Invasive Assessment of Hemodynamic, Metabolic and Ionic Consequences During Blood Flow Restriction Training

Arterial and Venous Pressure Dynamics in Blood Flow Restriction Versus Traditional Strength Training

Strength training responses are influenced by sets, repetitions, and mechanical load, whereas Blood Flow Restriction (BFR) training adds the variable of temporarily restricting blood flow via a tourniquet. This has intensified scientific discussions regarding the vascular responses and thereby safety of the BFR method. To address these concerns, we investigated intravascular pressure changes during low-load (LL-RT), low-load with BFR (LL-BFR-RT), and high-load (HL-RT) exercise. Ten healthy men (26.8 ± 4.59 years) performed unilateral biceps curls to failure in a randomized cross-over design: (1) LL-RT (30% 1RM), (2) LL-BFR-RT (30% 1RM, 50% LOP), and (3) HL-RT (75% 1RM). Total workload was significantly higher in LL-RT (692 ± 251 kg) compared to LL-BFR-RT (378 ± 58.7 kg) and HL-RT (327 ± 65.1 kg, p < 0.001). In terms of mean values, LL-BFR-RT resulted in higher diastolic and mean arterial pressures during rest periods between sets compared to other conditions (p ≤ 0.02). Both LL-RT and LL-BFR-RT led to longer durations spent at increased diastolic (above 90 mmHg, LL-RT: ~419 s vs. LL-BFR-RT: ~356 s vs. Hl-RT: ~122 s), systolic (above 140 mmHg, LL-RT: ~437 s vs. LL-BFR-RT: ~336 s vs. HL-RT: ~199 s), and mean arterial pressures (above 107 mmHg, LL-RT: ~451 s vs. LL-BFR-RT: ~384 s vs. HL-RT: ~168 s) compared to HL-RT (p ≤ 0.028). Relative to total exercise time, LL-BFR-RT resulted in higher proportion of time spent at elevated diastolic (above 90 mmHg, LL-RT: ~56.5% vs. LL-BFR-RT: ~68.7% vs. Hl-RT: ~33.5%) and mean arterial pressures (above 107 mmHg, LL-RT: ~60.8% vs. LL-BFR-RT: ~74.0% vs. HL-RT: ~45.7%) compared to HL-RT (p ≤ 0.034). Peripheral venous pressure was significantly higher in LL-BFR-RT compared to other conditions (p < 0.001), with both absolute and relative time spent at higher pressures (above 75 mmHg, LL-RT: ~57.0 s and ~ 9.12% vs. LL-BFR-RT: ~424 s and ~ 81.7% vs. HL-RT: ~36.0 s and ~ 8.99%, p ≤ 0.002). Our results suggest that BFR training performed to failure imposes greater arterial and venous stress in the exercising limb compared to high-load training without BFR, particularly due to prolonged exposure to elevated pressures. Further research is needed to assess the potential risks of elevated local arterial and venous pressure responses by frequent BFR use, particularly in populations with pre-existing medical conditions.

The role of the muscle metaboreflex on cardiovascular responses to submaximal resistance exercise with different pressures and modes of blood flow restriction

This study investigated the role of the muscle metaboreflex on cardiovascular responses to submaximal resistance exercise using different pressures and modes of blood flow restriction. Fifty-three adults completed six visits. The first visit involved a performance test (two sets of unilateral knee extension exercise until task failure at 30% 1RM) with continuous blood flow restriction (80% arterial occlusion pressure). In subsequent visits, participants performed (1) a nonexercise control (Control), 70% of the repetitions completed in the performance test with the cuff inflated to (2) continuously 80% arterial occlusion (LL + 80%), (3) continuously 40% arterial occlusion (LL + 40%), (4) intermittently 80% arterial occlusion during exercise (LL + 80%Int), and (5) 0 mmHg (LL), in a randomized order. Three minutes of post-exercise circulatory occlusion was employed to assess the muscle metaboreflex activation. Blood pressure and heart rate were measured at various time points. The pre-post increase in systolic blood pressure was not greater with LL + 80%Int (p = 0.987) but was greater with LL + 80% and LL + 40% (LL + 80% > LL + 40%, p = 0.005) than LL by 7 [95%CI: 4, 9] and 4 [95%CI; 2, 6] mmHg, respectively. Heart rate increased only with LL + 80% over LL and Control (p < 0.001). The changes in systolic blood pressure (p > 0.468) and heart rate (p > 0.543) did not differ among exercise conditions from immediate post-exercise to the end of the circulatory occlusion. Systolic/diastolic blood pressure returned to a similar level as Control (∼120, ∼70 mmHg, respectively) immediately after the cuff deflation. Continuous blood flow restriction, especially with higher pressure, accentuates muscle metaboreflex activation, resulting in amplified cardiovascular responses to the exercise.

