Blood flow restriction enhances post-resistance exercise angiogenic gene expression

Blood flow restriction as a post-exercise recovery strategy: A systematic review of the current status of the literature

The aim of this study was to systematically review the current literature on blood flow restriction (BFR) as a post-exercise recovery strategy. Experimental studies investigating the effect of BFR on recovery after exercise were included. Only studies meeting the following inclusion criteria were selected: (a) studies investigating about BFR as a post-exercise recovery strategy in athletes and healthy individuals; (b) the full text being available in English; (c) experimental research study design. Studies that exclusively analyzed BFR as a recovery strategy during the exercise (e.g., recovery strategy between bouts of exercise) were excluded. A literature review was conducted on the PubMed, Cochrane, and Web of Science electronic databases up until May 7th, 2023. The main findings were that (i) 9 studies investigated passive BFR as a post-exercise recovery strategy, which shows a significant lack of research in both team and individual sports (especially in female populations), and only 2 studies used active BFR protocols; (ii) although a high quality range of studies was observed, there were methodological limitations such as BFR interventions that were usually conducted after fatiguing protocols or fitness tests, which may not represent the real exercise (e.g., a sprint session of 6 sets of 50 m may induce muscle damage but it does not represent the demands of a team sport like rugby or soccer); (iii) there is a lack of consistency in BFR protocols (e.g., number of cycles or duration of the occlusion-reperfusion periods) for recovery; (iv) some studies showed beneficial effects while others found no positive or detrimental effects of BFR as a post-exercise recovery strategy in comparison with the control/SHAM group. In conclusion, only 11 studies investigated BFR as a post-exercise recovery strategy and there is not any significant amount of evidence in team or individual sports (especially in female populations). BFR could be a potential post-exercise recovery strategy, but practitioners should use caution when applying this method of recovery for their athletes and clients. In addition, it would be of interest for high performance-related practitioners to have a better understanding of the benefits of BFR interventions combined with either active or passive forms of exercise as a post-exercise recovery strategy.

Acute Responses to Different Velocity Loss Thresholds during Squat Exercise with Blood-Flow Restriction in Strength-Trained Men

(1) Background: The aim of this paper is to analyze the acute effects of different velocity loss (VL) thresholds during a full squat (SQ) with blood-flow restriction (BFR) on strength performance, neuromuscular activity, metabolic response, and muscle contractile properties. (2) Methods: Twenty strength-trained men performed four protocols that differed in the VL achieved within the set (BFR0: 0% VL; BFR10: 10% VL; BFR20: 20% VL; and BFR40: 40% VL). The relative intensity (60% 1RM), recovery between sets (2 min), number of sets (3), and level of BFR (50% of arterial occlusion pressure) were matched between protocols. Tensiomyography (TMG), blood lactate, countermovement jump (CMJ), maximal voluntary isometric SQ contraction (MVIC), and performance with the absolute load required to achieve 1 m·s-1 at baseline measurements in SQ were assessed before and after the protocols. (3) Results: BFR40 resulted in higher EMG alterations during and after exercise than the other protocols (p < 0.05). BFR40 also induced greater impairments in TMG-derived variables and BFR10 decreased contraction time. Higher blood lactate concentrations were found as the VL within the set increased. BFR0 and BFR10 showed significantly increased median frequencies in post-exercise MVIC. (4) Conclusions: High VL thresholds (BFR40) accentuated metabolic and neuromuscular stress, and produced increased alterations in muscles' mechanical properties. Low VL could potentiate post-exercise neuromuscular activity and muscle contractile properties.

Validity and reliability of a wearable blood flow restriction training device for arterial occlusion pressure assessment

Purpose

The blood flow restriction (BFR) training is an effective approach to promoting muscle strength, muscle hypertrophy, and regulating the peripheral vascular system. It is recommended to use to the percentage of individual arterial occlusion pressure (AOP) to ensure safety and effectiveness. The gold standard method for assessing arterial occlusive disease is typically measured using Doppler ultrasound. However, its high cost and limited accessibility restrict its use in clinical and practical applications. A novel wearable BFR training device (Airbands) with automatic AOP assessment provides an alternative solution. This study aims to examine the reliability and validity of the wearable BFR training device.

Methods

Ninety-two participants (46 female and 46 male) were recruited for this study. Participants were positioned in the supine position with the wearable BFR training device placed on the proximal portion of the right thigh. AOP was measured automatically by the software program and manually by gradually increasing the pressure until the pulse was no longer detected by color Doppler ultrasound, respectively. Validity, inter-rater reliability, and test-retest reliability were assessed by intraclass correlation coefficients (ICC) and Bland-Altman analysis.

Results

The wearable BFR training device demonstrated good validity (ICC = 0.85, mean difference = 4.1 ± 13.8 mmHg [95% CI: -23.0 to 31.2]), excellent inter-rater reliability (ICC = 0.97, mean difference = -1.4 ± 6.7 mmHg [95% CI: -14.4 to 11.7]), and excellent test-retest reliability (ICC = 0.94, mean difference = 0.6 ± 8.6 mmHg [95% CI: -16.3 to 17.5]) for the assessment of AOP. These results were robust in both male and female subgroups.

Conclusion

The wearable BFR training device can be used as a valid and reliable tool to assess the AOP of the lower limb in the supine position during BFR training.

Acute physiological responses of blood flow restriction between high-intensity interval repetitions in trained cyclists

Blood flow restriction (BFR) is increasingly being used to enhance aerobic performance in endurance athletes. This study examined physiological responses to BFR applied in recovery phases within a high-intensity interval training (HIIT) session in trained cyclists. Eleven competitive road cyclists (mean ± SD, age: 28 ± 7 years, body mass: 69 ± 6 kg, peak oxygen uptake: 65 ± 9 mL · kg-1 · min-1) completed two randomised crossover conditions: HIIT with (BFR) and without (CON) BFR applied during recovery phases. HIIT consisted of six 30-s cycling bouts at an intensity equivalent to 85% of maximal 30-s power (523 ± 93 W), interspersed with 4.5-min recovery. BFR (200 mmHg, 12 cm cuff width) was applied for 2-min in the early recovery phase between each interval. Pulmonary gas exchange (V̇O2, V̇CO2, and V̇E), tissue oxygen saturation index (TSI), heart rate (HR), and serum vascular endothelial growth factor concentration (VEGF) were measured. Compared to CON, BFR increased V̇CO2 and V̇E during work bouts (both p < 0.05, dz < 0.5), but there was no effect on V̇O2, TSI, or HR (p > 0.05). In early recovery, BFR decreased TSI, V̇O2, V̇CO2, and V̇E (all p < 0.05, dz > 0.8) versus CON, with no change in HR (p > 0.05). In late recovery, when BFR was released, V̇O2, V̇CO2, V̇E, and HR increased, but TSI decreased versus CON (all p < 0.05, dz > 0.8). There was a greater increase in VEGF at 3-h post-exercise in BFR compared to CON (p < 0.05, dz > 0.8). Incorporating BFR into HIIT recovery phases altered physiological responses compared to exercise alone.

Distinct adaptations of muscle endurance but not strength or hypertrophy to low-load resistance training with and without blood flow restriction

Low-load resistance training promotes muscle strength and hypertrophic adaptations when combined with blood flow restriction (BFR). However, the effect of BFR on muscle endurance remains unclear. The aim of this study was to clarify the effects of BFR on muscle performance and adaptation, with special reference to local muscle endurance. In experiment 1, eight healthy men performed unilateral elbow flexion exercise to failure at 30% of one-repetition maximum with BFR (at 40% of estimated arterial occlusion pressure) and free blood flow (FBF). During the exercise, muscle activity and tissue oxygenation were measured from the biceps brachii. In experiment 2, another eight healthy men completed 6 weeks of elbow flexion training with BFR and FBF. The number of repetitions to failure at submaximal load (Rmax), the estimated time for peak torque output to decay by 50% during repetitive maximum voluntary contractions (half-time), one-repetition maximum, isometric strength and muscle thickness of elbow flexors were measured pre- and post-training. Blood flow restriction resulted in fewer repetitions and lower muscle tissue oxygenation at the end of exercise than FBF, while the muscle activity increased similarly to repetition failure. Blood flow restriction also resulted in a smaller post-training Rmax, which was strongly correlated with the total exercise volume over the 6 week period. Despite the smaller exercise volume, BFR resulted in similar improvements in half-time, muscle strength and thickness compared with FBF. These results suggest that the application of BFR can attenuate muscle endurance adaptations to low-load resistance training by decreasing the number of repetitions during exercise, both acutely and chronically.

DNA methylation changes during a sprint interval exercise performed under normobaric hypoxia or with blood flow restriction: A pilot study in men

This crossover study evaluated DNA methylation changes in human salivary samples following single sprint interval training sessions performed in hypoxia, with blood flow restriction (BFR), or with gravity-induced BFR. Global DNA methylation levels were evaluated with an enzyme-linked immunosorbent assay. Methylation-sensitive restriction enzymes were used to determine the percentage methylation in a part of the promoter of the gene-inducible nitric oxide synthase (p-iNOS), as well as an enhancer (e-iNOS). Global methylation increased after exercise (p < 0.001; dz = 0.50). A tendency was observed for exercise × condition interaction (p = 0.070). Post hoc analyses revealed a significant increase in global methylation between pre- (7.2 ± 2.6%) and postexercise (10.7 ± 2.1%) with BFR (p = 0.025; dz = 0.69). Methylation of p-iNOS was unchanged (p > 0.05). Conversely, the methylation of e-iNOS increased from 0.6 ± 0.4% to 0.9 ± 0.8% after exercise (p = 0.025; dz = 0.41), independently of the condition (p > 0.05). Global methylation correlated with muscle oxygenation during exercise (r = 0.37, p = 0.042), while e-iNOS methylation showed an opposite association (r = -0.60, p = 0.025). Furthermore, p-iNOS methylation was linked to heart rate (r = 0.49, p = 0.028). Hence, a single sprint interval training increases global methylation in saliva, and adding BFR tends to increase it further. Lower muscle oxygenation is associated with augmented e-iNOS methylation. Finally, increased cardiovascular strain results in increased p-iNOS methylation.

