Does occlusion training mean more muscle?

I have to say I’ve long been intrigued by the use of occlusion training to promote muscle growth with low-intensity training. Occlusion training, otherwise known as blood flow restricted exercise, involves wearing an occlusive device, often a blood pressure cuff, tightly worn wrap, or commercially available device allowing for precise control of pressures, during the performance of exercise. There is variability across the methods used, however, generally a given pressure is applied that is sufficient to occlude venous return from a limb while still allowing for arterial flow to the exercising muscle (1).

Occlusion training has received increased attention as of late, and much of what circulates, at least in the popular press, focuses on the comparable hypertrophic and strength adaptations that occurs following either occluded, low-load training, or “normal”, high-intensity training. Given that a growing collection of studies have demonstrated that comparable hypertrophy occurs with both heavy (>70%-1RM) and light (<50%-1RM) loads (2-6), one has to question, what does occluding blood flow add while training at low intensity, if low-intensity training results in comparable hypertrophy to begin with?

This suggests that the comparison of interest is not necessarily that of high intensity strength training against low-intensity with occlusion, but rather, is there an additive effect of occlusion when training at the same low intensity with no occlusion? For ease of discussion, we can address this problem by evaluating studies that compare low intensity training alone against that with occlusion, and can group studies into those that equate volume/work/reps (work-matched), or those that train to concentric failure (effort-matched), for which there are far fewer studies.

Occlusion training results in greater growth to work-matched non-occluded training

It’s not surprising that when blood flow to an exercise muscle is restricted, performance is reduced. Fewer repetitions are completed at a given training intensity (7-12), and because of this, much of what has been done regarding the effects of occlusion attempts to match the number of repetitions completed in non-occluded conditions to those of occluded training (13-22).

When volume-equated, occlusion training is superior to non-occluded training with respect to muscle hypertrophy. Numerous studies have demonstrated enhanced growth to work/rep-matched, non-occluded training (13-24). A recent systematic review found a greater change in muscle cross-sectional area with occlusion versus non-occluded training across the literature (246 participants across 12 studies, 0.41 cm² greater than control) (25). Sure there is variation across the literature (8,26-29), which may be explained in part by differing methodologies (cuff size, cuff pressure, intermittent vs sustained pressures) (1), but ultimately, the literature is generally supportive of the superiority of occlusion training on a volume-equated basis (25).

Occlusion training against low-load training to failure

While it is relatively easy and reasonable to match experimental groups on a mechanical basis (work/volume), it is just as reasonable to use a fatigue, or effort-matched basis (concentric failure). This is nicely stated by Farup et al (30):

… as volitional fatigue is not reached during work- and load-TRT (traditional resistance training) protocols that are matched to BFR (blood flow restricted) protocols, it can be objected that the two conditions are not directly comparable if factors related to fatigue are strong determinants for muscle hypertrophy

In my opinion, one model isn’t better than the other, but understanding the differences between the two may provide additional insight into how muscle grows in response to training. While the work-matched data paints a more-or-less consistent picture of the hypertrophic superiority of occlusion training (25), when compared to low-load training to failure, the data is not as clear cut.

Two studies address hypertrophic adaptations following weeks of occlusion training against non-occluded training to failure. In the first, Farup et al (30) had participants train for six weeks using 40%-1RM for four sets of arm curls to concentric failure with each arm randomized to either occluded or non-occluded training. As expected, those in the occlusion condition completed fewer reps per set, total reps over the course of training, had reduced time-under-tension per set, and total training time. Despite these differences, both groups had similar changes in elbow flexor cross-sectional area as determined by MRI (11.5 vs 11.6%). These results suggest that occlusion training is not superior to low-intensity training when effort-matched, but does suggest that it provides a more efficient training stimulus (less work for a comparable growth).

In the second, Fahs et al (9) had individuals complete 18 training sessions of unilateral knee extension to fatigue (30%-1RM) with each limb randomized to either occluded or non-occluded training over six weeks. While there was no change in overall thigh circumference with training, increased muscle thickness was detected with B-mode ultrasound at three sites on both the anterior and lateral thigh. Of these, only one between-group difference was noted on the lateral thigh favoring occluded training. That being said, effect sizes at all sites favored occluded training for muscle thickness. It’s important to note that the adaptations in the occluded group were produced with approximately 36% less volume (13857±7030 kg in non-occluded versus 8844±3704 occluded).

There are methodological differences between the two studies that may have contributed to the differences (1). Yet despite the somewhat different hypertrophic results between Fahs et al (9) and Farup et al (30), a consistent theme arises from the interpretation of both; while occlusion training may (9), or may not (30), result in enhanced hypertrophy on an effort-matched basis, it represents a more efficient training stimulus, producing comparable growth with less total work at a given training intensity.

Is it time to change our messaging on occlusion training?

It’s not wrong to say that low-intensity blood flow restricted training is a comparable stimulus, at least in hypertrophic terms , to high-intensity training as numerous studies support this (17,24,31-35). I wonder if we create confusion by focusing solely on load, and that many may interpret this as saying occlusion is necessary to achieve comparable hypertrophy with low intensity training, which it’s not (2-6). Rather, it would seem to me that the data supports comparable hypertrophy at a similar training intensity with substantially less work when blood flow is occluded(9,30).

It is no doubt a less exciting message, and one that is difficult to interpret, as work-based recommendations for hypertrophy training really don’t exist, but at least it’s accurate.