Minimum velocity threshold in response to the free-weight back squat: reliability and validity of different submaximal loading schemes

PURPOSE

To explore if mean concentric velocity (MCV) of the last repetition before set failure differs between free-weight back squat protocols with greater emphasis on metabolic accumulation vs. mechanical loading. The between-set and between-day reliability of terminal MCV obtained with these different loading schemes was also determined.

METHODS

Fifteen healthy male participants (18-30 years) were included. They all were required to exhibit a relative strength ≥ 1.5 times their body mass. MCVs were obtained at one-repetition maximum (1RM) and with two submaximal protocols (metabolic emphasis: three sets of 40%1RM with blood-flow restriction vs. mechanical emphasis: three sets 80%1RM without blood-flow restriction). Participants were instructed to reach maximal intended concentric velocity in each repetition up to failure.

RESULTS

Set failure was achieved at a faster MCV with the metabolic protocol (p < 0.05). The reliability of MCV at failure reached higher values for the metabolic loading scheme. However, while the MCV achieved at failure during the metabolic protocol was systematically higher than the MCV at 1RM (p < 0.05), this was not entirely the case for the mechanical protocol (similar to 1RM MCV during the last sets in both testing days). Finally, the absolute error derived from estimating the MCV at 1RM based on the MCV obtained at set failure with the mechanical protocol was considerably high (≥ 0.05 m/s).

CONCLUSION

This study indicates that MCV obtained at set failure is dependent on the specificity of the physiological demands of exercise. Thus, MCVs obtained at failure with submaximal loads should not be used to estimate 1RM MCV.

Muscle Swelling and Neuromuscular Responses Following Blood Flow Restricted Exercise in Untrained Women

Purpose: There is conflicting evidence related to the prevalence and magnitude of exercise-induced muscle damage (EIMD) following four sets to volitional failure with BFR (BFR-F) or 75 total repetitions with BFR (1 × 30, 3 × 15, BFR-75). The purpose of this investigation was to examine muscle swelling, peak torque, and neuromuscular responses following BFR-75 and BFR-F. Methods: Thirteen untrained women completed unilateral isokinetic (120°s-1) leg extensions concentric-eccentric at 30% of their maximal voluntary isometric contraction (MVIC) using BFR-75 and BFR-F protocols, separated by 15 minutes. Ultrasound was used to assess muscle thickness, cross sectional area, and echo intensity of the rectus femoris and vastus lateralis before, 0-, 24-, 48-, 72-, and 96-hours post-exercise. Peak torque and surface electromyography (sEMG) were recorded during MVICs before, 24-, 48-, 72-, and 96-hours post-exercise to determine sEMG amplitude, frequency, and neuromuscular efficiency. Results: There were no differences between conditions. Collapsed across conditions, muscle thickness and cross-sectional area increased at 0-hours for the rectus femoris (2.5 ± 0.4, 2.8 ± 0.4 cm, 10.6 ± 1.8, 12.1 ± 1.8 cm2, respectively) and vastus lateralis (2.1 ± 0.5, 2.5 ± 0.7 cm; 22.2 ± 3.9, 25.1 ± 4.5 cm2, respectively), but returned to baseline at 24-hours. There were no changes in echo intensity, sEMG amplitude, sEMG frequency, or neuromuscular efficiency. MVIC peak torque increased relative to pre-exercise at 24-, 48-, 72-, and 96-hours (159.9 ± 34.9, 171.4 ± 30.1-179.1 ± 35.6 Nm). Conclusion: These results suggest that BFR-75 and BFR-F did not cause EIMD but caused an acute increase in muscle swelling that returned to baseline 24-hours post-exercise.

