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Blood flow restriction resistance training in tendon rehabilitation: a scoping review on intervention parameters, physiological effects, and outcomes
- Blood flow restriction (BFR) training has been shown to induce comparable changes in many relevant markers associated with positive outcomes in rehabilitation, including muscle mass, muscle strength, and pain relief; however, not much is known about the effect of BFR on tendons.
- This scoping review highlights the limited evidence thus far on the effect of BFR on both healthy and pathological tendons.
- Despite largely positive effects of BFR on tendon outcomes, the heterogeneities in the existing body of literature reduce the strength of recommendation as a primary approach when managing those with tendon-related pathologies.
BACKGROUND & OBJECTIVE
The growth of low intensity (20-30% 1RM) blood flow restriction (BFR) training into rehabilitation practices have sparked questions regarding its potential impact on tendinous structures given its established role in producing similar muscle mass and strength gains as high intensity (70+% 1RM) resistance training (1).
As pathological tendons may present with load intolerance, strategies like BFR may be helpful to bridge the gap between low intensity strength training to traditionally recommended approaches. With recent research indicating a potent hypoalgesic effect (2), the potential for BFR to positively impact numerous outcomes in relevant domains pertinent to rehabilitation professionals is expanding.
However, there exists concern that the use of BFR training may disproportionately impact the muscles at the expense of the tendon, furthering the potential for negative outcomes with chronic use (3).
The aim of this review article was to attempt to answer the following questions:
What outcomes have been reported for BFR training in healthy tendons and rehabilitation for tendon injuries, and which outcome measures have been used?
What BFR training intervention and cuff parameters have been used in published studies?
What physiological mechanisms explaining effects of BFR training on tendons and tendon injuries have been investigated in published studies?
When managing pathological tendons, blood flow restriction training is best used as an adjunct secondary to high intensity strength training.
The authors searched “blood flow restriction,” “occlusion training,” “kaatsu training,” and “tendon,” “tendinopathy,” and “tendon rupture” on MEDLINE, CINAHL, AMED, EMBase, SPORTDiscus, and the Cochrane Library along with surveying Clinical Trials on relevant registry databases and Google Scholar; for studies published up until March 1st 2022.
Inclusion Criteria: adults > 18 years old with/without a history/diagnosis of tendon injury; BFR had to be performed with bodyweight or external resistance; experimental and quasi-experimental studies as well as case study/series and non-randomized controlled studies; English language only.
13 articles were included in the review:
- 10 were longitudinal studies on healthy/unhealthy tendons
- 3 were acute studies on healthy tendons
Acute Results (Healthy Tendons) (n = 120; 3 studies)
All were on Achilles tendon and used non-failure exercise between 30-80% limb occlusion pressure (LOP)
BFR produced a decrease in tendon thickness in 2 studies compared to both low and high intensity strength training (using calf raises) without BFR immediately and up to 24 hours post-exercise
Longitudinal Results (Healthy Tendons) (n = 160; 5 studies)
Two studies on patellar tendon, two studies on Achilles tendon, and one study on supraspinatus tendon which used a mixture of failure and non-failure routines performed between 37.7%-60% LOP
- Conflicting evidence:
- BFR (performed between 20-35% 1RM) improved tendon stiffness and cross-sectional area similarly along with knee extension muscle strength and quadriceps cross-sectional area compared to heavy-load strength training (70-85% 1RM) over 14 weeks
- BFR (performed at 20% 1RM) did not induce tendon stiffness or property changes compared to high intensity strength training (performed at 80% 1RM) over 12 weeks, but did increase maximum voluntary contraction and thigh muscle volume of the quadriceps
- Conflicting evidence:
- Two studies showed similar benefits in muscle mass, strength and tendon property changes using low-intensity non-failure/failure BFR exercise (performed between 20-35% 1RM) compared to both low intensity failure exercise and non-failure high intensity exercise over 6-14 weeks
- BFR and low-intensity external rotation (performed at 30% 1RM) induced positive changes in supraspinatus tendon thickness and muscle strength with no difference between conditions over 8 weeks
