Differences in epinephrine and substrate responses between arm and leg exercise

The purpose of this study was to determine epinephrine (EPI) and selected substrate responses during arm crank (AC) and leg cycle (LC) exercise at the same absolute and relative exercise intensity. Nine males performed 30 min AC and LC tests at 70% of ergometer-specific peak oxygen uptake (VO₂), and a 30 min LC test eliciting a similar VO₂ required during the AC test. Blood samples (30 ml) were collected via an indwelling arm catheter at rest, and at minutes 13 and 28 of exercise for determinations of plasma EPI, serum free fatty acid (FFA), serum glycerol (GLY), blood glucose (GLU), and blood lactate (LA) concentrations. At equivalent VO₂, higher (P < 0.05) EPI, LA, and respiratory exchange ratio (RER) responses were obtained during AC than LC exercise. However, these physiologic responses were similar during AC and LC exercise at the same relative intensity. No significant differences over time were observed for FFA, GLY, and GLU between AC and LC exercise at either the same absolute or relative intensity. The results support previous hypotheses that AC exercise is physiologically more stressful than LC exercise at the same VO₂. The data further indicate that adrenomedullary activity (EPI response) and substrate utilization (LA and RER responses) are regulated by relative exercise intensity and not the exercising muscle mass.