The Discrepancy Between External and Internal Load/Intensity during Blood Flow Restriction Exercise: Understanding Blood Flow Restriction Pressure as Modulating Factor

Physical exercise induces acute psychophysiological responses leading to chronic adaptations when the exercise stimulus is applied repeatedly, at sufficient time periods, and with appropriate magnitude. To maximize long-term training adaptations, it is crucial to control and manipulate the external load and the resulting psychophysiological strain. Therefore, scientists have developed a theoretical framework that distinguishes between the physical work performed during exercise (i.e., external load/intensity) and indicators of the body's psychophysiological response (i.e., internal load/intensity). However, the application of blood flow restriction (BFR) during exercise with low external loads/intensities (e.g., ≤ 30% of the one-repetition-maximum, ≤ 50% of maximum oxygen uptake) can induce physiological and perceptual responses, which are commonly associated with high external loads/intensities. This current opinion aimed to emphasize the mismatch between external and internal load/intensity when BFR is applied during exercise. In this regard, there is evidence that BFR can be used to manipulate both external load/intensity (by reducing total work when exercise is performed to exhaustion) and internal load/intensity (by leading to higher physiological and perceptual responses compared to exercise performed with the same external load/intensity without BFR). Furthermore, it is proposed to consider BFR as an additional exercise determinant, given that the amount of BFR pressure can determine not only the internal but also external load/intensity. Finally, terminological recommendations for the use of the proposed terms in the scientific context and for practitioners are given, which should be considered when designing, reporting, discussing, and presenting BFR studies, exercise, and/or training programs.

Indices of exercise induced muscle damage following low load resistance exercise with blood flow restriction in untrained males

BACKGROUND

There is conflicting evidence regarding the presence and magnitude of exercise-induced muscle damage (EIMD) following low-load resistance training with blood flow restriction (LL+BFR), which may be related to the protocol implemented or exercise volume. Therefore, the purpose of this investigation was to examine the effects of a 75 repetition (BFR-75) (1×30, 3×15) and four sets to volitional failure (BFR-4x) protocols on indices of EIMD among untrained men.

METHODS

Twelve males with no history of lower-body resistance training during the previous six months volunteered for this investigation. One leg was randomly assigned to BFR-75, and the other to BFR-4x. Participants performed isokinetic, unilateral, concentric-eccentric, leg extension muscle actions at 30% of maximal strength with BFR. Indices of EIMD (limb circumference, perceived muscle soreness, pain pressure threshold [PPT], passive range of motion, and maximal strength [MVIC]) were recorded before exercise and 0, 24, 48, 72, and 96-hours post-exercise for each protocol.

RESULTS

There were no significant changes (P>0.05) in limb circumference, PPT, passive range of motion, or MVIC. For both BFR-75 and BFR-4x, perceived muscle soreness increased (P<0.001) similarly 24- (2.5±1.7 AU) and 48-hours (1.9±1.7 AU) post-exercise.

CONCLUSIONS

There was an increase in muscle soreness 24-48 hours post-exercise for both conditions, which may be due to metabolic stress, but this did not affect the force-generating capacity of the muscle (MVIC), suggesting minimal EIMD. The conflicting evidence of EIMD following LL+BFR may be related to differences in restriction time or overall exercise time.

Comparison of Metabolic, Ionic, and Electrolyte Responses to Exhaustive Low-Load Strength Training With and Without Blood Flow Restriction and High-Load Resistance Training

Low-load blood-flow-restriction resistance training (LL-BFR-RT) is gaining popularity, but its physiological effects remain unclear. This study aimed to compare LL-BFR-RT with low-load resistance exercise (LL-RT) and high-load resistance exercise (HL-RT) on metabolism, electrolytes, and ions in the lower extremities by invasive catheter measurements, which are crucial for risk assessment. Ten healthy men (27.6 ± 6.4 years) completed three trials of knee-extensor exercises with LL-RT (30% 1RM), LL-BFR-RT (30% 1RM, 50% limb occlusion pressure), and HL-RT (75% 1RM). The exercise protocol consisted of four sets to voluntary muscle failure with 1 min of rest between sets. Blood gas analysis was collected before, during, and after each trial through intravenous catheters at the exercising leg. LL-BFR-RT had lower total workload (1274 ± 237 kg, mean ± SD) compared to LL-RT (1745 ± 604 kg), and HL-RT (1847 ± 367 kg, p < 0.01), with no difference between LL-RT and HL-RT. Pain perception did not differ significantly. Exercise-induced drop in oxygen partial pressure, lactate accumulation and electrolyte shifts (with increased [K+]) occurred during under all conditions (p < 0.001). Creatine kinase and lactate dehydrogenase increased significantly 24- and 48-h postexercise under all three conditions (p < 0.001). This study, using invasive catheter measurements, found no significant differences in metabolic, ionic, and electrolyte responses among LL-BFR-RT, LL-RT, and HL-RT when exercised to voluntary muscular failure. LL-BFR-RT reduced time to failure without specific physiological responses.

