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

Combined effect of sprint interval training and post-exercise blood flow restriction on muscle deoxygenation responses during ramp incremental cycling

PURPOSE

This study investigated the effect of sprint-interval training combined with post-exercise blood flow restriction (i.e., SIT + BFR) on pulmonary gas exchange and microvascular deoxygenation responses during ramp incremental (RI) cycling.

METHODS

Nineteen healthy, untrained males (mean ± SD age: 24 ± 5 years; height: 178 ± 6 cm; body mass: 77.0 ± 10.7 kg) were assigned to receive 4 weeks of SIT or SIT + BFR. Before and after the intervention period, each participant completed a RI cycling test for determination of peak oxygen uptake (V ˙ O 2peak ) and the gas exchange threshold (GET) with deoxygenated heme (Δdeoxy[heme]) and tissue oxygenation index (TOI) measured by near-infrared spectroscopy (NIRS) in vastus lateralis (VL) muscle.

RESULTS

RelativeV ˙ O 2peak increased by 7% following both interventions (P ≤ 0.03). SIT + BFR increased peak Δdeoxy[heme] when normalized relative to leg arterial occlusion (PRE: 57.3 ± 13.0 vs. POST: 62.0 ± 13.2%; P = 0.009) whereas there was no significant difference following SIT (PRE: 64.9 ± 14.3 vs. POST: 71.4 ± 11.7%; P = 0.17). Likewise, TOI nadir decreased at exhaustion following SIT + BFR (PRE: 56.9 ± 9.1 vs. POST: 51.4 ± 9.2%; P = 0.002) but not after SIT (PRE: 58.5 ± 7.1 vs. POST: 56.3 ± 8.2%; P = 0.29). The absolute cycling power at the GET increased following SIT + BFR (PRE: 108 ± 13 vs. POST: 125 ± 17 W, P = 0.001) but was not significantly different following SIT (PRE: 112 ± 7 VS. POST: 116 ± 11 W, P = 0.54).

CONCLUSION

The addition of post-exercise BFR to SIT alters the mechanism underlying the enhancement inV ˙ O 2peak by increasing the peak rate of muscle fractional O2 extraction in previously untrained males.

Blood Flow-Restricted Training and Time Trial Performance: A Cohort Study of World-Class Rowers

INTRODUCTION

This study aimed to explore the potential impact of incorporating blood flow restriction (BFR) training within a training block characterized by minimal high-intensity work on 2000-m rowing ergometer time trial (TT) performance in elite/world-class rowers. Physiological markers often associated with endurance performance (maximal aerobic capacity, V̇O 2max ; blood lactate thresholds and hemoglobin mass, Hb mass ) were measured to determine whether changes are related to an improvement in performance.

METHODS

Using a quasi-experimental, observational study design (no control group), 2000-m TT performance, V̇O 2max , submaximal work rates eliciting blood lactate concentrations of ~2 and ~4 mmol·L -1 , and Hb mass were measured before and after 4 wk of noncompetitive season training, which included BFR rowing. BFR training consisted of 11 sessions of 2 × 10 min of BFR rowing at a workload equating to blood lactate concentrations of ~2 mmol·L -1 . Paired t -tests were used to compare pre-/postvalues, and Pearson correlation was used to examine whether physiological changes were associated with changes to TT performance.

RESULTS

TT performance improved in both female (1.09% ± 1.2%, ~4.6 ± 5.2 s; P < 0.01) and male (1.17% ± 0.48%, ~4.5 ± 1.9 s; P < 0.001) athletes. V̇O 2max increased in female rowers only ( P < 0.01), but both sexes had an increase in work rates eliciting blood lactate concentrations of 2 mmol·L -1 (female: 184 ± 16 to 195 ± 15 W, P < 0.01; male: 288 ± 23 to 317 ± 26 W, P = 0.04) and 4 mmol·L -1 (female: 217 ± 13 to 227 ± 14 W, P = 0.02; male: 339 ± 43 to 364 ± 39 W, P < 0.01). No changes in Hb mass (both sexes, P = 0.8) were observed. Improvements in TT performance were not related to physiological changes (all correlations P ≥ 0.2).

CONCLUSIONS

After 4 wk of training with BFR, the improvement in TT performance was greater than what is typical for this population. Physiological variables improved during this training block but did not explain improved TT performance.

Hemodynamic Effects of Intermittent Pneumatic Compression on Athletes: A Double-Blinded Randomized Crossover Study

PURPOSE

There are multiple postexercise recovery technologies available in the market based on the assumption of blood-flow enhancement. Lower-limb intermittent pneumatic compression (IPC) has been widely used, but the available scientific evidence supporting its effectiveness remains scarce, requiring a deeper investigation into its underlying mechanisms. The aim of this study was to assess the hemodynamic effects caused by the use of IPC at rest.

METHODS

Twenty-two soccer and track and field athletes underwent two 15-minute IPC protocols (moderate- [80 mm Hg] and high-pressure [200 mm Hg]) in a randomized order. Systolic peak velocity, end-diastolic peak velocity, arterial diameter, and heart rate were measured before, during (at the eighth minute), and 2 minutes after each IPC protocol.

RESULTS

Significant effects were observed between before and during (eighth minute) the IPC protocol for measures of systolic (P < .001) and end-diastolic peak velocities (P < .001), with the greater effects observed during the high-pressure protocol. Moreover, 2 minutes after each IPC protocol, hemodynamic variables returned to values close to baseline. Arterial diameter presented significant differences between pressures during the IPC protocols (P < .05), while heart rate remained unaltered.

CONCLUSION

IPC effectively enhances transitory blood flow of athletes, particularly when applying high-pressure protocols.

