Effects of ischaemia on subsequent exercise-induced oxygen uptake kinetics in healthy adult humans.

Leg muscles were occluded (33 kPa) prior to exercise to determine whether the induced metabolic changes, and reactive hyperaemia upon occlusion release just prior to the exercise, would accelerate the subsequent oxygen consumption (VO2) response. Eight subjects performed double bouts (6 min duration, 6 min rest in-between) of square wave leg cycle ergometry both below and above their lactate threshold (LT). Prior to exercise, large blood pressure cuffs were put around the upper thighs. Occlusion durations were 0 min (control), 5 min and 10 min. Ischaemia was terminated within 5 s prior to exercise onset. Heart rate, VO2, ventilatory rate (V(E)), electromyogram (EMG) and haemoglobin/myoglobin (Hb/Mb) saturation were recorded continuously. Single exponential modelling demonstrated that, compared to control (time constant = 53.9 +/- 13.9 s), ischaemia quickened the VO2 response (P < 0.05) for the first bout of exercise above LT (time constant = 48.3 +/- 14.5 s) but not to any other exercise bout below or above LT. The 3-6 min integrated EMG (iEMG) slope was correlated to the 3-6 min VO2 slope (r = 0.73). Hb/Mb saturation verified the ischaemia but did not show a consistent relation to the VO2 time course. Reactive hyperaemia induced a faster VO2 response for work rates above LT. The effect, while significant, was not large considering the expected favourable metabolic and circulatory changes induced by ischaemia.