Muscle acidosis during static exercise is associated with calf vasoconstriction

In this study we measured (n=6) the phosphocreatine-to-inorganic phosphate ratio (PCr/P(i)), P(i), and pH with ³¹P-nuclear magnetic resonance (³¹P-NMR) in the human forearm during static work at 30% of maximal voluntary contraction (MVC) for 2 min followed immediately by 3 min of circulatory arrest (forearm arterial occlusion). Static exercise, with its central volitional and skeletal muscle metabolic and mechanical afferent components, caused a rise in heart rate (HR, 32%), blood pressure (BP, 29%), and calf vascular resistance (calf R, 30%). During forearm occlusion after static exercise, HR returned to base line, the increase in BP was attenuated by 30%, and calf R remained elevated and unchanged. The percent change in calf R was correlated with forearm cellular pH (R=0.56, P<0.001) but only weakly associated with PCr/P(i) (R=0.33, P<0.042). 30% MVC for 1 min followed by arterial occlusion (3 min) reduced PCr/P(i) by 65% and pH by 0.16 U (P<0.05). Calf R was unchanged. Circulatory arrest alone (20 min) caused no change in either pH or calf R but large changes in PCr/P(i) (50% reduction). We conclude that 1) there is an association between forearm cellular acidosis and calf vasoconstriction during static forearm exercise and 2) large changes in PCr/P(i) without concomitant changes in pH are not associated with changes in calf R.