Acute neuromuscular, cardiovascular, and muscle oxygenation responses to low-intensity aerobic interval exercises with blood flow restriction

We investigated the influence of short- and long-interval cycling exercise with blood flow restriction (BFR) on neuromuscular fatigue, shear stress and muscle oxygenation, potent stimuli to BFR-training adaptations. During separate sessions, eight individuals performed short- (24 × 60 s/30 s; SI) or long-interval (12 × 120 s/60 s; LI) trials on a cycle ergometer, matched for total work. One leg exercised with (BFR-leg) and the other without (CTRL-leg) BFR. Quadriceps fatigue was quantified using pre- to post-interval changes in maximal voluntary contraction (MVC), potentiated twitch force (QT) and voluntary activation (VA). Shear rate was measured by Doppler ultrasound at cuff release post-intervals. Vastus lateralis tissue oxygenation was measured by near-infrared spectroscopy during exercise. Following the initial interval, significant (P < 0.05) declines in MVC and QT were found in both SI and LI, which were more pronounced in the BFR-leg, and accounted for approximately two-thirds of the total reduction at exercise termination. In the BFR-leg, reductions in MVC (-28 ± 15%), QT (-42 ± 17%), and VA (-15 ± 17%) were maximal at exercise termination and persisted up to 8 min post-exercise. Exercise-induced muscle deoxygenation was greater (P < 0.001) in the BFR-leg than CTRL-leg and perceived pain was more in LI than SI (P < 0.014). Cuff release triggered a significant (P < 0.001) shear rate increase which was consistent across trials. Exercise-induced neuromuscular fatigue in the BFR-leg exceeded that in the CTRL-leg and was predominantly of peripheral origin. BFR also resulted in diminished muscle oxygenation and elevated shear stress. Finally, short-interval trials resulted in comparable neuromuscular and haemodynamic responses with reduced perceived pain compared to long-intervals.

Five-Week, Low-Intensity Blood Flow Restriction Rowing Improves V̇ o2 max in Elite Rowers

ABSTRACT

Held, S, Rappelt, L, Rein, R, Deutsch, J-P, Wiedenmann, T, and Donath, L. Five-week, low-intensity, blood flow restriction rowing improves V̇ o2 max in elite rowers. J Strength Cond Res 38(6): e299-e303, 2024-This controlled intervention study examined the effects of low-intensity rowing with blood flow restriction (BFR) on maximal oxygen uptake (V̇ o2 max), peak power output during ramp testing (PPO), and 2000-m time trial performance (P2k). Eleven, highly elite, male rowers (22.1 ± 1.6 years; 92.6 ± 3.8 kg; 1.93 ± 0.04 m; 7.9. ± 2.2 years rowing experience; 20.4 ± 2.0 h·w -1 training volume; 11.9 ± 1.1 session per week) trained 5 weeks without BFR (Base) followed by a 5-week BFR intervention period. BFR of the lower limb was applied through customized elastic wraps. BFR took place 3 times a week (accumulated net pBFR: 60 min·wk -1 ; occlusion per session: 2 times 10 min·session -1 ) and was used exclusively at low intensities (<2 mmol·L -1 ). V̇ o2 max, PPO, and P2k were examined before, between, and after both intervention periods. Bayesian's credible intervals revealed relevantly increased V̇ o2 max +0.30 L·min -1 (95% credible interval: +0.00 to +0.61 L·min -1 ) adaptations through BFR. By contrast, PPO +14 W (-6 to +34 W) and P2k -5 W (-14 to +3 W) were not noticeably affected by the BFR intervention. This study revealed that 15 sessions of BFR application with a cumulative total BFR load of 5 h over a 5-week macrocycle increased V̇ o2 max remarkably. Thus, pBFR might serve as a promising tool to improve aerobic capacity in highly trained elite rowers.

Use of Inter-Effort Recovery Hypoxia as a New Approach to Improve Anaerobic Capacity and Time to Exhaustion

Putti, Germano Marcolino, Gabriel Peinado Costa, Matheus Silva Norberto, Carlos Dellavechia de Carvalho, Rômulo Cássio de Moraes Bertuzzi, and Marcelo Papoti. Use of inter-effort recovery hypoxia as a new approach to improve anaerobic capacity and time to exhaustion. High Alt Med Biol. 25:68-76, 2024. Background: Although adding hypoxia to high-intensity training may offer some benefits, a significant problem of this training model is the diminished quality of the training session when performing efforts in hypoxia. The purpose of this study was to investigate the effects of training and tapering combined with inter-effort recovery hypoxia (IEH) on anaerobic capacity, as estimated by alternative maximum accumulated oxygen deficit (MAODALT) and time to exhaustion (TTE). Methods: Twenty-four amateur runners performed, for 5 weeks, 3 sessions per week of training consisted of ten 1-minute bouts at 120% (weeks 1-3) and 130% (weeks 4 and 5) of maximum velocity (VMAX) obtained in graded exercise test, separated by a 2-minute interval in IEH (IEH, n = 11, FIO2 = 0.136) or normoxia (NOR, n = 13, fraction of inspired oxygen = 0.209). Before training, after training, and after 1 week of tapering, a graded exercise test and a maximal effort to exhaustion at 120% of VMAX were performed to determine TTE and MAODALT. The results were analyzed using generalized linear mixed models, and a clinical analysis was also realized by the smallest worthwhile change. Results: MAODALT increased only in IEH after training (0.8 ± 0.5 eq.lO2) and tapering (0.8 ± 0.5 eq.lO2), with time x group interaction. TTE increased for the pooled groups after taper (23 ± 11 seconds) and only for IEH alone (29 ± 16 seconds). Clinical analysis revealed a small size increase for NOR and a moderate size increase for IEH. Conclusions: Although the effects should be investigated in other populations, it can be concluded that IEH is a promising model for improving anaerobic performance and capacity. World Health Organization Universal Trial Number: U1111-1295-9954. University's ethics committee registration number: CAAE: 32220020.0.0000.5659.

