Immediate Effects of Hamstring Muscle Stretching on Pressure Pain Sensitivity and Active Mouth Opening in Healthy Subjects

ObjectiveThis study analyzed the immediate effect of hamstring muscle stretching on pressure pain sensitivity over the masseter and the upper trapezius muscles and maximum active mouth opening in healthy subjects.MethodsOne hundred twenty volunteers, 70 males and 50 females, between the ages of 22 and 47, were randomly divided into 3 groups: group 1 (control group) that did not receive any intervention, group 2 where a unilateral hamstring muscle stretching was applied, and group 3 where a bilateral stretching was applied. Pressure pain thresholds (PPTs) were bilaterally assessed over the masseter and upper trapezius muscles pre- and 5 minutes posttreatment by an assessor blinded to group assignment. Maximum mouth opening was also assessed pre- and 5 minutes posttreatment. Mixed-model analyses of variance (ANOVAs) were used to examine the effects of the intervention. The primary analysis was the group × time interaction.ResultsThe ANOVA revealed significant group × time interaction for changes in PPTs over the upper trapezius (F = 4.5; P = .01) and masseter (F = 6.3; P = .002) muscles. Pre-post effect sizes were moderate (0.5 > d > 0.7) for both stretching groups and negative (d < −0.2) for the control group. A significant group × time interaction (F = 8.15; P < .001) for maximum mouth opening was also found; both experimental groups showed greater improvement when compared to the control group (P < .001). Pre-post effect sizes were large (d > 0.7) for both stretching groups and negative (d < −0.2) for the control group.ConclusionsThe application of a stretching of the hamstring musculature produced an immediate increase in PPTs over both masseter and upper trapezius muscles in healthy subjects.