In today’s third installment of the 2020 research updates, I want to take a look at all that’s new and interesting in the realms of blood flow restriction aka #BFR. How effective is it? Who benefits? Who benefits the most? Will it speed up or slow down recovery? And why will it help you make gains even on untrained limbs? Sounds interesting? Well, here you go: My overview of selected new studies investigating the effects of blood flow restriction from early 2020 will answer these and (hopefully) any related questions you may have.
Table 1: comparison of strength gains for #BFR vs HLT – in some studies BFR was even superior (from Gronfeldt 2020)
Strength gains with low-resistance #BFR vs. classic heavy-load strength training (HLT) – Meta-analysis reports identical gains in 20-to-80-year-old healthy and habitually active adults — based on Gronfeldt et al. 2020
Important FYI: The scientists selected studies w/ “equal training outputs between HLT and BFR; e.g. training to fatigue/failure” (ibid.)
These results are particularly interesting, because previous studies had suggested that BFR may be equivalent in terms of size gains, yet not when it comes to strength.
As the individual datasets from the studies under review indicate, there are even instances where the BFR training was significantly better at improving strength compared to heavy-load strength training 😮… a generalization of the results to e.g. training noobs or pro-athletes is yet unwarranted.
- BFR will make women ‘bulky’… ah, as ‘jacked’ as men – Study confirms “[f]emales can produce muscular gains with ECC [eccentric] and BFR training similar to previous results seen in males” — based on Wells et al. 2019.
The fact that female athletes are more than just smaller and less muscular copies of their male counterparts is still (too) often ignored by researchers. Accordingly, it made sense for Elizabeth Wells and colleagues to assess the mechanical and metabolic effects of eccentric (ECC) resistance training and blood flow restriction (BFR) exercise on the elbow flexors, i.e. the biceps, in recreationally trained females.
- With N=17 normal-weight subjects aged 20-35 who had been randomized to two groups and trained twice weekly for four weeks, Wells’ study protocol was realistic and relevant for the average female gymrat, who may expect similar rather disappointing results:
“There was no significant group difference for any of the variables (P < 0.05). A training effect was shown with both groups increasing right arm circumference (P=0.004), muscle thickness (P < 0.001), CSA (P=0.001), 1-RM for the right (P=0.001) and left arms (P=0.014), and inverted rows (P=0.001). Both groups showed significant decreases in lactate (P=0.047) and RPE (P < 0.001).
As far as the details of the intervention are concerned, it’s important to note that the ECC+BFR group trained at 30% 1-rep max (1-RM), 3×20 repetitions, and the ECC group trained at 60% 1-RM, 3×10 repetitions. The BFR cuff was pressurized to 60% of maximal occlusion. Moreover, both groups performed the ECC portion of a bicep curl to failure, i.e. so that they would need assistance to return the arm back to starting position.
Testing was conducted at baseline and post-training and included: body composition, thickness and cross-sectional area (CSA) of the elbow flexors, arm circumference, bicep curl 1-RM, and inverted rows to exhaustion. With the latter being a well-known trigger for increasing (metabolic) stress, ‘going to failure’ may well explain why no significant inter-group differences were detected… a result, of which a brief review of the literature suggests that it is analogous to what we’ve seen in men and which suggest that BFR will be of greatest use to you if an injury keeps you from training heavy.
- Trainers must individually prescribe the ‘optimal’ #BFR protocol for a given athlete at a given time/point in the season/his career, German review highlights — based on Hanke et al. 2020. Ok, you’re probably not really surprised to hear that individualization and personalization are key – they always are! But maybe you find one of the other interesting findings intriguing:
- more experienced athletes see lower hypertrophy and strength gains with #BFR, whether that’s more pronounced than the decline with regular training remains to be established, though
- muscle activation (as measured by EMG) increases, as well – this is in line with individual reports of “bro, absolutely great mind-muscle-connection” 🤣
- the results were, on average, comparable to those achieved with classic high-load resistance training – even if intensities of only 20 % of the subjects 1 RM was used
- it seems feasible to significantly increase the training frequency; one study of track and field athletes observed a more pronounced muscle hypertrophy, increased strength, and improved sprinting performance compared to a regular training group within only 8 days of 2 times 3 sets of 15 repetitions each day (20% 1RM |BFR squats and leg curls).
