Similar acute increases in muscle size, but discrete perceptual responses to low-load blood flow restriction protocols.

The purpose of this investigation was to assess muscle size and perceptual responses following acute bouts of low-load blood flow restriction resistance exercise performed with a 75-repetition (1 × 30, 3 × 15), 3 sets to failure, and a 1 set to failure protocols. Nineteen females randomly performed a 75-repetition, 3 sets to failure, and 1 one set to failure low-load blood flow restriction protocols consisting of unilateral, submaximal (30% of maximal voluntary isometric contraction), isokinetic (90°·s-1), leg extension muscle actions. The minimal difference (MD) was used to determine real changes in each dependent variable from pretest to posttest. There were no significant (p = 0.191-0.567) interactions, main effects of Condition (p = 0.108-0.931), or main effects of Muscle (p = 0.103-0.958) for muscle thickness (MTH), cross-sectional area (CSA), or echo intensity (EI) of the rectus femoris or vastus lateralis. Across the protocols, the changes in MTH, CSA, and EI exceeded the minimal difference for 16-19, 18-19, and 11-19 of the 19 participants, respectively. Following the final set of each protocol, 3 sets to failure (8.94 ± 1.07 au) resulted in a greater rating of perceived exertion compared to the 1 set to failure (8.02 ± 1.08 au) and 75-repetition (8.05 ± 1.35 au) protocols. All three protocols resulted in comparable acute changes in muscle size; however, the 3 sets to failure resulted in the greatest perceptual response. Therefore, comparable acute muscle size responses can be achieved with the 75-repetition protocol or one set performed to failure with a reduced level of exertion.