We performed two experiments to describe the magnitude of delayed-onset muscle soreness (DOMS) associated with blood flow restriction (BFR) exercise and to determine the contribution of the concentric (CON) versus eccentric (ECC) actions of BFR exercise on DOMS. In experiment 1, nine subjects performed three sets of unilateral knee extension BFR exercise at 35% of maximal voluntary contraction (MVC) to failure with a thigh cuff inflated 30% above brachial systolic pressure. Subjects repeated the protocol with the contralateral limb without flow restriction. Resting soreness (0-10 scale) and algometry (pain-pressure threshold; PPT) were assessed before and 24, 48 and 96 h post-exercise. Additionally, MVC and vastus lateralis cross-sectional area (CSA) were measured as indices of exercise-induced muscle damage. At 24-h post-exercise, BFR exercise resulted in more soreness than exercise without BFR (2.8 +/- 0.3 vs 1.7 +/- 0.5) and greater reductions in PPT (15.2 +/- 1.7 vs. 20 +/- 2.3 N) and MVC (14.1 +/- 2.5% decrease vs. 1.5 +/- 4.5% decrease) (p

Sex diVerences in muscle fatigue-resistance have been observed in a variety of muscles and under several conditions. This study compared the time to task failure (TTF) of a sustained isometric elbow extensor (intensity 15% of maximal strength) contraction in young men (n = 12) and women (n = 11), and examined if their neurophysiologic adjustments to fatigue diVered. Motorevoked potential amplitude (MEP), silent period duration, interference electromyogram (EMG) amplitude, maximal muscle action potential (M max ), heart rate, and mean arterial pressure were measured at baseline, during the task, and during a 2-min ischemia period. Men and women did not diVer in TTF (478.2 § 31.9 vs. 500.4 § 41.3 s; P = 0.67). We also performed an exploratory post hoc cluster analysis, and classiWed subjects as low (n = 15) or high endurance (n = 8) based on TTF (415.3 § 16.0 vs. 626.7 § 25.8 s, respectively). The high-endurance group exhibited a lower MEP and EMG at baseline (MEP 16.3 § 4.1 vs. 37.2 § 3.0% M max , P < 0.01; EMG 0.98 § 0.18 vs. 1.85 § 0.26% M max , P = 0.03). These Wndings suggest no sex diVerences in elbow extensor fatigability, in contrast to observations from other muscle groups. The cluster analyses results indicated that high-and low-endurance groups displayed neurophysiologic diVerences at baseline (before performing the fatigue task), but that they did not diVer in fatigueinduced changes in their neurophysiologic adjustments to the task.

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