Effect of walk training combined with blood flow restriction on resting heart rate variability and resting blood pressure in middle-aged men

Development of a prediction equation to estimate lower-limb arterial occlusion pressure with a thigh sphygmomanometer

INTRODUCTION

Previous investigators have developed prediction equations to estimate arterial occlusion pressure (AOP) for blood flow restriction (BFR) exercise. Most equations have not been validated and are designed for use with expensive cuff systems. Thus, their implementation is limited for practitioners.

PURPOSE

To develop and validate an equation to predict AOP in the lower limbs when applying an 18 cm wide thigh sphygmomanometer (SPHYG18cm).

METHODS

Healthy adults (n = 143) underwent measures of thigh circumference (TC), skinfold thickness (ST), and estimated muscle cross-sectional area (CSA) along with brachial and femoral systolic (SBP) and diastolic (DBP) blood pressure. Lower-limb AOP was assessed in a seated position at the posterior tibial artery (Doppler ultrasound) using a SPHYG18cm. Hierarchical linear regression models were used to determine predictors of AOP. The best set of predictors was used to construct a prediction equation to estimate AOP. Performance of the equation was evaluated and internally validated using bootstrap resampling.

RESULTS

Models containing measures of either TC or thigh composition (ST and CSA) paired with brachial blood pressures explained the most variability in AOP (54%) with brachial SBP accounting for majority of explained variability. A prediction equation including TC, brachial SBP, and age showed good predictability (R2 = 0.54, RMSE = 7.18 mmHg) and excellent calibration. Mean difference between observed and predicted values was 0.0 mmHg and 95% Limits of Agreement were ± 18.35 mmHg. Internal validation revealed small differences between apparent and optimism adjusted performance measures, suggesting good generalizability.

CONCLUSION

This prediction equation for use with a SPHYG18cm provided a valid way to estimate lower-limb AOP without expensive equipment.

Muscle strength adaptation between high-load resistance training versus low-load blood flow restriction training with different cuff pressure characteristics: a systematic review and meta-analysis

Purpose: In this systematic review and meta-analysis, blood flow restriction (BFR) with low-load resistance training (BFR-RT) was compared with high-load resistance training (HL-RT) on muscle strength in healthy adults. The characteristics of cuff pressure suitable for muscle strength gain were also investigated by analyzing the effects of applying different occlusion pressure prescriptions and cuff inflation patterns on muscle strength gain. Methods: Literature search was conducted using PubMed, Ovid Medline, ProQuest, Cochrane Library, Embase, and Scopus databases to identify literature published until May 2023. Studies reporting the effects of BFR-RT interventions on muscle strength gain were compared with those of HL-RT. The risk of bias in the included trials was assessed using the Cochrane tool, followed by a meta-analysis to calculate the combined effect. Subgroup analysis was performed to explore the beneficial variables. Results: Nineteen articles (42 outcomes), with a total of 458 healthy adults, were included in the meta-analysis. The combined effect showed higher muscle strength gain with HL-RT than with BFR-RT (p = 0.03, SMD = -0.16, 95% CI: -0.30 to -0.01). The results of the subgroup analysis showed that the BFR-RT applied with incremental and individualized pressure achieved muscle strength gain similar to the HL-RT (p = 0.8, SMD = -0.05, 95% CI: -0.44 to 0.34; p = 0.68, SMD = -0.04, 95% CI: -0.23 to 0.15), but muscle strength gain obtained via BFR-RT applied with absolute pressure was lower than that of HL-RT (p < 0.05, SMD = -0.45, 95% CI: -0.71 to -0.19). Furthermore, muscle strength gain obtained by BFR-RT applied with intermittent pressure was similar to that obtained by HL-RT (p = 0.88, SMD = -0.02, 95% CI: -0.27 to 0.23), but muscle strength gain for BFR-RT applied with continuous pressure showed a less prominent increase than that for HL-RT (p < 0.05, SMD = -0.3, 95% CI: -0.48 to -0.11). Conclusion: In general, HL-RT produces superior muscle strength gains than BFR-RT. However, the application of individualized, incremental, and intermittent pressure exercise protocols in BFR-RT elicits comparable muscle strength gains to HL-RT. Our findings indicate that cuff pressure characteristics play a significant role in establishing a BFR-RT intervention program for enhancing muscle strength in healthy adults. Clinical Trial Registration: https://www.crd.york.ac.uk/PROSPERO/#recordDetails; Identifier: PROSPERO (CRD42022364934).

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 training on resting blood pressure and heart rate: a meta-analysis of the available literature

The purpose of this meta-analysis was to examine the effects of blood flow restriction training on resting blood pressure and heart rate. A meta-analysis was completed in May 2020 including all previously published papers on blood flow restriction and was analyzed using a random effects model. To be included, studies needed to implement a blood flow restriction protocol compared to the same exercise protocol without restriction. A total of four studies met the inclusion criteria for quantitative analysis including four effect sizes for resting systolic blood pressure, four effect sizes for resting diastolic blood pressure, and three effect sizes for resting heart rate. There was evidence of a difference [mean difference (95 CI)] in resting systolic blood pressure between training with and without blood flow restriction [4.2 (0.3, 8.0) mmHg, p = 0.031]. No significant differences were observed when comparing resting diastolic blood pressure [1.2 (-1, 3.5) mmHg p = 0.274] and resting heart rate [-0.2 (-4.7, 4.1) bpm, p = 0.902] between chronic exercise with and without blood flow restriction. These results indicate that training with blood flow restriction may elicit an increase in resting systolic blood pressure. However, lack of data addressing this topic makes any conclusion speculative. Based on the results of the present study along with the overall lack of long-term data, it is suggested that future research on this topic is warranted. Recommendations include making changes in resting blood pressure a primary outcome and increasing the sample size of the interventions.

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.