Normative Parameters of Gastrocnemius Muscle Stiffness and Associations with Patient Characteristics and Function

Background Quantifying muscle stiffness may aid in the diagnosis and management of individuals with muscle pathology. Therefore, the primary purpose of this study was to establish normative parameters and variance estimates of muscle stiffness in the gastrocnemius muscle in a resting and contracted state. A secondary aim was to identify demographic, anthropometric, medical history factors, and biomechanical factors related to muscle stiffness. Methods Stiffness of the gastrocnemius muscle was measured in both a resting and contracted state in 102 asymptomatic individuals in this cross-sectional study. Differences based on muscle state (resting vs contracted) and sex (female vs male) were assessed using a 2 X 2 analysis of variance (ANOVA). Associations between muscle stiffness and sex, age, BMI, race, exercise frequency, exercise duration, force production, and step length were assessed using correlation analysis. Results Gastrocnemius muscle stiffness significantly increased from a resting to a contracted state [mean difference: 217.5 (95% CI: 191.3, 243.8), p < 0.001]. In addition, muscles stiffness was 35% greater for males than females in a resting state and 76% greater in a contracted state. Greater muscle stiffness in a relaxed and contracted state was associated with larger plantarflexion force production (r = .26, p < 0.01 and r = .23, p < 0.01 respectively). Conclusion Identifying normative parameters and variance estimates of muscle stiffness in asymptomatic individuals may help guide diagnosing and managing individuals with aberrant muscle function.

Automated summary

This study aimed to establish normative parameters and variance estimates of muscle stiffness in gastrocnemius muscle, and to identify factors related to muscle stiffness including sex, age, BMI, race, exercise frequency, exercise duration, force production, and step length. Results showed that muscle stiffness significantly increased from resting to contracted state, with males having higher muscle stiffness than females. Muscle stiffness was positively correlated with plantarflexion force production.