The effect of exercise on blood concentrations of angiogenesis markers in older adults: A systematic review and meta-analysis

Impaired angiogenesis is associated with cognitive decline in older adults. While exercise has been broadly associated with increased angiogenesis, the relevant mechanisms in older adults are not clear. Here, we present a systematic review and meta-analysis on the relationship between exercise and specific blood angiogenesis markers in older adults to better understand the relevant mechanisms. MEDLINE, Embase, and Cochrane CENTRAL were searched for original reports of angiogenesis markers' concentrations in blood before and after exercise in older adults (≥50 years). Heterogeneity was investigated using sub-group analyses and meta-regressions. Of the 44 articles included in the review, 38 were included in the meta-analyses for five markers: vascular endothelial growth factor (VEGF), e-selectin (CD62E), endostatin, fibroblast growth factor 2, and matrix metallopeptidase-9. VEGF levels were higher (SMD[95%CI]= 0.18[0.03, 0.34], and CD62E levels were lower (SMD[95%CI]= -0.72[-1.42, -0.03], p = 0.04) after exercise. No other markers were altered. Although more studies are needed, changes in angiogenesis markers may help explain the beneficial effects of exercise on angiogenesis in older adults.

Salivary proteomic profile of response to different resistance training protocols: A case report

Resistance training (RT) with blood flow restriction (BFR) or high intensity (HI) are effective to increase muscle mass. To understand this effect, techniques known as "omics" are used to identify possible biomarkers. This study analyzed the salivary proteomic profile of healthy individuals trained before and after two RT protocols both designed with eight exercises for upper- and lower-limbs, one performed at low percentage of one-maximum repetition (%1RM) with BFR technique, and other at high %1RM (HI) without BRF technique. Four healthy males between 18 and 28 years participated in the study. Stimulated saliva was collected before (BBFR/BHI) and immediately after (ABFR/AHI) the two RT protocols. All protein-related processing was performed using label-free proteomic. The difference in expression between groups was expressed as p < .05 for downregulated proteins and 1-p > .95 for upregulated proteins. There was difference in salivary flow between ABFR and BBFR (p = .005). For HI, 87 proteins were found after the practice and 119 before. Three hemoglobin isoforms were increased in AHI compared with BHI. In the BFR comparison, 105 proteins were identified after (ABFR) and 70 before (BBFR). Among those increased ABFR, we highlight five hemoglobin isoforms and Deleted in malignant brain tumors 1 protein. Between ABFR and AHI, 17 isoforms of histones, Transaldolase, Transketolase, Glyceraldehyde-3-phosphate dehydrogenase, and Antileukoproteinase were decreased ABFR. For HI, there was an increase in proteins related to oxidative stress and metabolism of the musculoskeletal system, compared with BFR. HI seems to induce higher anabolic signaling to muscle mass increase and antiatherosclerotic effects.

The Influence of Interval Training Combined with Occlusion and Cooling on Selected Indicators of Blood, Muscle Metabolism and Oxidative Stress

There is increasing evidence to support the use of interval training and/or low-impact blood flow restriction exercises in musculoskeletal rehabilitation. The aim of the study was to assess the effect of interval training combined with occlusion and cooling in terms of changes in selected blood parameters affecting the development and progression of atherosclerosis of the lower limbs, as well as selected parameters of muscle metabolism and oxidative stress affecting the growth of muscle mass and regeneration after training.

MATERIAL AND METHODS

The study included 30 young, healthy and untrained people. The VASPER (Vascular Performance) training system was used-High-Intensity Interval Training with the simultaneous use of occlusion and local cryotherapy. Blood from the project participants was collected six times (2 weeks before the start of training, on the day of training, after the first training, after the 10th training, after the 20th training and two weeks after the end of training). The subjects were randomly divided into three groups: exercises only (controlled), with occlusion and with occlusion and local cryotherapy.

RESULTS

Statistical analysis of changes in the average values of indicators in all study groups showed a significant change increase due to the time of testing IGF-1 (F = 2.37, p = 0.04), XOD (F = 14.26, p = 0.00), D-Dimer (F = 2.90, p = 0.02), and decrease in MDA (F = 7.14, p = 0.00), T-AOC (F = 11.17, p = 0.00), PT Quick (F = 26.37, p = 0.00), INR (F = 8.79, p = 0.00), TT (F = 3.81, p = 0.00). The most pronounced changes were observed in the occlusion and cooling group.

CONCLUSIONS

Both interval training without and with the modifications used in the study influences coagulation and oxidative stress parameters and, to a small extent, muscle metabolism. It seems reasonable to use occlusion and local cryotherapy in combination with occlusion.

Low-intensity resistance exercise with blood flow restriction for patients with claudication: A randomized controlled feasibility trial

BACKGROUND

Claudication is a common and debilitating symptom of peripheral artery disease, resulting in poor exercise performance and quality of life (QoL). Supervised exercise programs are an effective rehabilitation for patients with claudication, but they are poorly adhered to, in part due to the high pain and effort associated with walking, aerobic, and resistance exercise. Low-intensity resistance exercise with blood flow restriction (BFR) represents an alternative exercise method for individuals who are intolerant to high-intensity protocols. The aim of this study was to evaluate the feasibility of a supervised BFR program in patients with claudication.

METHODS

Thirty patients with stable claudication completed an 8-week supervised exercise program and were randomized to either BFR (n = 15) or a control of matched exercise without BFR (control; n = 15). Feasibility, safety, and efficacy were assessed.

RESULTS

All success criteria of the feasibility trial were met. Exercise adherence was high (BFR = 78.3%, control = 83.8%), loss to follow up was 10%, and there were no adverse events. Clinical improvement in walking was achieved in 86% of patients in the BFR group but in only 46% of patients in the control group. Time to claudication pain during walking increased by 35% for BFR but was unchanged for the control. QoL for the BFR group showed improved mobility, ability to do usual activities, pain, depression, and overall health at follow up.

CONCLUSION

A supervised blood flow restriction program is feasible in patients with claudication and has the potential to increase exercise performance, reduce pain, and improve QoL. (Clinicaltrials.gov Identifier: NCT04890275).

BFR Training Improves Patients' Reported Outcomes, Strength, and Range of Motion After Casting for Colles' Fracture

PURPOSE

This study compared traditional rehabilitation as a treatment modality after plaster cast treatment of Colles' fracture with a combination of individualized blood flow restriction (BFR) and traditional rehabilitation.

METHODS

Twenty-eight participants were randomized into a BFR group and a non-BFR group after plaster cast treatment of Colles' fracture. The BFR group completed traditional rehabilitation with a medical grade tourniquet applied to the upper arm, and the non-BFR group underwent traditional rehabilitation only. Patients were followed up with radiographic outcomes (palmar tilt and radial inclination) to ensure the stability of the fracture. Clinical assessment of patient-rated wrist evaluation (PRWE) score, grip strength, pinch strength, wrist range of motion (ROM), and muscle stiffness was conducted at cast removal and 6 wk after cast removal. Two-way repeated-measures ANOVA determined significant interactions between time and group in the aforementioned variables. An independent-sample t -test assessed the differences in baseline variables and radiographic outcomes.

RESULTS

Significant interactions between time and group were noted for PRWE score ( F = 11.796, P = 0.002, η2p = 0.339), grip strength ( F = 5.445, P = 0.029, η2p = 0.191), and wrist ROM (ulnar deviation; F = 7.856, P = 0.010, η2p = 0.255). No significant interactions between time and group were found in measurements of pinch strength or wrist ROM (flexion, extension, radial deviation, pronation, supination). An independent-sample t -test showed no significant difference in baseline variables and radiographic outcomes between the groups before or after intervention.

CONCLUSIONS

This study found that combining individualized BFR with traditional rehabilitation resulted in greater increases in PRWE score, grip strength, and wrist ROM (ulnar deviation) than traditional rehabilitation alone. Therefore, adding individualized BFR to traditional rehabilitation might be a better option for treatment for similar patients.

Time to consider the potential role of alternative resistance training methods in cancer management?

Exercise has emerged as fundamental therapeutic medicine in the management of cancer. Exercise improves health-related outcomes, including quality of life, neuromuscular strength, physical function, and body composition, and it is associated with a lower risk of disease recurrence and increased survival. Moreover, exercise during or post cancer treatments is safe, can ameliorate treatment-related side effects, and may enhance the effectiveness of chemotherapy and radiation therapy. To date, traditional resistance training (RT) is the most used RT modality in exercise oncology. However, alternative training modes, such as eccentric, cluster set, and blood flow restriction are gaining increased attention. These training modalities have been extensively investigated in both athletic and clinical populations (e.g., age-related frailty, cardiovascular disease, type 2 diabetes), showing considerable benefits in terms of neuromuscular strength, hypertrophy, body composition, and physical function. However, these training modes have only been partially or not at all investigated in cancer populations. Thus, this study outlines the benefits of these alternative RT methods in patients with cancer. Where evidence in cancer populations is sparse, we provide a robust rationale for the possible implementation of certain RT methods that have shown positive results in other clinical populations. Finally, we provide clinical insights for research that may guide future RT investigations in patients with cancer and suggest clear practical applications for targeted cancer populations and related benefits.

