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

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Immobilization reduces muscle performance, and despite these performance losses being associated with neural impairments little is known regarding adaptations in cortical properties. We utilized transcranial magnetic stimulation to assess changes in flexor carpi radialis (FCR) intracortical facilitation (ICF), and short- and long-interval intracortical inhibition (SICI and LICI) in healthy humans undergoing 3 weeks of immobilization. Measurements were obtained at rest and during contraction (15% intensity). Central activation and the Hoffman reflex (H-reflex) were also assessed. Strength decreased 43.2% ± 6.1% following immobilization, and central activation also decreased (97.5% ± 2.4% to 73.2% ± 8.3%). No changes in ICF, SICI, or LICI were observed at rest; however, LICI was increased during contraction (67.5% ± 6.9% to 53.1% ± 6.7% of unconditioned response). The increase in LICI correlated with the loss of strength (r = −0.63). The H-reflex increased following immobilization. These findings suggest that immobilization increases intracortical inhibition during contraction, and this increase is primarily mediated by GABAB receptors.

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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