Prolonged ischaemia impairs muscle blood flow and oxygen uptake dynamics during subsequent heavy exercise

Muscle oxygen uptake (V(o2,mus)) dynamics at the onset of exercise can be affected by prior heavy exercise. We tested the hypothesis that elevated forearm blood flow (FBF) following prior circulatory occlusion would also be associated with accelerated (V(o2,mus)) dynamics during subsequent heavy hand-grip exercise. Ten trained young men performed 5 min of heavy hand-grip exercise at 30% MVC as a control (CON), and four additional heavy bouts after brief recovery from: (1) prior heavy exercise (Heavy A), (2) heavy exercise followed by 2 min occlusion (Heavy B), (3) 15 min occlusion (Heavy C), and (4) 5 min occlusion with1 min of moderate exercise during occlusion (Heavy D). FBF was measured by ultrasound and arterial venous oxygen content difference was calculated from venous blood samples to estimate V(o2,mus). FBF and V(o2,mus) dynamics were quantified from the rise time. All priming conditions elevated FBF immediately before the start of subsequent heavy bout (Heavy A: 207.4 +/- 92.8, B: 207.8 +/- 75.8, C: 135.8 +/- 59.2, D: 199.5 +/- 59.0 vs. CON: 57.4 +/- 16.6 ml min-1, P < 0.01). Unexpectedly, prior occlusion reduced FBF and O(2) extraction at the onset of subsequent heavy exercise and consequently slowed V(o2,mus) dynamics (Heavy C: rise time = 95.9 +/- 28.9 vs. CON: 58.6 +/- 14.3 s, P < 0.01). FBF and V(o2,mus) dynamics were faster in Heavy A, B and D compared to CON (P < 0.05). Overall, there was a positive correlation between the rise times for V(o2,mus) and FBF (r(2) = 0.75) indicating that V(o2,mus) dynamics during heavy forearm exercise are linked to O(2) delivery in trained young men. To investigate a possible mechanism for slower adaptation of V(o2,mus) following ischaemia, the prior occlusion condition was repeated after ingesting a high dose of ibuprofen. This resulted in restoration of the FBF and V(o2,mus) to control levels suggesting that a prostaglandin-mediated mechanism after occlusion retarded the adaptation of blood flow and oxygen consumption at the onset of subsequent heavy exercise.