Contracting biceps brachii elastic properties can be reliably characterized using supersonic shear imaging.

PURPOSE: Since experimental techniques classically used to investigate the mechanical behavior of muscle in vivo assess global mechanical properties of the musculo-articular complex, the aim of the present study was to assess the feasibility and reliability of localized contracting biceps brachii elastic properties' measurements using elastography.
METHODS: Twelve subjects participated in intra-session, inter-session and inter-observer reliability experiments. They were asked to perform a linear torque ramp of 30 s from 0 to 75 % of maximal voluntary contraction. Joint torque, electromyographic (EMG) activity and shear elastic modulus were synchronously measured in the biceps brachii. Elastic properties were determined by stiffness indexes calculated as the slopes of the linear regressions established between shear modulus and joint torque or EMG levels. Compliance indexes were also obtained by plotting logarithmic values of shear modulus versus torque or EMG.
RESULTS: Determination coefficients were high for the four relationships (0.87-0.94). In addition, reliability was significantly higher for the compliance index taking into account logarithmic values of EMG activity (mean coefficient of variation of 5.3 ± 4.1%; P = 0.003). Although not statistically different from other methods (P = 0.111), the mean intra-class correlation coefficient was excellent (0.98 ± 0.01) and the standard error in measurement very low (0.04 ± 0.01 for a mean index of -0.73 ± 0.28).
CONCLUSIONS: Biceps brachii elastic properties can be reliably investigated during contraction via elastography using the proposed fitting method. Use of this technique could provide new insights into the understanding of localized muscle elastic properties adaptations.