Blood flow restriction training activates the muscle metaboreflex during low-intensity sustained exercise

Effects of low-intensity blood flow restriction training on myocardial injury indices, antioxidant and anti-apoptotic capacity in rats

Objective

This study aims to investigate the effects of low-intensity blood flow restriction training on myocardial tissue in rats. By measuring the levels of myocardial injury biomarkers in serum and the expression of anti-apoptotic and antioxidant proteins in myocardial tissue, the study preliminarily explores the underlying mechanisms.

Methods

Male 3-month-old Sprague-Dawley rats were randomly divided into the following groups: control group (CON), low-intensity training group (LIRT), high-intensity training group (HIRT), and low-intensity blood flow restriction training group (LIBFR), with 6 rats in each group. Body weight, maximum voluntary carrying capacity, myocardial morphology, myocardial injury biomarkers, and the expression levels of Bcl-2, Bax, Nrf2, and Keap1 proteins in myocardial tissue were evaluated.

Results

(1)cTn1 Detection: The HIRT group showed a significant increase in cTn1 levels (P < 0.01), while the LIBFR group had a lower cTn1 level compared to the HIRT group (P < 0.05). (2)Nrf2 and Keap1 Results: Compared to the CON group, the LIBFR group showed an increase in Nrf2 (P < 0.05), and a significant increase in Keap1 (P < 0.01). (3)Bcl-2 and Bax Results: Compared to the CON group, Bcl-2 levels were significantly elevated in the HIRT group (P < 0.01) and increased in the LIBFR group (P < 0.05), while Bax expression was significantly reduced in the LIBFR group (P < 0.05). Regarding the Bcl-2/Bax ratio, the LIRT, HIRT, and LIBFR groups exhibited significantly higher values compared to the CON group (P < 0.01). Furthermore, the HIRT and LIBFR groups showed significantly higher Bcl-2/Bax ratios than the LIRT group (P < 0.01).

Conclusion

Low-intensity blood flow restriction training can effectively reduce cTn1 in rat serum, decrease cardiomyocyte apoptosis, and improve antioxidant capacity, which has a certain protective effect on the myocardium.

Effect of a new resistance training method on the metaboreflex in cardiac rehabilitation patients: a randomized controlled trial

Patients with cardiac disease exhibit exaggerated sympathoexcitation, pressor, and ventilatory responses to muscle metaboreflex activation (MMA). However, the effects of cardiac rehabilitation (CR) and especially resistance training (RT) modalities on MMA are not well known. This study investigated how CR impacts MMA in such patients, specifically examining the effects of two different resistance training (RT) protocols following 12 weeks of CR. In addition to endurance exercises, 32 patients were randomized into either a 3/7 RT modality (comprising 5 sets of 3-7 repetitions) or a control (CTRL) modality (involving 3 sets of 9 repetitions), with distinct inter-set rest intervals (15 s for 3/7 and 60 s for CTRL). MMA, gauged by blood pressure (BP) and ventilatory (Ve) responses during a handgrip exercise at 40% effort and subsequent post-exercise circulatory occlusion, demonstrated CR's significant impact. Systolic BP, initially at + 28 ± 23% pre-CR, improved to + 11 ± 15% post-CR (P = .011 time effect; P = .131 group effect). Diastolic BP showed a similar trend, from + 27 ± 23% to + 13 ± 15% (P = .099 time effect; P = .087 group effect). Ve, initially at + 60 ± 39%, reduced to + 14 ± 19% post-CR (P < .001 time effect; P = .142 group effect). Critical parameters-maximal oxygen consumption, lean mass, hand grip, and quadriceps strength-exhibited parallel increases in both 3/7 and CTRL groups (P < .05 time effect; P > .3 group effect). Ultimately, CR demonstrated comparable improvements in MMA across both RT modalities, indicating its positive influence on cardiovascular responses and physical performance in individuals with cardiac conditions.

Blood Flow Restriction Training for Improving Body Composition of a 26-Year-Old Male With L5-S1 Disc Protrusion and Nerve Root Compression: A Case Report

This case report explores the use of blood flow restriction (BFR) training to improve body composition in a 26-year-old male with L5-S1 disc protrusion and nerve root compression. BFR training, involving low-intensity exercises with restricted blood flow, offers a promising alternative for patients unable to engage in high-intensity workouts. The patient, a recreational gymgoer with a history of a significant lower back injury from a maximal deadlift event 20 months ago, presented with chronic pain, weight gain, and decreased stamina. Two attempts at spinal steroid injections during the 20-month period yielded only temporary relief, prompting the implementation of a 12-week BFR training regimen. The program combined BFR exercises with a calorie-deficit diet, resulting in substantial improvements in body composition and strength. Over 12 weeks, the patient lost 11.68 kg, reduced his body mass index from 26.50 to 22.85, and decreased his total body fat percentage from 28% to 22.43%. His lower back pain also significantly improved. This case highlights the effectiveness of BFR training in managing obesity and enhancing physical fitness in spinal injury patients, emphasizing the need for further research on its broader application.

