Blood Flow Restriction May Reduce Muscle Damage From Eccentric Biceps Curls - Effects on Gains Yet Unknown

Pretty much the study set-up, albeit with a Scott bench to support the arm and much more weight.
Surprising, isn't it? Wouldn't you expect that using a cuff set to restrict the blood flow in a way that increases the pressure in the arm to ca. 120mmHg and keeps all the metabolic byproducts from being carted away would, when it's used on top of an already muscle-damaging eccentric biceps workout, increase, not decrease the muscle damage?

Well, I did. After reading the complete study and taking a look at previous research, however, I have admit that the scientists' conclusion that "BFR attenuated HI-ECC-induced muscle damage and there was no increase in cardiovascular responses" is warranted - even if I'd say that the last word on the real-world effect on gains has not been spoken, yet.
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Let's first see, what the study looked like, though: Nine healthy men (26 +/- 1 years, BMI 24 +/- 1 kg m²) underwent unilateral elbow extension in two conditions: without (HI-ECC) and with BFR (HI-ECC+BFR). More specifically, all subjects performed single-arm Scott bench dumbbell biceps curls with both arms - once with, once without cuffs:
"The arms were randomly chosen to perform the exercise in one of the two conditions: without or with BFR (HI-ECC and HI-ECC+BFR conditions, respectively), and counterbalanced such that each condition included both dominant and non-dominant arms. For the experimental session, participants performed three sets of 10 repetitions of HI-ECC or HIECC+BFR (130% of 1RM) of unilateral elbow extension in the Scott bench using free weights (dumbbells)" (Curty 2017). 
The rest between sets was restricted to one minute, the cadence of eccentric action was 3 s between the initial position (elbow flexed) and full extension of the elbow, while the concentric action was performed passively by the staffs returning the dumbbell at the top of the movement so that only the eccentric action was performed. The experimental session with the contralateral arm was performed at the same day, after 30 min of rest.
In contrast to its effects on endurance capacity, post-exercise blood flow restriction as it was practiced in a recent study by Madarame et al. does not enhance the longitudinal increase in strength or size (Madarame 2017).
Does this mean I will gain more muscle? That's impossible to say without corresponding long-term data on the effects of BFR + eccentric training on strength and size gains. While muscle damage and soreness do not, as some people still falsely believe correlate with protein synthesis, it, or rather the concomitant inflammatory response plays an important role in the process of muscle remodeling that will eventually allow for continuous growth (learn more).

What I can tell you, though, is that Haruhiko Madarame and colleagues have shown just recently that postexercise blood flow restriction does not enhance muscle hypertrophy induced by multiple-set high-load resistance exercise. That's in contrast to the previously discussed results showing benefits on endurance performance with post-exercise cuffing, by the way.
The scientists measured (a) the ratings of perceived exertion (RPE) and pain (RPP) after each set and claim to have measured (b) the muscle damage by evaluating the range of motion (ROM), upper arm circumference (CIR) and muscle soreness using a visual analogue scale at different moments, i.e. pre-exercise, immediately after, 24 and 48 h postexercise (just in case you're asking yourselves: where's the creatine kinase (CK) measurement; think twice, you cannot measure CK individually for each arm, because the level in blood drawn from the left won't differ from that in the right arm ;-).
Figure 1: Indirect markers of muscle damage. Comparison of the HI-ECC versus HIECC+BFR conditions at different moments (pre-exercise, post-0 h, post-24h and post- 48 h) to muscle soreness (a), ROM (b) and CIR (c). Data are represented as D mean +/- SEM. ROM, range of motion; CIR, upper arm circumference (Curty 2017).
As expected, the range of motion decreased postexercise in both conditions; however, in HI-ECC+BFR group, it returned to pre-exercise condition earlier (post-24 h) than HI-ECC (post-48 h). Furthermore, the muscle circumference (CIR), which is probably the best measure of muscle damage used in the study, showed a response suggestive of (a) a lower initial and (b) similar total inflammation (I guess this based on the estimated AUC, the scientists didn't measure).
Figure 2: A similar study by Nosaka et al. (1996) shows a very different time-course of muscle swelling and thus biceps circumference - the significant and, in this context, experimentally relevant difference is the training status of the subjects - trained in the study at hand, untrained in Nosaka's.
So, did BFR protect the muscle from damage? I am still hesitant to say yes. While the scientists are right: the early recovery of the range of motion clearly indicates a reduced muscle damage (or faster recovery, but that appears unlikely). The CIR data, on the other hand, differs significantly from previous data (see Figure 2) from Nosaka et al. (1996), where the cell swelling kept increasing from immediately post to day 5.

So what? Well, there is a significant difference in the study design: the subjects in the study at hand were not just accustomed to resistance training (2-3 workouts per week). It is well-proven that muscle damage is reduced already after one bout of resistance training and keeps declining with one's training status. Against that background, I would subscribe to the scientists' conclusion.

The result also seems to be in line with the previous observation that BFR does not increase the muscle damage after low-intensity eccentric contractions with blood flow restriction (Thiebaud 2014) - the least we can say is thus: using cuffs during intense (eccentric) training does not, as one would expect, increase the exercise-induced muscle damage; in fact, it is even likely that it exerts protective effects - even if the accumulation of metabolic products (Pearson 2015) makes it harder to endure, because it increases the perceived pain.

Speaking of an accumulation of metabolic products, the latter are also one of the factors of which the authors speculate that they could explain the reduced muscle damage in HI-ECC+BFR condition: (1) the increase in [Ca2+], (2) the accumulation of intramuscular metabolites, (3) an increase in fibre recruitment, and (4) a potential reduction of neutrophil infiltration and thus inflammation | Comment on Facebook!
  • Curty, et al. "Blood flow restriction attenuates eccentric exercise-induced muscle damage without perceptual and cardiovascular overload." Clin Physiol Funct Imaging (2017).
  • Damas, Felipe, et al. "Resistance training‐induced changes in integrated myofibrillar protein synthesis are related to hypertrophy only after attenuation of muscle damage." The Journal of physiology 594.18 (2016): 5209-5222.
  • Madarame, et al. "Postexercise blood flow restriction does not enhance muscle hypertrophy induced by multiple-set high-load resistance exercise." Clin Physiol Funct Imaging (2017). Ahead of print.
  • Nosaka, Kazunori, and Priscilla M. Clarkson. "Changes in indicators of inflammation after eccentric exercise of the elbow flexors." Medicine and science in sports and exercise 28.8 (1996): 953-961.
  • Pearson, Stephen John, and Syed Robiul Hussain. "A review on the mechanisms of blood-flow restriction resistance training-induced muscle hypertrophy." Sports medicine 45.2 (2015): 187-200.
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