Increased FXYD1 and PGC-1α mRNA after blood flow-restricted running is related to fibre type-specific AMPK signalling and oxidative stress in human muscle

Mitochondrial and cardiovascular responses to aerobic exercise training in supine and upright positions in healthy young adults: a randomized parallel arm trial

Objectives

Aerobic exercise training can increase skeletal muscle mitochondrial content. Supine exercise training with legs above the heart potentially augments these increases. However, the impact of supine exercise training on mitochondrial biogenesis and cardiovascular adaptations remains unclear.

Methods

In this single-centred, randomized, parallel arm trial, 19 recreationally active individuals underwent seven sessions of either supine with legs up (SUP; n=9, 6 females) or upright with legs down (UP; n=10, 7 females) aerobic training on a recumbent bike at 71 ± 7 % and 71 ± 2 % of peak work rate (WRpeak), respectively. The study aimed to test the effects of training with decreased muscle oxygenation on indices of muscle mitochondrial remodelling. Secondary outcomes included exercise performance, muscle oxygenation, and cardiovascular responses.

Results

Secondary outcomes revealed significant interaction effects for time to fatigue (TTF) and WRpeak in the SUP group during supine testing, suggesting enhanced exercise tolerance and performance. No between group interaction effects were observed for upright testing. No clear effects on mitochondrial biogenesis were observed based on expression of mitochondrial protein subunits and transcriptional regulators. Acutely, HRpeak was lower during the SUP Test compared to the UP Test. No central cardiovascular adaptations were observed following training.

Conclusions

Our exploratory analyses showed that supine aerobic training more effectively improves supine exercise tolerance and performance compared with upright training, despite no differences in measured proteins related to mitochondrial biogenesis. Further research is needed to elucidate the mechanisms underlying these postural-specific training effects.

Registration

clinicaltrials.gov: NCT04151095.

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.

Unveiling the role of exercise in modulating plasma heat shock protein 27 levels: insights for exercise immunology and cardiovascular health

Cardiovascular disease is one of the leading causes of mortality worldwide, primarily driven by atherosclerosis, a chronic inflammatory condition contributing significantly to fatalities. Various biological determinants affecting cardiovascular health across different age and sex groups have been identified. In this context, recent attention has focused on the potential therapeutic and preventive role of increasing circulating levels of heat shock protein 27 (plasma HSP27) in combating atherosclerosis. Plasma HSP27 is recognized for its protective function in inflammatory atherogenesis, offering promising avenues for intervention and management strategies against this prevalent cardiovascular ailment. Exercise has emerged as a pivotal strategy in preventing and managing cardiovascular disease, with literature indicating an increase in plasma HSP27 levels post-exercise. However, there is limited understanding of the impact of exercise on the release of HSP27 into circulation. Clarifying these aspects is crucial for understanding the role of exercise in modulating plasma HSP27 levels and its potential implications for cardiovascular health across diverse populations. Therefore, this review aims to establish a more comprehensive understanding of the relationship between plasma HSP27 and exercise.

Effects of aerobic training with blood flow restriction on aerobic capacity, muscle strength, and hypertrophy in young adults: a systematic review and meta-analysis

Aerobic training with blood flow restriction (AT-BFR) has shown promise in enhancing both aerobic capacity and exercise performance. The aim of this review was to systematically analyze the evidence regarding the effectiveness of this novel training method on aerobic capacity, muscle strength, and hypertrophy in young adults. Studies were identified through a search of databases including PubMed, Scopus, Web of Science, SPORTDiscus, CINAHL, Cochrane Library, and EMBASE. A total of 16 studies, involving 270 subjects, were included in the meta-analysis. The results revealed that AT-BFR induced greater improvements in VO2max (SMD = 0.27, 95%CI: [0.02, 0.52], p < 0.05), and muscle strength (SMD = 0.39, 95%CI: [0.09, 0.69], p < 0.05), compared to aerobic training with no blood flow restriction (AT-noBFR). However, no significant effect was observed on muscle mass (SMD = 0.23, 95%CI: [-0.09, 0.56], p = 0.162). Furthermore, no moderating effects on the outcomes were found for individual characteristics or training factors. In conclusion, AT-BFR is more effective than AT-noBFR in improving aerobic capacity and muscle strength, making it a promising alternative to high-intensity training.

Systematic Review Registration

https://www.crd.york.ac.uk/prospero/, identifier CRD42024559872.

CaMKII protein expression and phosphorylation in human skeletal muscle by immunoblotting: Isoform specificity

Calcium (Ca2+)/calmodulin-dependent protein kinase II (CaMKII) is activated during exercise by reactive oxygen species (ROS) and Ca2+ transients initiating muscle contraction. CaMKII modulates antioxidant, inflammatory, metabolic and autophagy signalling pathways. CaMKII is coded by four homologous genes (α, β, γ, and δ). In rat skeletal muscle, δD, δA, γD, γB and βM have been described while different characterisations of human skeletal muscle CaMKII isoforms have been documented. Precisely discerning between the various isoforms is pivotal for understanding their distinctive functions and regulatory mechanisms in response to exercise and other stimuli. This study aimed to optimize the detection of the different CaMKII isoforms by western blotting using eight different CaMKII commercial antibodies in human skeletal muscle. Exercise-induced posttranslational modifications, i.e. phosphorylation and oxidations, allowed the identification of specific bands by multitargeting them with different antibodies after stripping and reprobing. The methodology proposed has confirmed the molecular weight of βM CaMKII and allows distinguishing between γ/δ and δD CaMKII isoforms. The corresponding molecular weight for the CaMKII isoforms resolved were: δD, at 54.2 ± 2.1 kDa; γ/δ, at 59.0 ± 1.2 kDa and 61.6 ± 1.3 kDa; and βM isoform, at 76.0 ± 1.8 kDa. Some tested antibodies showed high specificity for the δD, the most responsive isoform to ROS and intracellular Ca2+ transients in human skeletal muscle, while others, despite the commercial claims, failed to show such specificity.