Low- and high-volume blood-flow restriction treadmill walking both improve maximal aerobic capacity independently of blood volume

AIM

Assess the effect of low- and high-volume blood flow restriction training (BFR) on maximal aerobic capacity (VO2 max) and determine if alteration in VO2 max is mediated through changes in hemoglobin mass (Hbmass) and blood volume.

METHODS

Participants' Hbmass (CO-rebreathe), single, and double-leg VO2 max and blood volume regulating hormonal responses (renin and copeptin) were measured before and after BFR training. Training consisted of treadmill walking either (1) twice-daily for 4week (CON and BFRHV ) or (2) twice-weekly for 6week (BFRLV ). Each session consisted of five intervals (3 min, 5% incline, 5 km/h, 100% of lowest occlusion pressure), with 1 min of standing rest between sets.

RESULTS

VO2 max increased using both training exposures, in as quickly as 2-weeks (BFRLV baseline to 4week: +315 ± 241 mL (8.7%), p = 0.02; BFRHV baseline to 2week: +360 ± 261 mL (7.9%), p < 0.01), for the BFRLV and BFRHV groups, with no change in CON. Single- and double-leg VO2 max improved proportionately (single/double-leg VO2 max ratio: BFRLV 78 ± 4.9-78 ± 5.8%, BFRHV 79 ± 6.5-77 ± 6.5%), suggesting that the mechanism for increased VO2 max is not solely limited to central or peripheral adaptations. Hbmass remained unchanged across groups (CON: +10.2 ± 34 g, BFRLV : +6.6 ± 42 g, BFRHV : +3.2 ± 44 g; p = 0.9), despite a significant release of blood volume regulating hormones after initial BFR exposure (renin +20.8 ± 21.9 ng/L, p < 0.01; copeptin +22.0 ± 23.8 pmol/L, p < 0.01), which was blunted following BFRHV training (renin: +13.4 ± 12.4 ng/L, p = 0.09; copeptin: +1.9 ± 1.7 pmol/L, p = 0.98).

CONCLUSION

BFR treadmill walking increases VO2 max irrespective of changes in Hbmass or blood volume despite a large release of blood volume regulating hormones in response to BFR treadmill walking.

An Updated Panorama of Blood-Flow-Restriction Methods

BACKGROUND

Exercise with blood-flow restriction (BFR) is being increasingly used by practitioners working with athletic and clinical populations alike. Most early research combined BFR with low-load resistance training and consistently reported increased muscle size and strength without requiring the heavier loads that are traditionally used for unrestricted resistance training. However, this field has evolved with several different active and passive BFR methods emerging in recent research.

PURPOSE

This commentary aims to synthesize the evolving BFR methods for cohorts ranging from healthy athletes to clinical or load-compromised populations. In addition, real-world considerations for practitioners are highlighted, along with areas requiring further research.

CONCLUSIONS

The BFR literature now incorporates several active and passive methods, reflecting a growing implementation of BFR in sport and allied health fields. In addition to low-load resistance training, BFR is being combined with high-load resistance exercise, aerobic and anaerobic energy systems training of varying intensities, and sport-specific activities. BFR is also being applied passively in the absence of physical activity during periods of muscle disuse or rehabilitation or prior to exercise as a preconditioning or performance-enhancement technique. These various methods have been reported to improve muscular development; cardiorespiratory fitness; functional capacities; tendon, bone, and vascular adaptations; and physical and sport-specific performance and to reduce pain sensations. However, in emerging BFR fields, many unanswered questions remain to refine best practice.

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

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

Low-intensity climbing with blood flow restriction over 5 weeks increases grip and elbow flexor endurance in advanced climbers: A randomized controlled trial

Grip and elbow flexor strength and endurance are crucial performance surrogates in competitive climbing. Thus, we examined the effects of blood flow restricted (BFR) climbing on grip and elbow flexor performance. Fifteen trained climbers (8 females; 20.8 ± 7.0 yrs; 1.72 ± 0.08 m; 63.0 ± 9.7 kg; 21.7 ± 2.7 IRCRCA grade) were either assigned to the intervention (BFR) or control (noBFR) group, using the minimization method (Strata: age, height, body mass, gender, and IRCRA grade). While BFR was used during low-intensity climbing training (2-times 10 min/session; 3-times/week), noBFR followed identical training protocols without BFR over 5 weeks. BFR of the upper limb was applied via customized pneumatic cuffs (occlusion pressure: 120 ± 23 mmHg, 75%; occlusion pressure). Endurance and strength performances were assessed via one-handed rung pulling (GripSTRENGTH), one-handed bent arm lock off at 90° (ArmSTRENGTH), static-intermitted finger hang (GripENDURANCE), and bent arm hang (ArmENDURANCE). Bayesian credible intervals revealed increased GripENDURANCE (+21 s (95% credible interval: -2 to 43 s)) and ArmENDURANCE +11 s (-5 to 27 s); adaptations via BFR. In contrast, GripSTRENGTH +4 N (-40 to 48 N) and ArmSTRENGTH +4 N (-68 to 75 N) were not affected by the BFR intervention. Fifteen cumulative sessions of BFR application with a cumulative total BFR load of 5 h over a 5 weeks macrocycle remarkably increased grip and elbow flexor endurance. Thus, BFR might serve as a promising means to improve relevant performance surrogates in trained climbers.