Where Does Blood Flow Restriction Fit in the Toolbox of Athletic Development? A Narrative Review of the Proposed Mechanisms and Potential Applications

Blood flow-restricted exercise is currently used as a low-intensity time-efficient approach to reap many of the benefits of typical high-intensity training. Evidence continues to lend support to the notion that even highly trained individuals, such as athletes, still benefit from this mode of training. Both resistance and endurance exercise may be combined with blood flow restriction to provide a spectrum of adaptations in skeletal muscle, spanning from myofibrillar to mitochondrial adjustments. Such diverse adaptations would benefit both muscular strength and endurance qualities concurrently, which are demanded in athletic performance, most notably in team sports. Moreover, recent work indicates that when traditional high-load resistance training is supplemented with low-load, blood flow-restricted exercise, either in the same session or as a separate training block in a periodised programme, a synergistic and complementary effect on training adaptations may occur. Transient reductions in mechanical loading of tissues afforded by low-load, blood flow-restricted exercise may also serve a purpose during de-loading, tapering or rehabilitation of musculoskeletal injury. This narrative review aims to expand on the current scientific and practical understanding of how blood flow restriction methods may be applied by coaches and practitioners to enhance current athletic development models.

Hormonal, immune, and oxidative stress responses to blood flow-restricted exercise

INTRODUCTION

Heavy-load free-flow resistance exercise (HL-FFRE) is a widely used training modality. Recently, low-load blood-flow restricted resistance exercise (LL-BFRRE) has gained attention in both athletic and clinical settings as an alternative when conventional HL-FFRE is contraindicated or not tolerated. LL-BFRRE has been shown to result in physiological adaptations in muscle and connective tissue that are comparable to those induced by HL-FFRE. The underlying mechanisms remain unclear; however, evidence suggests that LL-BFRRE involves elevated metabolic stress compared to conventional free-flow resistance exercise (FFRE).

AIM

The aim was to evaluate the initial (<10 min post-exercise), intermediate (10-20 min), and late (>30 min) hormonal, immune, and oxidative stress responses observed following acute sessions of LL-BFRRE compared to FFRE in healthy adults.

METHODS

A systematic literature search of randomized and non-randomized studies was conducted in PubMed, Embase, Cochrane Central, CINAHL, and SPORTDiscus. The Cochrane Risk of Bias (RoB2, ROBINS-1) and TESTEX were used to evaluate risk of bias and study quality. Data extractions were based on mean change within groups.

RESULTS

A total of 12525 hits were identified, of which 29 articles were included. LL-BFRRE demonstrated greater acute increases in growth hormone responses when compared to overall FFRE at intermediate (SMD 2.04; 95% CI 0.87, 3.22) and late (SMD 2.64; 95% CI 1.13, 4.16) post-exercise phases. LL-BFRRE also demonstrated greater increase in testosterone responses compared to late LL-FFRE.

CONCLUSION

These results indicate that LL-BFRRE can induce increased or similar hormone and immune responses compared to LL-FFRE and HL-FFRE along with attenuated oxidative stress responses compared to HL-FFRE.

Blood flow restriction training activates the muscle metaboreflex during low-intensity sustained exercise

Blood flow restriction training (BFRT) employs partial vascular occlusion of exercising muscle and has been shown to increase muscle performance while using reduced workload and training time. Numerous studies have demonstrated that BFRT increases muscle hypertrophy, mitochondrial function, and beneficial vascular adaptations. However, changes in cardiovascular hemodynamics during the exercise protocol remain unknown, as most studies measured blood pressure before the onset and after the cessation of exercise. With reduced perfusion to the exercising muscle during BFRT, the resultant accumulation of metabolites within the ischemic muscle could potentially trigger a large reflex increase in blood pressure, termed the muscle metaboreflex. At low workloads, this pressor response occurs primarily via increases in cardiac output. However, when increases in cardiac output are limited (e.g., heart failure or during severe exercise), the reflex shifts to peripheral vasoconstriction as the primary mechanism to increase blood pressure, potentially increasing the risk of a cardiovascular event. Using our chronically instrumented conscious canine model, we utilized a 60% reduction in femoral blood pressure applied to the hindlimbs during steady-state treadmill exercise (3.2 km/h) to reproduce the ischemic environment observed during BFRT. We observed significant increases in heart rate (+19 ± 3 beats/min), stroke volume (+2.52 ± 1.2 mL), cardiac output (+1.21 ± 0.2 L/min), mean arterial pressure (+18.2 ± 2.4 mmHg), stroke work (+1.93 ± 0.2 L/mmHg), and nonischemic vascular conductance (+3.62 ± 1.7 mL/mmHg), indicating activation of the muscle metaboreflex.NEW & NOTEWORTHY Blood flow restriction training (BFRT) increases muscle mass, strength, and endurance. There has been minimal consideration of the reflex cardiovascular responses that could be elicited during BFRT sessions. We showed that during low-intensity exercise BFRT may trigger large reflex increases in blood pressure and sympathetic activity due to muscle metaboreflex activation. Thus, we urge caution when employing BFRT, especially in patients in whom exaggerated cardiovascular responses may occur that could cause sudden, adverse cardiovascular events.

Elevating athletic performance: Maximizing strength and power in long jumpers through combined low-intensity blood flow restriction and high-intensity resistance training

Purpose

This study aimed to evaluate the effects of low-intensity blood flow restriction (BFR) training and high-intensity resistance training (HI-RT) on the leaping performance of long-jumpers.

Materials and methods

Long jump players were divided into two groups; one group (group A) receiving HI-RT (n = 8) and the other group (group B) receiving combined low-intensity BFR training plus HI-RT (n = 8). Muscle power and knee muscle strength was assessed at baseline, 3 weeks and 6 weeks of intervention.

Results

1-RM was found to be significantly different between Group A and Group B at 3 and 6 weeks. Further, IKDQR, IKDHR and IKDQL was significantly improved in group B as compared to group A both at 3 and 6 weeks. There was significant time effect, group effect and time-group interaction in the strength of quadriceps and hamstring of both left and right leg measured through isokinetic device. Post-hoc analysis for 1-RM in group B showed a significant improvement at baseline and 6 weeks and the broad jump was significant at baseline and 3 weeks and at baseline and 6 weeks.

Conclusion

The combined effects of low-intensity BFR training and HI-RT is effective in improving the muscle strength and power of lower limbs in long jumpers.

ADAPTations to low load blood flow restriction exercise versus conventional heavier load resistance exercise in UK military personnel with persistent knee pain: protocol for the ADAPT study, a multi-centre randomized controlled trial

BACKGROUND

Muscle atrophy, muscle weakness and localised pain are commonly reported following musculoskeletal injury (MSKI). To mitigate this risk and prepare individuals to return to sport or physically demanding occupations, resistance training (RT) is considered a vital component of rehabilitation. However, to elicit adaptations in muscle strength, exercise guidelines recommend lifting loads ≥ 70% of an individual's one repetition maximum (1-RM). Unfortunately, individuals with persistent knee pain are often unable to tolerate such high loads and this may negatively impact the duration and extent of their recovery. Low load blood flow restriction (LL-BFR) is an alternative RT technique that has demonstrated improvements in muscle strength, hypertrophy, and pain in the absence of high mechanical loading. However, the effectiveness of high-frequency LL-BFR in a residential rehabilitation environment remains unclear. This study will compare the efficacy of high frequency LL-BFR to 'conventional' heavier load resistance training (HL-RT) on measures of physical function and pain in adults with persistent knee pain.

METHODS

This is a multicentre randomised controlled trial (RCT) of 150 UK service personnel (aged 18-55) admitted for a 3-week residential rehabilitation course with persistent knee pain. Participants will be randomised to receive: a) LL-BFR delivered twice daily at 20% 1-RM or b) HL-RT three-times per week at 70% 1-RM. Outcomes will be recorded at baseline (T1), course discharge (T2) and at three-months following course (T3). The primary outcome will be the lower extremity functional scale (LEFS) at T2. Secondary outcomes will include patient reported perceptions of pain, physical and occupational function and objective measures of muscle strength and neuromuscular performance. Additional biomechanical and physiological mechanisms underpinning both RT interventions will also be investigated as part of a nested mechanistic study.

DISCUSSION

LL-BFR is a rehabilitation modality that has the potential to induce positive clinical adaptations in the absence of high mechanical loads and therefore could be considered a treatment option for patients suffering significant functional deficits who are unable to tolerate heavy load RT. Consequently, results from this study will have a direct clinical application to healthcare service providers and patients involved in the rehabilitation of physically active adults suffering MSKI.

TRIAL REGISTRATION

ClinicalTrials.org reference number, NCT05719922.

Impact of Blood-Flow-Restricted Training on Arterial Functions and Angiogenesis-A Systematic Review with Meta-Analysis

Despite growing evidence of the significant influence of blood-flow-restricted (BFR) training on different body functions, its impact on the vascular system, especially the arteries, is controversial. Therefore, the objective of our study was to analyze how BFR exercise, compared to other types of exercise without the restriction of blood flow, influences arterial functions and angiogenesis in adults. Studies comparing the effect of BFR versus non-BFR training on arterial parameters were divided into three categories: endothelial function, angiogenesis, and other vasculature functions. The search was based on Cochrane Library, PubMed®, and Embase, and 38 studies were included. The meta-analysis revealed a more significant improvement in flow-mediated dilatation (FMD) (p = 0.002) and the production of the primary angiogenesis biomarker vascular endothelial growth factor (VEGF) (p = 0.009) after BFR compared to non-BFR training (p = 0.002). The analysis of the pulse wave velocity, ankle-brachial index, systolic blood pressure, and heart rate did not show significant differences in changes between BFR and non-BFR training. The other parameters examined did not have sufficient data to be included in the meta-analysis. The results obtained present trends that suggest significant impacts of BFR training on endothelial functions and angiogenesis. There is still a lack of multicenter randomized clinical trials including many participants, and such studies are necessary to confirm the advantage of BFR over non-BFR activity.

