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

Abstract

Muscle oxygen uptake ( ˙VO₂,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 ˙VO₂,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 with 1 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 ˙VO₂,mus. FBF and ˙VO₂,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±16.6mlmin−1, P <0.01). Unexpectedly, prior occlusion reduced FBF and O2 extraction at the onset of subsequent heavy exercise and consequently slowed ˙VO₂,mus dynamics (Heavy C: rise time=95.9±28.9 vs. CON: 58.6±14.3 s, P <0.01). FBF and ˙VO₂,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 ˙VO₂,mus and FBF (r² =0.75) indicating that ˙VO₂,mus dynamics during heavy forearm exercise are linked to O₂ delivery in trained young men. To investigate a possible mechanism for slower adaptation of ˙VO₂,mus following ischaemia, the prior occlusion condition was repeated after ingesting a high dose of ibuprofen. This resulted in restoration of the FBF and ˙VO₂,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.

Figure 1. The four different testing protocols

Four different testing protocols employed to examine the influence of prior heavy exercise (A), prior heavy exercise followed by 2 min occlusion (B), 15 min of occlusion (C), and 5 min of occlusion including 1 min of moderate exercise (D) on muscle oxygen uptake and forearm blood flow (FBF) responses during a subsequent heavy exercise bout. The specific testing heavy bouts are named based on the testing protocol, Heavy A, Heavy B, Heavy C, and Heavy D. The moderate and heavy exercise bouts were set at 15% and 30% MVC, respectively.

Figure 2. Representative tracing of MBV during resting (A) and heavy dynamic handgrip exercise (B)

During resting the MBV was averaged beat-to-beat synchronized with the ECG signal. During exercise MBV was averaged over the duty cycle (contraction-to-contraction). Beat-to-beat averages during exercise would not be representative of the true MBV, as the duty cycles were not synchronized to the ECG (see dashed lines).

Figure 3. FBF responses during exercise in the four Heavy bouts (A–D) compared to the CON

Heavy bouts A–D are shown in panels A–D, respectively. All priming conditions resulted in higher FBF at the start of the subsequent heavy exercise (bouts Heavy A–D) compared to the CON; however by the end of exercise there were no differences. During exercise, Heavy A, B and D all showed higher FBF compared to the CON. Data points are the average responses of 10 subjects. Data are means ±s.e.m., *P < 0.01, †P < 0.05.

Figure 4. responses during exercise in the four Heavy bouts (A–D) compared to the CON

All priming conditions resulted in lower at the start of the subsequent heavy exercise (bouts Heavy A–D) compared to the CON. By 45 s of exercise there were no significant differences in between CON and Heavy A, B and D. However, was lower up to 90 s of exercise in Heavy C compared to CON. There was an overshoot of at 90 s of exercise in CON and Heavy A compared to end exercise. Data points are the average responses of 10 subjects. Data are means ±s.e.m., *P < 0.01, †P < 0.05.

Figure 5. responses during exercise in the four Heavy bouts (A–D) compared to the CON

At the start of exercise, in all conditions was not different compared to the CON. in Heavy A was significantly higher than CON from the 1st minute through the end of exercise. in Heavy B was significantly higher during exercise onset (from 30 s through 2 min). in Heavy C was depressed during exercise onset, but reached the same level as CON by the 4th minute of exercise. Heavy D was not different from the CON condition. Data points are the average responses of 10 subjects. Data are means ±s.e.m., *P < 0.01, †P < 0.05.

Figure 6. Across all conditions the rise time (τ) for was significantly correlated to the rise time (τ) for FBF

; r²= 0.75, P < 0.001. Data points are individual values of 10 subjects in each of 5 conditions (CON and Heavy A–D).

Figure 7. FBF (A), (a - v) (B) and (C) responses during exercise in Placebo and Ibuprofen trials compared to Control

Prior occlusion with or without ibuprofen resulted in higher FBF and lower at the start of the subsequent heavy exercise (Placebo and Ibuprofen) compared to Control. During exercise in the Placebo condition, and responses were lower than Control up to 3 min, while with ibuprofen was lower than Control through the first 3 min with no differences in . Data points are the average responses of 8 subjects not included in previous figures. Data are means ±s.e.m., †P < 0.05 (Placebo vs. Control), ‡P < 0.05 (Ibuprofen vs. Control).