Electromechanical delay in biceps brachii assessed by ultrafast ultrasonography.

Using ultrasound we tested the utility of determining the relative contribution of the main muscle structures/mechanisms to the electromechanical delay in the biceps brachii. Nine subjects underwent electrically evoked contractions with the echographic probe maintained over the muscle and the myotendinous junction. No difference was found between the onset of muscle fascicle motion (Dm, 5.57 ± 1.37 ms) and the onset of myotendinous junction motion (Dt, 5.47 ± 1.38 ms), whereas significant differences were found between Dm/Dt and electromechanical delay (approximately 10 ms). Electromechanical delay can be used as a model for studying the effects of neuromuscular disorders or various constraints that affect excitation-contraction coupling and/or muscle force transmission.