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After training a few years ago, Mikaela Shiffrin put inflatable cuffs over her upper arms and legs and then cranked a 20-minute circle of relatively simple exercises. “In 15 minutes I was exhausted, more exhausted than I felt from a two-hour strength unit,” says the two-time Olympic champion. “I remember thinking, oh my god, my arms hurt like I’ve just done 200 pushups or something.”
Exhaustion was the point. The technique – also known as “blood flow restriction training” and also known as kaatsu – uses pressure around the arms and legs to significantly restrict blood flow and trigger a variety of adaptations in the body. Invented in 1966 by Yoshiaki Sato, a doctor and researcher, BFR training was first adopted by Japanese bodybuilders and powerlifters. It didn’t leave Japan until the early 2000s, thanks in part to Jim Stray-Gundersen, a physiologist and doctor and former medical advisor to the International Olympic Committee, the International Ski Federation, and NASA. After hearing about BFR training at a medical conference, he traveled to Japan in 2013 to study the technique. It wasn’t long before he teamed up with Sato to bring Kaatsu to North America. The two split, and Stray-Gundersen co-founded his own BFR system called B Strong.
Since 2010, more than 900 papers have been published on BFR, suggesting that combining it with relatively light resistance training or aerobic activity can lead to rapid increases in muscle size and strength, oxidative capacity, and tendon density. Its efficiency is why BFR has gained popularity over the past decade for rehabilitation of injuries, especially after surgery. Now athletes like Shiffrin and the marathon runner Galen Rupp use BFR to improve performance.
Do you know the feeling at the end of a long descent – that excruciating, painful, almost unbearable burning sensation in your legs? Imagine this feeling lasts and then builds up until your muscles fail completely. That is BFR training in a nutshell. Restricting blood flow during exercise restricts the supply of oxygen to the working muscles while accelerating the elimination of metabolic by-products such as lactate. That quickly disrupts homeostasis, the delicate physical and chemical balance in your body, and creates a temporary state of metabolic crisis that sends a strong signal of drowsiness to the brain that triggers a cascade of hormonal responses, explains Stray-Gundersen. “We create these anabolic resources by fooling the body into causing all kinds of great damage when in reality it’s a combination of simple exercise and restricting blood flow,” he says.
For a sport like alpine skiing, which requires a lot of strength and endurance, BFR checks “a lot of boxes,” says Jeff Lackie, Shiffrin’s strength and conditioning trainer. Since BFR involves relatively modest loads, Lackie and Shiffrin use it in the off-season to safely stack the volume during strength training sessions. Once the racing calendar begins, they rely on it to maintain their strength levels and help with recovery despite a chaotic travel plan.
There is a strong mental component. The overwhelming amount of lactate building up in the muscles feels terrible – but that’s exactly what Shiffrin experiences at the end of a long World Cup run, explains Lackie. By getting used to the discomfort, she can keep a cool head and stay coordinated during her final turns. “As with anything in life that makes you feel uncomfortable, there is a mental side to pushing it through,” says Shiffrin.
While fatigue is key to this method, there are downsides as well. “When people get tired, the mechanics break down,” says Nicole Haas, physiotherapist and founder of Boulder Physiolab in Colorado. Sloppy form can aggravate bad habits instead of improving the brain-body connection that is an important part of performance. “I worry that if I just try to tire myself out, I will get injured,” she says.
Haas also notes that while studies have shown that BFR can result in significant improvements in muscle size and VO2 max, it is not clear that those changes translate into real performance gains. In a 2015 study on the effects of supplementary BFR training on experienced cyclists, the participants increased VO2 max by an average of 4.5 percent. However, her 15-kilometer time trial performance did not improve. “There are so many variables in transitioning to exercise and performance, and that’s the hard part to measure,” says Haas. Since most clinical studies looking at BFR training are relatively short periods of time, much we do not know about the long-term effects. Could there be a strong response at the beginning of the training and a plateau later? And with so much exhaustion, is there a risk of overtraining? In addition, there is little agreement on how BFR training can be optimally implemented.
The scientific literature is limited, and only decades of experience – trial and error with different techniques in numerous sports involving all kinds of athletes – will weed out the bad ideas. Right now, “it’s an excellent tool in the toolbox,” says Lackie. But it’s just one tool: He and Haas are quick to point out that they see BFR as a supplement, not a substitute for, other training methods.
Nor is it a shortcut to performance. You still have to work. But with BFR, you can safely add volume to your workouts and recover faster, so you can get more workouts in a given week. “Ultimately, the more you exercise, the better your performance will be, as long as you recover from it,” says Stray-Gundersen.
When Shiffrin first tried BFR when her arms felt like lead? She woke up fresh enough from an afternoon nap to go back to her evening workout hard. “Not only did it make every session more effective, but I also recovered really well, maybe even better than before,” she says.
Important Precautions For Blood Flow Resistance Training
The type of cuff you use during unsupervised BFR training is crucial, says physiologist Jim Stray-Gundersen. He recommends an inflatable one (so you can control the pressure) and an elastic one (to accommodate changes in muscle size during exercise). Just make sure some blood flows into the limb while wearing it. BFR is safe for anyone who follows accepted protocols unless you have sickle cell anemia or lymphedema, are pregnant, have a fresh wound or fever, or are in pain from a healing injury. The following resources will help you get started.
B Strong training systems: These kits come with inflatable arm and leg straps, a hand pump, and an app with video instructions and tutorials. From $ 289
Certification as a Kaatsu specialist Program: An online resource at Kaatsu.org that teaches coaches, therapists and athletes how to properly administer BFR. $ 250
“Basics of circulatory disorders” Training”: Camp 4’s short online course was specially developed for climbers by strength and conditioning trainer Tyler Nelson. $ 60
“Blood Flow Restriction Exercise: Methodology, Application, and Safety Considerations”: This research paper, published in the journal Frontiers in Physiology, recommends a set of guidelines for BFR resistance and provides aerobic and preventive training with advice on how to proceed safely. frontiersin.org