Low-intensity swimming with blood flow restriction over 5 weeks increases VO2peak: A randomized controlled trial using Bayesian informative prior distribution

Peak oxygen uptake (VO₂peak) and speed at first (LT1, minimal lactate equivalent) and second lactate threshold (LT2 = LT1 +1.5 mmol·L^-1) are crucial swimming performance surrogates. The present randomized controlled study investigated the effects of blood flow restriction (BFR) during low-intensity swimming (LiT) on VO₂peak, LT1, and LT2. Eighteen male swimmers (22.7 ±3.0 yrs; 69.9 ±8.5 kg; 1.8 ±0.1 m) were either assigned to the BFR or control (noBFR) group. While BFR was applied during LiT, noBFR completed the identical LIT without BFR application. BFR of the upper limb was applied via customized pneumatic cuffs (75% of occlusion pressure: 135 ±10 mmHg; 8 cm cuff width). BFR training took place three times a week over 5 weeks (accumulated weekly net BFR training: 60 min·week^-1; occlusion per session: 2-times 10 min·session^-1) and was used exclusively at low intensities. VO₂peak, LT1, and LT2 diagnostics were employed. Bayesian credible intervals revealed notable VO₂peak improvements by +0.29 L·min^-1 kg^-1 (95% credible interval: -0.26 to +0.85 L·min^-1 kg^-1) when comparing BFR vs. noBFR. Speed at LT1 -0.01 m·s^-1 (-0.04 to +0.02 m·s^-1) and LT2 -0.01 m·s^-1 (-0.03 to +0.02 m·s^-1) did not change meaningfully when BFR was employed. Fifteen sessions of LIT swimming (macrocycle of 5 h over 5 weeks) with a weekly volume of 60 min with BFR application adds additional impact on VO₂peak improvement compared to noBFR LIT swimming. Occasional BFR applications should be considered as a promising means to improve relevant performance surrogates in trained swimmers. HighlightsLow-intensity swimming with blood flow restricted (BFR) induced superior peak oxygen consumption adaptations compared to non-restricted swimming training over a 5-week lasting training periodBFR and non-BFR swimming training-induced similar adaptations regarding swimming speed at first and second lactate thresholdIn conclusion, BFR served as a feasible, promising and beneficial complementary training stimuli to traditional swimming training regarding oxygen consumption adaptations.

Endogenous and Exogenous Antioxidants in Skeletal Muscle Fatigue Development during Exercise

Muscle fatigue is defined as a decrease in maximal force or power generated in response to contractile activity, and it is a risk factor for the development of musculoskeletal injuries. One of the many stressors imposed on skeletal muscle through exercise is the increased production of reactive oxygen species (ROS) and reactive nitrogen species (RNS), which intensifies as a function of exercise intensity and duration. Exposure to ROS/RNS can affect Na⁺/K⁺-ATPase activity, intramyofibrillar calcium turnover and sensitivity, and actin-myosin kinetics to reduce muscle force production. On the other hand, low ROS/RNS concentrations can likely upregulate an array of cellular adaptative responses related to mitochondrial biogenesis, glucose transport and muscle hypertrophy. Consequently, growing evidence suggests that exogenous antioxidant supplementation might hamper exercise-engendering upregulation in the signaling pathways of mitogen-activated protein kinases (MAPKs), peroxisome-proliferator activated co-activator 1α (PGC-1α), or mammalian target of rapamycin (mTOR). Ultimately, both high (exercise-induced) and low (antioxidant intervention) ROS concentrations can trigger beneficial responses as long as they do not override the threshold range for redox balance. The mechanisms underlying the two faces of ROS/RNS in exercise, as well as the role of antioxidants in muscle fatigue, are presented in detail in this review.

Exercise-induced skeletal muscle angiogenesis: impact of age, sex, angiocrines and cellular mediators

Exercise-induced skeletal muscle angiogenesis is a well-known physiological adaptation that occurs in humans in response to exercise training and can lead to endurance performance benefits, as well as improvements in cardiovascular and skeletal tissue health. An increase in capillary density in skeletal muscle improves diffusive oxygen exchange and waste extraction, and thus greater fatigue resistance, which has application to athletes but also to the general population. Exercise-induced angiogenesis can significantly contribute to improvements in cardiovascular and metabolic health, such as the increase in muscle glucose uptake, important for the prevention of diabetes. Recently, our understanding of the mechanisms by which angiogenesis occurs with exercise has grown substantially. This review will detail the biochemical, cellular and biomechanical signals for exercise-induced skeletal muscle angiogenesis, including recent work on extracellular vesicles and circulating angiogenic cells. In addition, the influence of age, sex, exercise intensity/duration, as well as recent observations with the use of blood flow restricted exercise, will also be discussed in detail. This review will provide academics and practitioners with mechanistic and applied evidence for optimising training interventions to promote physical performance through manipulating capillarisation in skeletal muscle.

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

ABSTRACT

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

Acute and Chronic Effects of Blood Flow Restricted High-Intensity Interval Training: A Systematic Review

Background

The implementation of blood flow restriction (BFR) during exercise is becoming an increasingly useful adjunct method in both athletic and rehabilitative settings. Advantages in pairing BFR with training can be observed in two scenarios: (1) training at lower absolute intensities (e.g. walking) elicits adaptations akin to high-intensity sessions (e.g. running intervals); (2) when performing exercise at moderate to high intensities, higher physiological stimulus may be attained, leading to larger improvements in aerobic, anaerobic, and muscular parameters. The former has been well documented in recent systematic reviews, but consensus on BFR (concomitant or post-exercise) combined with high-intensity interval training (HIIT) protocols is not well established. Therefore, this systematic review evaluates the acute and chronic effects of BFR + HIIT.

Methods

The Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines were used to identify relevant studies. A systematic search on 1 February 2022, was conducted on four key databases: ScienceDirect, PubMed, Scopus and SPORTDiscus. Quality of each individual study was assessed using the Physiotherapy Evidence Database (PEDro) scale. Extraction of data from included studies was conducted using an adapted version of the 'Population, Intervention, Comparison, Outcome' (PICO) framework.

