The effect of inter-electrode distance on radial muscle displacement and contraction time of the biceps femoris, gastrocnemius medialis and biceps brachii, using tensiomyography in healthy participants

BACKGROUND: The systematic effect of inter-electrode distance on electrically elicited radial muscle displacement (Dm) and contraction time (T c) of the biceps femoris, gastrocnemius medialis and biceps brachii using tensiomyography (TMG) is currently unavailable.
OBJECTIVE: To investigate the effects of inter-electrode distance (4 cm, 5 cm, 6 cm and 7 cm) on Dm and T c of the biceps femoris, gastrocnemius medialis and biceps brachii, when the current amplitude is standardised.
APPROACH: A within subject, repeated measures cross-over study.
PARTICIPANTS: 24 participants.
MAIN RESULTS: Biceps femoris and gastrocnemius medialis Dm increased with increased inter-electrode distance (biceps femoris: p   =  0.015; gastrocnemius medialis: p   =  0.000), yet T c were not affected (p   >  0.05). Biceps brachii Dm was not affected by inter-electrode distance (p   >  0.05), yet T c became shorter with increased inter-electrode distance (p   =  0.032).
SIGNIFICANCE: Inter-electrode distance affects Dm but not T c in two pennate muscles (biceps femoris and gastrocnemius medialis), and T c but not Dm in one parallel muscle (biceps brachii). Based on Dm measurements, optimal muscle specific inter-electrode distances were judged within the limits of this study. The following optimal inter-electrode distances are suggested: biceps femoris  =  6 cm, gastrocnemius medialis  =  7 cm and biceps brachii  =  4 cm. Our findings emphasise the importance of accurate implementation and reporting of inter-electrode distance, for the reproducibility and comparability of studies using TMG.