Downhill Running-Induced Muscle Damage in Trail Runners: An Exploratory Study Regarding Training Background and Running Gait

This study aimed to assess the effect of a downhill-running (DR) bout on muscle damage biomarkers. It also examined whether training background and gait kinematics may influence DR-induced muscle damage and strength loss. Thirty-six experienced trail runners (25 men, 11 women), participants of a 106 km ultra-trail, performed a 5 km DR bout at 15% decline and at an intensity equivalent to their first ventilatory threshold. Muscle damage biomarkers (creatine kinase, lactate dehydrogenase, and myoglobin) were analyzed before and 30 min after the DR protocol, and also before and after the UT race. Isometric strength was assessed before and after DR, and gait parameters were recorded during DR. All muscle damage biomarkers increased following DR (<i>d</i> = 0.19 to 1.85). Lactate dehydrogenase concentrations after the race and DR were associated (<i>r</i> = 0.64). Athletes who habitually performed downhill repetitions showed reduced creatine kinase (182 ± 73 U/L vs. 290 ± 192 U/L; <i>p</i> < 0.05; d = 0.64) and greater squat strength retention (4 ± 10% vs. -9.1 ± 16.8%; <i>p</i> <0.05; <i>d</i> = 0.87). Ankle plantar flexion and squat strength retention were inversely correlated with vertical oscillation (<i>r</i> = -0.44) and step length (<i>r</i> = -0.37), respectively. In summary, lactate dehydrogenase response to a short DR bout could indicate an athlete's readiness to handle ultra-trail-induced muscle damage, although further research is needed to confirm it. In addition, despite the exploratory nature of the study, regularly performing downhill intervals and adopting a more terrestrial gait pattern appear to soften strength loss and muscle damage response to DR.