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 exer cise tests on separate days in random order. One test consisted of 1-arm cr anking (5W.2 min(-1)), whereas the other exercise test was 2-leg cycling (2 0-25W.2 min(-1)). Blood samples were obtained from the nonexercising arm du ring 1-arm cranking and from the same arm and vein during 2-leg cycling. Th resholds for blood lactate (T-La), epinephrine (T-Epi) and norepinephrine ( T-NE) were determined for each subject under both exercise conditions and d efined 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 al l 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 +/- 0.0 7 L.min(-1)), and T-NE (1.07 +/- 0.09 L.min(-1)) occurred simultaneously. D uring 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 obse rved 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 concentrati on ([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 breakpo int in plasma [Epi] shifted in an identical manner and occurred simultaneou sly 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 reporte d to produce arise in blood lactate during Epi infusion at rest. These resu lts support the hypothesis that a rise in plasma [Epi] may contribute to th e breakpoint in blood lactate that occurs during incremental exercise.