Author(s): TALLIO, T., NORDEZ, A., BIZET, B., CATTAGNI, T., DOREL, S., Institution: NANTES UNIVERSITÉ, Country: FRANCE, Abstract-ID: 1275

INTRODUCTION:
Over the last 20 years, several studies showed that muscle-tendon interactions play a major role in movements (1). However, it remains unknown how the changes in muscle architecture due to training could influence these interactions. Eccentric studies have demonstrated an increase of the fascicle length following training in various muscles of the lower limb (2), and recently the benefits of training at high muscle length has been highlighted to induce more muscle adaptations, like hypertrophy or increase in fascicle length (3). Thus, the first aim of the current study is to investigate the potential change of fascicle behavior and tendon properties following an eccentric training at different muscle length. The second aim is to explore how these changes impact muscle-tendon interactions in vertical jump and running.
METHODS:
28 participants were randomised in two groups, High Length (HL) vs Short Length (SL). They performed 8 weeks (24 sessions) of eccentric training on the calf muscles at different range of motion (ROM). Measurements were made PRE and POST training. Fascicle length of the gastrocnemius medialis (GM) was measured with an ultrasound apparatus during maximal voluntary contractions (MVC) at 5 angles, eccentric contraction and through rate of force development (RFD) explosive contractions. We also estimated the stiffness of the Achilles tendon (AT) during ramp and RFD contractions. Finally, we measured the fascicle behavior of the GM during maximal vertical jumps (hopping and countermovement jump) and submaximal running.
RESULTS:
We found a significant change of the fascicle length for HL group (+7%, p<0,05) during passive condition, but only before the slack length. No difference was found for the SL group. Torque increased in both groups in isometric (HL +8%, SL +13% at 0°, p<0,01) and eccentric contraction (HL +18,7%, SL +12,9%, p<0,01) but no interactions group x time were found. No significant change in fascicle length was observed during MVC, and no change in optimal length was detected in both groups. RFD did not change in both groups after training. AT Stiffness increased significantly for HL group (+29,9%, p<0,05) but not in SL group. Data from vertical jumps and running are still in processing.
CONCLUSION:
No significant effects were found for fascicle-tendon interactions during maximal monoarticular contractions (RFD, MVC), suggesting that changes in muscle-tendon behavior (tendon stiffness and fascicle length) found in HL group does not impact the dynamic behavior of fascicles. We assume that these two factors offset each other’s influence during contractions. Multi-joint maximal (jumps) and submaximal (running) tasks will provide a deeper understanding of the training effects on fascicle-tendon interactions.

REFERENCES:
1) Ishikawa & Komi, Exerc. Sport Sci. Rev., 2008
2) Duclay et al., Muscle and Nerve, 2009
3) Marusic et al., SJMSS, 2020