Clinical safety of blood flow-restricted training? A comprehensive review of altered muscle metaboreflex in cardiovascular disease during ischemic exercise

Lower limb blood flow occlusion increases systemic pressor response without increasing brachial arterial blood flow redistribution in women

This study was conducted to investigate the systemic hemodynamic and vascular changes in women during and after two commonly used clinical blood flow restriction (BFR) pressures at rest. There are minimal data regarding the independent effects of BFR on hemodynamic and systemic vascular changes due to pressor response, particularly among women. Therefore, this study investigated BFR-induced alterations in pressor response and systemic flow redistribution at rest during two commonly used pressures (50% and 80% limb occlusion pressure [LOP]). Fifteen women (22.1 ± 4.2 years) completed two randomised sessions involving 8-min of bilateral, lower limb restriction at 50% or 80% LOP followed by 8-min of recovery post-deflation. Changes in vascular (arterial diameter [DIA], time-averaged mean velocity [TAMV], volume flow [VF], and area) and hemodynamic (heart rate [HR] and blood pressure) measures over time (pre-, during, post-occlusion) and by session (50% vs. 80% LOP) were tested using repeated measures analysis of variance. Repeated measures correlations (rrm) quantified common intraindividual associations between BFR-induced hemodynamic and vascular responses. HR increased from baseline during 50% LOP and remained elevated during recovery (p < 0.05). HR increased from baseline during 80% LOP, while tibial VF and TAMV decreased (p < 0.03 for all). HR and TAMV values returned to baseline during recovery, while brachial artery VF decreased (p < 0.05). Changes in HR, brachial VF, and brachial TAMV were similar between 50% and 80% LOP (rrm = 0.32-0.70, p < 0.05 for all). At 80% LOP, changes in HR were positively correlated with brachial VF (rrm = 0.38) and TAMV (rrm = 0.43) and negatively correlated with tibial VF (rrm = -0.36) and TAMV (rrm = -0.30) (p < 0.05 for all). Results suggest that BFR at 80% LOP elicits an acute systemic pressor reflex without concomitant increases in brachial arterial flow, while 50% LOP elicits a subdued response.

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 Resistance Training on Autonomic and Endothelial Function in Persons with Parkinson's Disease

Background

Autonomic dysfunction precedes endothelial dysfunction in Parkinson's disease (PD) and causes blood pressure and circulation abnormalities that are highly disruptive to one's quality of life. While exercise interventions have proven helpful for motor symptoms of PD, improving associated non-motor symptoms is limited. Low-intensity resistance training with blood flow restriction (LIRT-BFR) improves autonomic dysfunction in non-PD patients and high-intensity resistance training (HIRT) is recommended for motor symptom improvements for people with PD (PwPD).

Objective

To determine the effects of LIRT-BFR and HIRT on homocysteine and autonomic and endothelial function in PwPD and to determine the hemodynamic loads during LIRT-BFR and HIRT in PwPD using a novel exercise protocol.

Methods

Thirty-eight PwPD were assigned LIRT-BFR, HIRT or to a control (CNTRL) group. The LIRT-BFR and HIRT groups exercised three days per week for four weeks. The LIRT-BFR protocol used 60% limb occlusion pressure (LOP) and performed three sets of 20 repetitions at 20% of the one-repetition maximum (1RM). The HIRT group performed three sets of eight repetitions at 80% 1RM. The CNTRL group was asked to continue their normal daily routines.

Results

LIRT-BFR significantly improved orthostatic hypotension (p = 0.026), homocysteine levels (p < 0.001), peripheral circulation (p = 0.003), supine blood pressure (p = 0.028) and heart rate variability (p = 0.041); LIRT-BFR improved homocysteine levels (p < 0.018), peripheral circulation (p = 0.005), supine blood pressure (p = 0.007) and heart rate variability (p = 0.047) more than HIRT; and hemodynamic loads for LIRT-BFR and HIRT were similar.

Conclusions

LIRT-BFR may be more effective than HIRT for autonomic and endothelial function improvements in PwPD and hemodynamic loads may be lessened in LIRT-BFR protocols using single-joint exercises with intermittent blood flow restriction. Further research is needed to determine if non-motor symptoms improve over time and if results are sustainable.

Effects of 7-day quercetin intervention on motor unit activity and muscle contractile properties before and after resistance exercise in young adults randomized controlled trials

We investigated whether the alteration of the motor unit recruitment threshold (MURT) caused by quercetin ingestion intervention for 7 days modifies motor unit activation patterns before and after a single session of resistance exercise. Twenty young male and female adults were divided into two groups: ingestion of placebo (PLA) or quercetin glycosides at 200 mg/day (QUE). High-density surface electromyography during submaximal contractions was measured to assess the motor unit firing rate (MUFR) and MURT of the vastus lateralis muscle before (PRE) and after (POST) resistance exercise (DAY1). The same measurements were repeated after 7 days of placebo or quercetin glycoside ingestion (DAY8). In QUE, MURT decreased more from DAY1-PRE to DAY8-PRE (29.1 ± 9.1 to 27.1 ± 9.5% MVC, p < 0.001) but not in PLA (29.8 ± 10.4 to 28.9 ± 9.7% MVC, p < 0.167). For percentage change in MUFR following resistance exercise, there was a significant interaction (day × group, p < 0.001). The degree of changes in MURT from DAY1-PRE to DAY8-PRE was significantly correlated with the percentage change of MUFR from DAY8-PRE to DAY8-POST in QUE (p = 0.014, r = -0.363) but not in PLA (p = 0.518). The study suggests that 7-day quercetin ingestion alters the motor unit recruitment pattern, and this may induce changes in motor unit firing patterns during a single session of resistance training (Trial registration: UMIN000052255, R000059650).

Autoregulated and Non-Autoregulated Blood Flow Restriction on Acute Arterial Stiffness

This study aimed to investigate the acute effects of autoregulated and non-autoregulated applied pressures during blood flow restriction resistance exercise to volitional fatigue on indices of arterial stiffness using the Delfi Personalized Tourniquet System. Following a randomized autoregulated or non-autoregulated blood flow restriction familiarization session, 20 physically active adults (23±5 years; 7 females) participated in three randomized treatment-order sessions with autoregulated and non-autoregulated and no blood flow restriction training. Participants performed four sets of dumbbell wall squats to failure using 20% of one repetition maximum. Blood flow restriction was performed with 60% of supine limb occlusion pressure. Testing before and post-session included an ultrasonic scan of the carotid artery, applanation tonometry, and blood pressure acquisition.Carotid-femoral pulse wave velocity increased in the non-autoregulated and no blood flow restriction training groups following exercise while carotid-radial pulse wave velocity increased in the no blood flow restriction training group (all p<0.05). Carotid-femoral pulse wave velocity exhibited an interaction effect between autoregulated and non-autoregulated blood flow restriction in favor of autoregulated blood flow restriction (p<0.05). Autoregulated blood flow restriction training does not influence indices of arterial stiffness while non-autoregulated and no blood flow restriction training increases central stiffness.