The effect of blood flow-restrictive resistance training on the risk of atherosclerotic cardiovascular disease in middle-aged patients with type 2 diabetes: a randomized controlled trial

Introduction

The aim of this study was to investigate the effects of blood flow-restrictive resistance training (BFR-RT) on improving metabolic abnormalities, blood pressure (BP), obesity, and 10-year atherosclerotic cardiovascular disease (ASCVD) risk in middle-aged patients with type 2 diabetes mellitus (T2DM).

Method

We conducted a parallel-group, single blind randomized controlled trial. Participants who met the inclusion criteria were randomly divided into control group, BFR-RT group and aerobic exercise (AE) group. Control group received health education and follow-up; Two exercise groups received supervised collective training for a period of six months, three times per week. AE group trained at moderate-intensity for 60 minutes each time, while BFR-RT group trained at low-intensity for 40 minutes each time. The primary outcomes were change in 10-year ASCVD risk index and level, and the secondary outcomes included changes in fasting plasma glucose (FPG), glycosylated hemoglobin (HbA1c), blood lipids, BP, and obesity level within and across the three groups at baseline, the third and sixth months of intervention.

Result

Among 93 individuals (control group, n=31; AE, n=30; BFR-RT, n=32) were analyzed. At baseline, there were no significant differences in various indicators among the three groups (p>0.05). After intervention, the 10-year ASCVD risk index and risk level of both exercise groups significantly decreased compared to the control group and baseline (p<0.05), and the risk reduction became more pronounced over time. In the sixth month of intervention, the 10-year ASCVD risk index in the AE group decreased by 27.40%, and that in the BFR-RT group decreased by 26.78%. Meanwhile, apart from lipoprotein (a) and diastolic blood pressure, both exercise groups showed significant improvements in FPG, HbA1c, dyslipidemia, systolic blood pressure, and obesity indicators compared to the control group and baseline (p<0.05). There was no significant difference in various indicators between the two exercise groups (p>0.05).

Conclusion

BFR-RT could reduce the 10-year ASCVD risk in middle-aged T2DM patients for by improving metabolic abnormalities, BP and obesity, and its effect was similar to that of moderate-intensity AE.

Clinical trial registration

https://www.chictr.org.cn/showproj.html?proj=178886, identifier ChiCTR2300074357.

AMPK and glucose deprivation exert an isoform-specific effect on the expression of Na+,K+-ATPase subunits in cultured myotubes

In skeletal muscle, Na+,K+-ATPase (NKA), a heterodimeric (α/β) P-type ATPase, has an essential role in maintenance of Na+ and K+ homeostasis, excitability, and contractility. AMP-activated protein kinase (AMPK), an energy sensor, increases the membrane abundance and activity of NKA in L6 myotubes, but its potential role in regulation of NKA content in skeletal muscle, which determines maximum capacity for Na+ and K+ transport, has not been clearly delineated. We examined whether energy stress and/or AMPK affect expression of NKA subunits in rat L6 and primary human myotubes. Energy stress, induced by glucose deprivation, increased protein content of NKAα1 and NKAα2 in L6 myotubes, while decreasing the content of NKAα1 in human myotubes. Pharmacological AMPK activators (AICAR, A-769662, and diflunisal) modulated expression of NKA subunits, but their effects only partially mimicked those that occurred in response to glucose deprivation, indicating that AMPK does not mediate all effects of energy stress on NKA expression. Gene silencing of AMPKα1/α2 increased protein levels of NKAα1 in L6 myotubes and NKAα1 mRNA levels in human myotubes, while decreasing NKAα2 protein levels in L6 myotubes. Collectively, our results suggest a role for energy stress and AMPK in modulation of NKA expression in skeletal muscle. However, their modulatory effects were not conserved between L6 myotubes and primary human myotubes, which suggests that coupling between energy stress, AMPK, and regulation of NKA expression in vitro depends on skeletal muscle cell model.

The Effects of Blood Flow Restriction Aerobic Exercise on Body Composition, Muscle Strength, Blood Biomarkers, and Cardiovascular Function: A Narrative Review

Blood flow restriction exercise has emerged as a promising alternative, particularly for elderly individuals and those unable to participate in high-intensity exercise. However, existing research has predominantly focused on blood flow restriction resistance exercise. There remains a notable gap in understanding the comprehensive effects of blood flow restriction aerobic exercise (BFRAE) on body composition, lipid profiles, glycemic metabolism, and cardiovascular function. This review aims to explore the physiological effects induced by chronic BFRAE. Chronic BFRAE has been shown to decrease fat mass, increase muscle mass, and enhance muscular strength, potentially benefiting lipid profiles, glycemic metabolism, and overall function. Thus, the BFRAE offers additional benefits beyond traditional aerobic exercise effects. Notably, the BFRAE approach may be particularly suitable for individuals with low fitness levels, those prone to injury, the elderly, obese individuals, and those with metabolic disorders.

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.

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.

