole 3, insole 4 and insole 5 (Table 1) (G. F. Kogler et al., 1995, An et al., 27). Specifically, insole 2 has hardness below 15 and the type is round. Insole 3 has hardness below 15 and the type is stair. Insole 4 has hardness over 2 and the type is round. Insole 5 has hardness over 2 and the type is stair. The prototype insoles have the same forms at the arch except insole 1, which has height at the arch 3mm and the inclination 25 degrees ((Nigg, B et al., 26). Insole 1 was defined as the normal insole to be compared against the prototypes (Table 1) (Fig 1) (G. F. Kogler et al., 1995, An et al., 27). All subjects performed power walking exercises with prototype insoles and EMG recording which was repeated five times using ME-6 -T8 equipment and Mega Win Version program (Fig 2). The step width of all subjects was fixed on 8cm (in total 7.2m) which caused about 9 heel strikes (Fig 3). All subjects performed the exercise for 1 hour complying with the experiment regulations on a track (Taebeum Ryu, 26) (Fig. 4). They took a break time for 1 minute every 1 minutes to prevent fatigue accumulation. The EMG data was recorded at erector spinae of waist, vastus lateralis of the thigh and lateral gastrocnemius of the calf which cause the highest effects on muscle activities during walking (Fig. 5) (Lee et al., 26). To measure the muscle activities of subjects, MF (Median Frequency) and MPF (Mean Power Frequency) were used as indices of the muscle activities and one-way ANOVA analysis was performed for statistical analysis. Table 1. Specs of the prototype insoles Insole Hardness Metatarsal Arch angle type angle height Insole Insole 2 below 15 3 round 25 3mm Insole 3 below 15 3 stair 25 3mm Insole 4 over 2 3 round 25 3mm Insole 5 over 2 3 stair 25 3mm

4 Figure 1. Prototype insoles used the experiments Figure 2. ME6-T8 (Mega Win Ver ) Figure 3. Walking width for 1 step

5 Figure 4. The size of the track Figure 5. Measurement parts in the body 3. Results The muscle activities can be analyzed by measuring the frequency shift of the EMG. In this study, we used the MF (Median Frequency) and MPF (Mean Power Frequency) among the signals of the EMG. The degree of the frequency shift depended on muscle activities, moreover, the more muscle activities lead to higher frequency shifts (Peter, 25). 3.1 MF (Median Frequency) analysis The MF examined the degree of the EMG frequency shift can show muscle fatigue. The MF equation defined as the mean of the frequency is shown as follows: MF 1 MF = S( f ) df = S( f ) df S( f ) df = MF 2 (1) S( f ) = Re + Im 2 2 S( f ) = power spectrum, Re = real term, Im = imaginary term The highest variation of the MF appeared in insole 3. While it is classified by examined parts, the thigh has a high variation, then the calf has middle variation, and the waist has the lowest variation. Insole 3 showed significant difference on 95% confidence intervals at the thigh (p-value=.56) (Table 2) (Fig 6). The p-value was.13 at the calf and.19 at the waist. The significant difference on muscle activities appeared before and after 1 hour of exercise.

6 Excluding insole 3, the variation of MF at insole 2 values are high at most measured points. Followed by insole 5, and insole 4 was last. Conclusively, insoles having hardness below 15 affects muscle activities more than insoles having hardness over 2. Insole 2 and insole 3 have the same hardness but different shape. The mean of MF in insole 3 is higher than that of insole 2 in analyzing the difference depending on the shapes of insoles. The p-value is.3 at the thigh and.44 at the waist and there was significant difference on 95% confidence intervals before the exercise. On the other hand, there was no significant difference between two shapes of insoles after 1 hour of exercise. It means that the shape of the insole at the metatarsal doesn t affect muscle activities after walking for 1 hour (Table 4). As a result, insole 3 which the metatarsal shape has stair type and the hardness is below 15 can lead to high muscle activities. Namely, it is possible for the insole which has hardness below 15 to improve muscle activities under the exercise condition of power-walking for 1 hour. 3.2 MPF (Mean Power Frequency) analysis MPF analysis shows the degree of the muscle fatigue through the frequency shift. The MPF equation defined as the mean of the frequency is shown as follows: MPF = fs( f ) df S( f ) df S( f ) = Re + Im 2 2 S( f ) = power spectrum, Re = real term, Im = imaginary term (2) As a result of the MPF analysis, the highest variation of the frequency shift was shown on insole 3 and the highest value was shown at the calf. The p-value was.5 at the calf,.7 at the thigh, and.29 at the waist and there was significant difference with 95% confidence intervals (table 3). These results are the same as the result of MF. Excluding insole 3, insole 2 shows the second higher frequency shift value. And insole 5 has the next highest frequency shift value and insole 4 has the lowest frequency shift value. Insole 2 also shows significant difference on the 95% confidence intervals. The p-value was.19 at the calf and.45 at the thigh. It means that the insole which has hardness below 15 affects muscle activities more than the insole hardness over 2(Table 3). On analyzing MF and MPF, there are differences depending upon the shape of insoles. There is a little difference between the insole 2(round type) on the metatarsal and insole 3 (stair type) only before exercise. The mean frequency of insole 3 was higher than that of insole 2 before exercise. There were significant differences between insole 2 and insole 3(p-value:.21) on 9% confidence intervals. However, there is no significant difference after exercise (Table 5). The difference depending on shapes of insoles at the metatarsal affects muscle activities only before exercise.

