Two. Little. Words. My, how they have impacted the BFR world. What are the words?
Yep you guessed it…”It’s Systemic!!”
Those two words have been used, by few, to explain a lot of the effectiveness BFR “could have” in rehabilitation from musculoskeletal injuries or surgeries. So let me state this very clearly from the outset, before we venture into the nuance: to date NO clinical trial using BFR as an intervention has investigated whether or not BFR elicited a systemic response of any sort. It should then go without saying that no study has been designed for the expressed purpose of determining whether or not any sort of systemic response from BFR elicited a treatment effect. Those are two very, very large holes.
Presently, any claim that BFR elicits a systemic response that enhances the recovery from any condition has no support in the literature. Period. Thus, it should not be used as rationale to support the use of BFR.
Alright I feel better that’s out of the way, and to be fair that may be as far as many of you care to read. I have zero problem with that, but I do want to lay out some of the evidence there is on the topic of systemic effects from BFR exercise. Like with all things BFR related, we have to start with what we know about the systemic effects of exercise without BFR, as that body of literature is much larger and can help us identify relevant outcomes. This is where the problems begin for systemic effects; just check out this title, “Neither load nor systemic hormones determine resistance training-mediated hypertrophy or strength gains in resistance-trained young men.” That study was performed by the prestigious lab of Stu Phillips, PhD at McMasters University. It had resistance trained young men perform total body exercise for 12 weeks at either a 30-50% of 1RM load or a 75-90% of 1RM load. (Morton 2016) Trained subjects were used as there was some thought that anabolic hormone responses might matter more in trained individuals since all the unsuccessful prior work in this area had used highly adaptable, untrained individuals. News flash…it didn’t matter.
I think it’s important to layer in some nuance here as “systemic effects” is probably too broad a phrase. Technically systemic effects would involve changes to multiple systems like the cardiovascular, endocrine and other systems which of course BFR does as described by Miller 2021. Historically those who reference the systemic effects of BFR are referring to “systemic hormonal effects” as they are appropriately called by Morton 2016. This would mean exercise induced increases in things like growth hormone, testosterone, and the like.
Prior to the study referenced above, West et al examined the influence post exercise elevations in systemic hormones have on muscle protein synthesis (MPS) rates. (West 2009) This was done via crossover trial where subjects performed moderately loaded biceps curls to the point of failure. On one day they performed biceps curls on a randomly selected arm, ingested 25g of whey protein (to maximize the MPS response) and had blood draws and muscle biopsies to assess MPS rates, lactate, testosterone, growth hormone, IGF-1 and cortisol levels. On a different day they used the same protocol, but the subjects also performed a lower body exercise program previously shown to elicit a systemic hormonal response. The condition involving lower body exercise elicited significant increases in lactate, IGF-1, GH, cortisol and testosterone without augmenting MPS rates. At minimum this study shows us that systemic hormonal responses of exercise do not augment the acute effects of well dosed exercise.
Frequently when the systemic hormonal effects of BFR exercise are referenced, the context given is that contralateral BFR exercise can be used to preserve muscle mass and strength in an immobilized limb that has had a recent surgery or injury. As mentioned earlier, this has never been studied, but the above paper by West can provide us some insight into the plausibility of this claim. Chiefly it should be noted that subjects in the West study performed bilateral lower extremity exercise as follows: 5 sets of 10 leg press, then 3 sets of 12 leg extension/leg curl supersets at 90% of a 10RM. That’s a pretty good amount of lower body exercise, which did elicit a systemic hormone response. The fact these had no effect on MPS in an arm that performed biceps exercise sufficient to create adaptation certainly raises questions around claims that a BFR bicep curl might elicit a sufficient systemic response to preserve contralateral shoulder muscle mass after shoulder surgery.
Thinking critically though, it could be that in the aforementioned, subjects were maxed out; there was a ceiling effect if you will on what was physiologically possible given the biceps exercise on its own was enough to elicit adaptation. In this context we need to mention a couple BFR papers that indicate systemic effects of BFR exercise might actually reduce the amount of work remote tissue must perform in order to elicit adaptation. Madarame 2008 and May 2018 showed using very similar protocols that an underdosed unilateral biceps curl (50% 1RM), if coupled with bilateral BFR leg curls and extensions, elicited unexpected increases in biceps size and force output. They did not measure any systemic hormones, but their control group did do low load LE exercise without BFR and saw no changes in the moderately loaded biceps curl arm. So it appears that the addition of BFR here did reduce the amount of work necessary to create adaptations in muscle size and force production. However, this study also showed us that whatever BFR did here, it had no effect on the biceps that did not exercise. Thus, in light of this data, claiming preservation of function in inactive, remote muscle tissue in a clinical scenario becomes a very large leap.
