Reference values for muscle stiffness and asymmetry using myotonometry: a pilot study.

OBJECTIVES

To establish preliminary reference values for resting muscle stiffness and bilateral asymmetry in healthy young adults, and to explore associations with sex, age, BMI, and weekly exercise.

DESIGN

Cross-sectional observational pilot study.

SETTING

Osteopathic medical school facilities.

PARTICIPANTS

Twenty-six healthy individuals aged 18-29 years, 19 males and 7 females.

MAIN OUTCOME MEASURES: Resting muscle stiffness and left-right asymmetry across seven muscle groups, measured using the MyotonPRO. Associations with sex, age, BMI, and weekly exercise were analyzed.

RESULTS

Sex was the only significant predictor of muscle stiffness overall, model F(4,21) = 2.88, p = 0.048, R2 = 0.355, with higher stiffness in males, coefficient 44.6 N/m, p = 0.007. Global stiffness was greater in males than females, 236.2 ± 30.8 vs 196.2 ± 23.7 N/m, p = 0.017, Cohen d = 1.13. Age, BMI, and weekly exercise were not significant predictors, p = 0.388, 0.077, and 0.790, respectively. Sex-specific reference intervals, central 95%, for stiffness and asymmetry were derived for each muscle. Average bilateral asymmetry was small, about 10% to 14%, consistent with physiologic side-to-side differences.

CONCLUSIONS

This study demonstrates the feasibility of defining reference ranges for muscle stiffness and asymmetry using the MyotonPRO. These reference values may support musculoskeletal assessments in osteopathic and sports medicine and may help identify clinically meaningful deviations in tissue properties. Larger and more diverse cohorts are needed to refine intervals and to link stiffness to changes in patient outcomes.