Ischemic preconditioning accelerates muscle deoxygenation dynamics and enhances exercise endurance during the work-to-work test

Abstract

Ischemic preconditioning (IPC) improves maximal exercise performance. However, the potential mechanism(s) underlying the beneficial effects of IPC remain unknown. The dynamics of pulmonary oxygen uptake (VO2) and muscle deoxygenation during exercise is frequently used for assessing O2 supply and extraction. Thus, this study examined the effects of IPC on systemic and local O2 dynamics during the incremental step transitions from low- to moderate- and from moderate- to severe-intensity exercise. Fifteen healthy, male subjects were instructed to perform the work-to-work cycling exercise test, which was preceded by the control (no occlusion) or IPC (3 × 5 min, bilateral leg occlusion at >300 mmHg) treatments. The work-to-work test was performed by gradually increasing the exercise intensity as follows: low intensity at 30 W for 3 min, moderate intensity at 90% of the gas exchange threshold (GET) for 4 min, and severe intensity at 70% of the difference between the GET and VO2 peak until exhaustion. During the exercise test, the breath-by-breath pulmonary VO2 and near-infrared spectroscopy-derived muscle deoxygenation were continuously recorded. Exercise endurance during severe-intensity exercise was significantly enhanced by IPC. There were no significant differences in pulmonary VO2 dynamics between treatments. In contrast, muscle deoxygenation dynamics in the step transition from low- to moderate-intensity was significantly faster in IPC than in CON (27.2 ± 2.9 vs. 19.8 ± 0.9 sec, P < 0.05). The present findings showed that IPC accelerated muscle deoxygenation dynamics in moderate-intensity exercise and enhanced severe-intensity exercise endurance during work-to-work test. The IPC-induced effects may result from mitochondrial activation in skeletal muscle, as indicated by the accelerated O2 extraction.

Keywords: Exercise; mitochondria; near‐infrared spectroscopy; nitric oxide; skeletal muscle.

Figure 1

Endurance time to exhaustion during severe-intensity exercise in the work-to-work cycling exercise test. Values are presented as mean ± SE.

Figure 2

Pulmonary oxygen uptake (VO₂) and deoxy-Hb/Mb responses during work-to-work exercise. Panel A illustrates the pulmonary VO₂ responses during work-to-work exercise. Data are shown as 5-sec mean values after rectification. Panel B illustrates the deoxy-Hb/Mb responses during work-to-work exercise. Data are expressed as a percentage of the highest plateau value during 10-min arterial occlusion. The systemic and local O₂ responses following the CON and IPC trials are presented as open and solid circles, respectively. The dotted vertical line at zero in panels A and B indicates the transition from low-intensity exercise to moderate-intensity exercise. The dotted horizontal line in panel B indicates the baseline in deoxy-Hb/Mb. End-exercise values for pulmonary VO₂ and deoxy-Hb/Mb are presented as mean ± SE.

Figure 3

Muscle deoxygenation responses during moderate- and severe-intensity exercises in work-to-work exercise. Panels A and B illustrate the relative changes of deoxy-Hb/Mb during moderate- and severe-intensity exercises, respectively. Data are normalized relative to the end-exercise amplitude. Panel C shows the mean response time of muscle deoxygenation during moderate-intensity exercise. Values are presented as mean ± SE.