Repeated stimulation, inter-stimulus interval and inter-electrode distance alters muscle contractile properties as measured by Tensiomyography

CONTEXT: The influence of methodological parameters on the measurement of muscle contractile properties using Tensiomyography (TMG) has not been published. OBJECTIVE: To investigate the; (1) reliability of stimulus amplitude needed to elicit maximum muscle displacement (Dm), (2) effect of changing inter-stimulus interval on Dm (using a fixed stimulus amplitude) and contraction time (T(c)), (3) the effect of changing inter-electrode distance on Dm and T(c). DESIGN: Within subject, repeated measures. PARTICIPANTS: 10 participants for each objective. MAIN OUTCOME MEASURES: Dm and T(c) of the rectus femoris, measured using TMG. RESULTS: The coefficient of variance (CV) and the intra-class correlation (ICC) of stimulus amplitude needed to elicit maximum Dm was 5.7% and 0.92 respectively. Dm was higher when using an inter-electrode distance of 7cm compared to 5cm [P = 0.03] and when using an inter-stimulus interval of 10s compared to 30s [P = 0.017]. Further analysis of inter-stimulus interval data, found that during 10 repeated stimuli T(c) became faster after the 5(th) measure when compared to the second measure [P<0.05]. The 30s inter-stimulus interval produced the most stable T(c) over 10 measures compared to 10s and 5s respectively. CONCLUSION: Our data suggest that the stimulus amplitude producing maximum Dm of the rectus femoris is reliable. Inter-electrode distance and inter-stimulus interval can significantly influence Dm and/ or T(c). Our results support the use of a 30s inter-stimulus interval over 10s or 5s. Future studies should determine the influence of methodological parameters on muscle contractile properties in a range of muscles.