Blood flow-restricted exercise in space

Blood flow restriction: The acute effects of body tilting and reduced gravity analogues on limb occlusion pressure

Blood flow restriction (BFR) has been identified as a potential countermeasure to mitigate physiological deconditioning during spaceflight. Guidelines recommend that tourniquet pressure be prescribed relative to limb occlusion pressure (LOP); however, it is unclear whether body tilting or reduced gravity analogues influence LOP. We examined LOP at the leg and arm during supine bedrest and bodyweight suspension (BWS) at 6° head-down tilt (HDT), horizontal (0°), and 9.5° head-up tilt (HUT) positions. Twenty-seven adults (age, 26 ± 5 years; height, 1.75 ± 0.08 m; body mass, 73 ± 12 kg) completed all tilts during bedrest. A subgroup (n = 15) additionally completed the tilts during BWS. In each position, LOP was measured twice in the leg and arm using the Delfi Personalized Tourniquet System after 5 min of rest and again after a further 5 min. The LOP at the leg increased significantly from 6° HDT to 9.5° HUT in bedrest and BWS by 9-15 mmHg (Cohen's d = 0.7-1.0). Leg LOP was significantly higher during BWS at horizontal and 9.5° HUT postures relative to the same angles during bedrest by 8 mmHg (Cohen's d = 0.6). Arm LOP remained unchanged between body tilts and analogues. Intraclass correlation coefficients for LOP measurements taken after an initial and subsequent 5 min rest period in all conditions ranged between 0.91-0.95 (leg) and 0.83-0.96 (arm). It is advised that LOP be measured before the application of a vascular occlusion in the same body tilt/setting to which it is applied to minimize discrepancies between the actual and prescribed tourniquet pressure.

Physiological and perceptual responses to acute arm cranking with blood flow restriction

INTRODUCTION

Lower-body aerobic exercise with blood flow restriction (BFR) offers a unique approach for stimulating improvements in muscular function and aerobic capacity. While there are more than 40 reports documenting acute and chronic responses to lower-body aerobic exercise with BFR, responses to upper-body aerobic exercise with BFR are not clearly established.

PURPOSE

We evaluated acute physiological and perceptual responses to arm cranking with and without BFR.

METHODS

Participants (N = 10) completed 4 arm cranking (6 × 2 min exercise, 1 min recovery) conditions: low-intensity at 40%VO2peak (LI), low-intensity at 40%VO2peak with BFR at 50% of arterial occlusion pressure (BFR50), low-intensity at 40%VO2peak with BFR at 70% of arterial occlusion pressure (BFR70), and high-intensity at 80%VO2peak (HI) while tissue oxygenation, cardiorespiratory, and perceptual responses were assessed.

RESULTS

During exercise, tissue saturation for BFR50 (54 ± 6%), BFR70 (55 ± 6%), and HI (54 ± 8%) decreased compared to LI (61 ± 5%, all P < 0.01) and changes in deoxyhemoglobin for BFR50 (11 ± 4), BFR70 (15 ± 6), and HI (16 ± 10) increased compared to LI (4 ± 2, all P < 0.01). During recovery intervals, tissue saturation for BFR50 and BFR70 decreased further and deoxyhemoglobin for BFR50 and BFR70 increased further (all P < 0.04). Heart rate for BFR70 and HI increased by 9 ± 9 and 50 ± 15b/min, respectively, compared to LI (both P < 0.02). BFR50 (8 ± 2, 1.0 ± 1.0) and BFR70 (10 ± 2, 2.1 ± 1.4) elicited greater arm-specific perceived exertion (6-20 scale) and pain (0-10 scale) compared to LI (7 ± 1, 0.2 ± 0.5, all P < 0.05) and pain for BFR70 did not differ from HI (1.7 ± 1.9).

CONCLUSION

Arm cranking with BFR decreased tissue saturation and increased deoxyhemoglobin without causing excessive cardiorespiratory strain and pain.