- a high training frequency for #BFR has also been found to facilitate VO2Max gains in female basketball players who used the cuffs during a walking exercise
- #BFR can also be a useful addition to your warm-up as it has been found to improve local blood flow and to improve muscular oxygenation in American Football players
- as far as the #BFR parameters are concerned, the studies included in the review used blood pressures of 160-240mmHg and cuffs (preliminary evidence suggests: higher pressure = greater results) with a width of 3.3-11 cm (some research suggests that wider cuffs require lower blood pressure elevations to see results | Loenecke 2010)
- The review also highlights that you don’t necessarily have to measure the blood pressure during the sessions but could also be gauged subjectively, as long as the bands are elastic!
What remains to be determined irrespective of how you achieve #BFR is where and in which ways you can use it as an alternative or adjunct during different periods of micro-/macrocycles and/or when you’re injured or sick. Overall, Hanke et al. agree with the conclusion of older English-language reviews that #BFR for athletes “seems promising” (ibid.).
- Collateral strength gainz!? 🤔 When training your left arm w/ eccentric #BFR you’ll note strength gains in the untrained arm, too — based on Hill 2020 — #crossEducation is the keyword that describes strength and size gains in an untrained limb that occurs in response to the training of another limb.
The study was conducted in N=36 women who were randomly assigned to 4-wks of unilateral resistance training with Ecc-BFR (n = 12), Con-BFR (n = 12) or control (no intervention, n = 12) group. Eccentric peak torque, concentric peak torque, maximal voluntary isometric contraction torque, muscle thickness, and muscle activation were assessed from the contralateral, untrained arm.
Table 2: Unfortunately, neither of the training regimen the subjects followed for 3 training sessions per week (75 eccentric or concentric isokinetic (120°·s-1) biceps curls over 4 sets (1×30, 3×15)); 30 s rest between sets) yielded significant muscle size gains which is at least slightly disappointing (Hill 2020).
With increases of 4.9% within two and 13.0% within 4 weeks, the training turned out to be pretty productive. Importantly, though, the latter was observed only when the subjects used BFR and focussed on the eccentric portion of the exercise. Moreover, there were increases in muscle activation (collapsed across mode and group) regardless of training modality, but there were no changes in muscle size for any of the conditions.
Needless to say that the magic contralateral gains will occur only in muscle groups that can be trained separately… that’s not the case for “left and right chest” aka the left and right part of the pectoralis major, which in turn would benefit from the use of a recently invented new “Free-Grip Barbell” you can read about in the SuppVersity archives.
This obviously leaves us with the initially voiced question “Why will [BFR] help you make gains even on untrained limbs?” the answer is not 100% clear, but it seems likely that the counter-lateral effects of resistance training are mediated by signaling molecules and metabolic byproducts that arise when muscles contract. If we assume that that’s the case, these signaling molecules and triggers of strength increases would accumulate to a greater extent when #BFR cuffs are applied. This could well explain the observation in the study at hand, in which only the BFR + eccentric training worked the “counter-lateral gains”-magic.
And yes, this does also mean that the eccentric only and the concentric isokinetic training didn’t work. Why? Well, for the eccentric only prescription, the accumulation of signaling molecules and metabolic garbage from the trained arm won’t accumulate to a sufficient degree in the contralateral arm. With concentric isokinetic training, the ipselateral (=trained) muscle may simply not release enough signaling molecules and metabolic byproducts to see an effect. What clearly remains to be determined is if a longer study would facilitate greater size gains as well… remember: those were not significantly different in this relatively short 4-week study.
- Grønfeldt, B.M., Lindberg Nielsen, J., Mieritz, R.M., Lund, H. and Aagaard, P. (2020), Effect of blood‐flow restricted vs. heavy‐load strength training on muscle strength: Systematic review and meta‐analysis. Scand J Med Sci Sports. Accepted Author Manuscript. doi:10.1111/sms.13632
- Hanke, A.A., Wiechmann, K., Suckow, P. et al. Effektivität des „blood flow restriction training“ im Leistungssport. Unfallchirurg (2020). https://doi.org/10.1007/s00113-020-00779-6
- Hill, E. C. (2020). Eccentric, but not concentric blood flow restriction resistance training increases muscle strength in the untrained limb. Physical Therapy in Sport.
- Loenneke, J. P., Wilson, G. J., & Wilson, J. M. (2010). A mechanistic approach to blood flow occlusion. International journal of sports medicine, 31(01), 1-4.
- Spitz, RW, Wong, V, Bell, ZW, Viana, RB, Chatakondi, RN, Abe, T, and Loenneke, JP (2020). Blood flow restricted exercise and discomfort: A Review. J Strength Cond Res. Ahead of print.