Aerobic Training With Blood Flow Restriction for Endurance Athletes: Potential Benefits and Considerations of Implementation

ABSTRACT

Smith, NDW, Scott, BR, Girard, O, and Peiffer, JJ. Aerobic training with blood flow restriction for endurance athletes: potential benefits and considerations of implementation. J Strength Cond Res 36(12): 3541-3550, 2022-Low-intensity aerobic training with blood flow restriction (BFR) can improve maximal oxygen uptake, delay the onset of blood lactate accumulation, and may provide marginal benefits to economy of motion in untrained individuals. Such a training modality could also improve these physiological attributes in well-trained athletes. Indeed, aerobic BFR training could be beneficial for those recovering from injury, those who have limited time for training a specific physiological capacity, or as an adjunct training stimulus to provide variation in a program. However, similarly to endurance training without BFR, using aerobic BFR training to elicit physiological adaptations in endurance athletes will require additional considerations compared with nonendurance athletes. The objective of this narrative review is to discuss the acute and chronic aspects of aerobic BFR exercise for well-trained endurance athletes and highlight considerations for its effective implementation. This review first highlights key physiological capacities of endurance performance. The acute and chronic responses to aerobic BFR exercise and their impact on performance are then discussed. Finally, considerations for prescribing and monitoring aerobic BFR exercise in trained endurance populations are addressed to challenge current views on how BFR exercise is implemented.

Comparative Perceptual, Affective, and Cardiovascular Responses between Resistance Exercise with and without Blood Flow Restriction in Older Adults

Older adults and patients with chronic disease presenting with muscle weakness or musculoskeletal disorders may benefit from low-load resistance exercise (LLRE) with blood flow restriction (BFR). LLRE-BFR has been shown to increase muscle size, strength, and endurance comparable to traditional resistance exercise but without the use of heavy loads. However, potential negative effects from LLRE-BFR present as a barrier to participation and limit its wider use. This study examined the perceptual, affective, and cardiovascular responses to a bout of LLRE-BFR and compared the responses to LLRE and moderate-load resistance exercise (MLRE). Twenty older adults (64.3 ± 4.2 years) performed LLRE-BFR, LLRE and MLRE consisting of 4 sets of leg press and knee extension, in a randomised crossover design. LLRE-BFR was more demanding than LLRE and MLRE through increased pain (p ≤ 0.024, d = 0.8-1.4) and reduced affect (p ≤ 0.048, d = -0.5--0.9). Despite this, LLRE-BFR was enjoyed and promoted a positive affective response (p ≤ 0.035, d = 0.5-0.9) following exercise comparable to MLRE. This study supports the use of LLRE-BFR for older adults and encourages future research to examine the safety, acceptability, and efficacy of LLRE-BFR in patients with chronic disease.

Low-Load Resistance Exercise with Blood Flow Restriction Increases Hypoxia-Induced Angiogenic Genes Expression

The aim of the study was to determine whether low-load exercise (LL) with blood flow restriction (LL-BFR) would induce similar changes in expression of genes involved in hypoxia and angiogenesis compared to LL and high-load exercise (HL). Twenty-four males (age: 21.3 ± 1.9 years, body height: 1.74 ± 0.8 m, body mass: 73 ± 1.8 kg) were allocated into three groups: low-load exercise (LL), low-load exercise with blood-flow restriction (LL-BFR), and high-load exercise (HL). For the LL-BFR group a pneumatic cuff was inflated at 80% of the arterial occlusion pressure. All participants performed bilateral knee extension exercise, twice a week, for 8 weeks. LL and LL-BFR groups performed 3-4 sets of 15 reps at 20% 1RM, whilst the HL group performed 3-4 sets of 8-10 reps at 80% 1RM with a 60-s rest interval between sets. The hypoxia-inducible factor-1 alpha (HIF-1α) and beta (HIF-1β), vascular endothelial growth factor (VEGF), neuronal (nNOS), and inducible nitric oxide synthase (iNOS) genes expression were assessed before and after training. HIF-1α and HIF-1β mRNA levels significantly increased in the LL-BFR group and exceeded those elicited by HL and LL groups (p < .0001). VEGF gene expression was increased in both LL-BFR and HL groups, however, LL-BFR elicited a greater increase than LL (p < .0001). nNOS and iNOS genes expression significantly increased in all groups with greatest increases being observed in the LL-BFR group (p < .0001). The findings suggest that LL-BFR induces greater increases in genes expression related to hypoxia and angiogenesis than traditional resistance training.

Low- to Moderate-intensity Blood Flow Restricted Walking is not an Acute Equivalent for Unrestricted Jogging in Young Active Adults

This study investigated whether walking with blood flow restriction (BFR) increases acute cardio-respiratory demands to the point that it can be considered an alternative for jogging. Sixteen physically active adults completed five experimental sessions (order randomised), comprising 10 min of treadmill exercise. Two sessions included unrestricted walking, two sessions required walking with BFR cuffs positioned on the lower limbs inflated to 60% of individualised arterial occlusion pressure, and one session was conducted at a jogging pace. Comfortable walking and jogging speeds were calculated during the familiarisation session. Walking speeds were individualised to either 100% (speed: 6.0 ± 0.3km·h^-1[low-intensity]) or 120% (speed: 7.2 ± 0.3km·h^-1[moderate-intensity]) of comfortable walking speed. The jogging session was unrestricted (speed: 9.1 ± 0.7km·h^-1). Initial analysis compared walking conditions across heart rate, left cardiac work index, systolic blood pressure, relative oxygen consumption, minute ventilation, rating of perceived exertion and limb discomfort. Secondary analysis compared the walking session with the highest cardio-respiratory demands to jogging. Initial analysis identified that moderate-intensity with BFR induced the highest cardio-respiratory and perceptual responses compared with any other walking sessions (p < 0.01). Secondary analysis revealed that all cardio-respiratory measures were higher during jogging when compared with moderate-intensity with BFR (p < 0.01), except systolic blood pressure (p = 0.10). All perceptual measures were higher during moderate-intensity with BFR (p < 0.01) compared with jogging. Low- to moderate-intensity BFR-walking produces lower acute cardio-respiratory responses at higher ratings of perceived exertion and discomfort compared with jogging. Overall, BFR-walking does not seem to provide an equivalent exercise modality for unrestricted jogging in physically active adults.

A narrative review of the effects of blood flow restriction on vascular structure and function

Blood flow restriction is growing in popularity as a tool for increasing muscular size and strength. Currently, guidelines exist for using blood flow restriction alone and in combination with endurance and resistance exercise. However, only about 1.3% of practitioners familiar with blood flow restriction applications have utilized it for vascular changes, suggesting many of the guidelines are based on skeletal muscle outcomes. Thus, this narrative review is intended to explore the literature available in which blood flow restriction, or a similar application, assess the changes in vascular structure or function. Based on the literature, there is a knowledge gap in how applying blood flow restriction with relative pressures may alter the vasculature when applied alone, with endurance exercise, and with resistance exercise. In many instances, the application of blood flow restriction was not in accordance with the current guidelines, making it difficult to draw definitive conclusions as to how the vascular system would be affected. Additionally, several studies report no change in vascular structure or function, but few studies look at variables for both outcomes. By examining outcomes for both structure and function, investigators would be able to generate recommendations for the use of blood flow restriction to improve vascular structure and/or function in the future.

Effect of different recovery modes during resistance training with blood flow restriction on hormonal levels and performance in young men: a randomized controlled trial

BACKGROUND

Resistance training with blood flow restriction (BFR) results in hypertrophy, and its magnitude depends on various training variables. This study aimed to compare the long-term effect of passive recovery (PR) and active recovery (AR) during low-intensity resistance training with BFR on hormonal levels and performance in young men.

METHODS

In the randomized clinical trial, 20 men were randomly divided into PR and AR groups during resistance training with BFR. The intervention consisted of six upper and lower body movements with 30% of one maximum repetition (1RM), three sessions per week for six weeks. Both groups wore pneumatic cuffs on the proximal part of thighs and arms. The cuff pressure was 60% of the calculated arterial blood occlusion and increased 10% every two weeks. The AR group performed seven repetitions in 30 s break between sets by one second for concentric and eccentric phases and two seconds rest, and the other group had passive rest. The blood samples and a series of performance tests were gathered before and after the intervention. A repeated measure ANOVA was used to analyze data.

RESULTS

AR and PR interventions significantly improved the C-reactive protein (CRP) (- 38% vs. - 40%), Lactate dehydrogenase (LDH) (- 11% vs. - 3%), Sargent jump (9% vs. 10%), peak power (20% vs.18%), and average power (14% vs. 14%), upper 1RM (8% vs. 8%) and no significant differences were observed between groups. The AR intervention significantly increased growth hormone (GH) (423% vs. 151%, p = 0.03), lower body 1RM (18% vs. 11%) and muscle endurance (34% vs. 22% for the upper body, p = 0.02 and 32% vs. 24% for the lower body, p = 0.04) than the PR group. The PR intervention further increased the minimum power than the AR group (19% vs. 10%). There were no significant changes in testosterone (p = 0.79) and cortisol (p = 0.34) following interventions.

CONCLUSION

The findings indicated that by increasing muscle activation and higher metabolic load, AR during resistance training with BFR might cause more remarkable improvements in serum GH, muscle strength, and endurance. Thus, to gain further benefits, AR during training with BFR is recommended.

