Blood flow restriction prevents muscle damage but not protein synthesis signaling following eccentric contractions

Nutritional approaches targeting mitochondria for the prevention of sarcopenia

A decline in function and loss of mass, a condition known as sarcopenia, is observed in the skeletal muscles with aging. Sarcopenia has a negative effect on the quality of life of elderly. Individuals with sarcopenia are at particular risk for adverse outcomes, such as reduced mobility, fall-related injuries, and type 2 diabetes mellitus. Although the pathogenesis of sarcopenia is multifaceted, mitochondrial dysfunction is regarded as a major contributor for muscle aging. Hence, the development of preventive and therapeutic strategies to improve mitochondrial function during aging is imperative for sarcopenia treatment. However, effective and specific drugs that can be used for the treatment are not yet approved. Instead studies on the relationship between food intake and muscle aging have suggested that nutritional intake or dietary control could be an alternative approach for the amelioration of muscle aging. This narrative review approaches various nutritional components and diets as a treatment for sarcopenia by modulating mitochondrial homeostasis and improving mitochondria. Age-related changes in mitochondrial function and the molecular mechanisms that help improve mitochondrial homeostasis are discussed, and the nutritional components and diet that modulate these molecular mechanisms are addressed.

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.

Probing muscle recovery following downhill running using precise mapping of MRI T2 relaxation times

PURPOSE

Postexercise recovery rate is a vital component of designing personalized training protocols and rehabilitation plans. Tracking exercise-induced muscle damage and recovery requires sensitive tools that can probe the muscles' state and composition noninvasively.

METHODS

Twenty-four physically active males completed a running protocol consisting of a 60-min downhill run on a treadmill at -10% incline and 65% of maximal heart rate. Quantitative mapping of MRI T2 was performed using the echo-modulation-curve algorithm before exercise, and at two time points: 1 h and 48 h after exercise.

RESULTS

T2 values increased by 2%-4% following exercise in the primary mover muscles and exhibited further elevation of 1% after 48 h. For the antagonist muscles, T2 values increased only at the 48-h time point (2%-3%). Statistically significant decrease in the SD of T2 values was found following exercise for all tested muscles after 1 h (16%-21%), indicating a short-term decrease in the heterogeneity of the muscle tissue.

CONCLUSION

MRI T2 relaxation time constitutes a useful quantitative marker for microstructural muscle damage, enabling region-specific identification for short-term and long-term systemic processes, and sensitive assessment of muscle recovery following exercise-induced muscle damage. The variability in T2 changes across different muscle groups can be attributed to their different role during downhill running, with immediate T2 elevation occurring in primary movers, followed by delayed elevation in both primary and antagonist muscle groups, presumably due to secondary damage caused by systemic processes.

Selected Methods of Resistance Training for Prevention and Treatment of Sarcopenia

Resistance training is an extremely beneficial intervention to prevent and treat sarcopenia. In general, traditional high-load resistance training improves skeletal muscle morphology and strength, but this method is impractical and may even reduce arterial compliance by about 20% in aged adults. Thus, the progression of resistance training methods for improving the strength and morphology of muscles without applying a high load is essential. Over the past two decades, various resistance training methods that can improve skeletal muscle mass and muscle function without using high loads have attracted attention, and their training effects, molecular mechanisms, and safety have been reported. The present study focuses on the relationship between exercise load/intensity, training effects, and physiological mechanisms as well as the safety of various types of resistance training that have attracted attention as a measure against sarcopenia. At present, there is much research evidence that blood-flow-restricted low-load resistance training (20–30% of one repetition maximum (1RM)) has been reported as a sarcopenia countermeasure in older adults. Therefore, this training method may be particularly effective in preventing sarcopenia.

Comparison of the Local Temperature, Lactate and Glucose After Three Different Strength Training Methods

This study aimed to evaluate the local temperature, lactate, and blood glucose in three strength training methods. The study included 12 male subjects; (22.15 ± 5.77 years, 76.85 ± 9.15 kg, 1.72 ± 0.09 m), with minimum of 12 months of strength training experience, and all participated in the three training methods: the occlusion training (Kaatsu); the tension training (Tension); and the traditional training (Traditional). The Kaatsu training consisted in 3 sets of 10RM with occlusion device in both arms inflated to a 130% occlusion pressure. In addition, the tension method was performed with 30% of 1RM and the traditional training, consisted in 10 repetitions with 80% RM. Regarding the temperature variation, differences were observed between the Kaatsu and Traditional methods in relation to Tension (p = .049, η ² p = 0.187). While for blood glucose (p = .351, η ² p = 0.075) and lactate (p = .722, η ² p = 0.022) there were no differences between the methods. Regarding the temperature (°C) measured by thermography and asymmetry, the right side showed a decrease in the post-test, in relation to the pre-test, in all methods (p < .05, η ² p > 0.150). The left (p = .035, η ² p = 0.301) and right (p = .012, η ² p = 0.324) sides showed a decrease in temperature, in the post-test in relation to the pre-test, in the Kaatsu and traditional method. In asymmetry, the three methods showed an increase in the post-test in relation to the pre-test (p = .042, η ² p = 0.158). In conclusion, tension method seems to stimulate greater heat production than the other methods. This information can help coaches to choose among these training methods according to the desired physiological response.

