Superimposed Tendon Vibration Increases Time to Task Failure During Intermittent Isometric Knee Extensions: Effects of Contraction Intensity and Sex

Purpose: – To determine whether superimposed local vibration (SLV) increases time to task failure (TTF) during submaximal isometric knee extensor contractions at low and moderate intensities (respectively, 30% and 50% of maximal voluntary isometric contraction, MVIC) and to examine whether the SLV effect differs between sexes. Methods: – Fifty-two healthy young adults were assigned to either a 30% or 50% MVIC group (n = 26 each, 11 women per group). Each group performed a unilateral intermittent isometric knee-extension fatiguing task (15 s contraction/5 s rest) under two randomized conditions (SLV and control, CON), until task failure. Torque and electromyographic (EMG) activity of the knee extensor and flexor muscles were recorded for the entire duration of the task. TTF was defined as the time until torque output dropped more than 10% below the target force. Torque time integral (TTI) was calculated over the TTF. Results: – TTF was significantly greater (+9.5 ± 17.3%) in the SLV condition compared with the control (P < 0.001), independently of contraction intensity (30% vs 50% MVIC, P = 0.901) and sex (P = 0.183). TTI was greater in SLV than CON (+8.9 ± 17.4%, P < 0.001) with no significant sex or intensity interactions (both P > 0.183). Despite the longer TTF and higher TTI, no difference in EMG during the fatiguing task was observed between conditions (P > 0.173). Conclusions: – SLV enhances time to failure and force production during submaximal intermittent isometric contractions, regardless of sex or intensity. Unchanged EMG between conditions throughout the fatiguing task suggests greater time spent at high EMG levels with SLV, warranting further investigation.