Effect of eccentric training at different muscle lengths on the gastrocnemius medialis fascicle behaviour during single and multi-joint tasks

Purpose: The aim of this study was to investigate the effect of eight weeks of eccentric training at short versus long muscle lengths on the gastrocnemius medialis fascicle behaviour during single and multi-joint tasks. Methods: Twenty-seven participants were assigned to two groups and performed eccentric training for eight weeks at short (30° of plantar flexion to 0°) or at long (0° to maximal dorsiflexion) muscle lengths, which led to an increase in passive fascicle length for the latter group. Achilles tendon stiffness, maximal eccentric and maximal and explosive isometric plantar flexion torques were recorded before and after the training period. We also analysed the effect of training on the fascicle dynamic behaviour of the gastrocnemius medialis muscle during single-joint isometric tasks, and during various multi-joint tasks: submaximal running, maximal countermovement jumps and hopping. Results; An increase of isometric (13.0 ± 22.6% and 9.7 ± 15.6% p < 0.01 for short and long length groups) and eccentric maximal torque (7.2 ± 21.9% and 15.4 ± 23.3% p < 0.05 for short and long length groups) were obtained for both groups, while Achilles tendon stiffness increased in the long muscle length group (35 ± 32.3% p < 0.05) only. Training did not significantly alter fascicle dynamic behaviour in either single- or multi-joint tasks for both groups. Conclusion: While eccentric training at long muscle lengths appeared more effective in altering the muscle and tendon mechanical properties of the gastrocnemius medialis, it did not induce substantial changes in fascicle operating length during single- and multi-joint tasks.