Changes in Arterial Stiffness in Response to Blood Flow Restriction Resistance Training: A Narrative Review

Arterial stiffness naturally increases with age and is a known predictor of cardiovascular morbimortality. Blood flow restriction (BFR) training involves decreasing muscle blood flow by applying a strap or a pneumatic cuff during exercise. BFR induces muscle hypertrophy even at low intensities, making it an appealing option for older, untrained individuals. However, BFR use in patients with cardiovascular comorbidities is limited by the increased pressor and chronotropic response observed in hypertensive elderly patients. Furthermore, the impact of BFR on vascular function remains unclear. We conducted a comprehensive literature review according to PRISMA guidelines, summarizing available data on the acute and long-term consequences of BFR training on vascular function. Although evidence is still scarce, it seems that BFR has a mild or neutral long-term impact on arterial stiffness. However, current research shows that BFR can cause an abrupt, albeit transient, increase in PWV and central blood pressure. BFR and, preferably, lower-body BFR, should be prescribed with caution in older populations, especially in hypertensive patients who have an exacerbated muscle metaboreflex pressor response. Longer follow-up studies are required to assess the chronic effect of BFR training on arterial stiffness, especially in elderly patients who are usually unable to tolerate high-intensity resistance exercises.

Mechanosensitive channels in the mechanical component of the exercise pressor reflex

The cardiovascular response is appropriately regulated during exercise to meet the metabolic demands of the active muscles. The exercise pressor reflex is a neural feedback mechanism through thin-fiber muscle afferents activated by mechanical and metabolic stimuli in the active skeletal muscles. The mechanical component of this reflex is referred to as skeletal muscle mechanoreflex. Its initial step requires mechanotransduction mediated by mechanosensors, which convert mechanical stimuli into biological signals. Recently, various mechanosensors have been identified, and their contributions to muscle mechanoreflex have been actively investigated. Nevertheless, the mechanosensitive channels responsible for this muscular reflex remain largely unknown. This review discusses progress in our understanding of muscle mechanoreflex under healthy conditions, focusing on mechanosensitive channels.

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.

Blood flow restriction as a potential therapy to restore physical function following COVID-19 infection

Accumulating evidence indicates that some COVID-19 survivors display reduced muscle mass, muscle strength, and aerobic capacity, which contribute to impairments in physical function that can persist for months after the acute phase of illness. Accordingly, strategies to restore muscle mass, muscle strength, and aerobic capacity following infection are critical to mitigate the long-term consequences of COVID-19. Blood flow restriction (BFR), which involves the application of mechanical compression to the limbs, presents a promising therapy that could be utilized throughout different phases of COVID-19 illness. Specifically, we hypothesize that: 1) use of passive BFR modalities can mitigate losses of muscle mass and muscle strength that occur during acute infection and 2) exercise with BFR can serve as an effective alternative to high-intensity exercise without BFR for regaining muscle mass, muscle strength, and aerobic capacity during convalescence. The various applications of BFR may also serve as a targeted therapy to address the underlying pathophysiology of COVID-19 and provide benefits to the musculoskeletal system as well as other organ systems affected by the disease. Consequently, we present a theoretical framework with which BFR could be implemented throughout the progression from acute illness to outpatient rehabilitation with the goal of improving short- and long-term outcomes in COVID-19 survivors. We envision that this paper will encourage discussion and consideration among researchers and clinicians of the potential therapeutic benefits of BFR to treat not only COVID-19 but similar pathologies and cases of acute critical illness.

Cardiovascular Responses During Light-intensity Aerobic Exercise with Varying Levels of Limb Occlusion Pressures

The study aimed to assess cardiovascular responses to low-intensity aerobic exercise with varying levels of limb occlusion pressures (LOP) in a healthy population of men and women 30 to 60 years. The study was a single-session repeated measures design. Thirty individuals completed the study. All subjects participated in a single bout of low-intensity cycling (30-39% HRR) with bilateral lower extremity (LE) BFR for four 5-minute stages [0% (No BFR), 40%, 60%, and 80% LOP] with a 2-minute active rest between stages (BFR pressure released). The subjects' systolic blood pressure (SBP), diastolic blood pressure (DBP), mean arterial pressure (MAP), heart rate (HR), oxygen saturation (SpO2), and ratings of perceived exertion (RPE) were measured at rest, peak, immediately post, post-15 minutes, and post-30 minutes. Peak SBP (no BFR 160.7 ±19.1 mmHg; 40% LOP 173.6 ± 18.7 mmHg; 60 % LOP; 182.5 ± 21.1 mmHg; 80% LOP 193.5± 23.3 mmHg ; p<0.001; η P 2 = .747 ), DBP (no BFR 74.9 ± 8.5 mmHg; 40% LOP (83.0 ± 9.0 mmHg;60 % LOP 90.4 ± 8.7 mmHg; 80% LOP 97.7 ± 9.5 mmHg ;p<0.001; η P 2 = .924 ), MAP (no BFR 103.5 ± 10.1 mmHg; 40% LOP 113.2 ± 10.5 mmHg; 60% LOP 121.1 ± 11.7 mmHg; 80% LOP 129.7 ± 12.9 mmHg; p<0.001; η P 2 = .960 ), and RPE (No BFR 10.0 ± 2.0; 40 % LOP 11.5 ± 2.3; 60% LOP 13.2 ± 2.6; 80% LOP 14.5 ± 3.; p<0.001; η P 2 = .826 ) were significantly higher with each progressing stage. The results indicate that low-intensity cycling with bilateral LE BFR for each LOP stage resulted in elevated SBP, DBP, MAP, and RPE despite maintaining a fixed HR.

Effects of Sex and Cuff Pressure on Physiological Responses during Blood Flow Restriction Resistance Exercise in Young Adults

PURPOSE

The purpose of this study was to examine the physiological responses resulting from an acute blood flow restriction resistance exercise bout with two different cuff pressures in young, healthy men and women.

METHODS

Thirty adults (18-30 yr) completed a bilateral leg extension blood flow restriction bout consisting of four sets (30-15-15-15 repetitions), with cuffs applied at pressures corresponding to 40% and 60% of the minimum arterial occlusion pressure (AOP) needed to completely collapse the femoral arteries. During each of these conditions (40% and 60% AOP), physiological measures of near-infrared spectroscopy (NIRS) and EMG amplitude (EMG AMP) were collected from the dominant or nondominant vastus lateralis. After each set, ratings of perceived exertion (RPE) were collected, whereas only at baseline and at the end of the bout, mean arterial pressure (MAP) was assessed. Separate mixed-factorial ANOVA models were used to examine mean differences in the change in EMG AMP and NIRS parameters during each set. The absolute RPE and MAP values were also examined with separate ANOVAs. A P value ≤0.05 was considered statistically significant.

