An inability to lift loads great enough to disrupt muscular blood flow may impair the ability to fatigue muscles, compromising the hypertrophic response. It is unknown what level of blood flow restriction (BFR) pressure, if any, is necessary to reach failure at very low-loads [i.e., 15% one-repetition maximum (1RM)]. The purpose of this study was to investigate muscular adaptations following resistance training with a very low-load alone (15/0), with moderate BFR (15/40), or with high BFR (15/80), and compare them to traditional high-load (70/0) resistance training. Using a within/between subject design, healthy young participants (n = 40) performed four sets of unilateral knee extension to failure (up to 90 repetitions/set), twice per week for 8 weeks. Data presented as mean change (95% CI). There was a condition by time interaction for 1RM (p < 0.001), which increased for 70/0 [3.15 (2.04,4.25) kg] only. A condition by time interaction (p = 0.028) revealed greater changes in endurance for 15/80 [6 (4,8) repetitions] compared to 15/0 [4 (2,6) repetitions] and 70/0 [4 (2,5) repetitions]. There was a main effect of time for isometric MVC [change = 10.51 (3.87,17.16) Nm, p = 0.002] and isokinetic MVC at 180^°/s [change = 8.61 (5.54,11.68) Nm, p < 0.001], however there was no change in isokinetic MVC at 60^°/s [2.45 (−1.84,6.74) Nm, p = 0.261]. Anterior and lateral muscle thickness was assessed at 30, 40, 50, and 60% of the upper leg. There was no condition by time interaction for muscle thickness sites (all p ≥ 0.313). There was a main effect of time for all sites, with increases over time (all p < 0.001). With the exception of the 30% lateral site (p = 0.059) there was also a main effect of condition (all p < 0.001). Generally, 70/0 was greater. Average weekly volume increased for all conditions across the 8 weeks, and was greatest for 70/0 followed by 15/0, 15/40, then 15/80. With the exception of 1RM, changes in strength and muscle size were similar regardless of load or restriction. The workload required to elicit these changes lowered with increased BFR pressure. These findings may be pertinent to rehabilitative settings, future research, and program design.

To determine if muscle growth is important for increasing muscle strength or if changes in strength can be entirely explained from practicing the strength test. Thirty-eight untrained individuals performed knee extension and chest press exercise for 8 wk. Individuals were randomly assigned to either a high-volume training group (HYPER) or a group just performing the one repetition maximum (1RM) strength test (TEST). The HYPER group performed four sets to volitional failure (~8RM–12RM), whereas the TEST group performed up to five attempts to lift as much weight as possible one time each visit. Data are presented as mean (90% confidence interval). The change in muscle size was greater in the HYPER group for both the upper and lower bodies at most but not all sites. The change in 1RM strength for both the upper body (difference of −1.1 [−4.8, 2.4] kg) and lower body (difference of 1.0 [−0.7, 2.8] kg for dominant leg) was not different between groups (similar for nondominant). Changes in isometric and isokinetic torque were not different between groups. The HYPER group observed a greater change in muscular endurance (difference of 2 [1,4] repetitions) only in the dominant leg. There were no differences in the change between groups in upper body endurance. There were between-group differences for exercise volume (mean [95% confidence interval]) of the dominant (difference of 11,049.3 [9254.6–12,844.0] kg) leg (similar for nondominant) and chest press with the HYPER group completing significantly more total volume (difference of 13259.9 [9632.0–16,887.8] kg). These findings suggest that neither exercise volume nor the change in muscle size from training contributed to greater strength gains compared with just practicing the test.

When restricting blood flow for the purpose of increasing or maintaining muscle fitness, the aim is to reduce the amount of arterial flow into the limb and restrict the venous flow out of the limb. Doing so has been shown to elicit positive adaptations with regards to skeletal muscle size, and strength, while some evidence also eludes to beneficial effects on vascular and bone tissue. Regarding skeletal muscle, the main benefits of blood flow restriction are the ability to stimulate increases in size and strength while avoiding the greater mechanical stress associated with traditional high-load resistance training, and the greater volumes required when exercising with low loads to failure. While the most robust benefits are observed following blood flow restriction during low-load resistance training, evidence suggests positive adaptations occur while restricting blood flow during low-intensity aerobic exercise, and perhaps even during periods of disuse in the absence of exercise. Although the exact mechanisms are unclear, most of the evidence seems to allude to cell swelling and metabolite-induced fatigue during exercise stimulating synthetic pathways that can lead to muscle growth. While the blood flow restriction stimulus has been shown to be relatively safe for participants, the practitioner should be cognizant of the relative pressure being applied to the underlying tissue. This is important as cuff type, cuff width, and limb circumference can all influence the restrictive stimulus. Therefore, to ensure a similar, safe stimulus all variables should be accounted for.