Results

A total of 208 articles were identified, 18 of which met inclusion criteria. Of the 18 BFR + HIIT studies (244 subjects), 1 reported both acute and chronic effects, 5 examined acute responses and 12 investigated chronic effects. Acutely, BFR challenges the metabolic processes (vascular and oxygenation responses) during high-intensity repeated sprint exercise—which accelerates central and peripheral neuromuscular fatigue mechanisms resulting in performance impairments. Analysis of the literature exploring the chronic effects of BFR + HIIT suggests that BFR does provide an additive physiological training stimulus to HIIT protocols, especially for measured aerobic, muscular, and, to some extent, anaerobic parameters.

Conclusion

Presently, it appears that the addition of BFR into HIIT enhances physiological improvements in aerobic, muscular, and, to some extent, anaerobic performance. However due to large variability in permutations of BFR + HIIT methodologies, it is necessary for future research to explore and recommend standardised BFR guidelines for each HIIT exercise type.

Acute Responses to Cycling Exercise With Blood Flow Restriction During Various Intensities

ABSTRACT

Lauver, JD, Moran, A, Guilkey, JP, Johnson, KE, Zanchi, NE, and Rotarius, TR. Acute responses to cycling exercise with blood flow restriction during various intensities. J Strength Cond Res 36(12): 3366-3373, 2022-The purpose of this study was to investigate the acute physiological responses during cycling at various intensities with blood flow restriction (BFR). Subjects ( N = 9; V̇ o2 peak = 36.09 ± 5.80 ml·kg -1 ·min -1 ) performed 5 protocols: high-intensity (HIGH), control (CON-90), 90% of ventilatory threshold (VT) work rate with BFR (90-BFR), 70% of VT with BFR (70-BFR), and 30% V̇ o2 peak with BFR (30-BFR). Protocols consisted of five 2-minute work intervals interspersed with 1-minute recovery intervals. Blood flow restriction pressure was 80% of limb occlusion pressure. V̇ o2 , muscle excitation, tissue oxygen saturation (StO 2 ), discomfort, and level of perceived exertion (RPE) were assessed. Muscle excitation was higher during HIGH (302.9 ± 159.9 %BSL [baseline]) compared with 70-BFR (99.7 ± 76.4 %BSL) and 30-BFR (98.2 ± 70.5 %BSL). StO 2 was greater during 90-BFR (40.7 ± 12.5 ∆BSL), 70-BFR (34.4 ± 15.2 ∆BSL), and 30-BFR (31.9 ± 18.7 ∆BSL) compared with CON-90 (4.4 ± 11.5 ∆BSL). 90-BFR (39.6 ± 12.0 ∆BSL) resulted in a greater StO 2 -Avg compared with HIGH (20.5 ± 13.8 ∆BSL). Also, HIGH (23.68 ± 5.31 ml·kg -1 ·min -1 ) resulted in a greater V̇ o2 compared with 30-BFR (15.43 ± 3.19 ml·kg -1 ·min -1 ), 70-BFR (16.65 ± 3.26 ml·kg -1 ·min -1 ), and 90-BFR (18.28 ± 3.89 ml·kg -1 ·min -1 ); 90-BFR (intervals: 4 = 15.9 ± 2.3; intervals: 5 = 16.4 ± 2.5) resulted in a greater RPE compared with 30-BFR (intervals: 4 = 13.3 ± 1.4; intervals: 5 = 13.7 ± 1.7) during intervals 4 and 5. These results suggest that when adding BFR to various intensities of aerobic exercise, consideration should be given to peak work and VT to provide a balance between high local physiological stress and perceptual responses.

Beneficial Role of Blood Flow Restriction Exercise in Heart Disease and Heart Failure Using the Muscle Hypothesis of Chronic Heart Failure and a Growing Literature

Background: Blood flow restriction exercise (BFRE) has become a common method to increase skeletal muscle strength and hypertrophy for individuals with a variety of conditions. A substantial literature of BFRE in older adults exists in which significant gains in strength and functional performance have been observed without report of adverse events. Research examining the effects of BFRE in heart disease (HD) and heart failure (HF) appears to be increasing for which reason the Muscle Hypothesis of Chronic Heart Failure (MHCHF) will be used to fully elucidate the effects BFRE may have in patients with HD and HF highlighted in the MHCHF.

Methods: A comprehensive literature review was performed in PubMed and the Cochrane library through February 2022. Inclusion criteria were: 1) the study was original research conducted in human subjects older than 18 years of age and diagnosed with either HD or HF, 2) study participants performed BFRE, and 3) post-intervention outcome measures of cardiovascular function, physical performance, skeletal muscle function and structure, and/or systemic biomarkers were provided. Exclusion criteria included review articles and articles on viewpoints and opinions of BFRE, book chapters, theses, dissertations, and case study articles.

Results: Seven BFRE studies in HD and two BFRE studies in HF were found of which four of the HD and the two HF studies examined a variety of measures reflected within the MHCHF over a period of 8–24 weeks. No adverse events were reported in any of the studies and significant improvements in skeletal muscle strength, endurance, and work as well as cardiorespiratory performance, mitochondrial function, exercise tolerance, functional performance, immune humoral function, and possibly cardiac performance were observed in one or more of the reviewed studies.

Conclusion: In view of the above systematic review, BFRE has been performed safely with no report of adverse event in patients with a variety of different types of HD and in patients with HF. The components of the MHCHF that can be potentially improved with BFRE include left ventricular dysfunction, inflammatory markers, inactivity, a catabolic state, skeletal and possibly respiratory muscle myopathy, dyspnea and fatigue, ANS activity, and peripheral blood flow. Furthermore, investigation of feasibility, acceptability, adherence, adverse effects, and symptoms during and after BFRE is needed since very few studies have examined these important issues comprehensively in patients with HD and HF.