RESULTS

Regardless of sex or cuff pressure, the change in EMG AMP was lower in set 1 (14.8%) compared with the remaining sets (22.6%-27.0%). The 40% AOP condition elicited the greatest changes in oxy[heme] and deoxy[heme], while also providing lower RPEs. For MAP, there was an effect for time such that MAP increased from preexercise (87.5 ± 4.3 mm Hg) to postexercise (104.5 ± 4.1 mm Hg).

CONCLUSIONS

The major findings suggested that the 40% AOP condition permitted the greatest amount of recovery during the interset rest. In addition, there did not seem to be any meaningful sex-related difference in this sample of young healthy adults.

Acute cardiovascular responses to unilateral bicep curls with blood flow restriction

A consensus on the acute cardiovascular responses to low intensity (LI) resistance exercise (RE) combined with blood flow restriction (BFR) has not yet been reached. This study was designed to compare acute cardiovascular responses to a single bout of LIRE, high intensity (HI) RE, and LIRE with BFR in physically active young males. Participants completed 3 RE sessions in random order, where each session consists of 4 sets of unilateral dumbbell bicep curls. Cardiovascular hemodynamics were measured at baseline and right after each set of RE. Aortic augmentation index (AIx) was significantly higher after set 2,3,4 of RE in LI + BFR session compared to LI session (P < 0.05). Brachial systolic blood pressure (SBP), heart rate (HR), brachial rate pressure product (RPP), and central RPP responses did not differ between LI and LI + BFR sessions (P > 0.05). HI session had a higher central SBP, brachial RPP, central RPP, and aortic AIx compared to LI session after each set of RE (P < 0.05), but not brachial SBP (P > 0.05). Taken together, this study showed that LIRE combined with BFR acutely augmented aortic stiffness, as also observed in HI session, but myocardial oxygen consumption was only higher in HI session when compared to LI session. Thus, although BFR did not exaggerate cardiovascular responses nor cause extra myocardial oxygen consumption, it should be prescribed with caution when control of acute aortic stiffening is necessary during RE.

Application and progress of blood flow restriction training in improving muscle mass and strength in the elderly

As an emerging training method, blood flow restriction training has been proved to promote the growth of muscle mass and strength. In recent years, it has been gradually applied in different populations. However, there are few studies on how blood flow restriction training affects muscle mass and strength in the elderly. The relevant literature is compiled and summarized in this study. Through the comparison of blood flow restriction training with traditional training methods and its application in the elderly, it shows that blood flow restriction training can effectively increase muscle mass and strength, prevent muscle atrophy, improve cardiopulmonary function, facilitate injury and postoperative rehabilitation, and intervene in related degenerative diseases as a training method suitable for the elderly,. The main mechanism of blood flow restriction training promoting muscle mass and strength growth is metabolic stress response, including muscle fiber recruitment, protein synthesis signal pathway activation, hormone secretion, etc., and is also related to cell swelling caused by pressure. At present, although the application of blood flow restriction training in the elderly population is increasing, there is a lack of personalized programs. In the future, more research on the dose effect and safety of blood flow restriction training is needed to develop more accurate personalized training programs.

Blood flow restriction accelerates aerobic training-induced adaptation of [Formula: see text] kinetics at the onset of moderate-intensity exercise

It is unclear whether blood flow restriction (BFR) accelerates the adaptation of the time constant (τ) of phase II oxygen uptake ([Formula: see text]) kinetics in the moderate-intensity exercise domain via moderate-intensity aerobic training. Therefore, healthy participants underwent moderate-intensity [45-60% [Formula: see text] Reserve] aerobic cycle training with or without BFR (BFR group, n = 9; CON group, n = 9) for 8 weeks to evaluate [Formula: see text] kinetics during moderate-intensity cycle exercise before (Pre) and after 4 (Mid) and 8 (Post) weeks of training. Both groups trained for 30 min, 3 days weekly. BFR was performed for 5 min every 10 min by applying cuffs to the upper thighs. The τ significantly decreased by Mid in the BFR group (23.7 ± 2.9 s [Pre], 15.3 ± 1.8 s [Mid], 15.5 ± 1.4 s [Post], P < 0.01) and by Post in the CON group (27.5 ± 2.0 s [Pre], 22.1 ± 0.7 s [Mid], 18.5 ± 1.9 s [Post], P < 0.01). Notably, the BFR group's τ was significantly lower than that of the CON group at Mid (P < 0.01) but not at Post. In conclusion, BFR accelerates the adaptation of the [Formula: see text] kinetics of phase II by moderate-intensity aerobic training.

Blood flow restriction added to usual care exercise in patients with early weight bearing restrictions after cartilage or meniscus repair in the knee joint: a feasibility study

PURPOSE

Blood flow restriction - low load strength training (BFR-LLST) is theoretically superior to traditional heavy strength training when rehabilitating patients who cannot heavily load tissues following surgery. The main purpose of this study was to examine the feasibility of BFR-LLST added to usual care exercise early after cartilage or meniscus repair in the knee joint.

METHODS

We included 42 patients with cartilage (n = 21) or meniscus repair (n = 21) of the knee joint. They attended 9 weeks of BFR-LLST added to a usual care exercise program at an outpatient rehabilitation center. Outcome measures were assessed at different time points from four (baseline) to 26 weeks postoperatively and included adherence, harms, knee joint and thigh pain, perceived exertion, thigh circumference (muscle size proxy), isometric knee-extension strength, self-reported disability and quality of life.

RESULTS

On average, patients with cartilage or meniscus repair completed > 84% of the total BFR-LLST supervised sessions. Thirty-eight patients reported 146 adverse events of which none were considered serious. No decrease in thigh circumference or exacerbation of knee joint or quadriceps muscle pain of the operated leg was found in either group during the intervention period.

CONCLUSIONS

BFR-LLST added to usual care exercise initiated early after cartilage or meniscus repair seems feasible and may prevent disuse thigh muscle atrophy during a period of weight bearing restrictions. Harms were reported, but no serious adverse events were found. Our findings are promising but need replication using a RCT-design.

TRIAL REGISTRATION

NCT03371901 , preprint (open access):  https://www.medrxiv.org/content/10.1101/2022.03.31.22272398v1.

Resistance Training with Blood Flow Restriction and Ocular Health: A Brief Review

Despite the many health benefits of resistance training, it has been suggested that high-intensity resistance exercise is associated with acute increases in intraocular pressure which is a significant risk factor for the development of glaucomatous optic nerve damage. Therefore, resistance training using a variety of forms (e.g., resistance bands, free weights, weight machines, and bodyweight) may be harmful to patients with or at risk of glaucoma. An appropriate solution for such people may involve the combination of resistance training and blood flow restriction (BFR). During the last decade, the BFR (a.k.a. occlusion or KAATSU training) method has drawn great interest among health and sports professionals because of the possibility for individuals to improve various areas of fitness and performance at lower exercise intensities. In comparison to studies evaluating the efficiency of BFR in terms of physical performance and body composition changes, there is still a paucity of empirical studies concerning safety, especially regarding ocular health. Although the use of BFR during resistance training seems feasible for glaucoma patients or those at risk of glaucoma, some issues must be investigated and resolved. Therefore, this review provides an overview of the available scientific data describing the influence of resistance training combined with BFR on ocular physiology and points to further directions of research.

