Reliability of tensiomyography and myotonometry in detecting mechanical and contractile characteristics of the lumbar erector spinae in healthy volunteers

Tensiomyography (TM) (TMG) and MyotonPRO(A (R)) (MMT) are two non-invasive devices for monitoring muscle contractile and mechanical characteristics. This study aimed to evaluate the test-retest reliability of TMG and MMT parameters for measuring (TMG:) muscle displacement (D (m)), contraction time (T (c)), and velocity (V (c)) and (MMT:) frequency (F), stiffness (S), and decrement (D) of the erector spinae muscles (ES) in healthy adults. A particular focus was set on the establishment of reliability measures for the previously barely evaluated secondary TMG parameter V (c). Twenty-four subjects (13 female and 11 male, mean +/- SD, 38.0 +/- 12.0 years) were measured using TMG and MMT over 2 consecutive days. Absolute and relative reliability was calculated by standard error of measurement (SEM, SEM%), Minimum detectable change (MDC, MDC%), coefficient of variation (CV%) and intraclass correlation coefficient (ICC, 3.1) with a 95% confidence interval (CI). The ICCs for all variables and test-retest intervals ranged from 0.75 to 0.99 indicating a good to excellent relative reliability for both TMG and MMT, demonstrating the lowest values for TMG T (c) and between-day MMT D (ICC < 0.90). Absolute reliability was suitable for all parameters (CV 2-8%) except for D (m) (10-12%). V (c) demonstrated to be the most reliable and repeatable TMG parameter (ICC > 0.95, CV < 8%). The reliability for TMG V (c) could be established successfully. Its further applicability needs to be confirmed in future studies. MMT was found to be more reliable on repeated testing than the two other TMG parameters D (m) and T (c).