Plasma catecholamine concentration during dynamic exercise involving different muscle groups

Abstract

The change in plasma catecholamine concentration (ΔC) has been studied in four healthy male subjects during work, involving different muscle groups, whilst breathing air and 45% oxygen.

The results show that during arm and (1- and 2-) leg(s) work ΔC was more closely associated with relative (expressed as a % of $\dot V_{{\text{O}}_{{\text{2max}}} }$) than absolute work load; a rise in C occurred at ∼ 60% $\dot V_{{\text{O}}_{{\text{2max}}} }$ in all 3 forms of exercise. However, in arm and 1-leg work the curves relating ΔC to % $\dot V_{{\text{O}}_{{\text{2max}}} }$ were displaced to the right indicating the independence of the two variables. Further, breathing 45% oxygen reduced ΔC but was without effect on either $\dot V_{O_2 }$ at a given work load or $\dot V_{{\text{O}}_{{\text{2max}}} }$.

For a given $\dot V_{O_2 }$, ΔC was inversely related to the effective muscle (plus bone) volume used to perform the work and associated with change of blood lactic acid (LA) concentration, but again the use of exercise involving different muscle groups indicated that the changes in C and LA were essentially independent. This was also true of the changes of C with cardiac output but not cardiac frequency (f _H ).

Plasma C changed as a curvilinear function of f _H , the association between the two variables being independent of type of exercise and inspired O₂ concentration within the range used in this study. This suggests that the rise in C and f _H in exercise may be closely related to circulatory stress and may reflect the degree of vasoconstriction present in ‘non-active’ tissues and efficacy of the body's ability to maintain the integrity of systemic blood pressure in the face of increased demands of the exercising muscles for blood and the transport of oxygen.