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.

Potential implications of blood flow restriction exercise on patients with chronic kidney disease: a brief review

Combining blood flow restriction (BFR) with exercise is considered a relevant, helpful method in load-compromised individuals and a viable replacement for traditional heavy-load strength training. BFR exercise may be particularly useful for those unable to withstand high mechanical stresses on joints resulting in skeletal muscle dysfunction, such as patients with chronic kidney disease (CKD). Current literature suggests that BFR training displays similar positive health benefits to exercise training alone for CKD patients, including maintenance of muscle strength, glomerular filtration rate maintenance, uremic parameters, inflammatory profile, redox status, glucose homeostasis, blood pressure adjustments, and low adverse reports. In this review of nine studies in CKD patients, we clarify the potential safety and health effects of exercise training with BFR compared to exercise training alone and recommend insights for future research and practical use. Furthermore, we introduce relevant gaps in this emerging field, providing substantial guidance, critical discussion, and valuable preliminary conclusions in this demographic of patients. However, based on the limited studies in this area, more research is necessary to determine the optimal BFR exercise programming.

Arterial Baroreflex Inhibits Muscle Metaboreflex Induced Increases in Effective Arterial Elastance: Implications for Ventricular-Vascular Coupling

The ventricular-vascular relationship assesses the efficacy of energy transferred from the left ventricle to the systemic circulation and is quantified as the ratio of effective arterial elastance to maximal left ventricular elastance. This relationship is maintained during exercise via reflex increases in cardiovascular performance raising both arterial and ventricular elastance in parallel. These changes are, in part, due to reflexes engendered by activation of metabosensitive skeletal muscle afferents-termed the muscle metaboreflex. However, in heart failure, ventricular-vascular uncoupling is apparent and muscle metaboreflex activation worsens this relationship through enhanced systemic vasoconstriction markedly increasing effective arterial elastance which is unaccompanied by substantial increases in ventricular function. This enhanced arterial vasoconstriction is, in part, due to significant reductions in cardiac performance induced by heart failure causing over-stimulation of the metaboreflex due to under perfusion of active skeletal muscle, but also as a result of reduced baroreflex buffering of the muscle metaboreflex-induced peripheral sympatho-activation. To what extent the arterial baroreflex modifies the metaboreflex-induced changes in effective arterial elastance is unknown. We investigated in chronically instrumented conscious canines if removal of baroreflex input via sino-aortic baroreceptor denervation (SAD) would significantly enhance effective arterial elastance in normal animals and whether this would be amplified after induction of heart failure. We observed that effective arterial elastance (E_a), was significantly increased during muscle metaboreflex activation after SAD (0.4 ± 0.1 mmHg/mL to 1.4 ± 0.3 mmHg/mL). In heart failure, metaboreflex activation caused exaggerated increases in E_a and in this setting, SAD significantly increased the rise in E_a elicited by muscle metaboreflex activation (1.3 ± 0.3 mmHg/mL to 2.3 ± 0.3 mmHg/mL). Thus, we conclude that the arterial baroreflex does buffer muscle metaboreflex induced increases in E_a and this buffering likely has effects on the ventricular-vascular coupling.

The Effect of a Single Bout of Resistance Exercise with Blood Flow Restriction on Arterial Stiffness in Older People with Slow Gait Speed: A Pilot Randomized Study

Purpose: Low-intensity resistance exercise with moderate blood-flow restriction (LIRE-BFR) is a new trending form of exercises worldwide. The purpose of this study was to compare the acute effect of a single bout of traditional resistance exercise (TRE) and LIRE-BFR on arterial stiffness in older people with slow gait speeds. Methods: This was a randomized, controlled clinical study. Seventeen older adults (3 men; 14 women; 82 ± 5 years old) completed a session of TRE (n = 7) or LIRE-BFR (n = 10). At baseline and after 60 min post-exercise, participants were subject to blood pressure measurement, heart rate measurements and a determination of arterial stiffness parameters. Results: There was no significant difference between the TRE and LIRE-BFR group at baseline. Pulse-wave velocity increased in both groups (p < 0.05) post-exercise with no between-group differences. Both exercise modalities did not produce any adverse events. The increase in systolic blood pressure, pulse pressure, augmentation pressure and pulse wave velocity (all p > 0.05) were similar after both TRE and LIRE-BFR. Conclusion: TRE and LIRE-BFR had similar responses regarding hemodynamic parameters and pulse-wave velocity in older people with slow gait speed. Long-term studies should assess the cardiovascular risk and safety of LIRE-BFR training in this population.

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.

Title: Blood flow restricted exercise training: Perspectives of people with chronic obstructive pulmonary disease and health professionals

Objective

This descriptive qualitative study explored perspectives of people with chronic obstructive pulmonary disease (COPD) and health professionals concerning blood flow restricted exercise (BFRE) training.

Methods

People living with COPD and health professionals (exercise physiologists, physiotherapists, and hospital-based respiratory nurses and doctors) participated in interviews or focus groups, which included information about BFRE training and a facilitated discussion of positive aspects, barriers and concerns about BFRE training as a possible exercise-based intervention. Sessions were audio-recorded, and transcript data analysed using inductive content analysis.

Results

Thirty-one people participated (people with COPD n = 6; health professionals n = 25). All participant groups expressed positive perceptions of BFRE as a potential alternative low-intensity exercise mode where health benefits might be achieved. Areas of overlap in perceived barriers and concerns included the need to address the risk of potential adverse events, suitability of training sites and identifying processes to appropriately screen potential candidates.

Discussion

While potential benefits were identified, concerns about determining who is safe and suitable to participate, delivery processes, health professional training and effects on a variety of health-related outcomes need to be addressed before implementation of BFRE training for people with COPD.

Aging exaggerates blood pressure response to ischemic rhythmic handgrip exercise in humans

Ischemic skeletal muscle conditions are known to augment exercise-induced increases in blood pressure (BP). Aging is also a factor that enhances the pressor response to exercise. However, the effects of aging on the BP response to ischemic exercise remain unclear. We, therefore, tested the hypothesis that aging enhances the BP response to rhythmic handgrip (RHG) exercise during postexercise muscle ischemia (PEMI). We divided the normotensive participants without cardiovascular diseases into three age groups: young (n = 26; age, 18-28 years), middle-aged (n = 23; age, 35-59 years), and older adults (n = 23; age, 60-80 years). The participants performed RHG exercise with minimal effort for 1 min after rest with and without PEMI, which was induced by inflating a cuff on the upper arm just before the isometric handgrip exercise ended; the intensity was 30% of maximal voluntary contraction force. Under PEMI, the increase in diastolic BP (DBP) from rest to RHG exercise in the older adult group (Δ13 ± 2 mmHg) was significantly higher than that in the young (Δ5 ± 2 mmHg) and middle-aged groups (Δ6 ± 1 mmHg), despite there being no significant difference between the groups in the DBP response from rest to RHG exercise without PEMI. Importantly, based on multiple regression analysis, age remained a significant independent determinant of both the SBP and DBP responses to RHG exercise during PEMI (p < 0.01). These findings indicate that aging enhances the pressor response to ischemic rhythmic exercise.

