METHODS: Thirty subjects, 13 men and 17 women, without a current history of neck, shoulder, or upper extremity pain participated. Participants were randomly divided into 3 groups: experimental dominant group, subjects who received the manipulative thrust directed at the right side of the C7-T1 joint; experimental nondominant group, those who received the thrust on the left side of the C7-T1 joint; and a placebo group, those who received a sham-manual procedure. The outcome measure was the PPT on both right and left C5-C5 zygapophyseal joints, which was assessed at preintervention and 5 minutes postintervention by an assessor blinded to the treatment allocation of the subject. A 3-way repeated measures analysis of covariance was used to evaluate changes in PPT.
RESULTS: The analysis of covariance revealed time x group (F = 32.3; P < .001), time x side (F = 4.9; P < .05), time x sex (F = 7.93; P < .01), and time x group x sex (F = 7.606; P < .001) interactions. Post hoc analyses found that (a) both experimental groups showed greater improvements in PPT than the placebo group (P < .05), without significant differences between them (P > .6); (b) the right side had greater increases in PPT in both experimental groups (P < .05), but not within the placebo group (P > .8); (c) men experienced greater increases in PPT levels than women, particularly in the experimental nondominant group (P < .01). Within-group effect sizes were large for both experimental groups (d > 1), but small for the placebo condition (d < 0.2).
CONCLUSIONS: These results suggest that a C7-T1 manipulation induced changes in PPT in both right and left C5-C6 zygapophyseal joints in healthy subjects.
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