Blood flow restriction and stimulated muscle contractions do not improve metabolic or vascular outcomes following glucose ingestion in young, active individuals

Glucose ingestion and absorption into the blood stream can challenge glycemic regulation and vascular endothelial function. Muscular contractions in exercise promote a return to homeostasis by increasing glucose uptake and blood flow. Similarly, muscle hypoxia supports glycemic regulation by increasing glucose oxidation. Blood flow restriction (BFR) induces muscle hypoxia during occlusion and reactive hyperemia upon release. Thus, in the absence of exercise, electric muscle stimulation (EMS) and BFR may offer circulatory and glucoregulatory improvements. In 13 healthy, active participants (27±3yr, 7 female) we tracked post-glucose (oral 100g) glycemic, cardiometabolic and vascular function measures over 120min following four interventions: 1) BFR, 2) EMS, 3) BFR+EMS or 4) Control. BFR was applied at 2min intervals for 30min (70% occlusion), EMS was continuous for 30min (maximum-tolerable intensity). Glycemic and insulinemic responses did not differ between interventions (partial η2=0.11-0.15, P=0.2); however, only BFR+EMS demonstrated cyclic effects on oxygen consumption, carbohydrate oxidation, muscle oxygenation, heart rate, and blood pressure (all P<0.01). Endothelial function was reduced 60min post-glucose ingestion across interventions and recovered by 120min (5.9±2.6% vs 8.4±2.7%; P<0.001). Estimated microvascular function was not meaningfully different. Leg blood flow increased during EMS and BFR+EMS (+656±519mL•min-1, +433±510mL•min-1; P<0.001); however, only remained elevated following BFR intervention 90min post-glucose (+94±94mL•min-1; P=0.02). Superimposition of EMS onto cyclic BFR did not preferentially improve post-glucose metabolic or vascular function amongst young, active participants. Cyclic BFR increased blood flow delivery 60min beyond intervention, and BFR+EMS selectively increased carbohydrate usage and reduced muscle oxygenation warranting future clinical assessments.

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

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

Muscle Fatigue Is Attenuated When Applying Intermittent Compared With Continuous Blood Flow Restriction During Endurance Cycling

PURPOSE

The aim of this study was to identify a blood-flow-restriction (BFR) endurance exercise protocol that maximizes metabolic strain and minimizes muscle fatigue.

METHODS

Twelve healthy participants accomplished 5 different interval cycling endurance exercises (2-min work, 1-min rest) in a randomized order: (1) control, low intensity with unrestricted blood flow (CON30); (2) low intensity with intermittent BFR (i-BFR30, ∼150 mm Hg); (3) low intensity with continuous BFR (c-BFR, ∼100 mm Hg); (4) unloaded cycling with i-BFR0 (∼150 mm Hg); and (5) high intensity (HI) with unrestricted blood flow. Force production, creatine kinase activity, antioxidant markers, blood pH, and potassium (K+) were measured in a range of 5 minutes before and after each cycling exercise protocol.

RESULTS

HI showed the highest reduction (Δ = -0.26 [0.05], d = 5.6) on blood pH. Delta pH for c-BRF30 (Δ = -0.02 [0.03], d = 0.8) and Δ pH for i-BRF30 (Δ = -0.04 [0.03], d = 1.6) were different from each other, and both were higher compared with CON30 (Δ = 0.03 [0.03]). There was significant before-to-after force loss following HI (Δ = 55 [40] N·m-1, d = 1.5) and c-BFR30 (Δ = 27 [21] N·m-1, d = 0.7) protocols only, which were accompanied by significant increases in K+ (HI: Δ = 0.94 [0.65] mmol·L-1, d = 1.8; c-BFR30: Δ = 0.72 [0.85] mmol·L-1, d = 1.2). Moreover, all BFR conditions elicited slight increases in plasma creatine kinase, but not for HI and CON30. Glutathione changes from before to after were significant for all BFR conditions and HI, but not for CON30.

CONCLUSIONS

The attenuation in fatigue-induced reductions in maximal force suggests that i-BFR exercise could be preferable to c-BFR in improving exercise capacity, with considerably less biologic stress elicited from HI exercises.

Blood flow restriction during self-paced aerobic intervals reduces mechanical and cardiovascular demands without modifying neuromuscular fatigue

This study examined cardiovascular, perceptual, and neuromuscular fatigue characteristics during and after cycling intervals with and without blood flow restriction (BFR). Fourteen endurance cyclists/triathletes completed four 4-minute self-paced aerobic cycling intervals at the highest sustainable intensity, with and without intermittent BFR (60% of arterial occlusion pressure). Rest interval durations were six, four, and four minutes respectively. Power output, cardiovascular demands, and ratings of perceived exertion (RPE) were averaged over each interval. Knee extension torque and vastus lateralis electromyography responses following electrical stimulation of the femoral nerve were recorded pre-exercise, post-interval one (+1, 2, and 4-minutes) and post-interval four (+1, 2, 4, 6 and 8-minutes). Power output during BFR intervals was lower than non-BFR (233 ± 54 vs 282 ± 60W, p < 0.001). Oxygen uptake and heart rate during BFR intervals were lower compared to non-BFR (38.7 ± 4.5 vs 44.7 ± 6.44mL·kg^-1·min^-1, p < 0.001; 160 ± 14 vs 166 ± 10bpm, p < 0.001), while RPE was not different between conditions. Compared to pre-exercise, maximal voluntary contraction torque and peak twitch torque were reduced after the first interval with further reductions following the fourth interval (p < 0.001) independent of condition (p = 0.992). Voluntary activation (twitch interpolation) did not change between timepoints (p = 0.375). Overall, intermittent BFR reduced the mechanical and cardiovascular demands of self-paced intervals without modifying RPE or knee-extensor neuromuscular characteristics. Therefore, BFR reduced the cardiovascular demands while maintaining the muscular demands associated with self-paced intervals. Self-paced BFR intervals could be used to prevent cardiovascular and perceptual demands being the limiting factor of exercise intensity, thus allowing greater physiological muscular demands compared to intervals without BFR.