Resistance training in heart failure patients: a systematic review and meta-analysis

Aerobic training (AT) has been the primary mode of exercise training in cardiac rehabilitation. Historically, the reason for the prescription of AT was that it was speculated that although RT may be beneficial for some clinical outcomes, it may have an adverse effect on ventricular structure and function. However, RT has now made its way into current cardiac rehabilitation guidelines, including those directed towards patients with HF, albeit differences exist across institutions and guidelines. A systematic search of PubMed, EMBASE and Cochrane Trials Register on April 30, 2021, was conducted for exercise-based rehabilitation trials in HF. Randomised and controlled trials that reported on resistance training versus usual care or trials that directly compared RT to an AT intervention were included. Resistance training versus controls improves parameters of lower (SMD 0.76 (95%CI 0.26, 1.25, p = 0.003] and upper extremity muscle strength (SMD 0.85 (95%CI 0.35, 1.35), p = 0.0009], both key parameters of physical function throughout the lifespan. Importantly, RT in isolation, versus control, improves VO2peak [MD: 2.64 ml/kg/min (95%CI 1.67, 3.60), p < 0.00001] and 6MWD [MD: 49.94 m (95%CI 34.59, 65.29), p < 0.00001], without any detrimental effect on left ventricular parameters. Resistance training in HF patients is safe and improves parameters of physical function and quality of life. Where people with HF are unable to, or are not inclined to, partake in aerobic activity, RT alone is appropriate to elicit meaningful benefit.

Blood Flow Restriction Training Can Improve Peak Torque Strength in Chronic Atrophic Postoperative Quadriceps and Hamstrings Muscles

PURPOSE

To report a prospective study of patients who underwent blood flow restriction training (BFRT) for marked quadriceps or hamstring muscle deficits after failure to respond to traditional rehabilitation after knee surgery.

METHODS

The BFRT protocol consisted of 4 low resistance exercises (30% of 1 repetition maximum): leg press, knee extension, mini-squats, and hamstring curls with 60% to 80% limb arterial occlusion pressure. Knee peak isometric muscle torque (60° flexion) was measured on an isokinetic dynamometer.

RESULTS

Twenty-seven patients (18 females, 9 males; mean age, 40.1 years) with severe quadriceps and/or hamstrings deficits were enrolled from April 2017 to January 2020. They had undergone a mean of 5.3 ± 3.5 months of outpatient therapy and 22 ± 10 supervised therapy visits and did not respond to traditional rehabilitation. Prior surgery included anterior cruciate ligament reconstruction, partial or total knee replacements, meniscus repairs, and others. All patients completed 9 BFRT sessions, and 14 patients completed 18 sessions. The mean quadriceps and hamstrings torque deficits before BFRT were 43% ± 16% and 38% ± 14%, respectively. After 9 BFRT sessions, statistically significant improvements were found in muscle peak torque deficits for the quadriceps (P = .003) and hamstring (P = .02), with continued improvements after 18 sessions (P = .004 and P = .002, respectively). After 18 BFRT sessions, the peak quadriceps and hamstring peak torques increased > 20% in 86% and 76% of the patients, respectively. The failure rate of achieving this improvement in peak quadriceps and hamstring torque after 18 BFRT sessions was 14% and 24%, respectively.

CONCLUSIONS

BFRT produced statistically significant improvements in peak quadriceps and hamstring torque measurements after 9 and 18 sessions in a majority of patients with severe quadriceps and hamstring strength deficits that had failed to respond to many months of standard and monitored postoperative rehabilitation.

LEVEL OF EVIDENCE

Level IV therapeutic case series.

Efficacy of low-load resistance training combined with blood flow restriction vs. high-load resistance training on sarcopenia among community-dwelling older Chinese people: study protocol for a 3-arm randomized controlled trial

BACKGROUND

Sarcopenia is accompanied by a decline in muscle mass, muscle strength, and muscle function. Resistance training is the most potential training method for the prevention and treatment of sarcopenia. However, the conventional high-load resistance training (CRT) recommended by the American College of Sports Medicine is a challenge for older people with sarcopenia. As a novel training method, low-load resistance training combined with blood flow restriction (LRT-BFR) may elicit similar muscle mass and muscle strength gains as CRT but with less effort. The objectives of this study are to assess and compare the efficacy and safety of 12-week LRT-BFR and CRT on muscle strength, muscle performance, body composition, pulmonary function, blood biomarkers, CVD risk factors, and quality of life in community-dwelling older Chinese people with sarcopenia.

METHOD

This is a 12-week, assessor-blinded, 3-arm randomized controlled trial with a non-exercise control group. Community-dwelling people over 65 years will be screened for sarcopenia according to the diagnostic criteria of the Asian Working Group for Sarcopenia (AWGS). Fifty-one subjects will be randomized into a LRT-BFR group (n = 17), a CRT group (n = 17), and a no-strength training control group (n = 17). The primary outcome is lower limb muscle strength. The secondary outcomes are body composition, upper limb muscle strength, pulmonary function, blood biomarkers, CVD risk factors, and quality of life. Post-intervention follow-up will be performed for 12 weeks. These indicators will be assessed at baseline (0 week), after the 12-week intervention (12 weeks), and at follow-up (24 weeks). The adverse events will also be reported. Data will be analyzed for all participants in an intent-to-treat plan.

DISCUSSION

This study is the first RCT that will systematically measure and compare the efficacy and safety of LRT-BFR and CRT in older people with sarcopenia on muscle strength, body composition, pulmonary function, blood biomarkers (inflammatory biomarkers, hormone, and growth factors), CVD risk factors, and quality of life. This study can provide an efficient and safe method to prevent the progression of sarcopenia in older people.

TRIAL REGISTRATION

Chinese Clinical Trial Registry ChiCTR2100042803 . Registered on 28 January 2021.

Perceived Barriers to Blood Flow Restriction Training

Blood flow restriction (BFR) training is increasing in popularity in the fitness and rehabilitation settings due to its role in optimizing muscle mass and strength as well as cardiovascular capacity, function, and a host of other benefits. However, despite the interest in this area of research, there are likely some perceived barriers that practitioners must overcome to effectively implement this modality into practice. These barriers include determining BFR training pressures, access to appropriate BFR training technologies for relevant demographics based on the current evidence, a comprehensive and systematic approach to medical screening for safe practice and strategies to mitigate excessive perceptual demands of BFR training to foster long-term compliance. This manuscript attempts to discuss each of these barriers and provides evidence-based strategies and direction to guide clinical practice and future research.

