When it comes to building muscle, increasing weight is not always the only path to success. Blood flow restriction (BFR) training has gained attention for its potential to boost hypertrophy using lighter loads. However, the effectiveness of adding BFR to high-load resistance training in comparison to traditional lifting remains in question. This new study compared muscle growth from high-load resistance training alone to training with BFR and the results may be different than you suspect.
Overview
- What did they test? This study investigated the effects of high-load resistance training (HL-RT) alone compared to high-load resistance training with blood flow restriction (HL-BFR) on muscle growth. Muscle hypertrophy and metabolic stress were measured in 10 untrained participants, utilizing a within-subject design (one leg per protocol) over a 10-week period.
- What did they find? On average, both methods led to similar muscle growth. However, individual responses varied where half of the participants experienced greater muscle hypertrophy with HL-RT alone, despite HL-BFR causing higher metabolic stress.
- What does it mean for you? If you can safely lift heavy weights (≥ ~80% 1RM), adding blood flow restriction may not provide extra benefits and might even reduce muscle activation due to excessive metabolic stress. However, HL-BFR could still be useful for individuals who need to limit heavy loads due to injury or other reasons.
What’s the problem?
Prior research shows that both high-load resistance training (HL-RT) and low-load training with blood flow restriction (BFR) can stimulate muscle growth 1. It has been posited that BFR can promote hypertrophy through metabolite accumulation, or metabolic stress, as an additive effect to mechanical tension 2. Another hypothesis is that BFR might increase activation of higher threshold efferent (e.g., "motor") nerves, and thereby larger muscle fibers, due to metabolic stress-induced fatigue of smaller fibers innervated by lower threshold motor nerves 3. In other words, BFR may promote fatigue in smaller fibers earlier in a set which might instigate the recruitment of larger fibers earlier in a set. These effects appear to promote increases in molecular signaling pathways that can result in increases in muscle protein synthesis (MPS), satellite cell activation, and myonuclear content which can all contribute to muscle hypertrophy. The mechanisms by which BFR can promote hypertrophy are still being unraveled. Nearly every study that has investigated the effects of BFR on hypertrophy has utilized loads ranging from 20-40% 1RM. Some research has explored acute effects of BFR with loads up to 70-90% 1RM, but these primarily focused on power and velocity (not hypertrophy). For example, one study examined the effects of three weeks of strength training at 70% 1RM with BFR and reported greater improvements in strength and power in a small group of rugby athletes 4. Based on the current body of literature, it is unclear whether combining BFR with HL-RT would provide additive benefits for hypertrophy by increasing both mechanical tension and metabolic stress. This new study aimed to address whether certain individuals might benefit more from HL-BFR and if differences in metabolic stress could explain these individual responses.
Purpose
This study aimed to compare individual muscle hypertrophy responses to high-load resistance training (HL-RT) alone and HL-RT combined with blood flow restriction (HL-BFR). Additionally, the researchers sought to determine whether differences in metabolic stress—measured through blood deoxyhemoglobin (HHb) and total hemoglobin (tHb) concentrations using near-infrared spectroscopy (NIRS)—could explain variations in individuals' responsiveness to these protocols.
Hypothesis
This was an exploratory study. The authors stated it is reasonable to suggest that while some individuals may benefit from increased metabolic stress induced by adding BFR to HL-RT, others may not exhibit significant responses or may even experience attenuated gains.