Effects of blood flow restriction training on muscle fitness and cardiovascular risk of obese college students

Purpose: The aim of this study was to investigate the effect of blood flow restriction (BFR) combined with low-intensity resistance training (RT) on cardiovascular risk factors in obese individuals. Methods: Twenty-six male obese college students were recruited and randomly assigned to a control group (CON, n = 8), a low-intensity RT group (RT, n = 9), and a combined BFR training and low-intensity RT group (BFRT, n = 9). Results: The subjects in BFRT group showed significant reductions in body fat percentage and waist-to-hip ratio and a significant increase in lean mass and muscle mass; the peak torque, peak power, and endurance ratio of knee extensors and elbow flexors were significantly upregulated; the root mean square (RMS) for the medial femoral muscle, lateral femoral muscle and biceps significantly increased; the diastolic blood pressure (DBP) showed a significant decrease. The BFRT group also showed significant up-regulations in RMS of the difference between the adjacent R-R intervals (RMSSD), high-frequency power (HF) of parasympathetic modulatory capacity, the standard deviation of R-R intervals (SDNN) of overall heart rate variability (HRV) changes and low-frequency power (LF) of predominantly sympathetic activity. In addition, glycated hemoglobin (HbA1C), insulin resistance index (HOMA-IR) and fasting blood glucose (FBG) were all significantly downregulated in BFRT group. In parallel, low-density lipoprotein (LDL-C) significantly reduced while high-density lipoprotein (HDL-C) significantly increased in BFRT group. Conclusion: BFR combined with low-intensity RT training effectively improved body composition index, increased muscle mass, improved neuromuscular activation, enhanced muscle strength and endurance, which in turn improved abnormal glucolipid metabolism and enhanced cardiac autonomic regulation.

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.

Blood Flow Restriction Training for the Intervention of Sarcopenia: Current Stage and Future Perspective

Sarcopenia is a geriatric syndrome that is characterized by a progressive and generalized skeletal muscle disorder and can be associated with many comorbidities, including obesity, diabetes, and fracture. Its definitions, given by the AWGS and EWGSOP, are widely used. Sarcopenia is measured by muscle strength, muscle quantity or mass and physical performance. Currently, the importance and urgency of sarcopenia have grown. The application of blood flow restriction (BFR) training has received increased attention in managing sarcopenia. BFR is accomplished using a pneumatic cuff on the proximal aspect of the exercising limb. Two main methods of exercise, aerobic exercise and resistance exercise, have been applied with BFR in treating sarcopenia. Both methods can increase muscle mass and muscle strength to a certain extent. Intricate mechanisms are involved during BFRT. Currently, the presented mechanisms mainly include responses in the blood vessels and related hormones, such as growth factors, tissue hypoxia-related factors and recruitment of muscle fiber as well as muscle satellite cells. These mechanisms contribute to the positive balance of skeletal muscle synthesis, which in turn mitigates sarcopenia. As a more suited and more effective way of treating sarcopenia and its comorbidities, BFRT can serve as an alternative to traditional exercise for people who have marked physical limitations or even show superior outcomes under low loads. However, the possibility of causing stress or muscle damage must be considered. Cuff size, pressure, training load and other variables can affect the outcome of sarcopenia, which must also be considered. Thoroughly studying these factors can help to better determine an ideal BFRT scheme and better manage sarcopenia and its associated comorbidities. As a well-tolerated and novel form of exercise, BFRT offers more potential in treating sarcopenia and involves deeper insights into the function and regulation of skeletal muscle.

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.

Hemodynamic and Hemostatic Response to Blood Flow Restriction Resistance Exercise in Coronary Artery Disease: A Pilot Randomized Controlled Trial

BACKGROUND

Blood flow-restricted resistance training (BFR-RT) has been proven to be safe and efficacious in healthy older adults, but not in cardiovascular disease.

OBJECTIVE

The aim of this study was to investigate the acute and training induced effects of BFR-RT on hemostatic and hemodynamic responses in patients with coronary artery disease (CAD).