Finally, when discussing the systemic hormonal effects of BFR exercise, some seem to simply reference this as a mechanism for adaptation that is somehow unique to BFR. This typically occurs around the conversation of how to structure exercise programs, where the proponent of systemic effects might encourage whole body exercise without specifically targeting a muscle group via individualized loading, pressure, or effort levels in favor of 20 minutes of exercise because…it’s all systemic. The confusion here potentially centers around the fact that we know systemic hormones are in fact anabolic during puberty or when given exogenously (via injection). But context matters, during puberty or if given exogenously, testosterone levels for example are chronically supraphysiologic. When exercise causes supraphysiologic elevations in hormones, those elevations are transient. (West 2010) As discussed earlier, these transient increases do not affect anabolism. But perhaps BFR is doing something altogether different to systemic hormones than traditional heavy lifting. Laurentino et al sought to examine this as no one had directly compared the effects of low load BFR exercise to traditional heavy lifting. (Laurentino 2022) They used an 8 week bilateral knee extensions protocol with 20% 1RM and no BFR, 20% 1RM with BFR and 80% 1RM to examine this. The 20% 1RM groups did 4 sets of 15 reps and the 80% 1RM group did 4 sets of 8 reps. The BFR group used 80% LOP. Subjects had blood draws performed at their first and last sessions 15 minutes before and after the exercise protocol. These were used to assess testosterone, growth hormone, lactate, IGF-1 and cortisol levels. This protocol allowed them not only to get an individual session comparison, but also to determine if there were any adaptations in these responses over time as well as compare outcomes of muscle cross-sectional area and force output. They found no differences acutely or chronically in the systemic hormone responses to BFR or heavy loaded exercise. Further affirming that their study accurately compared the two conditions was the fact that there were no differences in the accretion of muscle or increases in quadriceps force output.
Thus, it doesn’t look like BFR is doing anything magical at the systemic hormonal level. Maybe, rather intense BFR exercise can sort of “prime the system” if you will for adaptation, but any remote tissue where you might be looking to create an effect is still going to have to do some moderate level work. And regardless, that effect can be achieved with or without BFR.
- Morton, R. W., Oikawa, S. Y., Wavell, C. G., Mazara, N., McGlory, C., Quadrilatero, J., Baechler, B. L., Baker, S. K., & Phillips, S. M. (2016). Neither load nor systemic hormones determine resistance training-mediated hypertrophy or strength gains in resistance-trained young men. Journal of Applied Physiology, 121(1), 129–138.
- West DW, Kujbida GW, Moore DR, Atherton P, Burd NA, Padzik JP, De Lisio M, Tang JE, Parise G, Rennie MJ, Baker SK, Phillips SM. Resistance exercise-induced increases in putative anabolic hormones do not enhance muscle protein synthesis or intracellular signalling in young men. J Physiol 587: 5239–5247, 2009.
- West DW, Burd NA, Tang JE, Moore DR, Staples AW, Holwerda AM, Baker SK, Phillips SM. Elevations in ostensibly anabolic hormones with resistance exercise enhance neither training-induced muscle hypertrophy nor strength of the elbow flexors. J Appl Physiol (1985) 108: 60–67, 2010.
- Miller, B. C., Tirko, A. W., Shipe, J. M., Sumeriski, O. R., & Moran, K. (2021). The Systemic Effects of Blood Flow Restriction Training: A Systematic Review. International Journal of Sports Physical Therapy, 16(4), 978–990.
- Madarame, H., Neya, M., Ochi, E., Nakazato, K., Sato, Y., & Ishii, N. (2008). Cross-transfer effects of resistance training with blood flow restriction. Medicine and Science in Sports and Exercise, 40(2), 258–263.
- May, A. K., Russell, A. P., & Warmington, S. A. (2018). Lower body blood flow restriction training may induce remote muscle strength adaptations in an active unrestricted arm. European Journal of Applied Physiology, 118(3), 617–627.
- West, D. W. D., Burd, N. A., Staples, A. W., & Phillips, S. M. (2010). Human exercise-mediated skeletal muscle hypertrophy is an intrinsic process. The International Journal of Biochemistry & Cell Biology, 42(9), 1371–1375.
- Laurentino, G. C., Loenneke, J. P., Ugrinowitsch, C., Aoki, M. S., Soares, A. G., Roschel, H., & Tricoli, V. (n.d.). Blood-flow-restriction-training-induced hormonal response is not associated with gains in muscle size and strength. https://doi.org/10.2478/hukin-2022-0095