Authors' Reply to Valenzuela et al: Comment on: "Assessment of Skeletal Muscle Contractile Properties by Radial Displacement: The Case for Tensiomyography"

Abstract

First paragraph: We thank Valenzuela et al. [1] for their insightful commentary regarding our review and appreciate the interest shown in our article [2]. We certainly agree that predicting performance by measuring muscle contractile properties with tensiomyography (TMG) is an intriguing proposition. As underlined by Valenzuela et al. [1], the progressive evidence for TMG predicting the distribution of type I/II muscle fibres is convincing, culminating in the robust study by Šimunič et al. [3], which we highlighted as the main source of construct validity assessment for TMG [2]. Furthermore, a recent study by Šimunič et al. [4] revealed slower contraction time (Tc) among those masters athletes with a higher proportion of type I and/or IIa muscle fibres than type IIx. That said, we urge caution regarding interpretation of muscle belly radial displacement (Dm) as a direct indicator of muscle stiffness. To date, there remains limited research experimentally isolating intrinsic muscle stiffness when evaluating TMG as a measure of contractile mechanics. As such, when TMG has been used to assess muscle status, it has been difficult to differentiate between changes associated with excitation–contraction coupling or muscle stiffness, as in most situations both parameters may be affected. We [2] referred to the shortage of studies directly assessing changes in Dm associated with altering muscle stiffness via experimental intervention; however, since then, we ourselves have published a study demonstrating increased Dm following a self-massage treatment [5]. Still, we cannot say for sure that these observed changes were the result of decreased muscle stiffness.