Changes in Skeletal Muscle Oxidative Capacity After a Trail Running Race

to evaluate the effects of a trail-running race on muscle oxidative function by measuring pulmonary gas exchange variables and muscle fractional O₂ extraction.

Eighteen athletes were evaluated before (PRE) and after (POST) a trail running competition of 32-km or 50-km with 2000 m or 3500 m of elevation gain, respectively. During the week before the race, runners performed an incremental uphill running test and an incremental exercise by utilizing a one-leg knee-extension (KE) ergometer. The KE exercise was repeated after the end of the race. During the KE test we measured oxygen uptake (V'O₂) and micromolar changes in deoxygenated hemoglobin (Hb)+myoglobin (Mb) concentrations (Δ[deoxy(Hb+Mb)]) on vastus lateralis with a portable near-infrared spectroscopy.

V'O₂peak was lower at POST vs. PRE (-23.9±9.0%, p<0.001). V'O₂peak at POST was lower than V'O₂ at the same workload at PRE (-8.4±15.6%, p<0.050). Peak power output and time to exhaustion decreased at POST by -23.7±14.3% and -18.3±11.3%, respectively (p<0.005). At POST the increase of Δ[deoxy(Hb + Mb)] as a function of work rate, from unloaded to peak, was less pronounced (from 20.2±10.1 to 64.5±21.1% of limb ischemia at PRE to 16.9±12.7 to 44.0±18.9% at POST). Peak Δ[deoxy(Hb+Mb)] values were lower at POST (by -31.2±20.5%; p<0.001).

trail running leads to impairment in skeletal muscle oxidative metabolism, possibly related to muscle damage from repeated eccentric contractions. In association with other mechanisms, the impairment of skeletal muscle oxidative metabolism is likely responsible of the reduced exercise capacity and tolerance during and following these races.