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.

Blood Flow Restriction Training: To Adjust or Not Adjust the Cuff Pressure Over an Intervention Period?

Blood flow restriction (BFR) training combines exercise and partial reduction of muscular blood flow using a pressured cuff. BFR training has been used to increase strength and muscle mass in healthy and clinical populations. A major methodological concern of BFR training is blood flow restriction pressure (BFRP) delivered during an exercise bout. Although some studies increase BFRP throughout a training intervention, it is unclear whether BFRP adjustments are pivotal to maintain an adequate BFR during a training period. While neuromuscular adaptations induced by BFR are widely studied, cardiovascular changes throughout training intervention with BFR and their possible relationship with BFRP are less understood. This study aimed to discuss the need for BFRP adjustment based on cardiovascular outcomes and provide directions for future researches. We conducted a literature review and analyzed 29 studies investigating cardiovascular adaptations following BFR training. Participants in the studies were healthy, middle-aged adults, older adults and clinical patients. Cuff pressure, when adjusted, was increased during the training period. However, cardiovascular outcomes did not provide a plausible rationale for cuff pressure increase. In contrast, avoiding increments in cuff pressure may minimize discomfort, pain and risks associated with BFR interventions, particularly in clinical populations. Given that cardiovascular adaptations induced by BFR training are conflicting, it is challenging to indicate whether increases or decreases in BFRP are needed. Based on the available evidence, we suggest that future studies investigate if maintaining or decreasing cuff pressure makes BFR training safer and/or more comfortable with similar physiological adaptation.

Blood flow restriction training and the high-performance athlete: science to application

The manipulation of blood flow in conjunction with skeletal muscle contraction has greatly informed the physiological understanding of muscle fatigue, blood pressure reflexes, and metabolism in humans. Recent interest in using intentional blood flow restriction (BFR) has focused on elucidating how exercise during periods of reduced blood flow affects typical training adaptations. A large initial appeal for BFR training was driven by studies demonstrating rapid increases in muscle size, strength, and endurance capacity, even when notably low intensities and resistances, which would typically be incapable of stimulating change in healthy populations, were used. The incorporation of BFR exercise into the training of strength- and endurance-trained athletes has recently been shown to provide additive training effects that augment skeletal muscle and cardiovascular adaptations. Recent observations suggest BFR exercise alters acute physiological stressors such as local muscle oxygen availability and vascular shear stress, which may lead to adaptations that are not easily attained with conventional training. This review explores these concepts and summarizes both the evidence base and knowledge gaps regarding the application of BFR training for athletes.

Does Resistance Training with Blood Flow Restriction Affect Blood Pressure and Cardiac Autonomic Modulation in Older Adults?

Resistance training (RT) with blood flow restriction (BFR) appears to accelerate muscle hypertrophy and strength gains in older populations. However, the training-related effects of RT with BFR upon blood pressure (BP) and cardiac autonomic modulation in the elderly remains unclear. The objective of this study is to compare the chronic effects of low-intensity RT performed with soft BFR (BFR) vs. high-intensity (HI) and low-intensity RT (CON) without BFR on BP and heart rate variability (HRV) indices in older adults. Thirty-two physically inactive participants (72 ± 7 yrs) performed RT for upper and lower limbs (50-min sessions, 3 times/week) for 12 weeks, being assigned into three groups: a) BFR; 30% of 1 repetition maximum (RM) with BFR corresponding to 50% of arterial occlusion pressure; b) HI; 70% of 1RM without BFR; c) CON; 30% of 1 RM without BFR. Resting BP and HRV were assessed at rest in the supine position, before and after exercise interventions. Systolic BP (Δ = -7.9 ± 8.0 mmHg; p = 0.002; effect size = 0.62), diastolic BP (Δ = trace length by the duration of the test 5.0 ± 6.0 mmHg; p = 0.007; effect size = 0.67) and mean arterial pressure (Δ = -6.3 ± 6.5 mmHg; p = 0.003/effect size = 0.77) reduced after BFR, remaining unaltered in HI and CON. HRV indices of sympathetic and vagal modulation did not change in all groups (p ≥ 0.07 for all comparisons). 12-wk RT with low intensity and relatively soft BFR substantially reduced BP at rest in older adults vs. traditional RT performed with either low or high intensity. Those reductions were not parallel to changes in autonomic modulation.

Low-load resistance training with blood flow restriction prevent renal function decline: The role of the redox balance, angiotensin 1-7 and vasopressin✰,✰✰

AIMS

We sought to investigate the effect of resistance training (RT) and low-load RT with moderate blood flow restriction (RT+BFR) on blood pressure, exercise pressor response, redox balance and vasoactive peptides, body composition and muscle strength in patients with stage two of chronic kidney disease (CKD).

METHODS

We conducted a 6-month randomized controlled exercise intervention in 90 male and female hypertensive CKD patients (58±9 years with estimated glomerular filtration rate (eGFR; of 66.1 ± 1.2 mL/kg/1.73m²). Participants were randomized to one of three groups (n = 30/group); control group (CTL), RT, and RT+BFR. RT and RT+BFR performed three weekly training sessions using similar periodization for six months (two-month mesocycles), but of different intensities.

RESULTS

There was similarly effects between RT and RT+BFR in reducing systolic and diastolic blood pressure during daytime and 24hour period (RT: 10.4%; RT+BFR: 10.3% of decrease), fat mass, F₂-isoprostanes, asymmetric dimethylarginine (ADMA) and vasopressin (p<0.05 pre-vs post). Also promoted the increase of angiotensin 1-7, nitric oxide (NO), catalase, Trolox equivalent and muscle strength (p<0.05). Both training models attenuated the decline of estimated glomerular filtration rate (p<0.0001 vs CTL). However, only RT+BFR was associated with lower discomfort during exercise (p<0.0001 pre-vs post). Statistical significance was considered with p < 0.05.

CONCLUSION

These findings suggest low-load RT+BFR as a promising non-pharmacological strategy to control blood pressure, oxidative stress, vasoactive peptides, and consequently, attenuate the decrease of the eGFR.

Oxidative stress: an evolving definition

Thirty-five years ago, Sies and colleagues insightfully described the universal phenomenon that the generation of reactive oxygen species could modify macromolecules in living organisms, resulting in a wide range of measurable damage. They used the term "oxidative stress" to define the loss of the balance between oxidants and antioxidants in favor of the former. After decades of research, it became increasingly clear that cells are not simply passive receivers of oxidative modification but can act dynamically to resist and adapt to oxidants. Furthermore, many redox-sensitive pathways have been identified wherein certain oxidants (mainly hydrogen peroxide and nitric oxide) are used as messenger molecules to transduce the signals required for these adaptations. Since the turn of the century, redox signaling has developed into a vibrant multidisciplinary field of biology. To reflect the evolution of the study in this field, the definition of oxidative stress is postulated to define a state in which the pro-oxidative processes overwhelm cellular antioxidant defense due to the disruption of redox signaling and adaptation.