Aerobic Training With Blood Flow Restriction on Muscle Hypertrophy and Strength: Systematic Review and Meta-analysis

ABSTRACT

de Lemos Muller, CH, Farinha, JB, Leal-Menezes, R, and Ramis, TR. Aerobic training with blood flow restriction on muscle hypertrophy and strength: systematic review and meta-analysis. J Strength Cond Res 38(7): 1341-1349, 2024-Integrating strength and endurance training in a single exercise session, even on separate days, can be physically demanding and time-consuming. Therefore, there is a growing interest in identifying efficient training methods that can concurrently enhance cardiovascular and neuromuscular performance through a singular training modality. This study conducted a systematic review and meta-analysis to explore the effects of aerobic training with blood flow restriction (AT + BFR) on muscle hypertrophy and strength gains in healthy individuals. Our study was registered at PROSPERO and used multiple databases (PubMed, Embase, Scopus, and Web of Science), seeking clinical trials that examined AT + BFR influence on muscle hypertrophy and strength gains in individuals aged 18-60 years and comparing with aerobic training without BFR. The risk of bias and method quality were assessed using the ROB2.0 tool and PEDro scale, respectively, and the quality of evidence was evaluated with the GRADE method. A random-effects model was used for meta-analysis, and standardized mean difference (SMD) was calculated for each outcome. Of 4,462 records, 29 full texts were assessed for eligibility, with 7 articles meeting the inclusion criteria. The results indicated that AT + BFR was more beneficial for inducing muscle hypertrophy than aerobic training without BFR (SMD [95% CI] = 0.86 [0.37-1.35]; I2 = 42%). Furthermore, AT + BFR was associated with greater improvements in muscle strength (SMD [95% CI] = 0.41 [0.10-0.72]; I2 = 0%). Despite the generally high risk of bias for both outcomes, these encouraging findings underscore the clinical significance of AT + BFR as a compelling tool for enhancing neuromuscular parameters.

Acute Effects of a Practical Blood Flow Restriction Device During Swimming Exercise

Purpose: The present study aimed to analyze: 1) the reliability of the tissue saturation index (TSI) and ratings of perceived discomfort (RPD) responses wearing a neoprene practical cuff (PrC), comparing with the responses from traditional (TrC) pneumatic cuffs (study I); 2) the effects of PrC on metabolic (blood lactate concentration, BLC), perceptual (rate of perceived effort, RPE) and kinematic responses at sub-maximal swimming velocities (study II). Methods: Study I; 1) PrC test-retest at rest and during swimming ergometer exercise; 2) BFR at rest with TrC inflated to different percentages of the minimum arterial occlusion pressure (MAOP; 60, 80, 100, 120 and 140%). Test-retest reliability of TSI and RPD was assessed by the intraclass correlation coefficient (ICC) and comparisons among conditions were analyzed by one-way repeated-measures ANOVA. Study II; 1) 50, 200 and 400 m swimming performances; 2) sub-maximal incremental swimming protocol with and without PrC. Two-way repeated measures ANOVA was used to compare all variables during sub-maximal velocities. Results: TSI (ICC = 0.81; 95%CI 0.62-0.91) and RPD (ICC = 0.97; 95%CI 0.94-0.99) were reliable under restricted exercise using PrC. TSI during restricted exercise was lower (p <.001) compared to unrestricted exercise (6.8 ± 6.1% vs. 21.6 ± 8.2% of physiological normalization). PrC showed higher BLC only at or above 91% of critical velocity (p < .03), while stroke rate and RPE were higher (p < .005), and stroke length was lower (p < .03) during all swimming velocities. Conclusion: This easy-to-handle and affordable practical BFR device increased physiological stress at sub-maximal efforts which could be an additional training tool for swimmers.

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.

Acute physiological responses of blood flow restriction between high-intensity interval repetitions in trained cyclists

Blood flow restriction (BFR) is increasingly being used to enhance aerobic performance in endurance athletes. This study examined physiological responses to BFR applied in recovery phases within a high-intensity interval training (HIIT) session in trained cyclists. Eleven competitive road cyclists (mean ± SD, age: 28 ± 7 years, body mass: 69 ± 6 kg, peak oxygen uptake: 65 ± 9 mL · kg-1 · min-1) completed two randomised crossover conditions: HIIT with (BFR) and without (CON) BFR applied during recovery phases. HIIT consisted of six 30-s cycling bouts at an intensity equivalent to 85% of maximal 30-s power (523 ± 93 W), interspersed with 4.5-min recovery. BFR (200 mmHg, 12 cm cuff width) was applied for 2-min in the early recovery phase between each interval. Pulmonary gas exchange (V̇O2, V̇CO2, and V̇E), tissue oxygen saturation index (TSI), heart rate (HR), and serum vascular endothelial growth factor concentration (VEGF) were measured. Compared to CON, BFR increased V̇CO2 and V̇E during work bouts (both p < 0.05, dz < 0.5), but there was no effect on V̇O2, TSI, or HR (p > 0.05). In early recovery, BFR decreased TSI, V̇O2, V̇CO2, and V̇E (all p < 0.05, dz > 0.8) versus CON, with no change in HR (p > 0.05). In late recovery, when BFR was released, V̇O2, V̇CO2, V̇E, and HR increased, but TSI decreased versus CON (all p < 0.05, dz > 0.8). There was a greater increase in VEGF at 3-h post-exercise in BFR compared to CON (p < 0.05, dz > 0.8). Incorporating BFR into HIIT recovery phases altered physiological responses compared to exercise alone.

Mechanistic of AMPK/ACC2 regulating myoblast differentiation by fatty acid oxidation of goat

Myoblast differentiation depends on fatty acid oxidation (FAO)，and its rate-limiting enzyme acetyl-CoA carboxylase 2 (ACC2) participate in the regulation skeletal muscle development. However, the precise regulatory mechanism is still unknown. Using previous RNA-sequencing data from our laboratory, we explored the effect of ACC2 on myoblast differentiation, as a candidate gene, since its expression is higher in myoblasts of lamb (first day of age) than that of the fetus (75th day of pregnancy). Our findings show that siACC2 inhibited myoblast proliferation, promoted differentiation, and boosted mitochondrial and fatty acid oxidation activities. The effect of ACC2 on goat muscle cell differentiation was modulated by Etomoxir, a CPT1A inhibitor. Notably, the AMPK/ACC2 pathway was found to regulate fatty acid oxidation and goat muscle cell differentiation. Inhibiting the AMPK/ACC2 pathway significantly reduced CPT1A expression. These findings indicate that AMPK/ACC2 regulate goat myoblast differentiation via fatty acid oxidation, contributing to understanding the mechanism of goat skeletal muscle development.