METHODS

Stable patients with CAD were randomized to 8 weeks of BFR-RT (30%-40% 1-repetition maximum unilateral knee extension) combined with aerobic training or aerobic training alone (control group). At baseline and after 4 and 8 weeks, blood samples were taken before and after BFR exercise, whereas hemodynamic parameters were monitored throughout the exercise.

RESULTS

Twenty-four patients (12 per group; mean age, 60 ± 2 years; mostly male [75%]) completed the study. The BFR-RT significantly improved systolic blood pressure (-10 mm Hg; P = .020) and tended to lower diastolic blood pressure (-2 mm Hg; P = .066). In contrast, no posttraining alterations were observed in N-terminal prohormone B-type natriuretic hormone, fibrinogen, and D-dimer values. During BFR exercise, all hemodynamic variables significantly increased after the first and second set, whereas blood pressure immediately lowered after the cuff was released in the third set. Last, significant interaction was only observed for repetitions × intensity (P < .001; partial η2 = 0.908) of diastolic blood pressure at higher exercise intensity (40% 1-repetition maximum).

CONCLUSIONS

The BFR-RT was proven to be safe, with favorable hemodynamic and hemostatic responses in patients with CAD, and can be recommended as an additional exercise modality in cardiac rehabilitation.Trial Registration:ClinicalTrial.gov Identifier: NCT03087292.

DI-5-Cuffs: Lumbar Intervertebral Disc Proteoglycan and Water Content Changes in Humans after Five Days of Dry Immersion to Simulate Microgravity

Most astronauts experience back pain after spaceflight, primarily located in the lumbar region. Intervertebral disc herniations have been observed after real and simulated microgravity. Spinal deconditioning after exposure to microgravity has been described, but the underlying mechanisms are not well understood. The dry immersion (DI) model of microgravity was used with eighteen male volunteers. Half of the participants wore thigh cuffs as a potential countermeasure. The spinal changes and intervertebral disc (IVD) content changes were investigated using magnetic resonance imaging (MRI) analyses with T1-T2 mapping sequences. IVD water content was estimated by the apparent diffusion coefficient (ADC), with proteoglycan content measured using MRI T1-mapping sequences centered in the nucleus pulposus. The use of thigh cuffs had no effect on any of the spinal variables measured. There was significant spinal lengthening for all of the subjects. The ADC and IVD proteoglycan content both increased significantly with DI (7.34 ± 2.23% and 10.09 ± 1.39%, respectively; mean ± standard deviation), p < 0.05). The ADC changes suggest dynamic and rapid water diffusion inside IVDs, linked to gravitational unloading. Further investigation is needed to determine whether similar changes occur in the cervical IVDs. A better understanding of the mechanisms involved in spinal deconditioning with spaceflight would assist in the development of alternative countermeasures to prevent IVD herniation.

Blood Flow Restriction Resistance Exercise Improves Muscle Strength and Hemodynamics, but Not Vascular Function in Coronary Artery Disease Patients: A Pilot Randomized Controlled Trial