7 Analyzing MF and MPF, the median and mean of the frequency respectively, there was a little gap in their data. However, the results of the MF and the MPF show similarly. As a conclusion, the highest frequency variation appeared at insole 3 and there was significant difference among insoles on the 95% confidence intervals. Namely, insole 3 which has hardness below 15 can help the muscle activities under the exercise condition such as walking for 1 hour. MF(Hz) hr 1 hr Thigh Insole3 MPF(Hz) hr 1 hr Calf Insole3 Figure 6. The MP and MPF value of 5 insoles

8 Table 2. The statistic analysis of the MF p<.5 Part Insole Hour M ± SD(Hz) Variation (%) P-value 477.7± ± ± ± ±593.2 waist Insole * ± ± ± ± ± ± ± ± ± ±752.2 thigh Insole * ± ± ± ± ± ± ± ± ± ±887.9 calf Insole * ± ± ± ± ±824.2 Table 3. The statistic analysis of the MPF p<.5 Part Insole Hour M ± SD(Hz) Variation (%) P-value 437.5± ± ± ± ±595.8 waist Insole * 1 3.4± ± ± ± ± ± ± ± * ± ±755.3 thigh Insole * ± ± ± ± ± ± ± ± * ± ±853.3 calf Insole * ± ± ± ± ±568.8 Table 4. The MP analysis with the insoles which have same hardness p<.5 Before exercise After exercise Part Insole M ± SD(Hz) P-value M ± SD(Hz) P-value 338.4± ± *.25 Insole3 61.4± ±268. waist Insoel ± ± * ± ± ± ± *.489 Insole ± ±519.1 thigh Insoel ± ± ± ± ± ± Insole ± ±451.2 calf Insoel4 481.± ± ± ±69.4 Table 5. The MPF analysis with the insoles which have same hardness Part Insole p<.5 Before exercise After exercise M ± SD(Hz) P-value M ± SD(Hz) P-value 38.1± ± Insole ± ±264.6 waist Insoel4 39.9± ± ± ± ± ± *.421 Insole ± ±467.2 thigh Insoel ± ± ± ±656.9 calf 523.6± ± Insole ± ± Insoel ± ± ± ±

9 4. DISCUSSION As various functional shoes and walking shoes have been developed, recently, the study for improving functions of those shoes has become quite active. The main purposes of walking shoes are to bring about natural walking and to improve muscle activities through inducing proper use of muscles. Most of recent studies are to maximize functions by transforming the shape of outsole and midsole. This study investigated muscle activities on the lower limbs and lumber after dynamic activity such as power walking, depending on the hardness and type of the insoles. As compared factors, MF and MPF obtained by EMG measurement were used to analyze muscle activities. The four prototype insoles used for our experiments were based on former researches. Insoles angle of the metatarsal was zero to 3 degrees and the hardness of the insole was below 15 and over 2. And shapes of insoles were divided into round type and the stair type. The experiment measured EMG (MF, MPF) of the calf, thigh, and waist using the prototype insoles before walking and after one hour of walking. As a result, the highest variation was shown on insole 3 which had hardness below 15 and type stair. Results of the MF of the calf, thigh, and waist had a variation from 91% to 15% on insole 3. The MPF also had a variation from 88% to 28% at all measurement parts. On insole 2, the variation was about 5% in MF and MPF, and the variation of insole 5, insole 4, and insole 1 were insignificant. Insole 3 has the highest value of frequency shift (MF) and the statistical significance (p-value <.5). Especially, the activities of calf and thigh muscles were much higher than that of the waist. Insole 4 and insole 5 had hardness over 2 and had lower a frequency shift than that of insole 2 and insole 3 which had hardness below 15. It means that insoles which had hardness were below 15 affects the muscle activity for 1 hour of exercise, as shown on insole 2 and insole 3. However a little difference is shown between insole 2 and insole 3 because of the shape of the insoles. As a result according to shapes, insole 3 stair type has a higher frequency shift than that of insole 2 round shapes at the metatarsal. However, there is little change of frequency between two insoles after exercise for 1 hour. Those results show that there is little correlation between the shapes of insole and the muscle activity after 1 hour of exercise. Walking shoes can improve muscle activities by wearing insoles having various functions. In this study, we confirmed the fact that the hardness as well as the type of the insole can affect muscle activities. Moreover, insoles have the ability to maximize the function of the shoes through transformation of the shapes. For the future study, if the stability and comfort of the shoes should be considered with the insoles having various hardness, elastic, and types etc. it can be possible to design more systematic walking shoes and also can be applied to other studies for the most excellent shoes.

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