Potential Moderators of the Effects of Blood Flow Restriction Training on Muscle Strength and Hypertrophy: A Meta-analysis Based on a Comparison with High-Load Resistance Training

BACKGROUND

While it has been examined whether there are similar magnitudes of muscle strength and hypertrophy adaptations between low-load resistance training combined with blood-flow restriction training (BFR-RT) and high-load resistance training (HL-RT), some important potential moderators (e.g., age, sex, upper and lower limbs, frequency and duration etc.) have yet to be analyzed further. Furthermore, training status, specificity of muscle strength tests (dynamic versus isometric or isokinetic) and specificity of muscle mass assessments (locations of muscle hypertrophy assessments) seem to exhibit different effects on the results of the analysis. The role of these influencing factors, therefore, remains to be elucidated.

OBJECTIVES

The aim of this meta-analysis was to compare the effects of BFR- versus HL-RT on muscle adaptations, when considering the influence of population characteristics (training status, sex and age), protocol characteristics (upper or lower limbs, duration and frequency) and test specificity.

METHODS

Studies were identified through database searches based on the following inclusion criteria: (1) pre- and post-training assessment of muscular strength; (2) pre- and post-training assessment of muscular hypertrophy; (3) comparison of BFR-RT vs. HL-RT; (4) score ≥ 4 on PEDro scale; (5) means and standard deviations (or standard errors) are reported or allow estimation from graphs. In cases where the fifth criterion was not met, the data were requested directly from the authors.

RESULTS

The main finding of the present study was that training status was an important influencing factor in the effects of BFR-RT. The trained individuals may gain greater muscle strength and hypertrophy with BFR-RT as compared to HL-RT. However, the results showed that the untrained individuals experienced similar muscle mass gains and superior muscle strength gains in with HL-RT compared to BFR-RT.

CONCLUSION

Compared to HL-RT, training status is an important factor influencing the effects of the BFR-RT, in which trained can obtain greater muscle strength and hypertrophy gains in BFR-RT, while untrained individuals can obtain greater strength gains and similar hypertrophy in HL-RT.

A century of exercise physiology: effects of muscle contraction and exercise on skeletal muscle Na+,K+-ATPase, Na+ and K+ ions, and on plasma K+ concentration-historical developments

This historical review traces key discoveries regarding K+ and Na+ ions in skeletal muscle at rest and with exercise, including contents and concentrations, Na+,K+-ATPase (NKA) and exercise effects on plasma [K+] in humans. Following initial measures in 1896 of muscle contents in various species, including humans, electrical stimulation of animal muscle showed K+ loss and gains in Na+, Cl- and H20, then subsequently bidirectional muscle K+ and Na+ fluxes. After NKA discovery in 1957, methods were developed to quantify muscle NKA activity via rates of ATP hydrolysis, Na+/K+ radioisotope fluxes, [3H]-ouabain binding and phosphatase activity. Since then, it became clear that NKA plays a central role in Na+/K+ homeostasis and that NKA content and activity are regulated by muscle contractions and numerous hormones. During intense exercise in humans, muscle intracellular [K+] falls by 21 mM (range - 13 to - 39 mM), interstitial [K+] increases to 12-13 mM, and plasma [K+] rises to 6-8 mM, whilst post-exercise plasma [K+] falls rapidly, reflecting increased muscle NKA activity. Contractions were shown to increase NKA activity in proportion to activation frequency in animal intact muscle preparations. In human muscle, [3H]-ouabain-binding content fully quantifies NKA content, whilst the method mainly detects α2 isoforms in rats. Acute or chronic exercise affects human muscle K+, NKA content, activity, isoforms and phospholemman (FXYD1). Numerous hormones, pharmacological and dietary interventions, altered acid-base or redox states, exercise training and physical inactivity modulate plasma [K+] during exercise. Finally, historical research approaches largely excluded female participants and typically used very small sample sizes.

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.

Impacts of altered exercise volume, intensity, and duration on the activation of AMPK and CaMKII and increases in PGC-1α mRNA

The purpose of this review is to explore and discuss the impacts of augmented training volume, intensity, and duration on the phosphorylation/activation of key signaling protein - AMPK, CaMKII and PGC-1α - involved in the initiation of mitochondrial biogenesis. Specifically, we explore the impacts of augmented exercise protocols on AMP/ADP and Ca²⁺ signaling and changes in post exercise PGC - 1α gene expression. Although AMP/ADP concentrations appear to increase with increasing intensity and during extended durations of higher intensity exercise AMPK activation results are varied with some results supporting and intensity/duration effect and others not. Similarly, CaMKII activation and signaling results following exercise of different intensities and durations are inconsistent. The PGC-1α literature is equally inconsistent with only some studies demonstrating an effect of intensity on post exercise mRNA expression. We present a novel meta-analysis that suggests that the inconsistency in the PGC-1α literature may be due to sample size and statistical power limitations owing to the effect of intensity on PGC-1α expression being small. There is little data available regarding the impact of exercise duration on PGC-1α expression. We highlight the need for future well designed, adequately statistically powered, studies to clarify our understanding of the effects of volume, intensity, and duration on the induction of mitochondrial biogenesis by exercise.