TRIAL REGISTRATION

IRCT20191207045644N1. Registration date: 14/03/2020. URL: https://www.irct.ir/search/result?query=IRCT20191207045644N1.

The Role of Plasma Extracellular Vesicles in Remote Ischemic Conditioning and Exercise-Induced Ischemic Tolerance

Ischemic conditioning and exercise have been suggested for protecting against brain ischemia-reperfusion injury. However, the endogenous protective mechanisms stimulated by these interventions remain unclear. Here, in a comprehensive translational study, we investigated the protective role of extracellular vesicles (EVs) released after remote ischemic conditioning (RIC), blood flow restricted resistance exercise (BFRRE), or high-load resistance exercise (HLRE). Blood samples were collected from human participants before and at serial time points after intervention. RIC and BFRRE plasma EVs released early after stimulation improved viability of endothelial cells subjected to oxygen-glucose deprivation. Furthermore, post-RIC EVs accumulated in the ischemic area of a stroke mouse model, and a mean decrease in infarct volume was observed for post-RIC EVs, although not reaching statistical significance. Thus, circulating EVs induced by RIC and BFRRE can mediate protection, but the in vivo and translational effects of conditioned EVs require further experimental verification.

A Useful Blood Flow Restriction Training Risk Stratification for Exercise and Rehabilitation

Blood flow restriction training (BFRT) is a modality with growing interest in the last decade and has been recognized as a critical tool in rehabilitation medicine, athletic and clinical populations. Besides its potential for positive benefits, BFRT has the capability to induce adverse responses. BFRT may evoke increased blood pressure, abnormal cardiovascular responses and impact vascular health. Furthermore, some important concerns with the use of BFRT exists for individuals with established cardiovascular disease (e.g., hypertension, diabetes mellitus, and chronic kidney disease patients). In addition, considering the potential risks of thrombosis promoted by BFRT in medically compromised populations, BFRT use warrants caution for patients that already display impaired blood coagulability, loss of antithrombotic mechanisms in the vessel wall, and stasis caused by immobility (e.g., COVID-19 patients, diabetes mellitus, hypertension, chronic kidney disease, cardiovascular disease, orthopedic post-surgery, anabolic steroid and ergogenic substance users, rheumatoid arthritis, and pregnant/postpartum women). To avoid untoward outcomes and ensure that BFRT is properly used, efficacy endpoints such as a questionnaire for risk stratification involving a review of the patient's medical history, signs, and symptoms indicative of underlying pathology is strongly advised. Here we present a model for BFRT pre-participation screening to theoretically reduce risk by excluding people with comorbidities or medically complex histories that could unnecessarily heighten intra- and/or post-exercise occurrence of adverse events. We propose this risk stratification tool as a framework to allow clinicians to use their knowledge, skills and expertise to assess and manage any risks related to the delivery of an appropriate BFRT exercise program. The questionnaires for risk stratification are adapted to guide clinicians for the referral, assessment, and suggestion of other modalities/approaches if/when necessary. Finally, the risk stratification might serve as a guideline for clinical protocols and future randomized controlled trial studies.

Anterior Segment Optical Coherence Tomography Angiography Following Trabecular Bypass Minimally Invasive Glaucoma Surgery

Objective

To assess anterior segment optical coherence tomography angiography (AS-OCTA) imaging of the episcleral vessels before and after trabecular bypass minimally invasive glaucoma surgery (MIGS).

Design

A prospective, clinical, single-centre, single-arm pilot feasibility study conducted at National University Hospital, Singapore.

Subjects

Patients with primary glaucomatous optic neuropathy undergoing Hydrus Microstent (Ivantis Inc., Irvine, CA, USA) implantation, who require at least one intra-ocular pressure-lowering medication. One or two eyes per patient may be enrolled.

Methods

We performed AS-OCTA (Nidek RS-3000 Advance 2, Gamagori, Japan) pre- and up to 6 months post-MIGS implantation using a standard protocol in all cornealimbal quadrants, to derive episcleral vessel densities (VD) using a previously described technique.

Main Outcome Measures

Episcleral VD pre- and post-surgery, in sectors with and without the implant.

Results

We obtained serial AS-OCTA images in 25 eyes undergoing MIGS implantation (23 subjects, mean age 70.3 ± 1.5, 61% female) with mean preoperative intraocular pressure (IOP) of 15.5 mmHg ± 4.0. We observed reductions in postoperative episcleral VD compared to preoperative VD at month 1 (mean difference −3.2, p = 0.001), month 3 (mean difference −2.94, p = 0.004) and month 6 (mean difference −2.19, p = 0.039) in sectors with implants (overall 6 month follow-up, p = 0.011). No significant changes were detected in episcleral VD in the sectors without implants (p = 0.910).

Conclusion

In our pilot study, AS-OCTA was able to detect changes in the episcleral VD following trabecular bypass MIGS, which may be a useful modality to evaluate surgical outcomes if validated in future studies.

The Effect of Blood Flow Restriction Exercise on Angiogenesis-Related Factors in Skeletal Muscle Among Healthy Adults: A Systematic Review and Meta-Analysis

Background

Blood flow restriction (BFR) exercise may be a potential exercise program to promote angiogenesis. This review aims to compare the effects of exercise with and without BFR on angiogenesis-related factors in skeletal muscle among healthy adults.

Methodology

Searches were made in Web of Science, Scopus, PubMed, and EBSCO databases from January 2001 to June 2021. Studies were screened, quality was evaluated, and data were extracted. The review protocol was registered at PROSPERO (PROSPERO registration number: CRD42021261367). Standardized mean differences (SMD) of vascular endothelial growth factor (VEGF), vascular endothelial growth factor receptor 2 (VEGFR-2), hypoxia inducible factor 1α (HIF-1α), peroxisome proliferator-activated receptorγcoactivator-1α (PGC-1α) and endothelial nitric oxide synthase (eNOS) were analyzed using Revman 5.4 software with a 95% confidence interval (95% CI).

Results

Ten studies fulfilled the inclusion criteria with a total of 75 participants for BFR group and 77 for CON group. BFR exercise elicits greater expression of VEGF (heterogeneity test, P = 0.09, I2 = 44%; SMD, 0.93 [0.38, 1.48], P &lt; 0.05), VEGFR-2 (heterogeneity test, P = 0.81, I2 = 0%; SMD, 0.64 [0.08, 1.21], P &lt; 0.05), HIF-1α (heterogeneity test, P = 0.67, I2 = 0%; SMD, 0.43 [0.03, 0.82], P &lt; 0.05), PGC-1α (heterogeneity test, P = 0.02, I2 = 54%; SMD, 0.74 [0.21, 1.28], P &lt; 0.05) and eNOS (heterogeneity test, P = 0.88, I2 = 0%; SMD, 0.60 [0.04, 1.17], P &lt; 0.05) mRNA than non-BFR exercise. In the sub-group analysis, resistance exercise with BFR elicits greater expression of VEGF (heterogeneity test, P = 0.36, I2 = 6%; SMD, 1.66 [0.97, 2.35], P &lt; 0.05) and HIF-1α (heterogeneity test, P = 0.56, I2 = 0%; SMD, 0.51 [0.01, 1.02], P &lt; 0.05) mRNA than aerobic exercise with BFR.

Conclusion

Exercise with BFR elicited more angiogenesis-related factors mRNA expression than exercise without BFR, but not VEGF and PGC-1α protein expression. Therefore, BFR training may be a potential training program to improve vascular function.

Systematic Review Registration

[https://www.crd.york.ac.uk/prospero/], identifier [CRD42021261367].

Aerobic Adaptations to Resistance Training: The Role of Time under Tension

Generally, skeletal muscle adaptations to exercise are perceived through a dichotomous lens where the metabolic stress imposed by aerobic training leads to increased mitochondrial adaptations while the mechanical tension from resistance training leads to myofibrillar adaptations. However, there is emerging evidence for cross over between modalities where aerobic training stimulates traditional adaptations to resistance training (e.g., hypertrophy) and resistance training stimulates traditional adaptations to aerobic training (e.g., mitochondrial biogenesis). The latter is the focus of the current review in which we propose high-volume resistance training (i.e., high time under tension) leads to aerobic adaptations such as angiogenesis, mitochondrial biogenesis, and increased oxidative capacity. As time under tension increases, skeletal muscle energy turnover, metabolic stress, and ischemia also increase, which act as signals to activate the peroxisome proliferator-activated receptor gamma coactivator 1-alpha, which is the master regulator of mitochondrial biogenesis. For practical application, the acute stress and chronic adaptations to three specific forms of high-time under tension are also discussed: Slow-tempo, low-intensity resistance training, and drop-set resistance training. These modalities of high-time under tension lead to hallmark adaptations to resistance training such as muscle endurance, hypertrophy, and strength, but little is known about their effect on traditional aerobic training adaptations.

Optimization of Exercise Countermeasures to Spaceflight Using Blood Flow Restriction

INTRODUCTION: During spaceflight missions, astronauts work in an extreme environment with several hazards to physical health and performance. Exposure to microgravity results in remarkable deconditioning of several physiological systems, leading to impaired physical condition and human performance, posing a major risk to overall mission success and crew safety. Physical exercise is the cornerstone of strategies to mitigate physical deconditioning during spaceflight. Decades of research have enabled development of more optimal exercise strategies and equipment onboard the International Space Station. However, the effects of microgravity cannot be completely ameliorated with current exercise countermeasures. Moreover, future spaceflight missions deeper into space require a new generation of spacecraft, which will place yet more constraints on the use of exercise by limiting the amount, size, and weight of exercise equipment and the time available for exercise. Space agencies are exploring ways to optimize exercise countermeasures for spaceflight, specifically exercise strategies that are more efficient, require less equipment, and are less time-consuming. Blood flow restriction exercise is a low intensity exercise strategy that requires minimal equipment and can elicit positive training benefits across multiple physiological systems. This method of exercise training has potential as a strategy to optimize exercise countermeasures during spaceflight and reconditioning in terrestrial and partial gravity environments. The possible applications of blood flow restriction exercise during spaceflight are discussed herein.Hughes L, Hackney KJ, Patterson SD. Optimization of exercise countermeasures to spaceflight using blood flow restriction. Aerosp Med Hum Perform. 2021; 93(1):32-45.