Low-Intensity Resistance Training with Moderate Blood Flow Restriction Appears Safe and Increases Skeletal Muscle Strength and Size in Cardiovascular Surgery Patients: A Pilot Study

We examined the safety and the effects of low-intensity resistance training (RT) with moderate blood flow restriction (KAATSU RT) on muscle strength and size in patients early after cardiac surgery. Cardiac patients (age 69.6 ± 12.6 years, n = 21, M = 18) were randomly assigned to the control (n = 10) and the KAATSU RT group (n = 11). All patients had received a standard aerobic cardiac rehabilitation program. The KAATSU RT group additionally executed low-intensity leg extension and leg press exercises with moderate blood flow restriction twice a week for 3 months. RT-intensity and volume were increased gradually. We evaluated the anterior mid-thigh thickness (MTH), skeletal muscle mass index (SMI), handgrip strength, knee extensor strength, and walking speed at baseline, 5-7 days after cardiac surgery, and after 3 months. A physician monitored the electrocardiogram, rate of perceived exertion, and the color of the lower limbs during KAATSU RT. Creatine phosphokinase (CPK) and D-dimer were measured at baseline and after 3 months. There were no side effects during KAATSU RT. CPK and D-dimer were normal after 3 months. MTH, SMI, walking speed, and knee extensor strength increased after 3 months with KAATSU RT compared with baseline. Relatively low vs. high physical functioning patients tended to increase physical function more after 3 months with KAATSU RT. Low-intensity KAATSU RT as an adjuvant to standard cardiac rehabilitation can safely increase skeletal muscle strength and size in cardiovascular surgery patients.

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.

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

Purpose: Medically recommended training often faces the dilemma that necessary mechanical intensities for muscle adaptations exceed patients' physical capacity. In this regard, blood flow restriction (BFR) training is becoming increasingly popular because it enables gains in muscle mass and strength despite using low-mechanical loads combined with external venous occlusion. Since the underlying mechanisms are still unknown, we applied invasive measurements during exercise with and without BFR to promote physiological understanding and safety of this popular training technique.

Methods: In a randomized cross-over design, ten healthy men (28.1 ± 6.5 years) underwent two trials of unilateral biceps curls either with (BFR) and without BFR (CON). For analysis of changes in intravascular pressures, blood gases, oximetry and electrolytes, an arterial and a venous catheter were placed at the exercising arm before exercise. Arterial and venous blood gases and intravascular pressures were analyzed before, during and 5 min after exercise.

Results: Intravascular pressures in the arterial and venous system were more increased during exercise with BFR compared to CON (p < 0.001). Furthermore, arterial and venous blood gas analyses revealed a BFR-induced metabolic acidosis (p < 0.05) with increased lactate production (p < 0.05) and associated elevations in [K⁺], [Ca²⁺] and [Na⁺] (p < 0.001).

Conclusion: The present study describes for the first time the local physiological changes during BFR training. While BFR causes greater hypertension in the arterial and venous system of the exercising extremity, observed electrolyte shifts corroborate a local metabolic acidosis with concurrent rises in [K⁺] and [Na⁺]. Although BFR could be a promising new training concept for medical application, its execution is associated with comprehensive physiological challenges.

Low-intensity resistance exercise with blood flow restriction and arterial stiffness in humans: A systematic review

Low-intensity resistance exercise with blood flow restriction exercise is an emerging type of exercise recognition worldwide. This systematic review evaluated the effects of low-intensity resistance exercise performed with concurrent blood flow restriction (LIRE-BFR) on acute and chronic measures of arterial stiffness in humans. A systematic search in six healthcare science databases and reference lists was conducted. Data selected for primary analysis consisted of post-intervention changes in arterial stiffness markers. This systematic review included randomized and non-randomized controlled trials of LIRE-BFR in humans. 156 articles were initially identified, 15 of which met inclusion criteria. Ten studies were excluded because they did not match predefined arterial stiffness markers. Thus, five articles were included in this review: two acute studies (N = 39 individuals, age = 20-30 years old, 30.8% women and 69.2% men) and three longitudinal studies (N = 51 individuals, age = 24-86-years old, 41.2% women and 58.8% men). Acute LIRE-BFR demonstrated both positive and negative effects on arterial stiffness in healthy young people. In contrast, longitudinal studies reported neutral effects in healthy young and older people. In conclusion, LIRE-BFR applied to the upper and lower limbs may acutely induce increases in central blood pressure and pulse wave velocity in healthy young people, whereas LIRE-BFR for the lower limbs may elicit positive effects related to indirect markers of arterial stiffness. Moreover, longitudinal LIRE-BFR studies showed no changes in arterial stiffness in young and older people. Hence, LIRE-BFR should be prescribed with a degree of caution to avoid non-intended responses in arterial stiffness markers in humans.

Increased sympathetic and haemodynamic responses to exercise and muscle metaboreflex activation in post-menopausal women with rheumatoid arthritis

KEY POINTS

Rheumatoid arthritis (RA) patients present exacerbated blood pressure responses to exercise, but little is known regarding the underlying mechanisms involved.  This study assessed autonomic and haemodynamic responses to exercise and to the isolated activation of muscle metaboreflex in post-menopausal women with RA.  Participants with RA showed augmented pressor and sympathetic responses to exercise and to the activation of muscle metaboreflex. These responses were associated with multiple pro- and anti-inflammatory cytokines and with pain.  The results of the present study support the suggestion that an abnormal reflex control of circulation is an important mechanism underlying the exacerbated cardiovascular response to exercise and increased cardiovascular risk in RA.

ABSTRACT

Studies have reported abnormal cardiovascular responses to exercise in rheumatoid arthritis (RA) patients, but little is known regarding the underlying mechanisms involved. This study assessed haemodynamic and sympathetic responses to exercise and to the isolated activation of muscle metaboreflex in women diagnosed with RA. Thirty-three post-menopausal women diagnosed with RA and 10 matched controls (CON) participated in this study. Mean arterial pressure (MAP), heart rate (HR) and muscle sympathetic nerve activity (MSNA frequency and incidence) were measured during a protocol of isometric knee extension exercise (3 min, 30% of maximal voluntary contraction), followed by post-exercise ischaemia (PEI). Participants with RA showed greater increases in MAP and MSNA during exercise and PEI than CON (ΔMAP_exercise  = 16 ± 11 vs. 9 ± 6 mmHg, P = 0.03; ΔMAP_PEI  = 15 ± 10 vs. 5 ± 5 mmHg, P = 0.001; ΔMSNA_exercise  = 17 ± 14 vs. 7 ± 9 bursts min^-1 , P = 0.04; ΔMSNA_PEI  = 14 ± 10 vs. 6 ± 4 bursts min^-1 , P = 0.04). Autonomic responses to exercise showed significant (P < 0.05) association with pro- (i.e. IFN-γ, IL-8, MCP-1 and TNFα) and anti-inflammatory (i.e. IL-1ra and IL-10) cytokines and with pain. In conclusion, post-menopausal women with RA showed augmented pressor and sympathetic responses to exercise and to the activation of muscle metaboreflex. These findings provide mechanistic insights that may explain the abnormal cardiovascular responses to exercise in RA.