A Scoping Review Investigating the "Gene-Dosage Theory" of Mitochondrial DNA in the Healthy Skeletal Muscle

This review provides an overview of the evidence regarding mtDNA and valid biomarkers for assessing mitochondrial adaptions. Mitochondria are small organelles that exist in almost all cells throughout the human body. As the only organelle, mitochondria contain their own DNA, mitochondrial DNA (mtDNA). mtDNA-encoded polypeptides are subunits of the enzyme complexes in the electron transport chain (ETC) that are responsible for production of ATP to the cells. mtDNA is frequently used as a biomarker for mitochondrial content, since changes in mitochondrial volume are thought to induce similar changes in mtDNA. However, some exercise studies have challenged this "gene-dosage theory", and have indicated that changes in mitochondrial content can adapt without changes in mtDNA. Thus, the aim of this scoping review was to summarize the studies that used mtDNA as a biomarker for mitochondrial adaptions and address the question as to whether changes in mitochondrial content, induce changes in mtDNA in response to aerobic exercise in the healthy skeletal muscle. The literature was searched in PubMed and Embase. Eligibility criteria included: interventional study design, aerobic exercise, mtDNA measurements reported pre- and postintervention for the healthy skeletal muscle and English language. Overall, 1585 studies were identified. Nine studies were included for analysis. Eight out of the nine studies showed proof of increased oxidative capacity, six found improvements in mitochondrial volume, content and/or improved mitochondrial enzyme activity and seven studies did not find evidence of change in mtDNA copy number. In conclusion, the findings imply that mitochondrial adaptions, as a response to aerobic exercise, can occur without a change in mtDNA copy number.

Six weeks of high-load resistance and low-load blood flow restricted training increase Na/K-ATPase sub-units α2 and β1 equally, but does not alter ClC-1 abundance in untrained human skeletal muscle

Contractile function of skeletal muscle relies on the ability of muscle fibers to trigger and propagate action potentials (APs). These electrical signals are created by transmembrane ion transport through ion channels and membrane transporter systems. In this regard, the Cl^- ion channel 1 (ClC-1) and the Na⁺/K^--ATPase (NKA) are central for maintaining ion homeostasis across the sarcolemma during intense contractile activity. Therefore, this randomized controlled trial aimed to investigate the changes in ClC-1 and specific NKA subunit isoform expression in response to six weeks (18 training sessions) of high-load resistance exercise (HLRE) and low-load blood flow restricted resistance exercise (BFRRE), respectively. HLRE was conducted as 4 sets of 12 repetitions of knee extensions performed at 70% of 1 repetition maximum (RM), while BFRRE was conducted as 4 sets of knee extensions at 30% of 1RM performed to volitional fatigue. Furthermore, the potential associations between protein expression and contractile performance were investigated. We show that muscle ClC-1 abundance was not affected by either exercise modality, whereas NKA subunit isoforms [Formula: see text]² and [Formula: see text]¹ increased equally by appx. 80-90% with BFRRE (p < 0.05) and 70-80% with HLRE (p < 0.05). No differential impact between exercise modalities was observed. At baseline, ClC-1 protein expression correlated inversely with dynamic knee extensor strength (r=-0.365, p = 0.04), whereas no correlation was observed between NKA subunit content and contractile performance at baseline. However, training-induced changes in NKA [Formula: see text]² subunit (r = 0.603, p < 0.01) and [Formula: see text]¹ subunit (r = 0.453, p < 0.05) correlated with exercise-induced changes in maximal voluntary contraction. These results suggest that the initial adaptation to resistance-based exercise does not involve changes in ClC-1 abundance in untrained skeletal muscle, and that increased content of NKA subunits may facilitate increases in maximal force production.

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.

Acute effect of low-load resistance exercise with blood flow restriction on oxidative stress biomarkers: A systematic review and meta-analysis

BACKGROUND

The purpose of this review was to analyze the acute effects of low-load resistance exercise with blood flow restriction (LLE-BFR) on oxidative stress markers in healthy individuals in comparison with LLE or high-load resistance exercise (HLRE) without BFR.

MATERIALS AND METHODS

A systematic review was performed in accordance with the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines. These searches were performed in CENTRAL, SPORTDiscus, EMBASE, PubMed, CINAHL and Virtual Health Library- VHL, which includes Lilacs, Medline and SciELO. The risk of bias and quality of evidence were assessed through the PEDro scale and GRADE system, respectively.

RESULTS

Thirteen randomized clinical trials were included in this review (total n = 158 subjects). Results showed lower post-exercise damage to lipids (SMD = -0.95 CI 95%: -1.49 to -0. 40, I2 = 0%, p = 0.0007), proteins (SMD = -1.39 CI 95%: -2.11 to -0.68, I2 = 51%, p = 0.0001) and redox imbalance (SMD = -0.96 CI 95%: -1.65 to -0.28, I2 = 0%, p = 0.006) in favor of LLRE-BFR compared to HLRE. HLRE presents higher post-exercise superoxide dismutase activity but in the other biomarkers and time points, no significant differences between conditions were observed. For LLRE-BFR and LLRE, we found no difference between the comparisons performed at any time point.

CONCLUSIONS

Based on the available evidence from randomized trials, providing very low or low certainty of evidence, this review demonstrates that LLRE-BFR promotes less oxidative stress when compared to HLRE but no difference in levels of oxidative damage biomarkers and endogenous antioxidants between LLRE.

TRIAL REGISTRATION

Register number: PROSPERO number: CRD42020183204.

Ammonium chloride administration prevents training-induced improvements in mitochondrial respiratory function in the soleus muscle of male rats

Exercise training can increase both mitochondrial content and mitochondrial respiration. Despite its popularity, high-intensity exercise can be accompanied by mild acidosis (also present in certain pathological states), which may limit exercise-induced adaptations to skeletal muscle mitochondria. The aim of this study was to determine if administration of ammonium chloride (0.05 g/kg) to Wistar rats before each individual exercise session (5 high-intensity exercise sessions/wk for 8 wk) reduced training-induced increases in mitochondrial content (measured by citrate synthase activity and protein content of electron transport system complexes) and respiration (measured in permeabilized muscle fibers). In the soleus muscle, the exercise-training-induced increase in mitochondrial respiration was reduced in rats administered ammonium chloride compared to control animals, but mitochondrial content was not altered. These effects were not present in the white gastrocnemius muscle. In conclusion, ammonium chloride administration before each exercise session over 8 wk reduced improvements in mitochondrial respiration in the soleus muscle but did not alter mitochondrial content. This suggests that mild acidosis may affect training-induced improvements in the respiration of mitochondria in some muscles.

