Author(s): DEMEUSOY, P., PIPONNIER, E., MANGINI, A., BOURENNE, J., BREGEON, F., PRIEUR-BLANC, N., HAYS, A., NICOL, C., Institution: AIX-MARSEILLE UNIVERSITÉ, Country: FRANCE, Abstract-ID: 2630

INTRODUCTION:
Endurance graded runs can result in mild and reversible lower limb muscle damage, inflammation and functional impairments [1]. Post-run muscle function has mostly been studied using multi-joint tasks or focusing mainly on the knee extensors [1-3]. However, other lower limb muscle groups can be affected and may not follow the same recovery pattern. This study investigated changes in maximal voluntary torque and muscle activity of the knee and ankle flexors and extensors up to 7 days post-race period.
METHODS:
Based on their real race performance, 10 runners (aged 25±7; 3 females) reproduced a graded 20 km race (D+ 382 m; D- 294 m) on a treadmill in an environmental room. The protocol included a familiarisation session and four experimental sessions conducted before (PRE) and 2, 4, and 7 days post-race (D2, D4 and D7, respectively). Each session began with muscle soreness rating (MS) using a visual analogue scale (0-10). Then, unilateral maximal voluntary isometric contractions of knee flexion and extension, as well as ankle plantarflexion and dorsiflexion, were performed using an isokinetic dynamometer. Surface electromyographic (EMG) activity was recorded from the vastus medialis and lateralis, rectus femoris, biceps femoris, semi tendinosus, gastrocnemius medialis and lateralis, soleus and tibialis anterior muscles. The peak torque and associated root mean squared (RMS) EMG values were selected. Repeated measures ANOVA and ART ANOVA (for MS data) were performed fitted with time as the main effect.
RESULTS:
The averaged running time was 1:39±0:13. No significant time effect was found (p>.05), but a large inter-individual variability was observed in all four torque tests. For example, knee extension relative torque changes from PRE averaged +0.1±9% [-12 to +12%] at D2, -3.9±5% [-9 to +6%] at D4 and -2.7±11% [-16 to +17%] at D7. Regarding RMS, a significant time effect was found only for the gastrocnemius lateralis during knee flexion (p<.05). Compared to all other time points, it was lower at D2, with a relative decrease of -18±19% from PRE, and only one participant increased (+23.1%). Regarding MS, a significant time effect was found for the quadriceps only (p<.01), with a higher value at D2 compared to D7 (1.5±1.5 A.U. vs. 0.5±0.8 A.U.; p<01).
CONCLUSION:
Despite relatively homogeneous running time and environmental conditions, the graded run induced highly individual neuromuscular responses. The previously reported D2 decrease in knee extensor torque after the same run on the road [2] was not observed after the treadmill run. By D7, none of the runners showed a complete neuromuscular recovery, although MS had disappeared. Our results emphasise that distinct lower limb muscles may be affected and recover differently, both within and between individuals. Forthcoming imaging analyses could provide further clarity on the links between neuromuscular, torque and structural changes during recovery [3].
[1] Chalchat et al., 2022
[2] Macchi et al., 2021
[3] Macchi et al., 2024