Bite-size study - Infographic style!

What’s new in sports Med U

Follow me on twitter/X for more insights and tools for rehab

Deeper look 

Background info

• Muscle atrophy effects are evident in both acute and chronic musculoskeletal injuries, which involve extended treatment or muscle immobilisation, such as fractures and ligament injuries.

• A significant loss of strength represents a major risk factor for osteoarthritis, the most prevalent musculoskeletal disease responsible for decreased functionality and the quality of life for individuals, affecting approximately 250 million adults worldwide

• Higher quadriceps strength has been associated with a reduced risk of symptomatic knee osteoarthritis, minimized joint space narrowing, decreased pain, and positive improvements in physical function.

• Muscle hypertrophy and strength gains are typically achieved with heavy exercise loads, roughly 70% of an individual's one repetition maximum (1RM).

• Recent research reveals that low-load training to failure can induce muscle hypertrophy of similar magnitude to heavy-load training after 6 to 8 weeks of thrice-weekly training.

• From a clinical musculoskeletal rehabilitation perspective, training to muscular failure can maximize hypertrophy when using low loads, especially when heavy loads are not feasible.

• Studies have shown that combining low-load resistance training with blood flow restriction (BFR) to the active musculature can lead to significant hypertrophy and strength gains, even with loads as low as 30%.

• Mechanistically, it is hypothesized that lower limb BFR creates an ischemic and hypoxic muscular environment, generating high metabolic stress and mechanical tension when combined with exercise.

• Proposed mechanisms include increased systemic hormone production, cell swelling, production of reactive oxygen species, intramuscular anabolic/anticatabolic signaling, and enhanced recruitment of fast-twitch muscle fibers.

• Lower limb -BFR strength training can serve as a clinically relevant tool in musculoskeletal rehabilitation, as it avoids the high joint forces associated with heavy-load exercise

Methods & Results

• A total of 20 studies were utilised in the analysis.

• All 20 studies were included in the systematic review.

• Out of these, 13 studies were employed for the meta-analysis.

• The studies encompassed various participant groups, including those with knee OA (3 studies), ligament injuries (3 studies), sporadic inclusion body myositis (1 study), and older adults at risk of sarcopenia (13 studies).

• The average age of the participants was 58 years (ranging from 10 to 41 individuals).

• BFR was applied in conjunction with low-load resistance training.

• Additionally, BFR training was combined with body weight exercises.

• BFR exercise loads varied from 10% to 30% of the one-repetition maximum (1RM) for resistance exercises and from 45% of the heart rate reserve to 67 meters per minute for aerobic and walking exercises.

• BFR was achieved using pneumatic cuffs, hand-pumped blood pressure cuffs, or elastic wraps with widths ranging from 3 to 18 centimeters.

• The occlusive pressure across the studies ranged from 60 to 270 mmHg.

• The duration of BFR training interventions spanned from 2 to 16 weeks, with training frequencies ranging from 2 to 6 sessions per week

Discussion | Meta analysis

• The findings demonstrate that supplementing low-load rehabilitation training with BFR can elicit more substantial improvements in muscular strength when contrasted with low-load training on its own.

• Currently, these strength gains seem to be somewhat smaller in magnitude than those attainable through heavy-load training.

• Lower limb-BFR training proves to be a more efficient alternative to standalone low-load training, potentially serving as a substitute for traditional heavy-load training.

• As of now, there is no existing literature offering a definitive explanation for how lower limb BFR training generates greater strength enhancements compared to low-load training within clinical populations.

• This difference is likely driven by hypertrophy and neural adaptations, similar to those observed in heavy-load training, and the underlying mechanism likely comparable.

• In BFR exercise, the amalgamation of tension and hypoxia may trigger these mechanisms. This review highlighted that the strength gains achieved with lower limb BFR training are somewhat less pronounced than those observed in heavy-load training.

Discussion | systematic analysis

• The systematic TESTEX analysis on exercise training studies in clinical MSK rehabilitation showed that a significant majority of studies do not mention any adverse events related to BFR.

• Lower limb-BFR training proves effective in enhancing physiological aspects, excluding muscle strength, and can be utilised independently to prevent muscle atrophy during early immobilisation.

• Incorporating BFR into low-load training does not seem to exacerbate conditions or cause exercise-related pain.

• Despite initial concerns about potential hemodynamic disruptions and ischaemic reperfusion injury, in-depth reviews confirm that properly implemented BFR training poses no greater risk than traditional exercise methods

Effective implementation of BFR training

• Current literature highlights a deficiency in personalised prescription of BFR training, particularly in the need for individualising occlusive pressure to ensure safe and effective application.

• Studies in healthy individuals reveal that thigh circumference plays a crucial role in determining occlusion pressure, with larger limbs necessitating higher pressure to achieve equivalent occlusion levels as smaller limbs.

• A recent method involves calculating total arterial limb occlusive pressure (LOP), enabling the selection of a pressure at a percentage of LOP to standardise occlusion levels across different cohorts.

• Registered Nurses can utilise this technique to calculate necessary tourniquet pressures during surgery, aiming to restrict blood flow and minimize the risk of adverse events.

• Studies utilizsng this method in BFR exercise reveal that achieving higher LOP pressures does not necessarily lead to greater enhancement of muscular responses compared to lower pressures.

• A research finding indicates that employing 40% LOP results in comparable improvements in muscle size, strength, and endurance over an 8-week training period, similar to those achieved with 90% LOP, but with significantly lower reported discomfort.

• The evidence suggests that opting for lower and more tolerable pressures in BFR training can induce adequate musculoskeletal adaptations while simultaneously reducing the risk of adverse events and minimizing discomfort, emphasizing the importance of personalized prescription in clinical BFR training.

Other physiological adaptations to BFR training

• Studies indicate that after 6 weeks of low-load BFR training, there is an observable rise in serum concentrations of bone alkaline phosphatase, suggesting a positive influence on bone health through increased bone turnover

• In older individuals, low-load walking training with BFR has shown to enhance various factors, including knee extensor and flexor torque, carotid arterial compliance, peak oxygen uptake, peak post-occlusive blood flow, vascular endothelial function, and peripheral nerve circulation.

• The benefits of this training approach extend beyond the older population, as it may be applicable to clinical groups experiencing musculoskeletal weakness and bone degradation, such as patients with osteoporosis, rheumatoid arthritis, multiple myeloma, and lymphoma

Clinical application

• Recent recommendations suggest that, for clinical populations, achieving enhanced strength adaptations can be accomplished with 2 to 3 low-load BFR training sessions per week, incorporating progressive overload.

• Loenneke et al. proposed a four-step progression model for BFR usage in early rehabilitation to high-load resistance training:

(1) BFR alone during bed rest;

(2) BFR combined with low-intensity walking exercise;

(3) BFR combined with low-load resistance exercise; and

(4) Low-load BFR training in conjunction with high-load exercise.

• Studies have demonstrated the effective prevention of muscle atrophy and the improvement of muscle strength using an occlusion protocol, even at a relatively low pressure of 50 mmHg.