Physiological Responses to Acute Cycling With Blood Flow Restriction

Aerobic exercise with blood flow restriction (BFR) can improve muscular function and aerobic capacity. However, the extent to which cuff pressure influences acute physiological responses to aerobic exercise with BFR is not well documented. We compared blood flow, tissue oxygenation, and neuromuscular responses to acute cycling with and without BFR. Ten participants completed four intermittent cycling (6 × 2 min) conditions: low-load cycling (LL), low-load cycling with BFR at 60% of limb occlusion pressure (BFR60), low-load cycling with BFR at 80% of limb occlusion pressure (BFR80), and high-load cycling (HL). Tissue oxygenation, cardiorespiratory, metabolic, and perceptual responses were assessed during cycling and blood flow was measured during recovery periods. Pre- to post-exercise changes in knee extensor function were also assessed. BFR60 and BFR80 reduced blood flow (~33 and ~ 50%, respectively) and tissue saturation index (~5 and ~15%, respectively) when compared to LL (all p < 0.05). BFR60 resulted in lower VO2, heart rate, ventilation, and perceived exertion compared to HL (all p < 0.05), whereas BFR80 resulted in similar heart rates and exertion to HL (both p > 0.05). BFR60 and BFR80 elicited greater pain compared to LL and HL (all p < 0.05). After exercise, knee extensor torque decreased by ~18 and 40% for BFR60 and BFR80, respectively (both p < 0.05), and was compromised mostly through peripheral mechanisms. Cycling with BFR increased metabolic stress, decreased blood flow, and impaired neuromuscular function. However, only BFR60 did so without causing very severe pain (>8 on pain intensity scale). Cycling with BFR at moderate pressure may serve as a potential alternative to traditional high-intensity aerobic exercise.

Aerobic-interval exercise with blood flow restriction potentiates early markers of metabolic health in man

AIM

This study examined whether aerobic-interval exercise with blood flow restriction (BFR) potentiates early markers of metabolic health compared to exercise with systemic hypoxia or normoxia in man.

METHODS

In a randomized-crossover fashion, eight healthy men completed nine 2-minute running bouts at 105% of their lactate threshold on three occasions separated by one week, either with BFR (BFR-trial), systemic hypoxia (HYP-trial) or normoxia (control; CON-trial). Near-infrared spectroscopy was used to assess the muscle level of hypoxia. A muscle biopsy was collected at rest and 3 hours after exercise to quantify genes involved in cholesterol synthesis (PGC-1α2), glucose disposal (GLUT4) and capillary growth (HIF-1α; VEGFA), as well as mitochondrial respiration (PGC-1α2/3), uncoupling (UCP3) and expansion (p53; COXIV-1/2; CS; AMPKα1/2).

RESULTS

The muscle level of hypoxia was matched between the BFR-trial and HYP-trial (~90%; P > .05), which was greater than the CON-trial (~70%; P < .05). PGC-1α2 increased most in the BFR-trial (16-fold vs CON-trial; 11-fold vs HYP-trial; P < .05). GLUT4 and VEGFA selectively increased by 2.0 and 3.4-fold, respectively in BFR-trial (P < .05), which was greater than CON-trial (1.2 and 1.3 fold) and HYP-trial (1.2 and 1.8 fold; P < .05). UCP3 increased more in BFR-trial than the HYP-trial (4.3 vs 1.6 fold), but was not different between BFR-trial and CON-trial (2.1 fold) or between CON-trial and HYP-trial (P > .05). No trial differences were evident for other genes (P > .05).

CONCLUSION

Independent of the muscle level of hypoxia, BFR-exercise potentiates early markers of metabolic health associated with the regulation of cholesterol production and glucose homeostasis in man.

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.

Intra-rater reliability of leg blood flow during dynamic exercise using Doppler ultrasound

Developing an exercise model that resembles a traditional form of aerobic exercise and facilitates a complete simultaneous assessment of multiple parameters within the oxygen cascade is critically for understanding exercise intolerances in diseased populations. Measurement of muscle blood flow is a crucial component of such a model and previous studies have used invasive procedures to determine blood flow kinetics; however, this may not be appropriate in certain populations. Furthermore, current models utilizing Doppler ultrasound use isolated limb exercise and while these studies have provided useful data, the exercise model does not mimic the whole-body physiological response to continuous dynamic exercise. Therefore, we aimed to measure common femoral artery blood flow using Doppler ultrasound during continuous dynamic stepping exercise performed at three independent workloads to assess the within day and between-day reliability for such an exercise modality. We report a within-session coefficient of variation of 5.8% from three combined workloads and a between-day coefficient of variation of 12.7%. These values demonstrate acceptable measurement accuracy and support our intention of utilizing this noninvasive exercise model for an integrative assessment of the whole-body physiological response to exercise in a range of populations.

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 in the presence or absence of muscle contractions does not preserve vasculature structure and function following 14-days of limb immobilization

PURPOSE

Limb immobilization causes local vasculature to experience detrimental adaptations. Simple strategies to increase blood flow (heating, fidgeting) successfully prevent acute (≤ 1 day) impairments; however, none have leveraged the hyperemic response over prolonged periods (weeks) mirroring injury rehabilitation. Throughout a 14-day unilateral limb immobilization, we sought to preserve vascular structure and responsiveness by repeatedly activating a reactive hyperemic response via blood flow restriction (BFR) and amplifying this stimulus by combining BFR with electric muscle stimulation (EMS).

