Crucial Points for Analysis of Ischemic Preconditioning in Sports and Exercise
The effects of ischemic preconditioning (IPC) on exercise performance have been tested since the 1950s with controversial results (6). Some studies have described beneficial effects (2). However, other studies have reported that these effects do not persist when the maneuver is applied several times, (7) and no physiological alterations have been found to explain an improvement in performance with IPC (6).
The recent study by Ferreira et al. (2) concluded that IPC improved sprint time in university swimmers, whereas a placebo intervention did not. However, both interventions promoted blood flow occlusion, although with different periods of duration. This could, at first glance, allow speculation that the time of occlusion is decisive for improvements in performance. Meanwhile many confounding factors could influence performance in exercise tests; for example, motivation, environment, and training level. The trigger of confounding factors cannot be discarded. An important point that should be considered is the cuff administration. In the majority of studies when a SHAM intervention (with low pressure) was applied, the results were not significantly different between IPC and SHAM (6). Interestingly, another study, (8) published by same group, concluded that IPC did not surpass a placebo effect: They compared a cuff administration to produce IPC with a simulated ultrasound intervention; neither treatment affected running performance. Because the procedures of cuff administration could be the key for a potential benefit of IPC in sports, the parameters of IPC protocols should be standardized to permit comparison of the same types of intervention and to reduce confounding factors.
One more point of interest concerns the analysis of obtained data. Although beneficial effects of 0.6% to 1.1% are reported for the Wingate cycle test after IPC intervention, (6) standard errors of measurement ranging from 2.6% to 3.7% have been described for this test in the literature (4).
Such results should be more carefully interpreted and the picture emerges that small improvements found after IPC were sometimes within the error of measurements and therefore of questionable import. So, not only statistical tests and effect size should be carefully analyzed but also the physiological meaning of these results has to be considered in the context of the training level of the athletes or type of exercise. With regard to the effect size in the Ferreira et al. study, (2). it was only trivial (<0.12) despite the finding of significant differences. In this context, the effects are likely irrelevant for recreational university swimmers, (1) because swimming technique may change substantially in such participants over time (3).
In conclusion, we should state that potential effects of IPC on performance are far from being understood, if existing at all on a physiological basis. In this context, a remarkable statement by Incognito and colleagues (5) underpinning the obvious uncertainty about IPC interventions and performance, was that IPC could affect some subjects but not others, and they classified them as IPC responders and nonresponders. In view of results from IPC and exercise performance included in the literature, such classification could provocatively be substituted by the terms believers and nonbelievers.