November, 2018: Blood Flow Restriction Therapy, Part II: Implications for Rehabilitation and Caveats
In last month’s Report on Hands, I discussed blood flow restriction (BFR) therapy as a proven means of stimulating muscle hypertrophy and hyperplasia by creating a low-oxygen environment. A venous tourniquet around the proximal portion of the limb restricts outflow of metabolites during low-intensity exercises and stimulates muscle growth. The technique has proven to have the desired effects on normal people who are interested in bulking up.
Since posting BFR Part I, I have reviewed several 2018 articles and have incorporated information from them in the Part II. Two of these references are included at the end of this post.
Much remains unknown about the best way to apply BFR. Cuffs that differ in width and composition will apply different degrees of pressure, and limbs with varying degrees of fat will respond individually. Cuff pressures ranging from 50-150 mmHg have proved effective, and some investigators have merely qualified cuff tightness as “loose, moderate, tight.” As evidence accumulates, cuff tightness is probably best personalized to the individual’s blood pressure because the idea is to restrict venous outflow, far greater than arterial inflow.
Then questions arise regarding the frequency of exercises, the number of repetitions, and the degree of resistance. Various protocols have achieved positive results, yet they are hard to compare to one another because of differences in subject ages, body habitus, and the type and width of the constricting band used.
For healthy individuals, BFR appears safe. Venous thrombosis would be a theoretical concern but occurred in 6 of about 12,600 individuals (.005%). In the same study, subcutaneous bleeding occurred in 13% and temporary numbness in 1.3%.
Does BFR work on people for whom it is unsafe or too painful to perform a conventional weight lifting routine? This might include patients requiring rehab for arthritic joints, healing tendons, and fragile bones both before and after surgery or instead of surgery. The concept is appealing: strengthen a biceps muscle following distal tendon attachment without risking a detachment, strengthen a digital flexor before a tendon repair mature, strengthen wrist and finger motors while the patient is still casted for a distal radius fracture, strengthen patients with limited cardiac and pulmonary reserves who cannot tolerate a heart-pounding workout? All these scenarios seem possible with a caveat.
It has been known since the 1930s that restricting blood flow to exercising muscle engages the so-called exercise pressor reflex (EPR), which contributes to the autonomic cardiovascular response to exercise. BFR exercise regimens also trigger the EPR, which could have adverse sympathetically mediated consequences for individuals with hypertension, heart failure, and peripheral artery disease. These dire consequences include stroke, myocardial infarction, and sudden death. Those individuals at risk even include “healthy” individuals who are using BFR for body building. Their baseline blood pressures may be unknowingly high related to use of cardio accelerants such as caffeine, sympathomimetics such as pseudoephedrine, and performance-enhancing drugs.
In 2015, Spranger et al, cited above, concluded their abstract by saying, “A more complete understanding of the consequences of BFR training is needed before this technique is passively explored by the layman athlete or prescribed by a health care professional.”
Since then, more studies have been published, especially related to rehabilitation following knee surgery. With regard to hypertension, Wong et al recently published a meta-analysis of 86 patients taken from six studies. They concluded that the cardiovascular response to exercise depended on the muscle group being exercised and on the parameters of BFR applied. In general, these responses were greater in the BFR group than in the non-BFR group.
BFR training certainly has potential for hastening rehabilitation in normal individuals and for allowing rehabilitation in individuals with comorbidities. It is certainly a topic that bears following as experimental results accumulate. Carefully controlled, prospective studies will help.
Wong M et al: Safety of Blood Flow Restricted Exercise in Hypertension: A Meta-Analysis and Systematic Review With Potential Applications in Orthopedic Care. Techniques in Orthopaedics, 2018: 33:80-88.