Exaggerated pressor response to blood flow restriction resistance exercise is associated with a muscle metaboreflex-induced increase in blood pressure in young, healthy humans

Some researchers are concerned that exercise training with the blood flow restriction (BFR) technique induces an exaggeration in blood pressure response and potentiates adverse cardiovascular events. In the present study, we demonstrate that the blood pressure response to arm-curl exercise was intensified by the BFR technique, and the degree of intensification was associated with a blood pressure response to postexercise muscle ischemia of the elbow flexors, which elicit a muscle metaboreflex. Novelty: BFR technique intensifies blood pressure response to exercise, which was associated with a blood pressure response in postexercise muscle ischemia-induced muscle metaboreflex.

Recent advances in exercise pressor reflex function in health and disease

Autonomic alterations at the onset of exercise are critical to redistribute cardiac output towards the contracting muscles while preventing a fall in arterial pressure due to excessive vasodilation within the contracting muscles. Neural mechanisms responsible for these adjustments include central command, the exercise pressor reflex, and arterial and cardiopulmonary baroreflexes. The exercise pressor reflex evokes reflex increases in sympathetic activity to the heart and systemic vessels and decreases in parasympathetic activity to the heart, which increases blood pressure (BP), heart rate, and total peripheral resistance through vasoconstriction of systemic vessels. In this review, we discuss recent advancements in our understanding of exercise pressor reflex function in health and disease. Specifically, we discuss emerging evidence suggesting that sympathetic vasoconstrictor drive to the contracting and non-contracting skeletal muscle is differentially controlled by central command and the metaboreflex in healthy conditions. Further, we discuss evidence from animal and human studies showing that cardiovascular diseases, including hypertension, diabetes, and heart failure, lead to an altered exercise pressor reflex function. We also provide an update on the mechanisms thought to underlie this altered exercise pressor reflex function in each of these diseases. Although these mechanisms are complex, multifactorial, and dependent on the etiology of the disease, there is a clear consensus that several mechanisms are involved. Ultimately, approaches targeting these mechanisms are clinically significant as they provide alternative therapeutic strategies to prevent adverse cardiovascular events while also reducing symptoms of exercise intolerance.

Training with blood flow restriction increases femoral artery diameter and thigh oxygen delivery during knee-extensor exercise in recreationally trained men

KEY POINTS

Endurance-type training with blood flow restriction (BFR) increases maximum oxygen uptake ( V ̇ O 2 max ) and exercise endurance of humans. However, the physiological mechanisms behind this phenomenon remain uncertain. In the present study, we show that BFR-interval training reduces the peripheral resistance to oxygen transport during dynamic, submaximal exercise in recreationally-trained men, mainly by increasing convective oxygen delivery to contracting muscles. Accordingly, BFR-training increased oxygen uptake by, and concomitantly reduced net lactate release from, the contracting muscles during relative-intensity-matched exercise, at the same time as invoking a similar increase in diffusional oxygen conductance compared to the training control. Only BFR-training increased resting femoral artery diameter, whereas increases in oxygen transport and uptake were dissociated from changes in the skeletal muscle content of mitochondrial electron-transport proteins. Thus, physically trained men benefit from BFR-interval training by increasing leg convective oxygen transport and reducing lactate release, thereby improving the potential for increasing the percentage of V ̇ O 2 max that can be sustained throughout exercise.

ABSTRACT

In the present study, we investigated the effect of training with blood flow restriction (BFR) on thigh oxygen transport and uptake, and lactate release, during exercise. Ten recreationally-trained men (50 ± 5 mL kg^-1  min^-1 ) completed 6 weeks of interval cycling with one leg under BFR (BFR-leg; pressure: ∼180 mmHg) and the other leg without BFR (CON-leg). Before and after the training intervention (INT), thigh oxygen delivery, extraction, uptake, diffusion capacity and lactate release were determined during knee-extensor exercise at 25% incremental peak power output (iPPO) (Ex1), followed by exercise to exhaustion at 90% pre-training iPPO (Ex2), by measurement of femoral-artery blood flow and femoral-arterial and -venous blood sampling. A muscle biopsy was obtained from legs before and after INT to determine mitochondrial electron-transport protein content. Femoral-artery diameter was also measured. In the BFR-leg, after INT, oxygen delivery and uptake were higher, and net lactate release was lower, during Ex1 (vs. CON-leg; P < 0.05), with an 11% larger increase in workload (vs. CON-leg; P < 0.05). During Ex2, after INT, oxygen delivery was higher, and oxygen extraction was lower, in the BFR-leg compared to the CON-leg (P < 0.05), resulting in an unaltered oxygen uptake (vs. CON-leg; P > 0.05). In the CON-leg, at both intensities, oxygen delivery, extraction, uptake and lactate release remained unchanged (P > 0.05). Resting femoral artery diameter increased with INT only in the BFR-leg (∼4%; P < 0.05). Oxygen diffusion capacity was similarly raised in legs (P < 0.05). Mitochondrial protein content remained unchanged in legs (P > 0.05). Thus, BFR-interval training enhances oxygen utilization by, and lowers lactate release from, submaximally-exercising muscles of recreationally-trained men mainly by increasing leg convective oxygen transport.

[Application and effects of blood flow restriction training]

Blood flow restriction (BFR) limits arterial and venous blood flow and leads to blood pooling, which could increase exercise-induced training effects. Strength training at lower intensities (20-30% of maximum strength) in combination with BFR showed similar effects on muscle hypertrophy as training with 70% without BFR. Low-intensity cycling endurance training with BFR improves muscle hypertrophy and endurance performance and activates angiogenesis. After determination of the complete occlusion pressure on the corresponding extremity, it is recommended that BFR training should be performed with 40-80% of the measured occlusion pressure. During strength training of the upper extremities, an occlusion of 60-80% leads to a reduction in the arterial blood flow by 20-50%. Local ischemia and hypoxia, a stronger metabolic stimulus, swelling of the muscle cells and the increased oxidative stress are discussed as causes for the increased training effects due to BFR. In short-term studies, comparable adjustments to parameters of fibrinolytic activity, coagulation and inflammation could be observed for strength training with and without BFR. So far, thromboses after BFR have been described only rarely but need to be further clarified by appropriate studies. The BFR training leads to a stronger activation of the muscular metabolic reflex and thus to a relatively greater increase in exercise blood pressure, so that cardiovascular parameters should be controlled during BFR training. First meta-analyses with small numbers of healthy people and patients indicate the effectiveness of BFR training. Standardization or guidelines for clinical use are still lacking.