Substrate utilization during arm and leg exercise relative to the ventilatory threshold in men

Background. The purpose of this study was to determine variations in substrate utilization in men during arm and leg exercise at 70 and 90% of mode specific ventilatory threshold (Tvent). Methods. Ten males served as subjects. Limb total and muscle volumes were estimated in the right arm and leg with anthropometry. Ventilatory equivalence, excess CO₂, and modified V-slope methods were used to determine Tvent. Subjects performed 15 min of exercise at 70 and 90% Tvent arm cranking (AC) exercise, and 70 and 90% Tvent leg cycling (LC) exercise. Results. VO₂, VE, and HR were higher during LC exercise at both intensities. However, arm and leg RPE were not different at 70 and 90% Tvent. There were no significant differences between modes at 70% Tvent in relative carbohydrate use (54.5±9.5 and 57.8±8.2% for AC and LC, respectively) and relative fat oxidation (45.5±9.5 and 42.2±8.2% for AC and LC, respectively). However, at 90% Tvent, relative carbohydrate oxidation was significantly higher during AC versus LC exercise (75.4±10.6 versus 68.6±9.0%, p<0.05). Energy expenditure (total kJ·min^-1) was significantly lower during AC exercise (14.5±2.9 and 18.4±3.4 for the 70 and 90% Tvent, respectively) versus LC exercise (27.1±3.3 and 34.8±4.1 for the 70 and 90% Tvent, respectively; p<0.05). Conclusions. These results indicate that substrate use during AC exercise is similar to LC exercise at 70% Tvent. However, as the exercise intensity increases, the smaller arm musculature becomes more dependent on carbohydrate utilization compared to the legs.