METHODS

Young healthy adults (M:F = 14:17, age = 22.4 ± 3.7 years) were randomly assigned to control, BFR, or BFR + EMS groups. BFR and BFR + EMS groups were treated for 30 min twice daily (3 × 10 min ischemia-reperfusion cycles; 15% maximal voluntary contraction EMS), 5 days/week (20 total sessions). Before and after immobilization, artery diameter, flow-mediated dilation (FMD) and blood flow measures were collected in the superficial femoral artery (SFA).

RESULTS

Following immobilization, there was less retrograde blood velocity (+ 1.8 ± 3.6 cm s^-1, P = 0.01), but not retrograde shear (P = 0.097). All groups displayed reduced baseline and peak SFA diameter following immobilization (- 0.46 ± 0.41 mm and - 0.43 ± 0.39 mm, P < 0.01); however, there were no differences by group or across time for FMD (% diameter change, shear-corrected, or allometrically scaled) nor microvascular function assessed by peak flow capacity.

CONCLUSION

Following immobilization, our results reveal (1) neither BFR nor BFR + EMS mitigate artery structure impairments, (2) intervention-induced shear stress did not affect vascular function assessed by FMD, and (3) retrograde blood velocity is reduced at rest offering potential insight to mechanisms of flow regulation. In conclusion, BFR appears insufficient as a treatment strategy for preventing macrovascular dysfunction during limb immobilization.

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.

The effect of blood-flow-restricted interval training on lactate and H+ dynamics during dynamic exercise in man

AIM

To assess how blood-flow-restricted (BFR) interval-training affects the capacity of the leg muscles for pH regulation during dynamic exercise in physically trained men.

METHODS

Ten men (age: 25 ± 4y; V ˙ O 2 max : 50 ± 5 mL∙kg^-1 ∙min^-1 ) completed a 6-wk interval-cycling intervention (INT) with one leg under BFR (BFR-leg; ~180 mmHg) and the other without BFR (CON-leg). Before and after INT, thigh net H⁺ -release (lactate-dependent, lactate-independent and sum) and blood acid/base variables were measured during knee-extensor exercise at 25% (Ex25) and 90% (Ex90) of incremental peak power output. A muscle biopsy was collected before and after Ex90 to determine pH, lactate and density of H⁺ -transport/buffering systems.

RESULTS

After INT, net H⁺ release (BFR-leg: 15 ± 2; CON-leg: 13 ± 3; mmol·min^-1 ; Mean ± 95% CI), net lactate-independent H⁺ release (BFR-leg: 8 ± 1; CON-leg: 4 ± 1; mmol·min^-1 ) and net lactate-dependent H⁺ release (BFR-leg: 9 ± 3; CON-leg: 10 ± 3; mmol·min^-1 ) were similar between legs during Ex90 (P > .05), despite a ~142% lower muscle intracellular-to-interstitial lactate gradient in BFR-leg (-3 ± 4 vs 6 ± 6 mmol·L^-1 ; P < .05). In recovery from Ex90, net lactate-dependent H⁺ efflux decreased in BFR-leg with INT (P < .05 vs CON-leg) owing to lowered muscle lactate production (~58% vs CON-leg, P < .05). Net H⁺ gradient was not different between legs (~19%, P > .05; BFR-leg: 48 ± 30; CON-leg: 44 ± 23; mmol·L^-1 ). In BFR-leg, NHE1 density was higher than in CON-leg (~45%; P < .05) and correlated with total-net H⁺ -release (r = 0.71; P = .031) and lactate-independent H⁺ release (r = 0.74; P = .023) after INT, where arterial [ HCO 3 - ] and standard base excess in Ex25 were higher in BFR-leg than CON-leg.

CONCLUSION

Compared to a training control, BFR-interval training increases the capacity for pH regulation during dynamic exercise mainly via enhancement of muscle lactate-dependent H⁺ -transport function and blood H⁺ -buffering capacity.

Effects of Blood Flow Restriction Exercise and Possible Applications in Type 2 Diabetes

Blood flow restriction resistance training (BFRT) employs partial vascular occlusion of exercising muscles via inflation cuffs. Compared with high-load resistance training, mechanical load is markedly reduced with BFRT, but induces similar gains in muscle mass and strength. BFRT is thus an effective training strategy for people with physical limitations. Recent research indicates that BFRT has beneficial effects on glucose and mitochondrial metabolism. BFRT may therefore qualify as a valuable exercise alternative for individuals with type 2 diabetes (T2D), a disorder characterized by impaired glucose metabolism, musculoskeletal decline, and exacerbated progression of sarcopenia. This review covers the effects of BFRT in healthy populations and in persons with impaired physical fitness, the mechanisms of action of this novel training modality, and possible applications for individuals with T2D.

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.

Elevated peak systolic blood pressure in endurance-trained athletes: Physiology or pathology?

Blood pressure is a function of cardiac output and peripheral vascular resistance. During graded exercise testing (GXT), systolic blood pressure (SBP) is expected to increase gradually along with work rate, oxygen consumption, heart rate, and cardiac output. Individuals exposed to chronic endurance training attain a greater exercise SBP than in their untrained state and sedentary counterparts, but it is currently unknown what is considered a safe upper limit. This review discusses key studies examining blood pressure response in sedentary individuals and athletes. We highlight the physiological characteristics of highly fit individuals in terms of cardiovascular physiology and exercise blood pressure and review the state of the current literature regarding the safety of high SBP during exercise in this particular subgroup. Findings from this review indicate that a consensus on what is a normal SBP response to exercise in highly fit subjects and direct causation linking high GXT SBP to pathology is lacking. Consequently, applying GXT SBP guidelines developed for a "normal" population to endurance-trained individuals appears unsupported at this time. Lack of evidence for poor outcomes leads us to infer that elevated peak SBP in this subgroup could more likely reflect an adaptive response to training, rather than a pathological outcome. Future studies should track clinical outcomes of those achieving elevated SBP and develop athlete-specific guidelines.

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.