Blood Flow Restricted Biceps Growth in Trained Individuals: 4-7% Increase in Sleeve Size in 4 Weeks. Is BFR More Than Just an Alternative for the Injured / Handicapped Athlete?

If the litmus test goes well, I would assume that you will soon see more guys training "strapped up like this" at the gym.

Yes, I am guilty - guilty of complaining about the subject selection in previous studies from the University of Tampa and other institutions, where scientists conducting research on the effects of blood flow restriction on the (resistance) training induced muscular adaptions. MRI-measured thigh muscle cross-sectional area and muscle volume increases of 4–7%, and a 8-10% increase in one repetition max and maximum isometric quadriceps strength as Takashe Abe et al. report in their 2006 paper are unquestionably impressive (Able. 2006). If you asked me, they are even too impressive - too impressive to assume that you would see similar gains from walking on a treadmill in trained individuals.

Is this the litmus test for blood flow restriction?

In view of the impressive results in untrained and older individuals, a study with 20 college-aged (mean age 23±5 years) men with a minumum of 1 year of resistance training experience could in fact be called a litmus test. So, if we take the subject selection as our main criteria, the study at hand is a litmus test..

Figure 1: Exercise selection for the two training sessions; BFR indicated blood flow restriction. All subjects trained twice a week for a total of 8 weeks, 4 weeks with, 4 weeks without cuffs on the biceps exercise (Lowery. 2013)

The young men were randomly assigned to one of the two arms of a crossover protocol, according to which they trained with restricted blood flow to the biceps brachii either during the first 4 weeks (BFR-HI) or the second 4 weeks (HI-BFR) of a standardized 8-week program resistance training program (see Figure 1) with a controlled overall training volume (sets x reps x weights).

Compared to conservative protocols, a "cross over" had the advantage of (a) providing a larger subject base and (b) allowing to control intra-individual variations, i.e. answering the question "What's the best protocol for person A?". The obvious downside wass that the total study duration for BFR and regular training wasonly 4 weeks per person.

As you can see in Figure 1 the only difference between the classic bicep curl that was performed either with or without the sujects' arms being wrapped at a perceived pressure of 6–7 or 0 on a 0-10 scale, respectively, is the sole difference between the two arms - the workload, on the other hand, was identical.

"During the first week of pBFR, subjects performed three sets of thirty repetitions with 30% of their calculated 1 RM. To control for total volume, the non-pBFR subjects performed three sets of curls at one-half of the repetitions and two times the load of their pBFR weeks for each week." (Lowery. 2013)

To explain what this means, Lowery et al. refer to the following example: Person A curls 30 reps at 30% of their individual one rep max (1RM) on the first set during the blood flow restricted session. To ensure that the total workout volume is identical person A must perform 15 repetitions at 60% of his 1RM for his first set in the non-BFR condition as well - even if he could have lifted more or would have been able to pump out additional 5 reps.
Speaking of standardization, it is probably worth mentioning that the subjects had to adhere to a diet consisting of 25% protein, 50% carbohydrates and 25% fat with meal plans that had been tailored to their individual demands. In addition, all 20 of them consumed a 24g bolus of hydrolysed whey protein (Dymatize Iso 100),  after every training session. To ensure the adherence to the dietary protocol a diet log that had been started two weeks before the actual trial to assess the baseline nutrient intake of the participants and had to be maintained over the whole study period.

Impressive or disappointing? That is the question.

In contrast to the initially cited study by Abe et al., the authors of the study at hand, Lowery, Joy, Loenecke Souza, Machado, Dudeck and Wilson, did not use MRI, but ultrasound images to determine the muscle thickness of the biceps at the end of weeks 0, 4 and 8.

Figure 2: Left, biceps muscle thickness - mean values (in cm) + increase within last weeks (in %) above the bars; right, individual levels in the HI-BFR and BFR-HI group (Lowery. 2013)

It should however go without saying that the use of a different measuring technique does not explain the at first sight probably disappointing difference between the results of the study at hand and the initially cited study by Abe, Kearns and Sato.

Body part specific effects and even the age and training status of the subjects are probably irrelevant, as well - not because things like that would not matter, but because there was a more profound methodological difference: The "control" condition in the study at hand. Despite being curbed by the volume prescription, the non-BFR condition was still "anabolic" enough to induce a respectable increase in muscle size. The latter cannot be said of the non-cuffed treadmill walking in the Abe study. To call the results "disappointing" is thus not warranted. Their real-world significance, however, remains questionable (see red box).
References:

• Abe T, Kearns CF, Sato Y. Muscle size and strength are increased following walk training with restricted venous blood flow from the leg muscle, Kaatsu-walk training. J Appl Physiol (1985). 2006 May;100(5):1460-6. Epub 2005 Dec 8.
• Lowery RP, Joy JM, Loenneke JP, de Souza EO, Machado M, Dudeck JE, Wilson JM. Practical blood flow restriction training increases muscle hypertrophy during a periodized resistance training programme. Clin Physiol Funct Imaging. 2013 Nov 4.