Ischemic Preconditioning Enhances Muscle Endurance during Sustained Isometric Exercise

Abstract

Ischemic preconditioning (IPC) enhances whole-body exercise endurance. However, it is poorly understood whether the beneficial effects originate from systemic (e. g., cardiovascular system) or peripheral (e. g., skeletal muscle) adaptations. The present study examined the effects of IPC on local muscle endurance during fatiguing isometric exercise. 12 male subjects performed sustained isometric unilateral knee-extension exercise at 20% of maximal voluntary contraction until failure. Prior to the exercise, subjects completed IPC or control (CON) treatments. During exercise trial, electromyography activity and near-infrared spectroscopy-derived deoxygenation in skeletal muscle were continuously recorded. Endurance time to task failure was significantly longer in IPC than in CON (mean±SE; 233±9 vs. 198±9 s, P<0.001). Quadriceps electromyography activity was not significantly different between IPC and CON. In contrast, deoxygenation dynamics in the quadriceps vastus lateralis muscle was significantly faster in IPC than in CON (27.1±3.4 vs. 35.0±3.6 s, P<0.01). The present study found that IPC can enhance muscular endurance during fatiguing isometric exercise. Moreover, IPC accelerated muscle deoxygenation dynamics during the exercise. Therefore, we suggest that the origin of beneficial effects of IPC on exercise performance may be the enhanced mitochondrial metabolism in skeletal muscle.

Ischemic preconditioning: Potential impact on exercise performance and underlying mechanisms

“…Beaven et al (2012) compared the early (immediate) and late (24 h later) effects of IPC on power production, and they found that IPC showed beneficial effects in both periods 8) . In addition, a recent study investigated the effects of IPC on static leg extension exercise and found that the endurance time to task failure was significantly longer in IPC than in CON 26) . Compared to its performance in whole-body exercise, it is possible that IPC may be more effective in improving exercise performance during local muscle contraction.…”

“…Because the peak values of blood lactate concentration (LApeak) after exercise may be an indicator of anaerobic capacity, several studies compared the LApeak between IPC and the control (or SHAM), and no effect in LApeak after exercise with IPC was found 4,[9][10][11][12][13][14]18,19,22) . Two studies focused on muscle activity, assessed by electromyography (EMG), between IPC and CON, and no differences in EMG were found during cycle sprints 4) or isometric leg extension 26) .…”

“…As mentioned previously, the results are equivocal. Several studies found an improvement in exercise performance, i.e., time to failure (time trial performance), peak power output, and repetitions, to name a few, after IPC on the primary or a part of the engaged limbs 4,8,[10][11][12][13][18][19][20][21]26) , whereas other studies did not show any beneficial effects [5][6][7]9,10,[14][15][16][17]22,24,25) . A few studies investigated the effects of remote IPC on exercise performance.…”

“…Further, the numbers of ischemic-reperfusion cycles were also varied in previous studies. For example, one study used 2×5 min cycles 8) , nine studies used 3×5 min cycles 5,7,10,[12][13][14]18,23,26) and 13 studies used 4×5 min cycles 4,6,9,11,[15][16][17][19][20][21][22]24,25) . As a result, a manipulation of 2 cycles showed improvement of exercise performance (100%), seven of nine studies using 3 cycles also showed improvement of exercise performance (78%), whereas, only five of 13 studies using 4 cycles showed positive effects with IPC (38%).…”

“…Previous studies used various populations, such as healthy volunteers and trained subjects (Table 1). Although an accurate classification is difficult because the detailed information of subjects is often not available, we attempted to classify subjects into 3 groups: healthy (including recreationally active) subjects 6,8,10,12,21,23,25,26) , trained athletes 4,5,7,9,11,[13][14][15][16][17][18]22,24) , and elite athletes 19,20) . This classification showed that the studies did not reach a consensus on the effects of IPC on exercise performance across different populations, i.e., different training levels.…”