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 one of three groups: positive-expectation, negative-expectation, or control. Participants completed leg-extension strength tests in four trials (2 × familiarization, 1 × baseline and 1 × experimental). Experimental trials consisted of participants receiving sham-IPC (3x5 cycles at only 20 mmHg). In positive- and negative-expectation groups, participants received verbal instructions that it would improve or worsen performance, respectively. Controls did not receive any verbal suggestion. Outcomes were maximum number of repetitions, maximal isometric voluntary contraction (MVIC) and muscle power output.

Results: Expectations about sham-IPC were significantly higher in the positive-expectation than negative-expectation and control group. Participants in the positive group reported a significantly greater number of repetitions than both the negative-expectation group (d = 1.11) and controls (d = 0.77). No differences between groups were shown for MVIC (d range = 0.05 to 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.