How do shock-absorber insoles influence the execution of a gymnastic vault?

Aim: The aim of this work is to report a preliminary evaluation of the effects of ad hoc shock-absorber insoles during the execution of a gymnastic vault. Methods: Seventeen young gymnasts (age: 10.8 ± 2.3 years; weight: 35.2 ± 10.8 kg; height: 142 ± 14.5 cm, mean ± standard deviation) participated in the study. The subjects were asked to perform a series of handspring vaults while wearing a pair of wireless accelerometers attached at the ankles by means of strap bands. They performed the exercise in 3 different conditions: a)with bare foot; b) wearing gymnastic shoes; c) wearing artistic gymnastic shoes with shock-absorber insoles made in styrene-ethylene/butylene-styrene (SEBS). For each trial of each subject, the acceleration signal (along the tibia) referring to the dominant foot was processed in order to identify the epoch corresponding to the phase of foot-springboard contact. Accelerations during such epochwere then processed to calculate the root mean square (RMS), the frequency spectrum and the following parameters: max intensity, max frequency, mean intensity, mean frequency, and median frequency. A one-way Repeated Measures ANOVA test, followed by a Bonferroni Multiple Comparison post-test, was performed on each parameter dataset to check for differences (p\0.05) between a), b), and c). Results: No statistically significant differences were found in terms of frequency-related parameters. The mean RMS value is greater in condition c) (6.2 g, g = 9.81 m/s2) with respect to condition b) (6.0 g) and a) (5.8 g). Statistical significance was found between conditions a) and c) (p = 0.016). The above results suggest that the acceleration of the dominant foot of the athletes, during the contact with the springboard, is greater when wearing the insole with respect to the bare foot condition. This was somehow confirmed by the fact that all the subjects, interviewed after the tests, claimed that while wearing the insoles they hit the springboard with more intensity, as they felt their feet more protected. Conclusion: SEBS insoles appear to have an effect in protecting the foot of the gymnasts who therefore feel more prone to hit the springboard with higher intensity than while doing the exercise with bare feet. Additional tests should be made to further investigate this phenomenon. The first step should be the evaluation of a possible placebo effect, by including a condition where vaults are executed with other types of insoles inserted in the shoes of the subjects. Moreover, for better studying the shock absorption effects of the insoles, the sampling rate of the accelerometer should be increased.