Exercise, Hypertrophy

March 8, 2014

Does Blood Flow Restriction Increase Muscle When Combined With Traditional Resistance Training?

Blood flow restriction (BFR) training is an emerging technique that consistently has been shown to improve muscle strength and size in a variety of populations. If you are not familiar with BFR, you can read my recent T-Nation article that details the hows and why’s of the topic. If you’re interested in the research, you can read the review that I co-authored here.

A new BFR study by Luebbers et al. has been creating a lot of buzz. A number of people have emailed me to ask my opinion on the paper, so I figured it was worthy of a blog post.

Briefly, the study was a follow up to a previous study by Yamanaka et al. , who reported significant increases in chest girth, as well as 1RM bench press and squat performance when BFR was combined with heavy resistance training in a group of well-trained college football players. Here are the particulars of the new study followed by my commentary and take home points.

Study Design:
The study used a protocol similar to the investigation carried out by Yamanaka et al. Sixty-two Division 2 football players took part in the study during their off-season from competition. Subjects were randomized into 1 of 4 groups:
• H/S/R Group. This group performed high-intensity training (H) consisting of traditional strength training exercises (bench press, overhead press, power cleans, squats, etc) and auxiliary lifts (bicep curls, triceps extensions, calf raises, and abdominal work). In addition, they performed supplemental lifts (S) at the end of each workout consisting of 4 additional sets of bench press on upper body day and 4 additional sets of squats on lower body day. The supplemental work was carried out under blood flow restriction (R).
• H/S Group. This group performed the exact workout as H/S/R except no BFR was used for the supplemental exercises.
• H Group: This group completed only the basic high-intensity training routine (H). They performed no supplemental exercise with or without BFR.
• M/S/R Group. This group performed only the auxiliary exercises but not the traditional strength training exercises. They also performed supplemental work with BFR at the end of each workout.

The BFR was a “practical” protocol that employed ~3 inch elastic wraps to occlude flow. The load for these exercises was set at 20% 1RM with the first set consisting of 30 reps followed by 3 sets of 20 reps separated by 45 seconds rest. For all groups, the training program employed an upper/lower body split performed 4 days per week for 7 weeks. The split followed a 2-on/1 off, 2-on/2-off format with workouts taking place Monday, Tuesday, Thursday, and Friday.

The Results
At the end of the 7 week study period, the group performing the traditional strength training protocol supplemented with BFR (H/S/R) showed significantly greater increases in 1RM squat compared to the other groups but there were no differences in 1 RM bench press between groups nor were there any differences in thigh, chest, or arm girth.

Commentary
The researchers should be commended for an ambitious study design. They had a fairly large sample size (over 60 subjects) and the 4 groups provided diverse info on a variety of possible program applications. Moreover, the subjects were all well-trained lifters (average of over 7 years resistance training experience), which rules out any confounding issues associated with an initial learning curve and inflated gains from sedentarism.

That said, the study had a number of substantial limitations that cloud the ability to draw relevant conclusions. First and foremost, the use of circumference measurements as a proxy for muscular gains is highly suspect as the technique does not specifically measure muscle tissue in isolated areas of the body. Indeed, imaging techniques such as ultrasound have been shown to detect increases in muscle hypertrophy not seen by measures of girth. Compounding matters, the researchers made no attempt to control for nutrition. Remember, the subjects were college football players in the offseason from competition. To put it mildly, it’s highly unlikely they weighed their food and adhered to a balanced nutritional regimen. Since girth measurements cannot discern between muscle tissue and subcutaneous fat, this certainly could have confounded results.

Another thing that jumped out at me when reading the methodology was the following statement: “All sessions were supervised by the same two primary researchers in order to ensure compliance.” The study had over 60 subjects who trained at one of three times during each training day. That means that there were over 20 subjects training at a given time. How can two researchers adequately supervise all these subjects and ensure that they are training as per protocol? In my lab, I have a dedicated research assistant work with each subject in a training study. They supervise every aspect of the workout protocol – from using proper technique, to exerting sufficient intensity of effort, to making sure that the rest intervals are rigidly upheld. If research assistants did not in fact help out with supervision here, I’d have to question how well subjects actually complied with the protocol.

Finally and importantly, the results don’t make a whole lot of sense. Specifically, how could lower body strength show greater increases with BFR without concomitantly greater increases in hypertrophy? There are two primary mechanisms for strength improvements: an increase in muscle size (there is a direct relationship between muscle cross sectional area and the ability to produce force) and/or an enhancement in neural response. Research indicates that neural enhancement is primarily achieved through the use of heavy loads, particularly in a well-trained population who have transitioned past the initial motor learning stage. Thus, I find it difficult to believe that BFR — which uses very light loads — had a significant impact on neural aspects such as rate coding or synchronization. If strength was significantly increased in the BFR group compared to the non-BFR groups, it would seem that these improvements would have to be due to greater gains in muscle mass.

Bottom Line
While this study (as well as the previous study by Yamanka et al.) provides interesting data on the potential use of BFR as an adjunct to traditional resistance training, the aforementioned limitations make it difficult to draw an practical conclusions. Similar studies should be carried out using a validated imaging technique (i.e. MRI, CT, ultrasound, etc) under well-supervised conditions to determine if there are in fact any benefits to combining BFR with heavy loads.