Exploring immediate cardiorespiratory responses: low-intensity blood flow restricted cycling vs. moderate-intensity traditional exercise in a randomized crossover trial

PURPOSE

Blood-flow restriction (BFR) endurance training may increase endurance performance and muscle strength similar to traditional endurance training while requiring a lower training intensity. We aimed to compare acute cardiorespiratory responses to low-intensity interval exercise under BFR with moderate-intensity traditional interval exercise (TRA).

METHODS

We conducted a randomized crossover study. The protocol involved three cycling intervals interspersed with 1 min resting periods. With a 48-h washout period, individuals performed the protocol twice in random order: once as BFR-50 (i.e., 50% incremental peak power output [IPPO] and 50% limb occlusion pressure [LOP]) and once as TRA-65 (65% IPPO without occlusion). TRA-65 intervals lasted 2 min, and time-matched BFR-50 lasted 2 min and 18 s. Respiratory parameters were collected by breath-by-breath analysis. The ratings of perceived breathing and leg exertion (RPE, 0 to 10) were assessed. Linear mixed models were used for analysis.

RESULTS

Out of the 28 participants initially enrolled in the study, 24 healthy individuals (18 males and 6 females) completed both measurements. Compared with TRA-65, BFR-50 elicited lower minute ventilation (VE, primary outcome) (-3.1 l/min [-4.4 to -1.7]), oxygen consumption (-0.22 l/min [-0.28 to -0.16]), carbon dioxide production (-0.25 l/min [-0.29 to -0.20]) and RPE breathing (-0.9 [-1.2 to -0.6]). RPE leg was significantly greater in the BFR-50 group (1.3 [1.0 to 1.7]).

CONCLUSION

BFR endurance exercise at 50% IPPO and 50% LOP resulted in lower cardiorespiratory work and perceived breathing effort compared to TRA at 65% IPPO. BFR-50 could be an attractive alternative for TRA-65, eliciting less respiratory work and perceived breathing effort while augmenting perceived leg muscle effort.

TRIAL REGISTRATION

NCT05163600; December 20, 2021.

Muscle metaboreflex stimulates the cardiac sympathetic afferent reflex causing positive feedback amplification of sympathetic activity: effect of heart failure

Exercise intolerance is a hallmark symptom of heart failure and to a large extent stems from reductions in cardiac output that occur due to the inherent ventricular dysfunction coupled with enhanced muscle metaboreflex-induced functional coronary vasoconstriction, which limits increases in coronary blood flow. This creates a further mismatch between O2 delivery and O2 demand, which may activate the cardiac sympathetic afferent reflex (CSAR), causing amplification of the already increased sympathetic activity in a positive-feedback fashion. We used our chronically instrumented conscious canine model to evaluate if chronic ablation of afferents responsible for the CSAR would attenuate the gain of muscle metaboreflex before and after induction of heart failure. After afferent ablation, the gain of the muscle metaboreflex control of mean arterial pressure was significantly reduced before (-239.5 ± 16 to -95.2 ± 8 mmHg/L/min) and after the induction of heart failure (-185.6 ± 14 to -95.7 ± 12 mmHg/L/min). Similar results were observed for the strength (gain) of muscle metaboreflex control of heart rate, cardiac output, and ventricular contractility. Thus, we conclude that the CSAR contributes significantly to the strength of the muscle metaboreflex in normal animals with heart failure serving as an effective positive-feedback amplifier thereby further increasing sympathetic activity.NEW & NOTEWORTHY The powerful pressor responses from the CSAR arise via O2 delivery versus O2 demand imbalance. Muscle metaboreflex activation (MMA) simultaneously elicits coronary vasoconstriction (which is augmented in heart failure) and profound increases in cardiac work thereby upsetting oxygen balance. Whether MMA activates the CSAR thereby amplifying MMA responses is unknown. We observed that removal of the CSAR afferents attenuated the strength of the muscle metaboreflex in normal and subjects with heart failure.