BACKGROUND & OBJECTIVE
The placebo effect is a commonly recognised phenomena seen by health professionals and researchers alike. Higher quality research recognises the huge effect placebo has on outcomes and is accounted for with double-blinded research studies. There is previous research that shows how placebo can improve symptoms, but the authors undertook this study as there is little research measuring the influence of the placebo effect on pain and function after acute musculoskeletal injury. The authors wanted to determine whether providing affirmational instructions about the efficacy of the treatment would affect response to a sham intervention.
In this study, they recruited 40 (29 female, 11 male) participants. They excluded responders who reported involvement in regular (2-3 times a week) resistance training exercise (e.g. weight lifting), had suffered any injury to the upper extremity (shoulder/arm/wrist/hand) in the past six months or who were taking anti-inflammatory medications or supplements.
The 40 participants were randomly assigned to an expectancy or non-expectancy group before completing the same resistance training program. The training program involved subjects using their dominant arm to perform 3 sets of 20 repetitions of isokinetic biceps curls. Following this protocol, both groups were given the same sham treatment from the same administrator. The sham treatment was laser treatment using a dummy electrode.
The expectancy group was primed with the following statement: “Hello, I have extensive experience with using the therapeutic laser and you can expect the treatment to significantly decrease your pain level and speed your recovery”. The non-expectancy group was told: “You will undergo a therapeutic treatment for your impairment and since this is a scientific study I will not be able to speak with you during the treatment”.
At reassessment on Day 3 and 5, pre-injury measures that included self-reported rating of muscle pain using a VAS, elbow range of motion (ROM), biceps muscle strength, and a self-report questionnaire for symptoms and disability of the upper extremity (QuickDASH) were reassessed.
There were no significant differences between groups in ROM, strength or self-reported disability on the QuickDASH questionnaire. There was however a significant difference in self-reported pain between the two groups. The expectancy group perceived less pain in their biceps compared