Muscle acidosis during static exercise is associated with calf vasoconstriction

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Abstract
In this study we measured (n = 6) the phosphocreatine-to-inorganic phosphate ratio (PCr/Pi), Pi, and pH with 31P-nuclear magnetic resonance (31P-NMR in the human forearm during static work at 30% of maximal voluntary contraction (MCV) 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%), blod 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/Pi (R = 0.33, P < 0.042). 30% MVC for 1 min followed by arterial occlusion (3 min) reduced PCr/Pi by 65% and pH by 0.16 U (P < 0.05). Calf R was unchanged. Cirulatory arrest alone (20 min) caused no change in either pH or calf R but large changes in PCr/Pi (50% reduction). We conclude that 1) there is an association between forearm cellular acidosis and calf vasconstriction during static forearm exercise and 2) large changes in PCr/Pi without concomitant changes in pH are not associated with changes in calf R.