BLOOD-PRESSURE RESPONSES TO DYNAMIC EXERCISE WITH LOWER-BODY POSITIVEPRESSURE

Cardiovascular responses were obtained during cycling with graded leve ls of lower-body positive pressure (LBPP) applied to the exercising li mbs. Seven men performed four incremental work rate (25 W.min(-1)) exe rcise (CWREx) tests to their limit of tolerance while exposed to 0, 15 , 30, or 45 Torr LBPP. They also performed four, 6-min constant work r ate exercise (CWREx) bouts at two work rates with LBPP's of 0 and 45 T orr. Cardiovascular data were obtained at rest and at 40%, 55%, 75%, a nd 90% of VO2peak, as well as at minute 5 of CWREx. LBPP did not alter VO2, HR, SV, or cardiac output (he)responses at rest or during exerci se. However, both 30 and 45 Torr LBPP produced increases in MAP at res t and during exercise (P < 0.05). During CWREx, elevations in blood pr essure were mediated via increases in TPR (P < 0.05). Only 45 Torr LBP P elicited a significantly greater blood pressure increase during exer cise than rest, suggesting muscle blood flow restriction at this level of LBPP was sufficient to activate a muscle metabo-reflex. These find ings suggest that the muscle metabo-reflex is not tonically active dur ing dynamic exercise under normal conditions, but may instead require a critical reduction in muscle blood flow before it is activated.