Postoperative Use of Blood Flow Restriction in Orthopedics

Blood flow restriction (BFR) therapy is being used more frequently for rehabilitation from orthopedic injuries. Several physiologic mechanisms of action, at local and systemic levels, have been proposed. Numerous studies have investigated the effects of BFR training in healthy athletes; however, limited clinical data exist supporting the use of BFR after surgery. Given that BFR training may facilitate muscle development using low-load resistance exercises, it offers a unique advantage for the post-surgical patient who cannot tolerate traditional high resistance training. [Orthopedics. 2021;44(6):e694-e698.].

Effects of Blood Flow Restriction Training on Blood Perfusion and Work Ability of Muscles in Elite Para-alpine Skiers

Purpose

The effects of short-term blood flow restriction (BFR) exercise on muscle blood flow perfusion and performance during high-intensity exercise were determined in elite para-alpine standing skiers to assess whether this would be an effective training regimen for elite athletes with disabilities.

Methods

Nine national-level para-alpine standing skiers (mean age, 20.67 ± 1.34 yr; four women) were recruited. Nondominant lower limbs were trained with BFR (eight in final analyses), and dominant lower limbs were trained without BFR (seven in final analyses). The 2-wk protocol included high-load resistance, local muscle endurance (circuit resistance training), and aerobic endurance (stationary cycling) training performed 4 times a week, with BFR during local muscle endurance and aerobic endurance sessions. Muscle strength was measured by maximal voluntary isometric contraction (MVIC) in the knee extensors; microcirculatory blood perfusion (MBP), by laser Doppler blood flow; and muscle strength and endurance, by the total amount of work (TW) performed during high-intensity centrifugal and concentric contractions.

Results

BFR significantly increased absolute and relative MVIC (P < 0.001, P = 0.001), MBP (P = 0.011, P = 0.008), and TW (P = 0.006, P = 0.007) from pretraining values, whereas only absolute MVIC increased without BFR (P = 0.047). However, the MVIC increase with BFR exercise (35.88 ± 14.83 N·m) was significantly greater (P = 0.040) than without BFR exercise (16.71 ± 17.79 N·m).

Conclusions

Short-term BFR exercise significantly increased strength endurance, muscle strength, and MBP in national-level para-alpine standing skiers. Our study provides new evidence that BFR exercise can improve local muscle blood perfusion during high-intensity exercise and informs BFR exercise strategies for athletes with disabilities.

Eight weeks of resistance training with blood flow restriction improve cardiac function and vascular endothelial function in healthy young Asian males

Background

Resistance training with blood flow restriction (BFR) is a physiological ischaemic training method. Before it is applied to patients with coronary artery disease, it must be proven safe and effective.

Methods

Twenty-four healthy adult males were randomly assigned to three groups: the resistance training (RT) group, low-pressure BFR and resistance training (LP-RT) group and high-pressure BFR and resistance training (HP-RT) group. The training protocol was 20 times/min/set, with a 2-min break, five sets/day and 5 d/week for 8 weeks. Cardiac function, haemodynamics and vascular endothelial function were evaluated before and after the first training and the last training.

Results

There were no significant differences among groups before and after training. After 8 weeks of training, the resting heart rate (p<0.05) of the three groups significantly decreased (p<0.05). The rate–pressure product in the LP-RT group significantly decreased (p<0.05) compared with before training. Just after the last training, heart rate (p<0.05) and cardiac output (p<0.05) in the LP-RT and HP-RT groups significantly decreased compared with those just after the first training. At the end of the experiment, vascular endothelial growth factor (VEGF; p<0.01), soluble VEGF receptor (VEGFR) (p<0.05) and interleukin-6 (p<0.01) significantly increased, except for soluble VEGFR in the RT group.

Conclusions

Low-intensity resistance training with BFR moderately alters cardiac function. The expression levels of proteins related to vascular endothelial function have significantly changed. Both findings suggest that low-intensity resistance training with BFR may be safely and effectively applied to patients with coronary artery disease.

Blood flow restriction exercise to attenuate postoperative loss of function after total knee replacement: a randomized pilot study

Aging well is directly associated with a healthy lifestyle. The focus of this paper is to relate that attenuation of postoperative loss of muscle function after a total knee arthroplasty (TKA) is an important consideration. Because patients usually do not tolerate standard high-resistance exercise in the preoperative or postoperative period, they often experience a decline in strength and function. Therefore, we tested the feasibility and acceptability of an alternative low-resistance exercise protocol with blood flow restriction (BFR) using a tourniquet in the preoperative period for patients awaiting TKA. We recruited patients undergoing a TKA and randomized six to the BFR exercise for 4 weeks prior to surgery and four to standard of care (no exercise). We measured physical function using the Short Physical Performance Battery (SPPB), the 6-Minute Walk Test (6MWT), leg strength (peak torque), and pain (numerical pain score) 4 to 5 weeks preoperatively and 2 weeks postoperatively. The clinical management, e.g., anesthetic management, did not differ between groups. No complications were observed. Our findings demonstrate the feasibility and acceptability of the BFR intervention. Although preliminary and not powered for comparison, the BFR group demonstrated less decline in SPPB following surgery (−2.2, 95%CI:−4.4,0.1) compared to the no exercise group (−4.8, 95%CI:−7.8,−1.7). No differences were noted for the 6MWT, leg strength, and pain measurements. We conclude that preoperative low-resistance exercise using the BFR is feasible and acceptable, and this test warrants investigation as an intervention to potentially attenuate the postoperative loss of physical function after TKA.

Effects of exercise training with blood flow restriction on vascular function in adults: a systematic review and meta-analysis

Background

Blood flow restricted exercise (BFRE) improves physical fitness, with theorized positive effects on vascular function. This systematic review and meta-analysis aimed to report (1) the effects of BFRE on vascular function in adults with or without chronic health conditions, and (2) adverse events and adherence reported for BFRE.

Methodology

Five electronic databases were searched by two researchers independently to identify studies reporting vascular outcomes following BFRE in adults with and without chronic conditions. When sufficient data were provided, meta-analysis and exploratory meta-regression were performed.

Results

Twenty-six studies were included in the review (total participants n = 472; n = 41 older adults with chronic conditions). Meta-analysis (k = 9 studies) indicated that compared to exercise without blood flow restriction, resistance training with blood flow restriction resulted in significantly greater effects on endothelial function (SMD 0.76; 95% CI [0.36–1.14]). No significant differences were estimated for changes in vascular structure (SMD −0.24; 95% CI [−1.08 to 0.59]). In exploratory meta-regression analyses, several experimental protocol factors (design, exercise modality, exercised limbs, intervention length and number of sets per exercise) were significantly associated with the effect size for endothelial function outcomes. Adverse events in BFRE studies were rarely reported.

Conclusion

There is limited evidence, predominantly available in healthy young adults, on the effect of BFRE on vascular function. Signals pointing to effect of specific dynamic resistance exercise protocols with blood flow restriction (≥4 weeks with exercises for the upper and lower limbs) on endothelial function warrant further investigation.

Molecular Regulation of Skeletal Muscle Growth and Organelle Biosynthesis: Practical Recommendations for Exercise Training

The regulation of skeletal muscle mass and organelle homeostasis is dependent on the capacity of cells to produce proteins and to recycle cytosolic portions. In this investigation, the mechanisms involved in skeletal muscle mass regulation-especially those associated with proteosynthesis and with the production of new organelles-are presented. Thus, the critical roles of mammalian/mechanistic target of rapamycin complex 1 (mTORC1) pathway and its regulators are reviewed. In addition, the importance of ribosome biogenesis, satellite cells involvement, myonuclear accretion, and some major epigenetic modifications related to protein synthesis are discussed. Furthermore, several studies conducted on the topic of exercise training have recognized the central role of both endurance and resistance exercise to reorganize sarcomeric proteins and to improve the capacity of cells to build efficient organelles. The molecular mechanisms underlying these adaptations to exercise training are presented throughout this review and practical recommendations for exercise prescription are provided. A better understanding of the aforementioned cellular pathways is essential for both healthy and sick people to avoid inefficient prescriptions and to improve muscle function with emergent strategies (e.g., hypoxic training). Finally, current limitations in the literature and further perspectives, notably on epigenetic mechanisms, are provided to encourage additional investigations on this topic.

Blood-flow-restricted exercise: Strategies for enhancing muscle adaptation and performance in the endurance-trained athlete

NEW FINDINGS

What is the topic of this review? Blood-flow-restricted (BFR) exercise represents a potential approach to augment the adaptive response to training and improve performance in endurance-trained individuals. What advances does it highlight? When combined with low-load resistance exercise, low- and moderate-intensity endurance exercise and sprint interval exercise, BFR can provide an augmented acute stimulus for angiogenesis and mitochondrial biogenesis. These augmented acute responses can translate into enhanced capillary supply and mitochondrial function, and subsequent endurance-type performance, although this might depend on the nature of the exercise stimulus. There is a requirement to clarify whether BFR training interventions can be used by high-performance endurance athletes within their structured training programme.

