Manual Diaphragm Therapy and Masseter Muscle Activity in Healthy Young Women: An Exploratory Randomized Study of sEMG, Mandibular Motor Function, and Perceived Stress

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Abstract
This exploratory randomized study examined whether manual diaphragm therapy is associated with masseter muscle activity, mandibular motor function, and perceived stress in healthy women. Forty-two asymptomatic women aged 20–30 years were randomized to an intervention group (n = 20), receiving six sessions over two weeks, or a no-intervention control group (n = 22). Before and after the intervention period, bilateral masseter surface electromyography (sEMG) was recorded at rest and during standardized mandibular motor tasks; mandibular range of motion was measured with an electronic caliper, and perceived stress was assessed using the Perceived Stress Questionnaire. Non-parametric tests with Bonferroni correction were applied. No significant within-group changes were observed in resting masseter sEMG. The only task-related within-group result that remained significant after correction was a reduction in normalized right masseter mean RMS amplitude during protrusion in the intervention group (p = 0.001; adjusted p = 0.032; r = 0.685). Mandibular range of motion increased in both groups, but change scores did not differ between groups. Stress-related outcomes and correlations with sEMG or mandibular motion were not significant after adjustment. These findings do not demonstrate consistent group-specific effects. The isolated within-group finding should be regarded as preliminary and hypothesis-generating and cannot be attributed specifically to manual diaphragm therapy.
Funding Information
  • University of Physical Culture in Krakow (367/BS/IRK/2024)

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