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.

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 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.

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.

Active Relative to Passive Ischemic Preconditioning Enhances Intense Endurance Performance in Well-Trained Men

PURPOSE

This study tested the hypothesis of whether ischemic exercise preconditioning (IPC-Ex) elicits a better intense endurance exercise performance than traditional ischemic preconditioning at rest (IPC-rest) and a SHAM procedure.

METHODS

Twelve men (average V˙O2max ∼61 mL·kg-1·min-1) performed 3 trials on separate days, each consisting of either IPC-Ex (3 × 2-min cycling at ∼40 W with a bilateral-leg cuff pressure of ∼180 mm Hg), IPC-rest (4 × 5-min supine rest at 220 mm Hg), or SHAM (4 × 5-min supine rest at <10 mm Hg) followed by a standardized warm-up and a 4-minute maximal cycling performance test. Power output, blood lactate, potassium, pH, rating of perceived exertion, oxygen uptake, and gross efficiency were assessed.

RESULTS

Mean power during the performance test was higher in IPC-Ex versus IPC-rest (+4%; P = .002; 95% CI, +5 to 18 W). No difference was found between IPC-rest and SHAM (-2%; P = .10; 95% CI, -12 to 1 W) or between IPC-Ex and SHAM (+2%; P = .09; 95% CI, -1 to 13 W). The rating of perceived exertion increased following the IPC-procedure in IPC-Ex versus IPC-rest and SHAM (P < .001). During warm-up, IPC-Ex elevated blood pH versus IPC-rest and SHAM (P ≤ .027), with no trial differences for blood potassium (P > .09) or cycling efficiency (P ≥ .24). Eight subjects anticipated IPC-Ex to be best for their performance. Four subjects favored SHAM.

CONCLUSIONS

Performance in a 4-minute maximal test was better following IPC-Ex than IPC-rest and tended to be better than SHAM. The IPC procedures did not affect blood potassium, while pH was transiently elevated only by IPC-Ex. The performance-enhancing effect of IPC-Ex versus IPC-rest may be attributed to a placebo effect, improved pH regulation, and/or a change in the perception of effort.

The Effect of Blood Flow Restriction Exercise on Angiogenesis-Related Factors in Skeletal Muscle Among Healthy Adults: A Systematic Review and Meta-Analysis

Background

Blood flow restriction (BFR) exercise may be a potential exercise program to promote angiogenesis. This review aims to compare the effects of exercise with and without BFR on angiogenesis-related factors in skeletal muscle among healthy adults.

Methodology

Searches were made in Web of Science, Scopus, PubMed, and EBSCO databases from January 2001 to June 2021. Studies were screened, quality was evaluated, and data were extracted. The review protocol was registered at PROSPERO (PROSPERO registration number: CRD42021261367). Standardized mean differences (SMD) of vascular endothelial growth factor (VEGF), vascular endothelial growth factor receptor 2 (VEGFR-2), hypoxia inducible factor 1α (HIF-1α), peroxisome proliferator-activated receptorγcoactivator-1α (PGC-1α) and endothelial nitric oxide synthase (eNOS) were analyzed using Revman 5.4 software with a 95% confidence interval (95% CI).

Results

Ten studies fulfilled the inclusion criteria with a total of 75 participants for BFR group and 77 for CON group. BFR exercise elicits greater expression of VEGF (heterogeneity test, P = 0.09, I2 = 44%; SMD, 0.93 [0.38, 1.48], P &lt; 0.05), VEGFR-2 (heterogeneity test, P = 0.81, I2 = 0%; SMD, 0.64 [0.08, 1.21], P &lt; 0.05), HIF-1α (heterogeneity test, P = 0.67, I2 = 0%; SMD, 0.43 [0.03, 0.82], P &lt; 0.05), PGC-1α (heterogeneity test, P = 0.02, I2 = 54%; SMD, 0.74 [0.21, 1.28], P &lt; 0.05) and eNOS (heterogeneity test, P = 0.88, I2 = 0%; SMD, 0.60 [0.04, 1.17], P &lt; 0.05) mRNA than non-BFR exercise. In the sub-group analysis, resistance exercise with BFR elicits greater expression of VEGF (heterogeneity test, P = 0.36, I2 = 6%; SMD, 1.66 [0.97, 2.35], P &lt; 0.05) and HIF-1α (heterogeneity test, P = 0.56, I2 = 0%; SMD, 0.51 [0.01, 1.02], P &lt; 0.05) mRNA than aerobic exercise with BFR.

Conclusion

Exercise with BFR elicited more angiogenesis-related factors mRNA expression than exercise without BFR, but not VEGF and PGC-1α protein expression. Therefore, BFR training may be a potential training program to improve vascular function.

Systematic Review Registration

[https://www.crd.york.ac.uk/prospero/], identifier [CRD42021261367].

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.

Acute Effect of Repeated Sprint Exercise With Blood Flow Restriction During Rest Periods on Muscle Oxygenation

Purpose

This study aimed to examine the effect of applying BFR during rest periods of repeated cycling sprints on muscle oxygenation.

Methods

Seven active males performed 5 × 10-s maximal pedaling efforts with 40-s passive rest, with or without BFR application during rest period. BFR was applied for 30 s between sprints (between 5 and 35 s into rest) through a pneumatic pressure cuff inflated at 140 mmHg. Vastus lateralis muscle oxygenation was monitored using near-infrared spectroscopy. In addition, blood lactate concentration and heart rate were also evaluated.

Results

The BFR trial showed significantly lower oxyhemoglobin (oxy-Hb) and tissue saturation (StO₂) levels than the CON trial (P < 0.05). However, power output and blood lactate concentration did not significantly differ between the two trials (P > 0.05).

Conclusion

Applying BFR during rest periods of repeated cycling sprints decreased muscle oxygenation of active musculature, without interfering with power output during sprints.