ABSTRACT

A key objective of the training programme for an endurance athlete is to optimize the underlying physiological determinants of performance. Training-induced adaptations are governed by physiological and metabolic stressors, which initiate transcriptional and translational signalling cascades to increase the abundance and/or function of proteins to improve physiological function. One important consideration is that training adaptations are reduced as training status increases, which is reflected at the molecular level as a blunting of the acute signalling response to exercise. This review examines blood-flow-restricted (BFR) exercise as a strategy for augmenting exercise-induced stressors and subsequent molecular signalling responses to enhance the physiological characteristics of the endurance athlete. Focus is placed on the processes of capillary growth and mitochondrial biogenesis. Recent evidence supports that BFR exercise presents an intensified training stimulus beyond that of performing the same exercise alone. We suggest that this has the potential to induce enhanced physiological adaptations, including increases in capillary supply and mitochondrial function, which can contribute to an improvement in performance of endurance exercise. There is, however, a lack of consensus regarding the potency of BFR training, which is invariably attributable to the different modes, intensities and durations of exercise and BFR methods. Further studies are needed to confirm its potential in the endurance-trained athlete.

EFFECTS OF BLOOD FLOW RESTRICTION TRAINING ON HANDGRIP STRENGTH AND MUSCULAR VOLUME OF YOUNG WOMEN

Background

High-intensity training methods are generally recommended to increase muscle mass and strength, with training loads of 60-70% 1RM for novice and 80-100% 1RM for advanced individuals. Blood flow restriction training, despite using lower intensities (30-50% 1RM), can provide similar improvements in muscle mass and strength. However, studies commonly investigate the effects of blood flow restriction training in large muscular groups, whereas there are few studies that investigated those effects in smaller muscle groups, such as the muscles involved in grasping (e.g, wrist flexors; finger flexors). Clinically, smaller muscular groups should also be considered in intervention programs, given that repetitive stress, such as repeated strain injuries, affects upper limbs and may lead to chronic pain and incapacity for work. The purpose of the present study was to examine the effects of blood flow restriction training in strength and anthropometric indicators of muscular volume in young women.

Hypothesis

The effect of blood flow restriction training in handgrip strength (HGS) and muscular volume of young women can be similar to traditional training, even with lower loads.

Methods

Twenty-eight university students, 18 to 25 years of age, were randomly assigned into two groups, blood flow restriction training (BFR, n = 14) and traditional training (TRAD, n = 14). The anthropometric measures and maximum handgrip strength (MHGS) test were performed before and after the intervention. The participants did three weekly sessions of dynamic concentric contraction exercises on a dynamometer for four weeks (12 sessions). Each session had a time length of five minutes and the intensity was established from a percentage of MHGS at 30-35% in the first week, 40-45% in the second and 50-55% in third/fourth weeks. Three sets of 15-25 handgrip repetitions were performed until a failure with a 30 seconds rest for BFR training and three sets of 8-12 repetitions with one-minute rest for TRAD training.

Results

A significant increase was found in the arm muscle circumference (20.6 ± 2.2 vs 21.6 ± 1.7cm) and right MHGS (32.7 ± 4.5 vs 34.3 ± 4.1 kgf) and left MHGS (28.0 ± 5.5 vs 30.9 ± 4.1 kgf) for the BFR training, and the left MHGS (27.6 ± 5.0 vs 31.0 ± 6.1 kgf) for the TRAD training.

Conclusion

Dynamometer training with blood flow restriction, performed with low to moderate loads, was more effective than the traditional training in increasing HGS and muscle volume in young women.

Level of evidence

2b.

Resveratrol and exercise combined to treat functional limitations in late life: A pilot randomized controlled trial

PURPOSE

To evaluate the safety and feasibility of combining exercise (EX) and resveratrol to treat older adults with physical function limitations.

METHODS

Three-arm, two-site pilot randomized, controlled trial (RCT) for community-dwelling adults (N = 60), 71.8 ± 6.3 years of age with functional limitations. Participants were randomized to receive either 12 weeks of (1) EX + placebo [EX0], (2) EX + 500 mg/day resveratrol [EX500], or (3) EX + 1000 mg/day resveratrol [EX1000]. EX consisted of two sessions a week for 12 weeks of center-based walking and whole-body resistance training. Safety was assessed through adverse events and feasibility through exercise session and supplement (placebo, or resveratrol) protocol adherence. Outcome measures included a battery of indices of physical function as well as skeletal muscle mitchondrial function. Data were adjusted for age and gender using the Intent-To-Treat approach.

RESULTS

Adverse event frequency and type were similar between groups (n = 8 EX0, n = 12 EX500, and n = 7 EX1000). Overall, 85% of participants met the supplement adherence via pill counts while 82% met the exercise session adherence. Adjusted within group mean differences (95% confidence interval) from week 0 to 12 for gait speed ranged from -0.04 (EX0: -0.1, 0.03) m/s to 0.04 (EX1000: -0.02, 0.11) and the six-minute walk test mean differences were 9.45 (EX0: -9.02, 27.7), 22.9 (EX500: 4.18, 41.6), and 33.1 (EX1000: 13.8, 52.4) meters. Unadjusted mean differences for citrate synthase were -0.80 (EX0: -15.45, 13.84), -1.38 (EX500: -12.16, 9.39), and 7.75 (EX1000: -4.68, 20.18) mU/mg. COX activity mean within group changes ranged from -0.05 (EX0) to 0.06 (EX500) k/s/mg. Additional outcomes are detailed in the text.

CONCLUSION

The pilot RCT indicated that combined EX + resveratrol was safe and feasible for older adults with functional limitations and may improve skeletal muscle mitochondrial function and mobility-related indices of physical function. A larger trial appears warranted and is needed to formally test these hypotheses.

Ischemic Therapy in Musculoskeletal Medicine

BACKGROUND

The competitive environment of athletics has promoted the exploration of any technology application that may offer an edge with performance and recovery from injury. Ischemic therapy is one such technology that has rapidly been incorporated into training rooms and physical therapy clinics worldwide. This therapy modality is reported to increase an athlete's ability to improve muscle mass, strength, and endurance.

PURPOSE

To provide the sports medicine physician with an understanding of the current state of ischemic therapy technology, including treatment specifications, known physiological effects, hypothesized mechanisms, biochemical effects, athletic applications, medical applications, animal models, and future research recommendations.

STUDY DESIGN

Literature review.

METHODS

A computer-based search of the PubMed database was used to perform a comprehensive literature review on musculoskeletal ischemic therapy.

RESULTS

The current research on ischemic therapy is largely composed of case series with varying equipment, methods, and therapy specifications. The publication of case series has value in identifying this technology for future research, but the results of these studies should not be justification for application to athletes without validation of safety and effectiveness.

CONCLUSION

To date, ischemic therapy remains unvalidated, and the mechanism by which it improves muscle performance is not clear.

Potential Implications of Blood Flow Restriction Exercise on Vascular Health: A Brief Review

Blood flow restriction (BFR) exercise (a.k.a. occlusion training) has emerged as a viable surrogate to traditional heavy-load strength rehabilitation training for a broad range of clinical populations including elderly subjects and rehabilitating athletes. A particular benefit of BFR exercise is the lower stress upon the joints as compared to traditional heavy resistance training, with similar gains in muscle strength and size. The application of an inflatable cuff to the proximal portion of the limbs increases the pressure required for venous return, leading to changes in venous compliance and wall tension. However, it is not known if long-term benefits of BFR exercise on muscle strength and size outweigh potential short and long-term complications on vascular health. BFR exercise could lead to clinical deterioration of the vasculature along with sympathetic overactivity and decreased vascular function associated with retrograde shear stress. This raises a fundamental question: Given the concern that excessive restriction could cause injury to endothelial cells and might cause detrimental effects on endothelial function, even in healthy individuals, should we critically re-evaluate the safety of this method for the general population? From this perspective, the purpose of this manuscript is to review the effects of BFR exercise on vascular function, and to provide relevant insights for training practice as well as future directions for research.

Endocrine Mechanisms Connecting Exercise to Brown Adipose Tissue Metabolism: a Human Perspective

PURPOSE OF REVIEW

To summarize the state-of-the-art regarding the exercise-regulated endocrine signals that might modulate brown adipose tissue (BAT) activity and/or white adipose tissue (WAT) browning, or through which BAT communicates with other tissues, in humans.

RECENT FINDINGS

Exercise induces WAT browning in rodents by means of a variety of physiological mechanism. However, whether exercise induces WAT browning in humans is still unknown. Nonetheless, a number of protein hormones and metabolites, whose signaling can influence thermogenic adipocyte's metabolism, are secreted during and/or after exercise in humans from a variety of tissues and organs, such as the skeletal muscle, the adipose tissue, the liver, the adrenal glands, or the cardiac muscle. Overall, it seems plausible to hypothesize that, in humans, exercise secretes an endocrine cocktail that is likely to induce WAT browning, as it does in rodents. However, even if exercise elicits a pro-browning endocrine response, this might result in a negligible effect if blood flow is restricted in thermogenic adipocyte-rich areas during exercise, which is still to be determined. Future studies are needed to fully characterize the exercise-induced secretion (i.e., to determine the effect of the different exercise frequency, intensity, type, time, and volume) of endocrine signaling molecules that might modulate BAT activity and/or WAT browning or through which BAT communicates with other tissues, during exercise. The exercise effect on BAT metabolism and/or WAT browning could be one of the still unknown mechanisms by which exercise exerts beneficial health effects, and it might be pharmacologically mimicked.

The Acute Impact of External Compression on Back Squat Performance in Competitive Athletes

The aim of the present study was to evaluate the effects of external compression with blood flow restriction on power output and bar velocity changes during the back-squat exercise (SQ). The study included 10 judo athletes (age = 28.4 ± 5.8 years; body mass = 81.3 ± 13.1 kg; SQ one-repetition maximum (1-RM) 152 ± 34 kg; training experience 10.7 ± 2.3 years).

