Impact of Fatiguing, Submaximal High- vs. Low-Torque Isometric Exercise on Acute Muscle Swelling, and Echo Intensity in Resistance-Trained Men

To evaluate the effects of repeated, fatiguing isometric knee extension contractions performed at high-torque (HT) vs. low-torque (LT) maximal voluntary isometric contraction (MVIC) on acute muscle swelling, and echo intensity (EI) of the rectus femoris (RF) and vastus lateralis (VL) muscles in resistance-trained males. Twenty-two resistance-trained men performed either HT (70% MVIC) or LT (30% MVIC) isometric contractions to fatigue on separate days. Before and after exercise, muscle cross-sectional area (mCSA) and EI of the RF and VL were assessed through ultrasound. Muscle cross-sectional area and EI (collapsed across muscle) increased similarly after HT (mean +/- 95% confidence interval: mCSA[DELTA]: 3.52 +/- 0.52 cm2; EI[DELTA]: 4.58 +/- 1.65 au) and LT (mCSA[DELTA]: 3.61 +/- 0.59 cm2; EI[DELTA]: 3.30 +/- 1.36 au) exercise. No relationships between mCSA[DELTA] and time to task failure (TTF), normalized MVIC, or the tension-time integral were observed during either HT or LT exercise. During both conditions, EI[DELTA] was related to TTF (HT: r = 0.44; LT: r = 0.66) and normalized MVIC (HT: r = -0.60; LT: r = -0.57). These results suggest that acute muscle swelling and increased EI observed in response to intermittent, submaximal, fatiguing isometric exercise are similar for the RF and VL and are not dependent on the torque-level or tension-time integral when exercise is performed to failure. Factors such as the duration of time performing exercise and relative muscle strength may influence the magnitude of change in EI, but not acute muscle swelling, during intermittent fatiguing isometric exercise.