Medial Gastrocnemius Muscle Activity during Single-Leg Hopping to Exhaustion.

This study described changes in leg muscle activation characteristics during exhaustive single-leg hopping. Twenty-seven healthy men performed trials (132 hops/min) to exhaustion, without a target height, to a target height with visual feedback and target height with tactile feedback. Mean muscle activation amplitude of the medial gastrocnemius (MG) decreased during the anticipatory period while duration of MG activity was maintained when hopping to a target height and contrasted the changes during hopping without a target height. Changes to MG activity were specific to whether the hopping height had been maintained or not. Changes during the anticipatory period of MG activity, indicative of adaptation in descending motor pathways, implicate utility of a motor learning strategy to allow completion of an exhaustive task.

Does providing real-time augmented feedback affect the performance of repeated lower limb loading to exhaustion?

INTRODUCTION: This study aimed to determine whether real-time augmented feedback influenced performance of single-leg hopping to volitional exhaustion. METHODS: Twenty-seven healthy, male participants performed single-leg hopping (2.2 Hz) with (visual and tactile feedback for a target hop height) or without feedback on a force plate. Repeated measures ANOVA were used to determine differences in vertical stiffness (k), duration of flight (tf) and loading (tl) and vertical height displacement during flight (zf) and loading (zl). A Friedman 2-way ANOVA was performed to compare the percentage of trials between conditions that were maintained at 2.2 Hz ± 5%. Correlations were performed to determine if the effects were similar when providing tactile or visual feedback synchronously with the audible cue. RESULTS: Augmented feedback resulted in maintenance of the tf, zf and zl between the start and end of the trials compared to hopping with no feedback (p<0.01). With or without feedback there was no change in tl and k from start to end. Without feedback, 21 of 27 participants maintained >70% of total hops at 2.2 ± 5% Hz and this was significantly lower (p=0.01) with tactile (13/27) and visual (15/27) feedback. There was a strong correlation between tactile and visual feedback for duration of hopping cycle (Spearman's r=0.74, p ≤ 0.01). CONCLUSION: Feedback was detrimental to being able to maintain hopping cadence in some participants while other participants were able to achieve the cadence and target hop height. This indicates variability in the ability to use real-time augmented feedback effectively.