Author(s): MONOT, T., LACROIX, V., MILLET, G., COLOSIO, A., Institution: UNIVERSITÉ JEAN MONNET, Country: FRANCE, Abstract-ID: 2237

INTRODUCTION:
Physiological determinants of endurance performance, such as exercise thresholds, have been shown to deteriorate during prolonged exercise, which forms the basis of the physiological resilience concept. However, underpinnings mechanisms are still unclear, and one candidate for this alteration could be exercise-induced muscle damage (EIMD). EIMD occurs when performing an unaccustomed exercise, particularly when it is associated with eccentric contractions, like in downhill running (DR). This study investigated the effects of prolonged DR and cycling on the power outputs (PO) at the gas exchange threshold (GET) and at the respiratory compensation point (RCP).
METHODS:
Twelve healthy subjects (9 males, VO2peak: 47.6±7.8 mL/min/kg) performed one maximal cycling ramp incremental (RI) test to assess baseline (BSL) PO at the GET and at the RCP and one submaximal DR RI test (-15% slope) to determine the speed at the GET. Maximal RI in cycling were repeated on three occasions: (i) after 45 min of cycling at 80% of PO at the GET (C), (ii) after 45 min of DR at 80% of speed at the GET (R), (iii) 48h after R (R48H). Knee extensors maximal isometric voluntary torque (MVT) and the torque evoked by potentiated doublet of electrical stimulation of the femoral nerve at 10 (Db10) and 100Hz (Db100) were measured pre and 20min post fatiguing exercise in cycling and DR and at R48H, all prior to the ramp. A linear mixed-effects model combined with ANOVA was used for statistical analysis. Results are presented as estimated marginal means [95% CI].
RESULTS:
There was no effect of condition for PO at the GET (BSL: 167 [138-197] vs C: 162 [132-192] vs R: 165 [135-196] vs R48H: 164 [134-194] W, p=0.908) and at the RCP (250 [209-291] vs 242 [201-283] vs 245 [204-286] vs 247 [206-289] W, p=0.696). There was a significant decrease in MVT (301 [252-351] vs 280 [230-329], p<0.001) and Db10/Db100 (0.953 [0.911-0.996] vs 0.848 [0.806-0.891], p<0.001), with no effect of condition, nor time x condition interaction for both variables. There was no difference in MVT (299 [249-349] vs 310 [260-361], p=0.5) and Db10/Db100 (0.95 [0.9-1] vs 0.98 [0.93-1.03], p=0.749) between pre-R and R48H.
CONCLUSION:
There was no effect of neither fatiguing exercises on the PO at the GET and at the RCP. Nevertheless, the similar changes in MVT and Db10/Db100 observed after the cycling exercise suggest that they were induced by the metabolic load that was equivalent between conditions, instead of being the consequence of EIMD. Thus, despite the abundant literature showing that prolonged DR results in EIMD, we conclude that the metabolic and mechanical loads were insufficient to significantly reduce the PO at the GET and at the RCP and that 45 min of DR at -15% slope in the moderate intensity domain does not alter EIMD markers.