No Long-Term Muscle or Strength Gain Benefits of Blood Flow Restriction - Even W/ Low Weights, BFR Gains Don't Surpass Those of Classic Strength Training to Failure

The benefits of blood flow restriction in healthy athletes may be less pronounced than the advocates would have it.

After the initial hype abated, only few people are still talking about blood flow restriction and its potential beneficial effects on strength and muscle gains. One of the reasons for the reduced enthusiasm among muscle heads is that all beneficial effects were observed in low intensity training; and "low intensity" = using low weights is not exactly what bros like to do.

Against that background it would be all the more important to be sure that reducing your training weights to 40% to do your blood flow restricted biceps curls is actually worth it.
A recent study from the Department of Public Health at the Aarhus University does now suggest: It is not worth it! In said study, Farup et al. the hypertrophic potential of load-matched blood-flow restricted resistance training (BFR) vs free-flow traditional resistance training (low load TRT) performed to fatigue.

Figure 1: Study design. The upper timeline displays the overall study period whereas the lower timeline displays the 6 weeks training period. Measures of muscle thickness (by ultrasound; UL), muscle soreness (by visual analog scale; VAS), muscle volume and muscle water content (by magnetic resonance imaging; MRI), isometric strength (by maximal voluntary contraction; MVC), dynamic strength (by three repetition maximum; 3 RM), and muscle activity (by electromyography; EMG) were performed on specific time points as indicated.

To this ends, they recruited ten healthy young subjects who performed unilateral BFR and contralateral low-load traditional strength training for the elbow flexor with dumbbell curls and a weight amounting to 40% of their individual 1-repetition maximum.

• Strength and size don't always go hand in hand... and BFR training appears to be better suited for strength | more.

  All sets were performed until volitional concentric failure, meaning no add. rep with accurate form could be performed. 
• The athletes trained three days per week for a total study duration of 6 weeks (that's more than in many other studies). 
• Prior to and at 3 (post-3) and 10 (post-10) days post-training, magnetic resonance imaging (MRI) was used to estimate elbow flexor muscle volume and muscle water content accumulation.

The results shows that the total work (number of reps x weight lifted) was threefold lower for BFR compared with low-load TRT ( P < 0.001).

Figure 2:Pre-post comparison of muscle size and strength gains show no differences between regular and BFR training if the exercises are performed to failure (Farup. 2015).

On the other hand, both BRF and low-load TRT increased muscle volume by approximately 12% with no significant difference in the MRI-determined water content and the muscle size being measured three and ten days after the last workout. Due to the exercise induced muscle swelling the muscle size was yet increased to a greater extent with BRF ( P < 0.05) in the early training phase, i.e. up to 48h after a workout.
References:

• Farup et al. "Blood flow restricted and traditional resistance training performed to fatigue produce equal muscle hypertrophy." Scand J Med Sci Sports (2015): Accepted Article.
• Loenneke, Jeremy P., et al. "Low intensity blood flow restriction training: a meta-analysis." European journal of applied physiology 112.5 (2012): 1849-1859.