Abstract
We investigated the acute and chronic effects of low-intensity concentric or eccentric resistance training with blood flow restriction (BFR) on muscle size and strength. Ten young men performed 30% of concentric one repetition maximal dumbbell curl exercise (four sets, total 75 reps) 3 days/week for 6 weeks. One arm was randomly chosen for concentric BFR (CON-BFR) exercise only and the other arm performed eccentric BFR (ECC-BFR) exercise only at the same exercise load. During the exercise session, iEMG for biceps brachii muscles increased progressively during CON-BFR, which was greater (p<0.05) than that of the ECC-BFR. Immediately after the exercise, muscle thickness (MTH) of the elbow flexors acutely increased (p<0.01) with both CON-BFR and ECC-BFR, but was greater with CON-BFR (11.7%) (p<0.01) than ECC-BFR (3.9%) at 10-cm above the elbow joint. Following 6-weeks of training, MRI-measured muscle cross-sectional area (CSA) at 10-cm position and mid-upper arm (12.0% and 10.6%, respectively) as well as muscle volume (12.5%) of the elbow flexors were increased (p<0.01) with CON-BFR. Increases in muscle CSA and volume were lower in ECC-BFR (5.1%, 0.8% and 2.9%, respectively) than in the CON-BFR and only muscle CSA at 10-cm position increased significantly (p<0.05) after the training. Maximal voluntary isometric strength of elbow flexors was increased (p<0.05) in CON-BFR (8.6%), but not in ECC (3.8%). These results suggest that CON-BFR training leads to pronounced acute changes in muscle size, an index of muscle cell swelling, the response to which may be an important factor for promoting muscle hypertrophy with BFR resistance training.
Highlights
In the past decade, several studies have reported that lowintensity resistance training (20–30% 1RM) combined with blood flow restriction (BFR) elicits similar muscle hypertrophy as traditional high-intensity resistance training (.70% 1-RM) regardless of age [1,2,3,4]
Recent studies demonstrated that a single bout of low-intensity resistance exercise with BFR stimulates the anabolic cell signaling mammalian target of rapamycin pathway, resulting in increased muscle protein synthesis within 3 hours after exercise [5,6,7]
Statistical analysis was performed by a two-way analysis of variance (ANOVA) with repeated measures [trials (CON-BFR vs. eccentric BFR (ECC-BFR))6time]
Summary
Several studies have reported that lowintensity resistance training (20–30% 1RM) combined with blood flow restriction (BFR) elicits similar muscle hypertrophy as traditional high-intensity resistance training (.70% 1-RM) regardless of age [1,2,3,4]. Following a single bout of low-intensity BFR bench press exercise, acute changes in muscle size were observed in both the blood flow restricted triceps muscle as well as the blood flow non-restricted chest muscle, and both the triceps and chest muscles increased muscle cross-sectional area following BFR bench press training [14]. It appears that BFR training-induced muscle cell swelling may contribute significantly to the anabolic benefits of BFR [15,16]
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