Pectic Oligogalacturonide Facilitates the Synthesis and Activation of Adiponectin to Improve Hepatic Lipid Oxidation

SCOPE

Adiponectin (ADPN), a kind of adipokines, plays an important role in the regulation of lipid metabolism. The objective of this study is focused on the ADPN to investigate the functional mechanisms of pectin oligosaccharide (POS) from hawthorn fruit in the improvement of hepatic fatty acid oxidation.

METHOD AND RESULTS

High-fat fed mice are used in this experiment. POS is administrated with the doses of 0.25, 0.75, and 1.5 g kg^-1 diet, respectively. The results demonstrate that gene and protein expressions of ADPN synthesis regulators involved in PKA/ERK/CREB and C/EBPα/PPARγ pathways are upregulated by POS administration. POS also activates the AdiopR1/AMPKα/PGC1 and AdipoR2/PPARα signaling pathways to improve the fatty acid oxidation in the liver, which is further accelerated by the enhancement of mitochondrial functions.

CONCLUSION

POS can act as an ADPN activator to improve lipid metabolism, leading it to the applications of biomedical and functional foods for ameliorating chronic liver diseases resulted from a high-energy diet.

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.

Muscle Ionic Shifts During Exercise: Implications for Fatigue and Exercise Performance

Exercise causes major shifts in multiple ions (e.g., K⁺ , Na⁺ , H⁺ , lactate^- , Ca²⁺ , and Cl^- ) during muscle activity that contributes to development of muscle fatigue. Sarcolemmal processes can be impaired by the trans-sarcolemmal rundown of ion gradients for K⁺ , Na⁺ , and Ca²⁺ during fatiguing exercise, while changes in gradients for Cl^- and Cl^- conductance may exert either protective or detrimental effects on fatigue. Myocellular H⁺ accumulation may also contribute to fatigue development by lowering glycolytic rate and has been shown to act synergistically with inorganic phosphate (Pi) to compromise cross-bridge function. In addition, sarcoplasmic reticulum Ca²⁺ release function is severely affected by fatiguing exercise. Skeletal muscle has a multitude of ion transport systems that counter exercise-related ionic shifts of which the Na⁺ /K⁺ -ATPase is of major importance. Metabolic perturbations occurring during exercise can exacerbate trans-sarcolemmal ionic shifts, in particular for K⁺ and Cl^- , respectively via metabolic regulation of the ATP-sensitive K⁺ channel (K_ATP ) and the chloride channel isoform 1 (ClC-1). Ion transport systems are highly adaptable to exercise training resulting in an enhanced ability to counter ionic disturbances to delay fatigue and improve exercise performance. In this article, we discuss (i) the ionic shifts occurring during exercise, (ii) the role of ion transport systems in skeletal muscle for ionic regulation, (iii) how ionic disturbances affect sarcolemmal processes and muscle fatigue, (iv) how metabolic perturbations exacerbate ionic shifts during exercise, and (v) how pharmacological manipulation and exercise training regulate ion transport systems to influence exercise performance in humans. © 2021 American Physiological Society. Compr Physiol 11:1895-1959, 2021.

Molecular regulation of skeletal muscle mitochondrial biogenesis following blood flow-restricted aerobic exercise: a call to action

Blood flow-restricted (BFR) exercise can induce training adaptations comparable to those observed following training in free flow conditions. However, little is known about the acute responses within skeletal muscle following BFR aerobic exercise (AE). Moreover, although preliminary evidence suggests chronic BFR AE may augment certain training adaptations in skeletal muscle mitochondria more than non-BFR AE, the underlying mechanisms are poorly understood. In this review, we summarise the acute BFR AE literature examining mitochondrial biogenic signalling pathways and provide insight into mechanisms linked to skeletal muscle remodelling following BFR AE. Specifically, we focus on signalling pathways potentially contributing to augmented peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α) mRNA following work-rate-matched BFR AE compared with non-BFR AE. We present evidence suggesting reductions in muscle oxygenation during acute BFR AE lead to increased intracellular energetic stress, AMP-activated protein kinase (AMPK) activation and PGC-1α mRNA. In addition, we briefly discuss mitochondrial adaptations to BFR aerobic training, and we assess the risk of bias using the Cochrane Collaboration risk of bias assessment tool. We ultimately call for several straightforward modifications to help minimise bias in future BFR AE studies.

Acute exercise and cognition: A review with testable questions for future research into cognitive enhancement with blood flow restriction

Blood flow restriction, in combination with low load/intensity exercise, has consistently been shown to increase both muscle size and strength. In contrast, the effects of blood flow restricted exercise on cognition have not been well studied. Therefore, the purpose of this paper is 1) to review the currently available literature investigating the impact of blood flow restricted exercise on cognition and 2) to provide some hypotheses for how blood flow restriction might provide an additive stimulus for augmenting specific cognitive domains above exercise alone. Given the lack of research in this area, the effects of blood flow restricted exercise on cognition are still unclear. We hypothesize that blood flow restricted exercise could potentially enhance several cognitive domains (such as attention, executive functioning, and memory) through increases in lactate production, catecholamine concentration, and PGC-1α expression. We review work that suggests that blood flow restriction is not only a beneficial strategy to improve musculoskeletal function but could also be a favorable method for enhancing multiple domains of cognition. Nonetheless, it must be emphasized this is a hypothesis that currently has only minimal experimental support, and further investigations in the future are necessary to test the hypothesis.

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.

Ammonium chloride administration prior to exercise has muscle-specific effects on mitochondrial and myofibrillar protein synthesis in rats

AIM

Exercise is able to increase both muscle protein synthesis and mitochondrial biogenesis. However, acidosis, which can occur in pathological states as well as during high-intensity exercise, can decrease mitochondrial function, whilst its impact on muscle protein synthesis is disputed. Thus, the aim of this study was to determine the effect of a mild physiological decrease in pH, by administration of ammonium chloride, on myofibrillar and mitochondrial protein synthesis, as well as associated molecular signaling events.

