Objectives: To quantify the extent to which the participant-provider interaction influences the response to sham treatment following exercised-induced acute musculoskeletal pain.
Methods: Forty participants between the ages of 18 and 35 volunteered for the study. Participants came to the laboratory for three test sessions 48-hours apart (Day 1, 3 and 5). During the initial session, baseline measures were assessed and participants underwent a fatigue protocol for the biceps brachii. Participants were then assigned to a positive expectation or a no-expectation condition before receiving a sham laser therapy treatment. The positive expectation group received symptom improvement priming prior to their sham treatment. Participants allocated to the no-expectation condition received no feedback prior to the sham treatment. Maximum voluntary isometric contraction (MVIC); relaxed elbow angle (RANG); visual analogue scale (VAS); and the QuickDash (QD) questionnaire were used as outcome measures.
Results: The positive expectation group had a significant reduction in perceived pain compared to the no-expectation group at day 3 follow-up, with the mean scores being 34.65 mm (SE=4.44) compared to 49.4 mm (SE=5.79) respectively. There were no between-group differences with respect to MVIC, QD or RANG outcomes. In addition, there were no significant between-group differences observed with expected pain on follow-up visits, the effect sizes were d=0.26 on day 1 for day 3 and d=0.51 on day 3 for day 5.
Discussion: Positive expectations before a sham treatment enhanced reduction in pain intensity but did not improve functional impairments following exercise induced acute musculoskeletal injury.
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