The effect of material characteristics of shoe soles on muscle activation and energy aspects during running
Introduction
Heel–toe runners experience impact forces between 1.0 and 2.5 times body weight. One would expect impact forces to produce substantial vibrations of the soft tissue packages of the lower extremities (e.g. quadriceps, hamstrings, triceps surae). However, impact related soft tissue vibrations are small or not apparent. Thus, the soft tissue packages must have mechanical characteristics that correspond to heavily or critically damped mechanical systems. Since vibrations are small for any shoe-surface combination the mechanical characteristics of the soft tissues must be adjusted by muscle pre-activation (Nigg, 1997; Wakeling and Nigg, 2001) and one should expect muscle and subject specific reactions for different shoe conditions.
Thus, one may speculate that muscles are programmed to avoid vibrations (Nigg, 1997). A specific muscle group should change its activity when the frequency of the input signal is close to its natural frequency and the changes in activity should depend on the mass of the soft tissue package and its mechanical characteristics. Furthermore, it is speculated that any change in muscle activity affects work and performance of the human locomotor system (Nigg, 2000). Thus, effects on muscle activity should be observable by studying EMG signals and effects on work by studying oxygen consumption. However, experimental evidence for such phenomena is not available.
The purposes of this study were:
- (a)
to determine group and individual differences in oxygen consumption during heel–toe running and
- (b)
to quantify the differences in EMG activity for selected muscle groups of the lower extremities.
When running in shoes with different mechanical heel characteristics.
Specifically the following hypotheses were tested:
- H1
The group differences in oxygen consumption between the elastic and the viscous shoe condition are small and not significant.
- H2
There are groups of subjects with significantly less, equal and more oxygen consumption when running in shoes with elastic and viscous heels.
- H3
Changes in shoe conditions change EMG activity of selected lower extremity muscles. The differences are muscle and subject specific.
Section snippets
Methods
Twenty proficient male runners participated in this study and gave written informed consent. They were free of any serious injuries at the time of study.
Two shoe conditions were used in this study. The two shoes were identical (same uppers, outsoles, insoles, etc.) but differed in the midsole materials of the heel. One heel material was of medium hardness (shore C=45) and mainly elastic. The other heel material was softer (shore C=26) and more viscous. To quantify the differences between the
Results
The results are grouped with respect to the following aspects, (a) description of a typical EMG data set for treadmill running, (b) group results and (c) individual results for oxygen consumption and EMG data.
Individual results
The individual differences in oxygen consumption are illustrated in Fig. 4. Five subjects (2, 3, 8, 18 and 19) used in all four comparisons less oxygen for the elastic shoe–heel situation. Five subjects (4, 6, 7, 16 and 20) used in all four comparisons less oxygen for the viscous shoe heel situation. Eight subjects (1, 5, 9, 10, 11, 12, 14 and 17) had not consistent results for the four comparisons. Thus, hypothesis H2 was supported by the results of this study.
The RMS of the EMG showed muscle
Discussion
The purposes of the study were to determine group and individual differences in oxygen consumption during heel–toe running in shoes with elastic or visco-elastic heel materials and to investigate whether observed differences would be associated with changes in muscle activity.
Acknowledgements
This study has been financially supported by Adidas, NSERC and the da Vinci Foundation.
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