Abstract
Different factors were shown to alter the vibration characteristics of soft-tissue compartments during running. Changing pre-heel strike muscle activation or changing footwear conditions represents two possibilities to influence the vibration response via frequency shift or altered damping. Associated with the study of muscle pre-tuning is the difficulty in quantifying clean experimental data for the acceleration of soft-tissue compartments and muscle activities in heterogeneous populations. The purpose of this study was to determine the vibration and pre-tuning response to footwear across a wide range of participants during running and establish and describe groups formed according to the damping coefficient. 32 subjects were used for further analysis. The subjects ran at a self-selected speed (5 min) on a treadmill in two different shoes (soft & hard), while soft-tissue accelerations and muscle activation at the gastrocnemius medialis were quantified. Damping coefficients, total muscle intensity and dominant vibration frequencies were determined. Anthropometrics and skinfold measurements of the lower limbs were obtained. According to the damping coefficient response to the footwear intervention, three groups were formed, with most runners (n = 20) showing less damping in the hard shoe. Total muscle intensity, anthropometrics, and dominant vibration frequency across footwear were not different for these three groups. Most runners (84.4%) used the strategy of adjusting the damping coefficients significantly when switching footwear. Despite damping being the preferred adjustment to changes in footwear, muscle pre-tuning might not be the only mechanism to influence damping as previously suggested. Future studies should focus on the subject-specific composition of soft-tissue compartments to elucidate their contribution to vibrations.
Highlights
When a runner contacts the ground, the impact forces during landing initiate vibrations of the soft-tissue compartments of the lower extremities [1, 2]
Soft-tissue vibrations in participants with a wide range of body types are mainly affected by their damping coefficients when footwear changes during treadmill running
Damping coefficients were successful in determining three groups according to damping responses in the tested footwear conditions
Summary
When a runner contacts the ground, the impact forces during landing initiate vibrations of the soft-tissue compartments of the lower extremities [1, 2]. The anthropometrics are a given for each subject They are speculated to influence the soft-tissue vibration propagation tremendously [3] and were shown to affect the preferred adaptation strategy (damping or shifting the frequency) [4]. To actively change vibrations during running in preparation for the impact, an anticipatory change in muscle activation is necessary [5], called pre-tuning. These changes in muscle activation will alter the metabolic cost while running and would energetically not be advantageous [6, 7]. It was shown that tensing muscles reduces skin-movement artefacts [11] as they are major contributors to skin motion [12]
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