Study of biomechanical and muscle activity patterns during a 30min downhill running test and subsequent muscle damage in male trailers.

Introduction: Downhill running (DR) sections, a common component in off-road races, can lead to exercise-induced muscle damage (EIMD) due to the greater eccentric work of some lower limb muscles. Running biomechanics and muscle activation may change during prolonged DR but these adjustments have not been clearly identified in trailers yet. Therefore, this study aimed to characterize the running pattern over a 30min downhill running test and to investigate the DR-induced muscle damage.
Methods: Recreational male trailers (n=12; 27.9 ± 8.9 yrs) underwent a maximal VO2max test on a treadmill to determine their maximal aerobic speed (MAS). Then, they were submitted to a 30min DR protocol at 90% MAS (-15% gradient). Physiological and biomechanical parameters (using a 3D motion system) were measured during DR (at the start, middle, and end), coupled with surface electromyography (EMG) recordings. Plasma creatine kinase (CK), maximal isometric force (MIF) of the knee extensors and muscle soreness were assessed pre, 24h and 48h after DR.
Results: The subjects (VO2max: 56.94 ± 7.15 mlO2.min-1.kg-1) completed 30min DR at 90% MAS (14.11 ± 1.58 km/h). While significant differences between level running and DR were found, the spatiotemporal parameters (step frequency, swing and stance times) and kinematics data did not change over the DR test. Concurrent EMG analysis revealed significant differences from the start to the end of the DR for vastus lateralis (VL) and biceps femoris (BF) muscles. VL muscle activity increased during the swing phase (p<0.05) while BF muscle displayed a decreased activation during the stance phase (p<0.05) over the DR. No significant change was found for any other studied muscles (rectus femoris, vastus medialis, gastrocmemius lateralis and medialis muscles). Plasma CK activity significantly increased from pre (190 ± 88.48 UI/l) to 24h (615.75 ± 260.96 UI/l) and 48h (362 ± 145.13 UI/l) post-exercise (p<0.01). A significant decrease in MIF was observed at 24h (-5.49 ± 6.47%) and 48h (-4.51 ± 6.22%) post-DR compared to pre (p<0.05). Significant muscle soreness was also observed with the highest values found for the quadriceps (3.58 ± 2.49 a.u) and the gluteal (4.04 ± 2.51 a.u) muscles at 48h post-exercise (p<0.01).
Conclusions: Our data highlighted significant changes in muscle activity for vastus lateralis and biceps femoris muscles over a 30min downhill running test while no biomechanical adjustment was found. The DR induced muscle damage as reflected by significant changes in EIMD indirect markers. Further correlation studies between muscle activity during DR and subsequent EIMD may help to better understand performance in trail disciplines.