The Influence of Expectations Induced by Information Prior to Exercise on the Change in Pain Perception After a 3 Min Wallsquat Exercise in Healthy Subjects: A Randomized Controlled Trial.

Painful conditions are a major societal and economic problem and in Denmark, almost every fifth person suffers from long-lasting pain. Effective treatment of these conditions is vital not only to alleviate the pain but also to prevent repeated episodes of personal disorder and impaired work ability. Based on the hypothesis that physical activity and exercise lead to a change in pain perception, Pain Center South, Odense University Hospital has conducted a series of research projects which have investigated the immediate effect of various types of acute exercise on the pain sensitivity of both healthy subjects, patients with chronic pain in the knee and in patients with more 'complex' chronic pain who were referred to treatment at the Pain Center. The results showed that healthy subjects achieved a reduced overall pain sensitivity after both high intensity aerobic exercise (cycling) and low and high intensity isometric training (strength-like exercise on the arm and leg). This phenomenon is called 'exercise-induced hypoalgesia' or 'training-induced pain relief'. A recently published study from Australia has also shown that the effect of exercise can be positively influenced by the information given prior to exercise, indicating that some of the experience of exercise may be related to expectations of the effect. This may be one of the reasons why patients with chronic pain do not experience a positive effect, as opposed to healthy people, as chronic pain patients may previously have experienced no effect of exercise or perhaps even worsening / flareup in post-workout pain.

The purpose of this study is to investigate how expectations induced by information given prior to exercise influence the magnitude of exercise-induced hypoalgesia after a 3 min wallsquat exercise in healthy subjects. The pain sensitivity of the deep structures is investigated with two different pressure-gauges for the testing of mechanical pressure pain sensitivity. Pain sensitivity is examined on the leg and arm before and after the exercise. Pressure-sensitivity is evaluated using a handheld pressure-algometer for testing mechanical pressure pain-threshold in the deeper musculoskeletal structures. The pain-threshold is evaluated on the thigh and shoulder.

To investigate additional facets of pain-sensitivity, computer-controlled cuff geometry is used. The computer-controlled cuff algorithm is less affected by local differences in pain sensitivity to the handheld pressure algometer and the cuff algorithm can also affect a larger portion of the deep tissue than the pressure algometer can.

The cuff gauge consists of a blood pressure cuff placed around one lower leg and then slowly inflated. The pain response is registered continuously and the stimulus response function can then be established. The cuff algorithm has a maximum pressure that ensures no tissue damage to the subject and the device is automatically stopped at 100 kPa. Both the handheld pressure gauge and the cuff algorithm have proven to be a valid and reliable techniques for investigating the pain-sensitivity of healthy subjects.

The person performing the measurements before and after the exercise is blinded to what information the subject has received, likewise the patient is blinded to the group randomization.