SCHNEIDER, D. A., T. M. McLELLAN, and G. C. GASS. Plasma catecholamine and blood lactate responses to incremental arm and leg exercise. Med. Sci. Sports Exerc., Vol. 32, No. 3, pp. 608–613, 2000. 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 (TLa), epinephrine (TEpi) and norepinephrine (TNE) 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, TLa, TEpi, and TNE were all significantly lower for 1-arm cranking than for 2-leg cycling (P < 0.01). During 1-arm cranking, TLa (0.96 ± 0.10 L·min−1), TEpi (1.02 ± 0.07 L·min−1), and TNE (1.07 ± 0.09 L·min−1) occurred simultaneously. During 2-leg cycling, TLa (1.77 ± 0.20 L·min−1), TEpi (1.74 ± 0.17 L·min−1), and TNE (1.98 ± 0.17 L·min−1) occurred at similar levels of V̇O2 and were not significantly different. The correlation observed between the V̇O2 measured at the TLa and TEpi was 0.917 for arm and 0.929 for leg exercise (P < 0.001). The epinephrine concentration ([Epi]) obtained at the TLa 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 TLa regardless of the mode of exercise (arm or leg). The Epi concentrations observed at the TLa agree with those previously reported to produce a rise 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.
The oxygen uptake (V̇O2 ) or work rate just below that at which there is a systematic rise in blood lactate ([La]) concentration during incremental exercise is now referred to as the blood lactate threshold (TLa). Wasserman and his associates (25) used the term anaerobic threshold to describe this inflection point because they felt that the sudden increase in blood [La] was due to muscle tissue hypoxia and increased anaerobic glycolysis. In recent years, some investigators have challenged the concept of the anaerobic threshold and the idea that muscle hypoxia is the sole cause of the TLa. Factors that may play a role in the production of the lactate threshold that occurs during incremental exercise include muscle fiber recruitment (2,14,28), muscle anaerobiosis (8,25), a decreased rate of lactate removal from the blood (2), and hormonal regulation of muscle glycogenolysis and glycolysis (2,6,16,17,21–23,27).
Plasma epinephrine ([Epi]) and norepinephrine ([NE]) concentrations are also known to demonstrate inflection points (or thresholds) at submaximal work rates during incremental exercise (15–18,27). In addition, the abrupt increases in plasma [Epi] and blood [La] have been reported to occur at identical work rates during incremental exercise (16,17).
Epinephrine is known to activate phosphorylase and to stimulate muscle glycogenolysis (4,5). This will increase the rate of glycolytic flux, enhance muscle lactate production, and increase the rate of lactate appearance in the blood. Moreover, Epi infusion has been found to produce an increase in La output from contracting gastrocnemius muscle in dogs (22). Infusion of Epi in humans increases blood [La] both at rest (6,20,23) and during exercise (10,12,24). These studies suggest a causal relationship between increases in plasma [Epi] and La production during submaximal exercise. Thus, it has been argued that the rise in plasma [Epi] during graded exercise is the primary factor influencing the TLa (3,16,17,24).
Blomqvist et al. (1) and Davies et al. (7) found a lower plasma [Epi] at any given relative work intensity during incremental exercise performed with the arms than with the legs. These investigators did not attempt to determine a breakpoint for the rise in plasma [Epi] during incremental exercise, but their results suggest that the TEpi may occur at a higher % of V̇O2 peak for arm than for leg exercise. A study by Davis et al. (9) found a lower anaerobic threshold for arm cranking than for either cycling or running. They reported that the anaerobic threshold for arm cranking occurred at about 47% of V̇O2 peak, whereas the threshold for leg cycling occurred at 59% of V̇O2 peak. The findings of these studies suggest that TLa and TEpi may not occur together during arm exercise. Moreover, these findings suggest that TEpi may occur after TLa during arm-cranking exercise. Researchers have suggested that a dissociation of the thresholds indicates that they are not causally related (16–18).
However, analysis of threshold behavior without consideration of the actual concentration of lactate and epinephrine may provide an inaccurate assessment of the association between blood La and plasma Epi (27). During Epi infusion in resting subjects, several investigators have demonstrated that a critical plasma [Epi] was necessary before blood [La] rose above resting values (6,20,23). Weltman et al. (27) suggested that the critical [Epi] may occur at TLa but not necessarily at the point where an abrupt increase in plasma [Epi] occurs during incremental exercise (i.e., at the Epi threshold). Therefore, it would be inappropriate to conclude that a dissociation of TLa and TEpi during arm or leg exercise suggests that plasma Epi is not influencing blood lactate behavior.
No study has examined the relationship between TLa and TEpi during both arm cranking and leg cycling. The present study was conducted to examine the plasma Epi and blood La responses to incremental arm and leg exercise. The purpose was to determine if the blood lactate and epinephrine thresholds would occur together during both arm and leg exercise. A secondary objective was to determine whether the Epi concentrations observed at the TLa for arm and leg exercise are within the range of [Epi] values previously reported to increase blood [La] above resting values (150–288 pg·mL−1).