Plasma catecholamine and blood lactate responses to incremental arm and leg exercise

Purpose and Methods: The present study was conducted to examine the pattern of plasma catecholamine and blood lactate responses to incremental arm and leg exercise. Seven untrained male subjects performed two incremental exercise tests on separate days in random order. One test consisted of 1-arm cranking (5W.2 min(-1)), whereas the other exercise test was 2-leg cycling (20-25W.2 min(-1)). Blood samples were obtained from the nonexercising arm during 1-arm cranking and from the same arm and vein during 2-leg cycling. Thresholds for blood lactate (T-La), epinephrine (T-Epi) and norepinephrine (T-NE) were determined for each subject under both exercise conditions and defined as breakpoints when plotted as a function of power output. Results: When the two modes of exercise were compared, T-La, T-Epi, and T-NE were all significantly lower for 1-arm cranking than for 2-leg cycling (P < 0.01). During 1-arm cranking, T-La (0.96 +/- 0.10 L.min(-1)), T-Epi (1.02 +/- 0.07 L.min(-1)), and T-NE (1.07 +/- 0.09 L.min(-1)) occurred simultaneously. During 2-leg cycling, T-La (1.77 +/- 0.20 L.min(-1)),T-Epi (1.74 +/- 0.17 L.min(-1)), and T-NE (1.98 +/- 0.17 L.min(-1)) occurred at similar levels of (V) over dotO(2) and were not significantly different. The correlation observed between the (V) over dotO(2) measured at the T-La and T-Epi was 0.917 for arm and 0.929 for leg exercise (P < 0.001). The epinephrine concentration ([Epi]) obtained at the T-La was not significantly different for arm (0.144 ng.mL(-1)) and leg (0.152 ng.mL(-1)) exercise. Conclusions: The breakpoint in plasma [Epi] shifted in an identical manner and occurred simultaneously with that of T-La regardless of the mode of exercise (arm or leg). The Epi concentrations observed at the T-La agree with those previously reported to produce arise in blood lactate during Epi infusion at rest. These results support the hypothesis that a rise in plasma [Epi] may contribute to the breakpoint in blood lactate that occurs during incremental exercise.