What is the effect of ischemic preconditioning on the kinetics of pulmonary oxygen uptake and muscle deoxygenation during exercise?

Ischemic preconditioning (IPC, brief cycles of ischemia) induces protection against ischemia–reperfusion injury, due to IPC-mediated change in the metabolism of skeletal muscles and microand macrovascular function. Since high-intensity aerobic exercise depends on such physiological factors, it has been hypothesized that IPC can also improve exercise performance. Although some studies confirmed this hypothesis (Salvador et al. 2015), others did not (Salvador et al. 2015). Moreover, even when IPC improved exercise performance, the mechanisms involved were unclear. For example, increase in maximal oxygen consumption (V̇O2max) (De Groot et al. 2010) and decrease in blood lactate concentration (Bailey et al. 2012) have been reported, but these findings were not unanimous among studies (Salvador et al. 2015). In this context, a recent study by Kido et al. (2015) examined the effects of IPC of the lower limbs on the kinetics of pulmonary V̇O2 and muscle deoxygenation during square-wave transitions from lowto moderateintensity and from moderateto severe-intensity cycling exercise. Besides, authors assessed the effect of IPC on the time to exhaustion in the severe-intensity workload. Authors found that IPC increased the time to exhaustion, which supports an increase in exercise performance. Furthermore, IPC did not change the pulmonary V̇O2 kinetics, but changed the kinetics of muscle deoxygenation. These findings are original and advance the knowledge about the effect of IPC on exercise physiology. However, some aspects of the experimental protocol and data analysis deserve attention to interpret these findings. Authors used just one exercise transition to calculate the pulmonary V̇O2 kinetics. Nevertheless, repetitions of exercise transitions are crucial to increase the signal-tonoise ratio. This was proposed by Lamarra et al. (1987), who described the following equation to estimate the confidence interval (Kn) of the time constant: Kn 1⁄4 L SD=ðD _ VO2 ffiffiffi