Reliability and validity of a semi-electronic tissue compliance meter to assess muscle stiffness

Most methods assessing soft tissue stiffness are associated with high costs and considerable technical effort. A previous study demonstrated that the tissue compliance meter represents an affordable alternative with straightforward handling. However, little data exists describing its measurement properties.

The study aimed to elucidate the reliability and validity of a semi-electronic tissue compliance meter (STCM).

Tissue stiffness at the lateral calf was examined in 34 healthy participants (24 ± 5 yrs, 21 men). Measurements on two consecutive days were used to estimate test-retest reliability, day-to-day reliability and inter-rater reliability. Validity was examined twofold. Firstly, STCM data were correlated with those of another method, the myotonometry. Secondly, STCM measurements at different levels of isometric contraction (M.gastrocnemius) were examined for systematic differences.

Intraclass correlations (ICC) revealed high test-retest reliability (ICC 0.84, 95% CI: 0.70 to 0.92; p< 0.05) and day-to-day reliability (0.84, 0.71 to 0.92; p< 0.05). Inter-rater reliability was sufficient to good (0.75, 0.56 to 0.87; p< 0.05). Cross-validation with myotonometry revealed a strong correlation of both methods (r= 0.86; p< 0.05). Stiffness assessments during isometric contraction demonstrated that the STCM can discriminate different force levels (χ2= 57.1, p< 0.05).

The STCM provides valid and reliable measurements of tissue stiffness. Further study is needed to provide norm values for different body regions and to reveal alterations in patients with musculoskeletal disorders.