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

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.

Cross-sectional observational pilot study.

Osteopathic medical school facilities.

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

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.

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.

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.