METHODS

Male Wistar rats were given either a placebo or ammonium chloride prior to a short interval training session. Rats were killed before exercise, immediately after exercise, or 3 h after exercise.

RESULTS

Myofibrillar (p = 0.036) fractional protein synthesis rates was increased immediately after exercise in the soleus muscle of the placebo group, but this effect was absent in the ammonium chloride group. However, in the gastrocnemius muscle NH4 Cl increased myofibrillar (p = 0.044) and mitochondrial protein synthesis (0 h after exercise p = 0.01; 3 h after exercise p = 0.003). This was accompanied by some small differences in protein phosphorylation and mRNA expression.

CONCLUSION

This study found ammonium chloride administration immediately prior to a single session of exercise in rats had differing effects on mitochondrial and myofibrillar protein synthesis rates in soleus (type I) and gastrocnemius (type II) muscle in rats.

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.

The role of AMPK in regulation of Na+,K+-ATPase in skeletal muscle: does the gauge always plug the sink?

AMP-activated protein kinase (AMPK) is a cellular energy gauge and a major regulator of cellular energy homeostasis. Once activated, AMPK stimulates nutrient uptake and the ATP-producing catabolic pathways, while it suppresses the ATP-consuming anabolic pathways, thus helping to maintain the cellular energy balance under energy-deprived conditions. As much as ~ 20-25% of the whole-body ATP consumption occurs due to a reaction catalysed by Na⁺,K⁺-ATPase (NKA). Being the single most important sink of energy, NKA might seem to be an essential target of the AMPK-mediated energy saving measures, yet NKA is vital for maintenance of transmembrane Na⁺ and K⁺ gradients, water homeostasis, cellular excitability, and the Na⁺-coupled transport of nutrients and ions. Consistent with the model that AMPK regulates ATP consumption by NKA, activation of AMPK in the lung alveolar cells stimulates endocytosis of NKA, thus suppressing the transepithelial ion transport and the absorption of the alveolar fluid. In skeletal muscles, contractions activate NKA, which opposes a rundown of transmembrane ion gradients, as well as AMPK, which plays an important role in adaptations to exercise. Inhibition of NKA in contracting skeletal muscle accentuates perturbations in ion concentrations and accelerates development of fatigue. However, different models suggest that AMPK does not inhibit or even stimulates NKA in skeletal muscle, which appears to contradict the idea that AMPK maintains the cellular energy balance by always suppressing ATP-consuming processes. In this short review, we examine the role of AMPK in regulation of NKA in skeletal muscle and discuss the apparent paradox of AMPK-stimulated ATP consumption.

Moving human muscle physiology research forward: an evaluation of fiber type-specific protein research methodologies

Human skeletal muscle is a heterogeneous tissue composed of multiple fiber types that express unique contractile and metabolic properties. While analysis of mixed fiber samples predominates and holds value, increasing attention has been directed toward studying proteins segregated by fiber type, a methodological distinction termed “fiber type-specific.” Fiber type-specific protein studies have the advantage of uncovering key molecular effects that are often missed in mixed fiber homogenate studies but also require greater time and resource-intensive methods, particularly when applied to human muscle. This review summarizes and compares current methods used for fiber type-specific protein analysis, highlighting their advantages and disadvantages for human muscle studies, in addition to recent advances in these techniques. These methods can be grouped into three categories based on the initial processing of the tissue: 1) muscle-specific fiber homogenates, 2) cross sections of fiber bundles, and 3) isolated single fibers, with various subtechniques for performing fiber type identification and protein quantification. The relative implementation for each unique methodological approach is analyzed from 83 fiber type-specific studies of proteins in live human muscle found in the literature to date. These studies have investigated several proteins involved in a wide range of cellular functions that are important to muscle tissue. The second half of this review summarizes key findings from this ensemble of fiber type-specific human protein studies. We highlight examples of where this analytical approach has helped to improve understanding of important physiological topics such as insulin sensitivity, muscle hypertrophy, muscle fatigue, and adaptation to different exercise programs.

Role of CaMKII and sarcolipin in muscle adaptations to strength training with different levels of fatigue in the set

Strength training promotes a IIX-to-IIA shift in myosin heavy chain (MHC) composition, likely due to changes in sarcoplasmic [Ca²⁺ ] which are sensed by CaMKII. Sarcoplasmic [Ca²⁺ ] is in part regulated by sarcolipin (SLN), a small protein that when overexpressed in rodents stimulates mitochondrial biogenesis and a fast-to-slow fiber type shift. The purpose of this study was to determine whether CaMKII and SLN are involved in muscle phenotype and performance changes elicited by strength training. Twenty-two men followed an 8-week velocity-based resistance training program using the full squat exercise while monitoring repetition velocity. Subjects were randomly assigned to two resistance training programs differing in the repetition velocity loss allowed in each set: 20% (VL20) vs 40% (VL40). Strength training caused muscle hypertrophy, improved 1RM and increased total CaMKII protein expression, particularly of the δ_D isoform. Phospho-Thr²⁸⁷ -CaMKII δ_D expression increased only in VL40 (+89%), which experienced greater muscle hypertrophy, and a reduction in MHC-IIX percentage. SLN expression was increased in VL20 (+33%) remaining unaltered in VL40. The changes in phospho-Thr²⁸⁷ -CaMKII δ_D were positively associated with muscle hypertrophy and the number of repetitions during training, and negatively with the changes in MHC-IIX and SLN. Most OXPHOS proteins remained unchanged, except for NDUFB8 (Complex I), which was reduced after training (-22%) in both groups. The amount of fatigue allowed in each set critically influences muscle CaMKII and SLN responses and determines muscle phenotype changes. With lower intra-set fatigue, the IIX-to-IIA MHC shift is attenuated.