• Bretischwerdt C
• Rivas-Cano L
• Palomeque-del-Cerro L
• Fernández-de-las-Peñas C
• Alburquerque-Sendín F

• Masseter Muscle
• Mouth
• Muscle Stretching Exercises
• Neck Muscles
• Pain Threshold

Methods: One 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.

Results: The 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.

Conclusions: The application of a stretching of the hamstring musculature produced an immediate increase in PPTs over both masseter and upper trapezius muscles in healthy subjects.

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