Acute Results (Pathological Tendons)
- No studies were included that investigated the acute tendon responses to BFR exercise in pathological tendons
Longitudinal Results (Pathological Tendons) (n = 12; 5 studies)
Three studies investigated patellar tendon, one study investigated chronic Achilles tendon rupture/repair, and one investigated biceps brachii tendon rupture/repair
- All investigated patellar tendinopathy over 3-12 weeks duration using between 120-180 mmHg pressure and/or 80% LOP
- All were case studies/series and involved no control group
- These reports indicate reductions in tendon vascularity and hypoechoic regions, improvements in knee extensor strength and thigh girth, as well as decreased symptoms following BFR intervention protocol
- Supported positive effect of BFR intervention on relevant markers of “successful” tendon rehabilitation
- BFR improved muscle strength and power to the calf complex and helped assist in return to sport using a non-failure protocol at 80% LOP over 6 weeks
Biceps Brachii Tendon
- Non-failure BFR isometrics and elbow flexion/extension included as part of the post-surgical plan of care helped pain, functional outcome scores and Mayo Elbow Performance Index at 80 mmHg applied pressure over 14 weeks
In addition to the limited number of studies, heterogeneity in the BFR application parameters, frequency of training, duration of training and relevant exercise prescription factors limited extrapolation of BFR prescription protocols in practice.
Few studies have investigated the differences in tendon material properties (e.g. Young’s Modulus) in different regions and types of BFR protocols.
The results of this scoping review indicate that despite the lack of strong evidence, the limited studies on a variety of both healthy and pathological tendons largely support the inclusion of BFR into the plan of care to help with a myriad of factors thought to be important in rehabilitation from injury. These factors include perceptual (e.g. reduction in pain), musculoskeletal (e.g. improvements in muscle mass and strength), physiological (e.g. reduction in vascularity in pathological tendons), and return to sport performance (e.g. getting back to unrestricted athletics). However, the heterogeneity in its application limits extrapolation to practice given the wide array of published pressures, repetition schemes, and exercises investigated.
Currently, the evidence appears to support that low intensity BFR exercise can be a helpful adjunct to a rehabilitation plan or to improve the properties of healthy tendons; but beyond that, more research with stronger designs (e.g. having both a low-intensity and high intensity control group) are needed to make firmer conclusions about the specific effects of BFR.
As of right now, best clinical practice recommendations are to implement BFR into a tendinopathy plan of care only if the patient is load compromised secondary to pain (1). Using BFR prior to a heavy loading training session (e.g. the “gold standard”) may reduce the pain response to allow for a therapeutic effect. It is not recommended that BFR be the sole modality used in a painful tendinopathy, particularly as it appears that tendon strain magnitude and/or loading magnitude (e.g. % 1RM) is a large determinant of the positive effects of strength training (4).
Due to the low intensity of loading employed with BFR, it likely does not induce comparable strain magnitude as high intensity strength training, potentially reducing its efficacy in altering tendon mechanical properties. It is important for the rehabilitation provider to be informed of best practice when managing pathological tendons, and as the evidence currently stands BFR is best used as an adjunct secondary to high intensity strength training.
Burton I, McCormack A (2022) Blood Flow Restriction Resistance Training in Tendon Rehabilitation: A Scoping Review on Intervention Parameters, Physiological Effects, and Outcomes. Frontiers in Sports and Active Living. EPublished ahead of print.
- Rolnick et al. (2021). Perceived barriers to blood flow restriction training. Frontiers in Rehabilitation Science, 2: 697082.
- Hughes et al. (2020). The effect of blood flow restriction exercise on exercise-induced hypoalgesia and endogenous opioid and endocannabinoid mechanisms of pain modulation. J Appl Physiol (1985). 128(4): 914-924.
- Behringer et al. (2019). Application of blood flow restriction to optimize exercise countermeasures for human space flight. Front. Physiol.
- McMahon G. (2022). No strain, no gain? The role of strain and load magnitude in human tendon responses and adaptation to loading. JSCR. [Published Ahead of Print]