PHYSICAL THERAPY

From the Battlefield to the Barn

BFR breaks into equine rehab

By Paul Basilio

Although it was first developed in the 1960s, blood flow restriction (BFR) training has recently experienced a type of renaissance.

Conceived and developed by Yoshiaki Sato in the 1960s, it was virtually unknown outside of Japan until the 2000s. Now, thanks to innovations by the military to help wounded veterans, as well as free publicity from professional sports trainers, this orthopedic rehab modality is making its way to the equine world.

What is it?

BFR employs a pressurized cuff to safely and temporarily reduce blood flow to an exercising limb. By applying patient-specific amounts of occlusion pressure to the limb, arterial inflow is greatly reduced while venous outflow is occluded distal to the site. Through low-intensity exercise, the body can reap high-intensity benefits.

All images courtesy of Dr. Sherry Johnson.

“Basically, it’s been successfully utilized as a ‘biohack’ to improve muscle size and strength without the use of damaging loads,” said Sherry Johnson, DVM, MS, PhD, DACVSMR, of Equine Sports Medicine and Rehabilitation in Whitesboro, TX. “In humans, rapid, irreversible muscle loss occurs quickly within 1 week of bedrest, so it's become an ‘in vogue’ modality for human orthopedic rehab.”

Patients undergoing BFR training typically perform high-repetition, low-intensity exercise with weight that is around 20% to 30% of their one-repetition maximum. The exact mechanism by which it works is not fully known, but there are some hypotheses.

“Throughout the literature, consistent supraphysiologic levels of growth hormones—up to 290 times baseline—have been documented, along with lactate accumulation,” Dr. Johnson said during a presentation at the 68th Annual AAEP Convention in San Antonio. “Downstream signaling as a result of these two physiologic accumulations seem to be the most consistently reported driving forces behind these muscle-strength gains.

The equine frontier

While the BFR craze has set up shop in the world of human medicine, the number of animal studies—let alone studies of horses in particular—was severely lacking.

In the mid-2000s, a few studies from a Japanese team did find BFR to be safe in horses, and effective in increasing muscle thickness of the ulnaris lateralis. However, those studies were extremely small, and the investigators were primarily human-focused.

To set the equine stage, Dr. Johnson and her team worked closely with leading BFR experts of Delfi Medical Innovations, Inc., Owens Recovery Science and Brian Noehren , PT, PhD, FACSM, of Univeristy of Kentucky to develop a BFR cuff and protocol for use in the horse. They then evaluated short-term effects of BFR on equine superficial digital flexor (SDF) muscle oxidative capacity. Over the course of the 10-day study, they found that acute metabolic adaptions of both increased mitochondrial density and an improved ability to oxidize fuels was possible.

Patients undergoing BFR training typically perform high-repetition, low-intensity exercise with weight that is around 20% to 30% of their one-repetition maximum.

“The specific BFR walk protocol that we utilized consisted of a 10-minute interval walk protocol under 80% vascular occlusion,” she said. This protocol was extrapolated from human exercise protocols following numerous think-tanks amongst the translational BFR ‘dream-team’ of Colorado State University, Delfi Medical Innovations, Owens Recovery Science and Dr. Noehren.

This study

Using that same protocol, Dr. Johnson and her team set their attention on the safety of BFR in a longterm clinical setting.

One barrier is that established levels of limb occlusion pressure (LOP) have not been determined in horses. LOP is the pressure required to achieve full vascular occlusion, and it varies among patients.

Significant physiologic benefit can be obtained in a more comfortable manner using about 40% to 80% of a patient’s measured LOP, so fine-tuning is needed for each patient.

“Basically, a patient comes in for BFR training, the LOP gets measured, the occlusion percentage is automatically back-calculated, and then the session begins with the patient-specific pressure levels,” she explained.

But before BFR can be introduced on a widespread level in equine medicine, steps needed to be taken to ensure that the modality does not result in harmful gait dysfunction. “We also need to know just how variable LOPs are between horses and between an individual horse’s limbs,” Dr. Johnson explained.

To get those results, Dr. Johnson and her team enrolled 4 healthy horses to perform 40 unilateral forelimb BFR exercise sessions over a 56-day study period. Clinical examinations and objective gait analysis were performed by a blinded, board-certified equine sports medicine clinician.

LOP values were determined daily by Doppler ultrasonography immediately prior to the BFR walk sessions, and those daily values were back-calculated to deliver 80% vascular occlusion while at a walk.

“All of the study horses seemed to tolerate the BFR sessions pretty well,” Dr. Johnson explained. “A couple horses would intermittently paw at the treadmill belt during the stop periods, but there were no ‘worker strikes.’”

To evaluate whether BFR was contributing to clinical or biomechanical lameness, a total of 20 kinematic/kinetic parameters were evaluated, such as stride length, peak vertical force, and stance duration. Subjective lameness evaluation and limb palpation were also included.

Results showed that no gait dysfunction was introduced, and lameness scores did not change over the course of the study period.

“No evidence of venous or arterial thrombosis was noted in any horse at any evaluation time point based on our clinical examination,” she said. “There was no evidence of dermatitis, swelling, thickening, or sensitivity [at the area of the BFR cuff.]”

The team recorded a total of 160 LOP readings over the course of the study. Mean limb occlusion pressure was about 189 mm Hg, with a standard deviation of about 22 mm Hg.

Interestingly, there was a significant difference in mean LOP between the measures of left and right forelimbs—mean LOP in the right forelimbs was about 174 mm Hg, and mean LOP in the left forelimbs was about 205 mm Hg.

“Pressures of 75 to 150 mm Hg would likely simulate the 50% to 80% vascular occlusion levels in our standing, non-sedated horses,” Dr. Johnson explained. “Our results suggest that differences between horses and measured limbs will necessitate patient-specific pressure readings.” MeV

Disclosure statement: Members of the investigative team are partners of Equine Core an entity that is involved in the development of equine-specific blood flow restriction devices.

THE HISTORY OF BFR

According to Dr. Sherry Johnson , one of BFR’s first high-profile utilizations was when the US Department of Defense employed the modality to combat debilitating levels of muscle loss in wounded veterans, particularly those with traumatic blast-related wounds that required limb salvage procedures or even amputation.

Even after the damaged portions of the limb were removed, the soldiers still lacked the muscle strength and the function to successfully use prosthetic devices.

“It was actually through the use of BFR that the military started to circumvent these muscle losses in extreme injury,” she explained, “and they were able to tremendously improve prosthetic suitability.”

After whispers of its success in the military population, the modality eventually broke into the high-profile world of professional sports. NFL player Jadeveon Clowney’s use of BFR following a meniscal injury brought widespread attention, and it wasn’t long until strength conditioning coaches were using the technique on their healthy patients to maintain peak physical fitness without the use of damaging loads.

“With the advent of lower, more comfortable pressures, even the geriatric population uses BFR to combat sarcopenia,” Dr. Johnson noted. “One of the latest, greatest uses is in human patients with neurologic dysfunction.”