Research Spotlight: Low-load squat training with blood flow restriction causes as much hypertrophy as high-load training in experienced squatters

Research Spotlight articles share concise breakdowns of interesting studies. The study reviewed is "Acute Cellular and Molecular Responses and Chronic Adaptations to Low-Load Blood Flow Restriction and High-Load Resistance Exercise in Trained Individuals" by Davids et al.

A recent study compared the effects of low-load training with blood flow restriction (BFR) and high-load training without BFR on squat strength, quad growth, and various molecular outcomes over nine weeks in trained subjects of both sexes.

All subjects did lower body training three days per week, with a routine consisting of squats, leg press, and knee extensions days one and three, and Bulgarian split squats and knee extensions on day two. The group doing high-load training started with ~75% 1RM loads, and did sets of eight with two minutes between sets. The group doing low-load training with BFR started with ~30% 1RM loads, and used the standard 30-15-15-15 protocol (Note: MASS subscription required to view link) with 45 seconds between sets. Reps in reserve were assessed after each set. Loads were progressed in the high-load group if subjects had more than two reps in reserve after consecutive sets, and loads were progressed in the low-load BFR group if subjects had more than four reps in reserve after consecutive sets.

The researchers assessed a lot of outcomes, but I’m most interested in the maximal strength, whole-muscle hypertrophy, and muscle fiber hypertrophy results.

Unsurprisingly, squat 1RM increased to a significantly greater extent in the high-load group, but it did significantly increase in both groups (+9kg in the low-load BFR group, and +19kg in the high-load group). Furthermore, quadriceps cross-sectional area and type II fiber cross-sectional area (from the vastus lateralis) increased to a similar degree in both groups. Type I fiber cross-sectional area didn’t significantly increase in either group.

A prior study found that low-load training with BFR caused significant fiber type-specific hypertrophy in powerlifters (Note: MASS subscription required to view link), leading to disproportionate type I fiber growth. The present study did not corroborate those findings, suggesting that disproportionate type I fiber growth following low-load BFR training may not be a generalizable phenomenon; it may have just been a quirk observed in powerlifters who habitually do a lot of low-rep training.

This study is also informative about the relationship between proximity to failure and hypertrophy. It’s been argued that low-load training only results in hypertrophy that’s equivalent to high-load training if low-load sets are taken to failure (to be clear, that’s never been my own position). In the present study, subjects didn’t intentionally train to failure (though I’m sure they probably inadvertently reached failure occasionally), and the low-load BFR group likely trained further from failure than the high-load group, on average. Their training loads only increased if they completed consecutive sets with more than four reps in reserve, and their training loads increased from 30.5% to 56.3% of pre-training 1RM; in other words, the subjects in the low-load BFR group did a lot of sets with more than four reps in reserve. However, they still experienced quad growth that was comparable to that of the high-load group (+7.4 ± 4.3% for the low-load BFR group, and +4.6 ± 2.9% for the high-load group; p = 0.37), which likely trained a bit closer to failure. One could contend that the results of the present study may not extend to low-load training without BFR, but I personally haven’t seen any research which would lead me to such an assumption.

Overall, the study provides further evidence that low-load training (with BFR, in this case) leads to hypertrophy responses that are comparable to those of high-load training. Furthermore, while high-load training is better for strength gains (since it’s a more specific stimulus), low-load training should be sufficient to at least maintain strength – that’s good news for lifters who resort to low-load training when they can’t train with heavier loads for a period of time (when training around an injury, for example). Finally, this study provides us with evidence that low-load training can cause a robust growth response even when it’s not performed to failure.

This Research Spotlight was originally published in MASS Research Review. Subscribe to MASS to get a monthly publication with breakdowns of recent exercise and nutrition studies.

Credit: Graphics by Kat Whitfield.

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