Resistance training may be associated with unfavorable cardiovascular responses (such as hemodynamic alterations, anginal symptoms or ventricular arrhythmias). In healthy adults, blood flow-restricted (BFR) resistance training improves muscle strength and hypertrophy improvements at lower loads with minimal systemic cardiovascular adverse responses. The aim of this study was to assess the safety and efficacy of BFR resistance training in patients with coronary artery disease (CAD) compared to usual care. Patients with stable CAD were randomized to either 8 weeks of supervised biweekly BFR resistance training (30-40% 1RM unilateral knee extension) or usual exercise routine. At baseline and after 8 weeks, patients underwent 1-RM knee extension tests, ultrasonographic appraisal of vastus lateralis (VL) muscle diameter and of systemic (brachial artery) flow-mediated dilation, and determination of markers of inflammation (CD40 ligand and tumor necrosis factor alfa), and fasting glucose and insulin levels for homeostatic model assessment (HOMA). A total of 24 patients [12 per group, mean age 60 ± 2 years, 6 (25%) women] were included. No training-related adverse events were recorded. At baseline groups significantly differ in age (mean difference: 8.7 years, p < 0.001), systolic blood pressure (mean difference: 12.17 mmHg, p = 0.024) and in metabolic control [insulin (p = 0.014) and HOMA IR (p = 0.014)]. BFR-resistance training significantly increased muscle strength (1-RM, +8.96 kg, p < 0.001), and decreased systolic blood pressure (-6.77 mmHg; p = 0.030), whereas VL diameter (+0.09 cm, p = 0.096), brachial artery flow-mediated vasodilation (+1.55%; p = 0.079) and insulin sensitivity (HOMA IR change of 1.15, p = 0.079) did not improve significantly. Blood flow restricted resistance training is safe and associated with significant improvements in muscle strength, and may be therefore provided as an additional exercise option to aerobic exercise to improve skeletal muscle functioning in patients with CAD. Clinical Trial Registration: www.ClinicalTrials.gov, identifier: NCT03087292.

Application of Blood Flow Restriction to Optimize Exercise Countermeasures for Human Space Flight

In recent years there has been a strong increase in publications on blood flow restriction (BFR) training. In particular, the fact that this type of training requires only low resistance to induce muscle strength and mass gains, makes BFR training interesting for athletes and scientists alike. For the same reason this type of training is particularly interesting for astronauts working out in space. Lower resistance during training would have the advantage of reducing the risk of strain-induced injuries. Furthermore, strength training with lower resistances would have implications for the equipment required for training under microgravity conditions, as significantly lower resistances have to be provided by the training machines. Even though we are only about to understand the effects of blood flow restriction on exercise types other than low-intensity strength training, the available data indicate that BFR of leg muscles is also able to improve the training effects of walking or running at slow speeds. The underlying mechanisms of BFR-induced functional and structural adaptations are still unclear. An essential aspect seems to be the premature fatigue of Type-I muscle fibers, which requires premature recruitment of Type-II muscle fibers to maintain a given force output. Other theories assume that cell swelling, anabolic hormones, myokines and reactive oxygen species are involved in the mediation of BFR training-related effects. This review article is intended to summarize the main advantages and disadvantages, but also the potential risks of such training for astronauts.

Blood Flow Restriction Resistance Exercise as a Rehabilitation Modality Following Orthopaedic Surgery: A Review of Venous Thromboembolism Risk

Synopsis Restoration of skeletal muscle mass and strength is critical to successful outcomes following orthopaedic surgery. Blood flow restriction (BFR) resistance exercise has emerged as a promising means of augmenting traditional low-intensity physical rehabilitation exercise and has yielded successful outcomes in a wide range of applications. Though BFR is well tolerated and safe for most individuals, patients who have undergone orthopaedic surgery may be an exception, due to their heightened risk for venous thromboembolism (VTE). While the pathogenesis of VTE is multifactorial and specific to the individual, it is commonly described as a combination of blood stasis, endothelial injury, and alterations in the constituents of the blood leading to hypercoagulability. The collective literature suggests that, given the pathogenic mechanisms of VTE, limited use of a wide, partially occluding cuff during resistance exercise should be low risk, and the likelihood that BFR would directly cause a VTE event is remote. Alternatively, it is plausible that BFR may enhance blood flow and promote fibrinolysis. Of greater concern is the individual with pre-existing asymptomatic VTE, which could be dislodged during BFR. However, it is unknown whether the direct risk associated with BFR is greater than the risk accompanying traditional exercise alone. Presently, there are no universally agreed-upon standards indicating which postsurgical orthopaedic patients may perform BFR safely. While excluding all these patients from BFR may be overly cautious, clinicians need to thoroughly screen for VTE signs and symptoms, be cognizant of each patient's risk factors, and use proper equipment and prescription methods prior to initiating BFR. J Orthop Sports Phys Ther 2019;49(1):17-27. Epub 12 Sep 2018. doi:10.2519/jospt.2019.8375.