Does ischemic preconditioning enhance sports performance more than placebo or no intervention? A systematic review with meta-analysis

Background: Ischemic preconditioning (IPC) is purported to have beneficial effects on athletic performance, although findings are inconsistent, with some studies reporting placebo effects. The majority of studies have investigated IPC alongside a placebo condition, but without a control condition that was devoid of experimental manipulation, thereby limiting accurate determination of the IPC effects. Therefore, the aims of this study wereto assess the impact of the IPC intervention, compared to both placebo and no intervention, on exercise capacity and athletic performance.

Methods: A systematic search of PubMed, Embase, SPORTDiscus, Cochrane Library, and Latin American and Caribbean Health Sciences Literature (LILACS) covering records from their inception until July 2023 was conducted. To qualify for inclusion, studies had to apply IPC as an acute intervention, comparing it with placebo and/or control conditions. Outcomes of interest were performance (force, number of repetitions, power, time to exhaustion, and time trial performance), physiological measurements (maximum oxygen consumption, and heart rate), or perceptual measurements (RPE). For each outcome measure, we conducted 3 independent meta-analyses (IPC vs. placebo, IPC vs. control, placebo vs. control) using an inverse-variance random-effects model. The between-treatment effects were quantified by the standardized mean difference (SMD), accompanied by their respective 95% confidence intervals. Additionally, we employed the Grading of Recommendations, Assessment, Development and Evaluation (GRADE) approach to assess the level of certainty in the evidence.

Results: Seventy-nine studies were included in the quantitative analysis. Overall, IPC demonstrates a comparable effect to the placebo condition (using a low-pressure tourniquet), irrespective of the subjects'training level (all outcomes presenting p > 0.05), except for the outcome of time to exhaustion, which exhibits a small magnitude effect (SMD = 0.37; p = 0.002). Additionally, the placebo exhibited effects notably greater than the control condition (outcome: number of repetitions; SMD=0.45; p = 0.03), suggesting a potential influence of participants' cognitive perception on the outcomes. However, the evidence is of moderate to low certainty, regardless of the comparison or outcome.

Conclusion: IPC has significant effects compared to the control intervention, but it did not surpass the placebo condition. Its administration might be influenced by the cognitive perception of the receiving subject, and the efficacy of IPC as an ergogenic strategy for enhancing exercise capacity and athletic performance remains questionable.