Cardiovascular reflexes during sustained handgrip exercise: role of muscle fibre composition, potassium and lactate.

Six healthy men performed sustained static handgrip exercise for 2 min at 40% maximal voluntary contraction followed by a 6-min recovery period. Heart rate (fc), arterial blood pressures, and forearm blood flow were measured during rest, exercise, and recovery. Potassium ([K+]) and lactate concentrations in blood from a deep forearm vein were analysed at rest and during recovery. Mean arterial pressure (MAP) and fc declined immediately after exercise and had returned to control levels about 2 min into recovery. The time course of the changes in MAP observed during recovery closely paralleled the changes in [K+] (r = 0.800, P < 0.01), whereas the lactate concentration remained elevated throughout the recovery period. The close relationship between MAP and [K+] was also confirmed by experiments in which a 3-min arterial occlusion period was applied during recovery to the exercised arm by an upper arm cuff. The arterial occlusion affected MAP while fc recovered at almost the same rate as in the control experiment. Muscle biopsies were taken from the brachioradialis muscle and analysed for fibre composition and capillary supply. The MAP at the end of static contraction and the [K+] appearing in the effluent blood immediately after contraction were positively correlated to the relative content of fast twitch (% FT) fibres (r = 0.886 for MAP vs % FT fibres, P < 0.05 and r = 0.878 for [K+] vs % FT fibres, P < 0.05). Capillary to fibre ratio showed an inverse correlation to % FT fibres (r = -0.979, P < 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)