Ischemic Preconditioning Blunts Loss of Knee Extensor Torque Complexity with Fatigue

Introduction Neuromuscular fatigue reduces the temporal structure, or complexity, of muscle torque output, purportedly through an effect on motor unit behavior. Ischemic preconditioning (IPC), an emerging ergogenic aid, has been demonstrated to have a potent effect on muscular output and endurance. We therefore tested the hypothesis that IPC would attenuate the fatigue-induced loss of muscle torque complexity. Methods Ten healthy participants (6 males/4 females) performed intermittent isometric knee extension contractions (6 s contraction, 4 s rest) to task failure at 40% maximal voluntary contraction. Contractions were preceded by either IPC (three bouts of 5 min proximal thigh occlusion at 225 mm Hg, interspersed with 5 min rest) or SHAM (as IPC, but occlusion at only 20 mm Hg) treatments. Torque and EMG signals were sampled continuously. Complexity and fractal scaling were quantified using approximate entropy (ApEn) and the detrended fluctuation analysis (DFA) alpha scaling exponent. Muscle oxygen consumption (mVO(2)) was determined using near-infrared spectroscopy. Results IPC increased time to task failure by 43% +/- 13% (mean +/- SEM, P = 0.047). Complexity decreased in both trials (decreased ApEn, increased DFA alpha; both P < 0.001), although the rate of decrease was significantly lower after IPC (ApEn, -0.2 +/- 0.1 vs -0.4 +/- 0.1, P = 0.013; DFA alpha, 0.2 +/- 0.1 vs 0.3 +/- 0.1, P = 0.037). Similarly, the rates of increase in EMG amplitude (P = 0.022) and mVO(2) (P = 0.043) were significantly slower after IPC. Conclusion These results suggest that the ergogenic effect of IPC observed here is of neural origin and accounts for the slowing of the rates of change in torque complexity, EMG amplitude, and mVO(2) as fatigue develops.

Automated summary

The study found that ischemic preconditioning (IPC) can reduce the decrease in muscle torque complexity during fatigue at the neural level, leading to an extended time to task failure. IPC has an impact on the changes in EMG amplitude and oxygen consumption rate during muscle fatigue development.