Adiposity-related indices influence the interpretation of myotonometric assessment of muscle mechanical and viscoelastic properties.

Biomechanical and viscoelastic behaviour of skeletal muscles is increasingly investigated using non-invasive techniques such as myotonometry, which provide indirect estimates of tissue mechanical characteristics derived from the oscillatory response of the muscle-superficial tissue complex to a brief mechanical impulse. However, the interpretation of these measurements may be influenced by body composition, particularly subcutaneous adipose tissue, which can alter mechanical signal propagation. This study aimed to determine whether adiposity influences the interpretation of myotonometric measurements of muscle mechanical properties and to identify the most relevant adiposity-related factors affecting these measurements. A total of 133 healthy adults (63 females, 70 males; mean age 35.16 ± 8.29 years) were included. Body mass index (BMI), percentage body fat (%BF) estimated from skinfold measurements and the sum of four skinfold thickness (SFT) sites were assessed. Muscle mechanical properties (tone, stiffness, decrement, relaxation, and creep) of the biceps brachii, triceps brachii, rectus femoris, gastrocnemius medialis, and rectus abdominis were measured using the MyotonPRO device. Associations were analyzed using Spearman's rank correlation, while predictive value was evaluated using linear regression models adjusted for age and sex. Model fit was compared using the Akaike Information Criterion (AIC). %BF and SFT showed strong and consistent associations with muscle properties, including negative correlations with tone and stiffness (up to ρ = -0.821) and positive correlations with viscoelastic parameters (up to ρ = 0.847; all p < 0.001), whereas BMI showed weak and mostly non-significant relationships. Regression analyses identified %BF as the most robust predictor (β up to 0.83; R2 up to 0.69), particularly for viscoelastic parameters. SFT demonstrated lower and more variable predictive value, while BMI showed minimal explanatory power. The magnitude and consistency of these associations suggest that adiposity substantially affects the mechanical response captured by myotonometry. Subcutaneous adiposity significantly influences myotonometric measurements and may affect the interpretation of muscle mechanical properties. These findings highlight the need to consider body composition when using myotonometry as a tool for muscle assessment.