Positive and Negative Verbal Instructions Associated With Sham Ischemic Preconditioning Moderate Improvements of Knee-Extension Resistance Exercise in Trained Men.

Purpose: To verify the effects of positive and negative verbal instructions regarding sham ischemic preconditioning (sham-IPC) on leg-extension resistance-exercise performance.

Methods: Thirty-five trained men were randomized to 1 of 3 groups: positive expectation, negative expectation, or control. Participants completed leg-extension strength tests in 4 trials (2 familiarization, 1 baseline, and 1 experimental). Experimental trials consisted of participants' receiving sham-IPC (3 × 5 cycles at only 20 mmHg). In positive- and negative-expectation groups, participants received verbal instructions that would improve or worsen performance, respectively. Controls did not receive any verbal suggestion. Outcomes were maximum number of repetitions, maximal isometric voluntary contraction, and muscle power output.

Results: Expectations about sham-IPC were significantly higher in the positive-expectation than in the negative-expectation and control groups. Participants in the positive group reported a significantly greater number of repetitions than both the negative-expectation (d = 1.11) and control groups (d = 0.77). No differences between groups were shown for maximal isometric voluntary contraction (d range = 0.05-0.67) and power output (d range = -0.08 to 1.02).

Conclusions: Our results highlight the importance of measuring expectations prior to sham-IPC, which may significantly influence the results of randomized controlled trials.