<strong>Effect Size – A Nuanced Perspective</strong>
The partial restriction of blood flow in combination with muscles contractions creates short-term edema (cell swelling) around the muscle cells, which limits the supply of oxygen and nutrients so that metabolites accumulate (Cayot et al., 2014). This initiates a cascade of physiologic processes, like the increase of growth hormone secretion, as approximately 2-3 fold greater compared to conventional resistance training. But also the increased activation of muscle satellite cells, about two-fold larger than conventional resistance training. This upregulates the net protein synthesis.(Yasuda et al., 2014; Segal et al., 2010; Roos and Lohmander, 2003). Check also the Blog post from September 17, 2020.
↑ Muscle oxygenation – hypoxia leading to short term ischemia ↑ Metabolite accumulation – accumulation of waste products ↑ Recruiting fast twice muscle fibers ↑ Cell Swelling ↑ Growth hormone 200-300% compared to conventional resistance training – relevant for bone and tendon health ↑ Satellite cell proliferation
↓ Secretion of muscle growth inhibitors (myostatin) – especially important for building muscle tissue ↑ Netto protein synthesis = Hypertrophy (muscle growth) ↑ Muscle strength and endurance ↓ Metabolic resistance – relevant for metabolic syndrome and diabetes ↑ Anaerobic threshold ↑ Mitochondrial content
These processes are further described in the scientific literature, by especially the leading researcher and Associate Professor of Exercise Science Jeremy P. Loenneke. He has contributed to the body of evidence and accumulated knowledge concerning BFR. For the past 12-14 years, he has co-authored several mechanistic and effect studies concerning Blood Flow Restriction.
Currently, a quick search on BFR via Pubmed shows >500 published scientific papers across all continents, which manifests the effects of BFR Training.
<strong>Nerd Alert – The Adaptive Muscle Response</strong>
There are many ways to compare the effect of Low-load resistance occlusion training (BFR) (20-50% of 1RM) vs. conventional Resistance Training (RT) / No-BFR, this results in varying conclusions of wherever BFR is more or less effective.
Low-load BFR (20-50% of 1RM) vs High-load No-BFR (60-90% of 1RM) – Repetitions to failure
Short-term muscle mass: Probably BFR Long-term muscle mass: Similar Short-term muscle strength: Similar Long-term muscle strength: Probably High-Load Muscle endurance: BFR Rate of Force Development (RFD) / explosive strength– e.g. fall prevention, vertical jump, etc: High-load RT
Low-load BFR (20-50% of 1RM) vs Low-load No-BFR (20-50% of 1RM) – Volume matched (equal load and repetitions)
Short-term muscle mass: BFR Long-term muscle mass: BFR Short-term muscle strength: BFR Long-term muscle strength: BFR Muscle endurance: BFR Rate of Force Development (RFD) / explosive strength e.g. fall prevention, vertical jump, etc: Probably BFR
Low-load BFR (20-50% of 1RM) vs Low-load No-BFR (20-50% of 1RM) – Load matched but repetitions to failure
Short-term muscle mass: Similar Long-term muscle mass: Similar Short-term muscle strength: Similar Long-term muscle strength: Similar Muscle endurance: Similar
Rate of Force Development (RFD) / explosive strength e.g. fall prevention, vertical jump, etc: Similar
Source: Slysz et al. (2016) – The efficacy of blood flow restricted exercise A systematic review & meta-analysis Hughes et al. (2017) – Blood flow restriction training in clinical musculoskeletal rehabilitation in systematic review and meta-analysis Grønfeldt et al. (2020) effect of blood-flow restricted vs. heavy-load strength training on muscle strength: systematic review and meta-analysis
When comparing (LL-BFR) vs (LL-No-BFR) as load matched and taken to failure, the number of repetitions needed to elicit muscular adaptions is significantly less. The most recent literature shows 10-60% fewer repetitions are needed to reach the same state of muscular fatigue. But the time-benefit of doing BFR is relative to the amount of relative pressure, being that higher pressure 70-90% of Limb Occlusion Pressure (LOP) seems to be favorable for most circumstances. This is particularly relevant when using very low-load (<25% 1RM), as there seems to be a threshold of at least 60% LOP when using very low load. From the literature, it seems that relative load and relative pressure exist on a mutually affected continuum. When using moderate-loads (40-50% of 1RM) use less pressure (40-60% LOP). On the other hand, when utilizing very low-load (<25% of 1 RM) It is strongly recommended to use higher relative pressures (70-90% LOP).
The load-pressure continuum appears to be a very important consideration, especially post-operation with prescribed load restrictions. Conversely, using BFR in gym settings without any strict load restriction, it is probably favorable to utilize lower pressure (40-60% LOP) but the higher relative load (30-50% 1RM).
Source: Cerqueira et al. (2021) Repetition Failure Occurs Earlier During Low-Load Resistance Exercise With High But Not Low Blood Flow Restriction Pressures: A Systematic Review and Meta-analysis Pignanelli et al. (2019) Low-load resistance training to task failure with and without blood flow restriction- Muscular functional and structural adaptations
<strong>Other Effects Associated with BFR</strong>
Treatment of sarcopenia by increasing muscle mass (protective for a wide range of age-related issues and chronic conditions (101 BFR Research Papers)
Greater muscle strength – directly transferable to everyday activities (ADL) Fall prevention
Improved circulatory system
Better self-reported health
Improved bone, cartilage & tendon properties
Increased aerobic & anaerobic fitness
Enhanced body composition
Shorter training time
Shorter restitution time
Alternative or supplement to heavy training during the season (due to less mechanical strain)
Use during periodization training with a focus on high rep / low-load Occlusion training