Local and systemic changes in pain sensitivity after 4 weeks of calf muscle stretching in a nonpainful population: a randomized trial

Background: Stretching is often used in clinical practice for a variety of purposes, including pain therapy. The possible mechanism behind the effect of stretching remains to be clarified. Aim: To investigate whether 4 weeks of unilateral stretching of the calf muscles would affect local and central pain sensitivity. Method: This study was a randomized assessor-blinded clinical study. Healthy participants (age 18 to 40) were included and randomized. Participants in the intervention group were instructed to perform 2 stretching exercises targeting the calf muscles; 3 times 30 seconds, 7 days a week for 4 weeks on the dominant leg. Participants in the control group were instructed not to do any stretching for 4 weeks. Pressure pain threshold (PPT) and temporal summation (TS) of pressure pain were measured on the stretched calf, the contra-lateral calf, and contra-lateral lower arm using a computerized cuff algometer. Analyses of variance on the per-protocol population (defined as participants that adhered to the protocol) were used to assess group differences in the changes from baseline. Result: Forty healthy volunteers were included, of which 34 participants adhered to the protocol (15 intervention group/19 control group). No statistically significant group differences in the changes from baseline were found regarding PPT and TS measurements for the stretched calf, the contra-lateral calf, and the arm. Conclusion: Four weeks of regular stretching of the calf muscles does not affect pressure pain sensitivity, suggesting that pressure pain sensitivity is unaffected by stretching in a healthy population. The mechanisms underlying any benefits of regular stretching remain to be explained.