METHODS

The experiment was performed following a randomized crossover design, where each participant performed three different exercise protocols: (1) control, without external compression (CONT); (2) intermittent external compression with pressure of 100% arterial occlusion pressure (AOP) (EC-100); and (3) intermittent external compression with pressure of 150% AOP (EC-150). To assess the differences between conditions, the participants performed 3 sets of 3 repetitions of the SQ at 70% 1-RM. The differences in peak power output (PP), mean power output (MP), peak bar velocity (PV), and mean bar velocity (MV) between the three conditions were examined using repeated measures two-way ANOVA.

RESULTS

The post hoc analysis for the main effect of conditions showed a significant increase in PP (p = 0.03), PV (p = 0.02), MP (p = 0.04), and MV (p = 0.03), for the EC-150, compared to the CONT. Furthermore, a statistically significant increase in PP (p = 0.04), PV (p = 0.03), MP (p = 0.02), and MV (p = 0.01) were observed for the EC-150 compared to EC-100. There were no significant changes in PP, PV, MP, and MV, between EC-100 and CONT conditions.

CONCLUSION

The results indicate that the use of extremely high-pressure external compression (150% AOP) during high-loaded (70% 1-RM) lower limb resistance exercise elicits an acute increase in power output and bar velocity.

Skeletal Muscle Microvascular Changes in Response to Short-Term Blood Flow Restricted Training-Exercise-Induced Adaptations and Signs of Perivascular Stress

Aim: Previous reports suggest that low-load muscle exercise performed under blood flow restriction (BFR) may lead to endurance adaptations. However, only few and conflicting results exist on the magnitude and timing of microvascular adaptations, overall indicating a lack of angiogenesis with BFR training. The present study, therefore, aimed to examine the effect of short-term high-frequency BFR training on human skeletal muscle vascularization.

Methods: Participants completed 3 weeks of high-frequency (one to two daily sessions) training consisting of either BFR exercise [(BFRE) n = 10, 22.8 ± 2.3 years; 20% one-repetition maximum (1RM), 100 mmHg] performed to concentric failure or work-matched free-flow exercise [(CON) n = 8, 21.9 ± 3.0 years; 20% 1RM]. Muscle biopsies [vastus lateralis (VL)] were obtained at baseline, 8 days into the intervention, and 3 and 10 days after cessation of the intervention to examine capillary and perivascular adaptations, as well as angiogenesis-related protein signaling and gene expression.

Results: Capillary per myofiber and capillary area (CA) increased 21–24 and 25–34%, respectively, in response to BFRE (P < 0.05–0.01), while capillary density (CD) remained unchanged. Overall, these adaptations led to a consistent elevation (15–16%) in the capillary-to-muscle area ratio following BFRE (P < 0.05–0.01). In addition, evaluation of perivascular properties indicated thickening of the perivascular basal membrane following BFRE. No or only minor changes were observed in CON.

Conclusion: This study is the first to show that short-term high-frequency, low-load BFRE can lead to microvascular adaptations (i.e., capillary neoformation and changes in morphology), which may contribute to the endurance effects previously documented with BFR training. The observation of perivascular membrane thickening suggests that high-frequency BFRE may be associated with significant vascular stress.

Upper-extremity blood flow restriction: the proximal, distal, and contralateral effects-a randomized controlled trial

BACKGROUND

Blood flow restriction (BFR) training with low weight is purported to induce similar physiological changes to high-weight regimens with the benefit of less tissue stress. We hypothesized that low-weight training with BFR would produce increased gains in strength and hypertrophy for muscle groups proximal, distal, and contralateral to tourniquet placement compared with low-weight training alone.

METHODS

In this prospective, randomized controlled trial, healthy subjects were randomized into a 6-week low-weight training program either with or without BFR on 1 extremity. Outcome measures included limb circumference and strength. Comparisons were made between the BFR and non-BFR extremities, BFR and control groups, and non-BFR extremity and control groups.

RESULTS

A total of 24 subjects (14 BFR and 10 control subjects) completed the protocol. Significantly greater gains were observed in dynamometric strength both proximal (shoulder scaption [30% greater], flexion [23%], and abduction [22%]) and distal (grip strength [13%]) to the tourniquet in the BFR limb compared with both the non-BFR extremity and the control group (P < .05). Arm and forearm circumferences significantly increased in the BFR limb compared with the non-BFR limb and control group (P = .01). The non-BFR extremity demonstrated greater grip strength than the control group (9%, P < .01). No adverse events were reported.

CONCLUSION

Low-weight BFR training provided a greater increase in strength and hypertrophy in the upper-extremity proximal and distal muscle groups compared with the control group. The non-BFR extremity showed a significant increase in grip strength compared with the control group, indicating a potential systemic effect.

Blood flow restriction exercise stimulates mobilization of hematopoietic stem/progenitor cells and increases the circulating ACE2 levels in healthy adults

Adult CD34⁺ hematopoietic stem/progenitor cells (HSPC) in the systemic circulation are bone marrow-derived and have the propensity of maintaining cardiovascular health. Activation of angiotensin-converting enzyme-2 (ACE2)-angiotensin-(1-7)-Mas receptor pathway, the vascular protective axis of the renin-angiotensin system (RAS), stimulates vasculogenic functions of HSPCs. In a previous study, exposure to hypoxia increased the expressions of ACE2 and Mas, and stimulated ACE2 shedding. The current study tested if blood flow restriction exercise (BFR)-induced regional hypoxia recapitulates the in vitro observations in healthy adults. Hypoxia was induced by 80% limb occlusion pressure (LOP) via inflation cuff. Muscle oxygen saturation was determined using near-infrared spectroscopy. Peripheral blood was collected 30 min after quiet sitting (control) or after BFR. Lin^-CD45^lowCD34⁺ HSPCs were enumerated by flow cytometry, and ACE and ACE2 activities were determined in plasma and cell lysates and supernatants. Regional hypoxia resulted in muscle oxygen saturation of 17.5% compared with 49.7% in the control condition (P < 0.0001, n = 9). Circulating HSPCs were increased following BFR (834.8 ± 62.1/mL) compared with control (365 ± 59, P < 0.001, n = 7), which was associated with increased stromal-derived factor 1α and vascular endothelial growth factor receptor levels by four- and threefold, respectively (P < 0.001). ACE2 activity was increased in the whole cell lysates of HSPCs, resulting in an ACE2-to-ACE ratio of 11.7 ± 0.5 in BFR vs 9.1 ± 0.9 in control (P < 0.05). Cell supernatants have threefold increase in the ACE2-to-ACE ratio following BFR compared with control (P < 0.001). Collectively, these findings provide strong evidence for the upregulation of ACE2 by acute regional hypoxia in vivo. Hypoxic exercise regimens appear to be promising means of enhancing vascular regenerative capacity.NEW & NOTEWORTHY Although many studies have explored the mechanisms of skeletal muscle growth and adaptation with hypoxia exercise interventions, less attention has been given to the potential for vascular adaptation and regenerative capacity. This study shows for the first time an acute upregulation of the angiotensin-converting enzyme 2 and increase in CD34⁺ vasculogenic cells following an acute bout of blood flow restriction with low-intensity exercise. These rapid changes collectively promote skeletal muscle angiogenesis. Therefore, this study supports the potential of hypoxic exercise interventions with low intensity for vascular and muscle health.

Perioperative Blood Flow Restriction Rehabilitation in Patients Undergoing ACL Reconstruction: A Systematic Review

Background:

Low-load blood flow restriction (BFR) training has attracted attention as a potentially effective method of perioperative clinical rehabilitation for patients undergoing orthopaedic procedures.

Purpose:

To (1) compare the effectiveness of low-load BFR training in conjunction with a standard rehabilitation protocol, pre- and postoperatively, and non-BFR interventions in patients undergoing anterior cruciate ligament reconstruction (ACLR) and (2) evaluate protocols for implementing BFR perioperatively for patients undergoing ACLR.

Study Design:

Systematic review; Level of evidence, 2.

Methods:

A systematic review of the 3 medical literature databases was conducted to identify all level 1 and 2 clinical trials published since 1990 on BFR in patients undergoing ACLR. Patient demographics from included studies were pooled. Outcome data were documented, including muscle strength and size, and perceived pain and exertion. A descriptive analysis of outcomes from BFR and non-BFR interventions was performed.

Results:

A total of 6 studies (154 patients; 66.2% male; mean ± SD age, 24.2 ± 3.68 years) were included. Of these, 2 studies examined low-load BFR as a preoperative intervention, 1 of which observed a significant increase in muscle isometric endurance (P = .014), surface electromyography of the vastus medialis (P < .001), and muscle blood flow to the vastus lateralis at final follow-up (P < .001) as compared with patients undergoing sham BFR. Four studies investigated low-load BFR as a postoperative intervention, and they observed significant benefits in muscle hypertrophy, as measured by cross-sectional area; strength, as measured by extensor torque; and subjective outcomes, as measured by subjective knee pain during session, over traditional low-load resistance training (all P < .05). BFR occlusion periods ranged from 3 to 5 minutes, with rest periods ranging from 45 seconds to 3 minutes.

Conclusion:

This systematic review found evidence on the topic of BFR rehabilitation after ACLR to be sparse and heterogeneous likely because of the relatively recent onset of its popularity. While a few authors have demonstrated the potential strength and hypertrophy benefits of perioperative BFR, future investigations with standardized outcomes, long-term follow-up, and more robust sample sizes are required to draw more definitive conclusions.