Effect of blood flow restriction training on health promotion in middle-aged and elderly women: a systematic review and meta-analysis

Background: Physical activities play an important role in alleviating the aging problem and improving the physical fitness of middle-aged and elderly people. Blood flow restriction (BFR) training, also known as pressure training, has been widely used to improve athletes' performance and rehabilitation, which is a relatively novel exercise method for improving the physical fitness of middle-aged and elderly people. The purpose of this study is to conduct a systematic review and meta-analysis of domestic and foreign randomized controlled trial studies on BFR training for middle-aged and elderly women, further explore the impact of BFR training on health status. Methods: Meta-analysis was performed according to PRISMA standards, and charts were drawn using Review Manager 5.4 and Stata 17 software. In this study, the keywords such as "pressure training", "blood restriction training", "elderly women", "KAATSU", "blood flow restriction training" were used on CNKI, China Science and Technology Journal Database, PubMed, Embase, Web of Science, Cochrane Library, EBSCO, Scopus, and randomized controlled trials were searched in all languages. The search was performed from the establishment of database to 2 January 2024. The results of the combined effect were represented by standard mean differences. Results: Among the 681 literature retrieved, six eligible English articles were included in this meta-analysis. The overall effect test of the combined effect was performed on 10 groups of data, and the results were SMD = -0.18 (95%CI: -0.91 to 0.56; p > 0.05), the maximum dynamic force of 1RM SMD = 0.97 (95%CI: 0.35 to 1.58; p < 0.05), leg compression force SMD = -0.10 (95%CI: -0.78 to 0.57; p > 0.05), heart rate SMD = 0.33 (95%CI: -2.50 to 3.17; p > 0.05), systolic blood pressure (SBP) SMD = -1.44 (95%CI: -2.17 to -0.70; p < 0.05), diastolic blood pressure (DBP) SMD = -0.69 (95%CI: 2.54 to 1.15; p > 0.05). Conclusion: BFR training had a significant effect on the increase of the maximum dynamic force of 1RM and decrease of blood pressure in middle-aged and elderly women, but there was no significant difference found in heart rate and leg compression force. Systematic Review Registration: https://www.crd.york.ac.uk/prospero/, identifier CRD42024491642.

Effects of low-load blood flow restriction on the venous system in comparison to traditional low-load and high-load exercises

Purpose: Blood-Flow-Restriction (BFR) training provides the ability to achieve hypertrophy effects even though only light mechanical loads are applied. However, its impact on venous pressures and function are still unknown. Therefore, the present study investigates the influence of BFR-training on intravascular venous pressure and venous function in comparison to control exercises with low or high mechanical loads. Methods: In a randomized cross-over design, ten healthy men (27.6 ± 6.4 years) underwent three trials of unilateral knee-extensor exercise with three different training protocols, low-load- (LL-RT, 30% of the individual 1-repetition-maximum, 1RM), low-load BFR- (LL-BFR-RT, 30% 1RM, 50% limb occlusion pressure, LOP) and high-load resistance exercise (HL-RT, 75% 1RM). Exercise protocols contain about four sets of knee extension exercise (Range-of-Motion: 0-0-95°), separated by 60 s of rest. Each set was performed until volitional muscle failure. For analysis of changes in intravascular venous pressures and venous function, a venous catheter was placed at the exercising leg before each trial. Whereas venous pressures were recorded throughout the exercise trials, phlebodynamometric investigations were performed before and after each trial. Furthermore, subjective pain perception during and after exercise was accessed by visual analogue scale. One-way ANOVA was used to assess mean differences between training protocols, while two-way repeated-measures ANOVA (rANOVA; time x condition) was performed to compare changes in measures over time among conditions. Data were given as means ± standard deviation (SD). Results: In comparison to the exercise trials without venous occlusion, total workload was significantly lower in the LL-BFR-RT (LL-RT: 1745 ± 604 kg vs LL-BFR-RT: 1274 ± 237 kg vs HL-RT: 1847 ± 367 kg, p = 0.004) without indicating statistical differences in venous pressures during the exercise sets (interaction: p = 0.140) or pain perception (interaction: p = 0.574). Similarly, phlebodynamometric assessment of venous function (e.g. refill-time of the venous system pre-vs. post exercise trials-LL-RT: 29.7 ± 11.0 s vs 25.5 ± 9.6 s, LL-BFR-RT: 26.6 ± 13.0 s vs 27.3 ± 13.8 s, HL-RT: 25.9 ± 10.9 s vs 23.1 ± 8.2 s) revealed no time (p = 0.156), condition effect (p = 0.802) or their interactions (p = 0.382). Conclusion: The present study is the first one describing the acute effects of LL-BFR-RT to muscle failure on venous pressures and function in comparison to a LL- and HL-RT in the lower limbs. In contrast to the existing literature, LL-BFR-RT does not elevate the venous pressures during exercise higher than a comparative exercise without BFR and does not show any adverse effects on venous function after the exercise.

