Metabolic stress training resulted in in a small to moderate favorable effect on gaining muscle. Metabolic stress training with longer rest periods (>120 seconds) and weights between 60-80% of a 1-RM was favorable for gaining muscle. Severe hypoxia was worse for muscle hypertrophy than moderate hypoxia.
BLOOD FLOW RESTRICTION AND HYPOXIA: SUMMARY
- Metabolic stress training (i.e., blood flow restriction training) resulted in in a small to moderate favorable effect on gaining muscle.
- Metabolic stress training with longer rest periods (>120 seconds) and weights between 60-80% of a 1-RM was favorable for gaining muscle.
- Severe hypoxia was worse for muscle hypertrophy than moderate hypoxia.
BRAD SCHOENFELDS MECHANISMS OF HYPERTROPHY
In 2010, Brad Schoenfeld, an acclaimed expert in muscle development, proposed that three elements – mechanical tension, metabolic stress, and muscle harm – can increase the growth of muscle fibers. (Schoenfeld, 2010)
This review was published in 2010; since that time, muscle damage seems to be less of a factor for muscle hypertrophy. Additionally, a full range of motion and the amount of time rested between sets can also influence muscle growth. (Schoenfeld & Grgic, 2020)
WHAT IS MECHANICAL TENSION?
Mechanical tension is the amount of force applied to the muscle while working out. The amount of weight used (i.e., heavy load) in a set increases mechanical tension or the force applied to a muscle. The use of light weight and low mechanical load is one of the main reasons Super Slow training is inferior to regular resistance exercise.
Mechanical tension has been considered by many the main driving factor in gaining muscle. Eccentric overload, or using a heavier weight and slowly lowering it, is a form of mechanical tension overload.
WHAT IS BEST TO GAIN MUSCLE? MECHANICAL TENSION VS METABOLIC STRESS (i.e., BLOOD FLOW RESTRICTION)?
Over the past decade, it’s been emphasized that athletes looking to gain muscle need to maximize metabolic stress by taking short rest periods (i.e., 30 second rest between sets). What is metabolic stress?
Metabolic stress is the build-up of metabolic byproducts in muscle cells, such as lactate, hydrogen ions, etc., during exercise. The feeling of getting a muscle pump is the result of metabolic byproducts building up in the muscle. Short rest periods between sets can elicit a greater metabolic stress response and anabolic signaling hormones (i.e., growth hormone) than longer rest periods.
HOW LONG TO REST BETWEEN SETS
Short rest periods, rest-pause training, dropsets, triset training, and blood flow restriction training all increase metabolic stress. Blood flow restriction utilizes a tourniquet or other compression device around a muscle to reduce blood flow and create metabolic stress.
A 2020 study found that calf muscle thickness increased after blood flow restriction training (BFR) in well-trained resistance exercise men, despite a lower training volume. Despite the higher training volume, the traditional resistance training group had slightly less muscle growth (+1.94%) than the BFR group (3.29%). It was suggested that the higher metabolic stress resulted in greater muscle growth. (Gavanda et al., 2020)
Although many bodybuilders have been told to take less than a minute rest periods between sets for optimal muscle growth, new research suggests this is not favorable for muscle growth. Dr. Schoenfeld found that men who rested 3 minutes between sets had greater increases in lower leg muscle growth than those who rested 1 minute between sets. (Schoenfeld et al., 2016)
In sum, hypertrophy rest time between sets for muscle growth should be greater than 3 minutes for larger muscle groups like the legs, chest, and back. Smaller body parts, such as the arms, calves, etc., can probably use shorter rest periods without impaired muscle growth.
MECHANISMS OF BLOOD FLOW RESTRICTION -RELATED MUSCLE HYPERTROPHY
The benefits of short rest periods between sets (i.e., < 30-second rest periods) and BFR training are greater metabolic stress, anabolic stress, cytokines, cellular swelling, etc. (Schoenfeld, 2013; Scott et al., 2014) These greater metabolic responses could possibly lead to greater increases in muscle size and strength compared to normal training.(Nishimura et al., 2010)
Despite the metabolic benefits of training in low-oxygen states, not all the research has found that hypoxic training (i.e., low oxygen) increases muscle growth greater than normal training. (Ramos-Campo et al., 2018)
One study compared subjects who lifted the weight in 1 second and lowered it in 1 second with no pause (i.e., did not lockout between reps) with a heavier weight (i.e., ~80% 1RM) training to complete failure. The second part of the study had subjects exercise with a lighter weight (~50% 1RM) with a slow lifter speed and a 1-second pause (3 seconds concentric, 3 seconds eccentric, 1-second isometric) training to failure.
The subjects who did not pause between reps had higher metabolic stress and lower oxygenation; however, both groups had similar increases in muscle hypertrophy. (Tanimoto & Ishii, 2006)
BLOOD FLOW RESTRICTION TRAINING STUDIES
Researchers went and did a large-scale review of all the existing literature. They looked at 17 studies on metabolic stress training, BFR training, and studies that compared hypoxia training to normal training. The researchers did not find compelling results that metabolic stress training is going to lead to greater increases in muscle growth compared to normal training. The researchers found a small to medium advantage to the use of moderate training loads and longer rest periods at moderate hypoxia for stimulating muscle growth.(Benavente et al., 2023)
Another interesting finding was that moderate hypoxia or metabolic stress was more favorable for muscle growth than severe hypoxia. When the researchers went thru the data, they did not find that short rest period (i.e., < 60-120) were less favorable for muscle gains than longer rest periods (> 120 seconds).
The research concluded that hypoxia/metabolic stress training might be beneficial for stimulating muscle growth under the following conditions:
1) Training programs that employ loads between 60 and 80% 1RM and inter-set rest intervals ≥ 120 s show greater increases in muscle strength and muscle hypertrophy compared to normal training.
2) Moderate hypoxia seems to be more suitable for improvement in muscle hypertrophy compared to severe hypoxia; however, this does not seem to enhance strength gains.
Benavente, C., Schoenfeld, B. J., Padial, P., & Feriche, B. (2023). Efficacy of resistance training in hypoxia on muscle hypertrophy and strength development: a systematic review with meta-analysis. Scientific Reports, 13(1), 3676. https://doi.org/10.1038/s41598-023-30808-4
Gavanda, S., Isenmann, E., Schlöder, Y., Roth, R., Freiwald, J., Schiffer, T., Geisler, S., & Behringer, M. (2020). Low-intensity blood flow restriction calf muscle training leads to similar functional and structural adaptations than conventional low-load strength training: A randomized controlled trial. PLoS One, 15(6), e0235377-e0235377. https://doi.org/10.1371/journal.pone.0235377
Nishimura, A., Sugita, M., Kato, K., Fukuda, A., Sudo, A., & Uchida, A. (2010). Hypoxia increases muscle hypertrophy induced by resistance training. Int J Sports Physiol Perform, 5(4), 497-508. https://doi.org/10.1123/ijspp.5.4.497
Ramos-Campo, D. J., Scott, B. R., Alcaraz, P. E., & Rubio-Arias, J. A. (2018). The efficacy of resistance training in hypoxia to enhance strength and muscle growth: A systematic review and meta-analysis. Eur J Sport Sci, 18(1), 92-103. https://doi.org/10.1080/17461391.2017.1388850
Schoenfeld, B. J. (2010). The Mechanisms of Muscle Hypertrophy and Their Application to Resistance Training. The Journal of Strength & Conditioning Research, 24(10). https://journals.lww.com/nsca-jscr/Fulltext/2010/10000/The_Mechanisms_of_Muscle_Hypertrophy_and_Their.40.aspx