Comparison of the lower limb muscle activity during a downhill run and the subsequent muscle damage in trail versus road runners.

Introduction: Downhill running (DR) sections, a common component of off-road racing, can lead to exercise-induced muscle damage (EIMD) due to the greater eccentric work of some lower limb muscles. Repeated exposure to eccentric work is known to reduce or prevent EIMD. Running patterns may change during prolonged DR but the relationship between these adaptations and the EIMD has not been fully understood. Therefore, this study aimed to compare the running patterns during a 30min DR test and the magnitude of EIMD between trail and road runners.

Methods: Recreational male trail runners (TR; n=22; 23.8 ± 3.7 yrs) and road runners (RR; n=21; 30.5 ± 8.8 yrs) underwent a treadmill VO2max test to determine their maximal aerobic speed (MAS). They then performed a 30min DR protocol at 90% MAS (-15% gradient). Spatiotemporal parameters (using a 3D motion system) were measured during DR, coupled with surface electromyography recordings. Plasma creatine kinase (CK) and delayed-onset muscle soreness (DOMS) were measured before, 24h and 48h after DR. Squat jump (SJ) performance was assessed before, immediately and 24h after exercise.

Results: The VO2max values of the TR and RR groups were 55.9 ± 5.3 and 52.5 ± 6 mlO2/min.kg, respectively. The increase in plasma CK activity was significantly higher in RR group at 24h (1306 ± 630 UI/l) and 48h (852 ± 553 UI/l) post-exercise compared to TR group (772 ± 540 UI/l; 382 ± 151 UI/l; respectively). Similarly, the RR experienced higher muscle soreness of the knee extensors at 24 and 48h post-exercise (5 ± 2.4 and 4.5 ± 2.2 a.u) than the TR (3.6 ± 2.3; 3.7 ± 2.4 a.u). SJ performance decreased immediately and 24h after DR only in the RR group (-8.7 ± 7.6 and -7.3 ± 5.4%). While no significant differences in stride frequency, swing and stance times were found between groups, the duration of the stance phase significantly increased from the beginning to the end of the run (2.3 ± 4.2%). Muscle activity of lower limbs did not differ between groups but significant changes were found over time. Muscle activity increased for the biceps femoris, rectus femoris, vastus lateralis and medialis during the stance phase whereas the gastrocnemius lateralis and medialis showed a decreased activation from the start to the end of DR.

Conclusions: As expected, the RR showed greater changes in EIMD indirect markers than TR after DR but no difference in muscle activity was found between groups. Further correlation analysis between running patterns and subsequent EIMD may help to better understand the relationship between these parameters.