Standard Values for Muscle Stiffness and Asymmetry: A Pilot Study

Background and/or Objectives: Osteopathic, sports medicine, and physical medicine physicians often assess muscle quality and asymmetry. However, standardized quantitative measures of muscle hypertonicity and asymmetry remain undefined. This study aimed to establish normative values for muscle stiffness and percent asymmetry in healthy adults to facilitate future research on pathologic deviations.

Design: A total of 26 healthy adults (ages 18-29) were recruited. Muscle stiffness was measured at seven sites: upper trapezius, triceps brachii, lumbar paraspinals, biceps femoris, lateral gastrocnemius, rectus femoris, and long head of the biceps brachii. Measurement order was randomized, and assessments were performed using the MyotonPro by trained researchers. Descriptive statistics (mean ± SD) were calculated for each muscle, with two standard deviations defining thresholds for abnormally high or low stiffness. Pearson’s correlation analysis and independent samples t-tests were used to assess relationships between demographic factors and muscle stiffness. A significant difference in stiffness values was observed between men and women (P < 0.01) using an independent samples t-test.

Setting : Osteopathic Medical School

Participants : n= 26 healthy adults aged 18-29

Interventions: Observational study

Main Outcome Measures: Descriptive statistics including mean and Standard deviation

Results: Mean stiffness values (N/m) were established for each muscle site: trapezius (X ± Y), triceps (X ± Y), lumbar paraspinals (X ± Y), biceps femoris (X ± Y), lateral gastrocnemius (X ± Y), rectus femoris (X ± Y), and biceps brachii (X ± Y). The average percent asymmetry across all sites was 2.33% ± 3.13%, with values above C% suggesting potential clinical significance.

Conclusions: This study defines normative muscle stiffness and asymmetry values for young adults, providing a foundation for future investigations into muscle dysfunction. The significant differences observed between men and women highlight the need for sex-specific reference ranges. These findings may aid in identifying abnormal muscle tone in clinical and research settings.