The effect of muscle glycogen loading on cardiorespiratory responses during aerobic exercise was investigated in twelve healthy females.
　Subjects performed bicycling exercise at a given workload (50～65% Vo₂max) for 31 min before (normal glycogen state : NG) and after muscle glycogen loading (high glycogen state : HG). The HG state was induced by a bout of exhaustive bicycling (up to 75% Vo₂max for 130～160 min) and carbohydrate-rich diet (4～5 days). Oxygen uptake (Vo₂), Heart rate (HR), rating of percieved exertion (RPE), respiratory exchange ratio (RER), surface EMG and plasma lactate concentration (LA) during exercise were compared between NG and HG. Significant decreases in Vo₂ (P< 0.01), HR (P< 0.05) and RPE (P< 0.05) were found in HG compared to NG. The lower Vo₂max in HG associated with significant increases in RER (P< 0.01) and LA (P< 0.05). Furthermore, integrated EMG picked up from m. vastus lateralis was significantly higher in HG than in NG (P< 0.05).
　From these data, it is indicated that muscle glycogen loading may reduce Vo₂ required for the identical exercise through enhanced glycolysis and glycogenolysis pathways in active muscles. It is also suggested that the reduced Vo₂ in HG might be attributed to preferential recruitment of fast-twich (FT) fibers since FT fibers are known to induce a higher LA production and amplitude of surface EMG. Thus, present findings also indicate affirmative effect of muscle glycogen loading on exercise performance.

DESCENTE SPORTS SCIENCE Vol.15/THE DESCENTE AND ISHIMOTO MEMORIAL FOUNDATION FOR THE PROMOTION SPORTS SCIENCE