The effect of glycogen reduction on cardiorespiratory and metabolic responses during downhill running.

PURPOSE: Exercise-induced muscle damage and lowered glycogen are common during heavy training periods, and may prolong recovery. We examined the effects of lowered glycogen on cardiorespiratory, metabolic and perceptual responses to downhill running.

METHODS: Twelve men performed two downhill runs (-12 % gradient, 12.1 ± 1.1 km h(-1)) separated by 6 weeks, under normal (NORM) and reduced glycogen (RED) conditions in a crossover design. For RED, participants performed exhaustive cycling at 60 % [Formula: see text]O2max power (95 ± 13 min) in the evening, and the next morning completed a downhill run comprising of five stages of 8 min running, with 2 min recovery (1 % gradient, 8 km h(-1)) between each stage. Expired gas, heart rate, rating of perceived exertion (RPE) and blood lactate (bLa) and glucose were measured for each stage.

RESULTS: Blood glucose (P < 0.05) and respiratory exchange ratio (P < 0.01) were lower in RED, than NORM, throughout the downhill run. RED demonstrated higher bLa until stage Four (P < 0.05), and RPE for stages Two and Five (P < 0.05).Ventilatory equivalent of carbon dioxide output ([Formula: see text]/[Formula: see text]) was higher for stages One (P < 0.01), Two and Five (P < 0.05), and oxygen uptake ([Formula: see text] E/[Formula: see text]O2) was lower for stages Three and Four (P < 0.05) for RED.

CONCLUSIONS: Downhill running with reduced glycogen, elevated fat oxidation and bLa response, and, in part, increased effort perception. The alterations in [Formula: see text] E/[Formula: see text]O2 and bLa may suggest that carbon dioxide removal was somewhat impaired.