75-repetition versus sets to failure of blood flow restriction exercise on indices of muscle damage in women

ABSTRACTThere is conflicting evidence regarding the prevalence and magnitude of exercise-induced muscle damage (EIMD) following low-load resistance exercise with blood flow restriction (LL + BFR) that may be related to exercise protocols. The purpose of this investigation was to examine the effects of 75-repetition (BFR-75) (1 × 30, 3 × 15) and 4 sets to failure (BFR-4x) protocols on indices of EIMD among untrained women. Thirteen women completed this investigation. One leg was randomly assigned to BFR-75 and the other to BFR-4x. Each leg performed isokinetic, unilateral, concentric-eccentric, leg extension muscle actions at 30% of maximal strength. Indices of EIMD (muscle soreness, range of motion [ROM], limb circumference, pain pressure threshold [PPT], and maximal voluntary isometric contraction [MVIC]) were recorded before exercise, 0-, 24-, 48-, 72-, and 96-hours post-exercise. There were no changes for ROM, circumference, or PPT. Muscle soreness increased similarly in both conditions 0-, 24-, and 48-hours post-exercise and MVIC increased 24-, 48-, 72-, and 96-hours post-exercise. These findings suggested BFR-75 and BFR-4x were not associated with EIMD and elicited similar physiological responses. The increases in muscle soreness may be due to metabolic stress associated with LL + BFR protocols apart from EIMD.

[Blood flow restriction training as a treatment option for lateral elbow tendinopathy-a study presentation]

Blood flow restriction training, developed in 1966 in Japan, is a training modality that utilizes partial arterial and complete venous blood flow occlusion. Combined with low load resistance training, it aims to induce hypertrophy and strength gains. This makes it particularly suitable for people recovering from injury or surgery, for whom the use of high training loads is unfeasible. In this article, the mechanism behind blood flow restriction training and its applicability for the treatment of lateral elbow tendinopathy is explained. An ongoing prospective, randomized, controlled trial on the treatment of lateral elbow tendinopathy is presented.

Neuromuscular Responses to Failure vs Non-Failure During Blood Flow Restriction Training in Untrained Females

Applying blood flow restriction (BFR) during resistance exercise is a potent stimulus of muscular adaption, but there is little direct comparison of its effect on neuromuscular function. The purpose of this investigation was to compare surface electromyography amplitude and frequency responses during a 75 (1 × 30, 3 × 15) repetition bout (BFR-75) of BFR to 4 sets to failure (BFR-F). Twelve women (mean ± SD age = 22 ± 4 years; body mass = 72 ± 14.4 kg; height = 162.1 ± 4.0 cm) volunteered for the investigation. One leg was randomly assigned to complete BFR-75 and the other to BFR-F. Each leg performed isokinetic, unilateral, concentric-eccentric, leg extension at 30% of maximal strength while surface electromyographic (sEMG) data was recorded. More repetitions (p = 0.006) were completed during set 2 for BFR-F (21.2 ± 7.4) than BFR-75 (14.7 ± 1.2), but there were no other between condition differences for set 1 (29.8 ± 0.9 vs 28.9 ± 10.1), set 3 (14.4 ± 1.4 vs 17.1 ± 6.9), or set 4 (14.8 ± 0.9 vs 16.3 ± 7.0). Collapsed across condition, normalized sEMG amplitude increased (p = 0.014, 132.66 ± 14.03% to 208.21 ± 24.82%) across the first three sets of exercise then plateaued, while normalized sEMG frequency decreased (p = 0.342, 103.07 ± 3.89% to 83.73 ± 4.47%) across the first two sets then plateaued. The present findings indicated that BFR-75 and BFR-F elicited similar acute neuromuscular fatigue responses. The plateau in amplitude and frequency suggested that maximal motor unit excitation and metabolic buildup may be maximized after two to three sets of BFR-75 and BFR-F.

Impact of a Six-Week Prehabilitation With Blood-Flow Restriction Training on Pre- and Postoperative Skeletal Muscle Mass and Strength in Patients Receiving Primary Total Knee Arthroplasty

Introduction: Total Knee Arthroplasty (TKA) is one of the most successful interventions in gonarthrosis, however the operation is leading to muscle atrophy and long-term muscular deficits. To enhance rehabilitation after TKA, exercise programs try to improve muscle function preoperatively, called prehabilitation. Blood-Flow-Restriction Exercises (BFRE) is a training method which is characterized by using tourniquets to reduce arterial and occlude venous blood flow simultaneously during the exercise to increase metabolic stress. The present study aimed to evaluate the effects of a 6-week prehabilitation with BFR on pre- and postoperative muscle mass, strength, and quality of life (QoL).

Methods: 30 patients with end-stage gonarthrosis participated in this study. Patients were randomized into one of three groups: 1) Control-Group (CON): Standard clinical approach without prehabilitation. 2) Active-Control-Group (AC): Participation in a prehabilitation with sham-BFR. 3) BFR-Group (BFR): Participation in a prehabilitation with BFR. The prehabilitation protocol consist of a cycling-ergometer-based training performed twice per week over 6 weeks. During exercise, BFR was applied periodically three times per leg with a pressure of 40% of the individual-limb-occlusion-pressure. Measurement time points were six- (baseline), 3-weeks and 5-days before the surgery (Pre-OP), as well as three- and 6-months postoperatively. Outcome measures were muscular strength of the thigh muscles, thigh circumference as well as QoL and functional activity, examined by 6-min walking- and chair rising test.

Results: Both training groups indicated significantly improved leg muscle strength following the prehabilitation period with a superior effect for the BFR-group (BFR: ∼170% vs. AC: ∼91%, p < 0.05). No significant changes in leg strength occurred in the CON (∼3%, p = 0.100). Further, patients in BFR-group indicated significantly improved skeletal muscle mass assessed by femoral circumference following prehabilitation period (∼7%, p < 0.05), while no significant changes occurred in the CON (−1.14%, p = 0.131) and AC-group (∼3%, p = 0.078). At 3-months Post-OP, the CON and BFR-group revealed a significant decrease in femoral circumference compared to the Pre-OP (CON: ∼3%, BFR: ∼4%; p < 0.05), but BFR-group remained above the baseline level (∼3%, p < 0.05). No significant change in femoral circumference was found for AC-group (∼2%, p = 0.078). In addition, the prehabilitation with BFR provided notably improved Knee Injury and Osteoarthritis Outcome Scores (KOOS) especially in pain perception with significant higher effect compared to other groups (CON: −2%, AC: 13%, BFR: 41%; p < 0.05). In long-term rehabilitation after 6-months, all groups showed significantly improved KOOS scores in all dimensions (CON: ∼110%, AC: ∼132%, BFR: ∼225%; p < 0.01), and functional examinations (CON: ∼26%, AC: ∼16%, BFR: ∼53%; p < 0.01).

Conclusion: The present findings show that BFR-prehabilitation induce significant improvements in muscle function and QoL before TKA surgery. In addition, the supporting effect of prehabilitation on postoperative regeneration and QoL should be highlighted, illustrating prolonged beneficial effects of BFR on muscular and functional performance in a “better in, better out”-manner.

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.

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.