Comparison of skeletal muscle ultrastructural changes between normal and blood flow-restricted resistance exercise: A case report

NEW FINDINGS

What is the main observation in this case? The main observation of this case report is that blood flow-restricted exercise can cause myofibrils to have an aberrant wave-like appearance that is accompanied by irregular pockets of sarcoplasm in the intermyofibrillar space, while traditional forms of damage to the Z-discs and contractile elements are not as apparent. What insights does it reveal? Our findings indicate that blood flow restriction-mediated fluid pooling might cause alterations in skeletal muscle ultrastructure after exercise that might be directly related to myofibre swelling.

ABSTRACT

The acute effects of blood flow-restricted (BFR) exercise training on skeletal muscle ultrastructure are poorly understood owing to inconsistent findings and the use of largely imprecise systemic markers for indications of muscle damage. The purpose of this study was to compare myofibrillar ultrastructure before and 30 min after normal and BFR resistance exercise using transmission electron microscopy in a single individual to evaluate the feasibility of this more nuanced approach. One apparently healthy male with 13 years of resistance exercise completed six sets of both BFR [30% of one-repetition maximum (1-RM)] and normal non-occluded (70% of 1-RM) unilateral angled leg press on the contralateral leg, as a control, after assessment of 1-RM 72 h before. Vastus lateralis muscle biopsies were collected before and 30 min after each exercise session. The lengths and widths of 250 sarcomeres and the sarcoplasmic area were assessed via 20 individual transmission electron photomicrographs. Analysis revealed that BFR training (1.769 ± 0.12 μm) increased sarcomere length when compared with normal exercise (1.64 ± 0.17 μm; P < 0.001), without differences in sarcomere width between conditions (BFR, 0.90 ± 0.26 μm; normal, 0.93 ± 0.27 μm; P = 0.172). Furthermore, there were no significant interaction (P = 0.168) or condition effects between BFR (25.98 ± 4.17%) and normal (27.3 ± 6.49%) resistance exercise for sarcoplasmic area (P = 0.229). Exercise also increased sarcoplasmic area within the myofibril (pre-exercise, 24.42 ± 5.13%; postexercise, 28.95 ± 5.92%) for both conditions (P = 0.001). This case study demonstrates a unique BFR training-induced alteration in myofibril ultrastructure that appeared wave like and was accompanied by intracellular abnormalities that appeared to be fluid pockets of sarcoplasm disrupting the surrounding myofibrils.

Effect of resistance training with blood flow restriction on muscle damage markers in adults: A systematic review

Background

The purpose of this review was to systematically analyze the evidence regarding the occurrence of muscle damage (changes in muscle damage markers) after resistance training with blood flow restriction sessions.

Materials and methods

This systematic review was conducted in accordance with the PRISMA recommendations. Two researchers independently and blindly searched the following electronic databases: PubMed, Scopus, Web of Science, CINAHL, LILACS and SPORTdicus. Randomized and non-randomized clinical trials which analyzed the effect of resistance training with blood flow restriction on muscle damage markers in humans were included. The risk of bias assessment was performed by two blinded and independent researchers using the RoB2 tool.

Results

A total of 21 studies involving 352 healthy participants (men, n = 301; women, n = 51) were eligible for this review. The samples in 66.6% of the studies (n = 14) were composed of untrained individuals. All included studies analyzed muscle damage using indirect markers. Most studies had more than one muscle damage marker and Delayed Onset Muscle Soreness was the measure most frequently used. The results for the occurrence of significant changes in muscle damage markers after low-load resistance training with blood flow restriction sessions were contrasting, and the use of a pre-defined repetition scheme versus muscle failure seems to be the determining point for this divergence, mainly in untrained individuals.

Conclusions

In summary, the use of sets until failure is seen to be determinant for the occurrence of significant changes in muscle damage markers after low-load resistance training with blood flow restriction sessions, especially in individuals not used to resistance exercise.

Trial registration

Register number: PROSPERO number: CRD42020177119.

Exercise-induced muscle damage: mechanism, assessment and nutritional factors to accelerate recovery

There have been a multitude of reviews written on exercise-induced muscle damage (EIMD) and recovery. EIMD is a complex area of study as there are a host of factors such as sex, age, nutrition, fitness level, genetics and familiarity with exercise task, which influence the magnitude of performance decrement and the time course of recovery following EIMD. In addition, many reviews on recovery from exercise have ranged from the impact of nutritional strategies and recovery modalities, to complex mechanistic examination of various immune and endocrine signaling molecules. No one review can adequately address this broad array of study. Thus, in this present review, we aim to examine EIMD emanating from both endurance exercise and resistance exercise training in recreational and competitive athletes and shed light on nutritional strategies that can enhance and accelerate recovery following EIMD. In addition, the evaluation of EIMD and recovery from exercise is often complicated and conclusions often depend of the specific mode of assessment. As such, the focus of this review is also directed at the available techniques used to assess EIMD.

EFFECTS OF BLOOD FLOW RESTRICTION IN LARGE AND SMALL MUSCLE GROUPS

ABSTRACT Introduction It is known that strength training brings improvements in health and sports performance by causing muscle hypertrophy and increased strength, as well as modifying some hemodynamic and physiological factors. Several strength training methodologies have been developed, one of which is vascular occlusion. There are few studies with large muscle groups due to poor adherence to the training style and the fact that vascular occlusion of large muscle groups is more difficult. Objective To verify and compare the hemodynamic effects of exercise with and without vascular occlusion in different muscle groups. Methods Quantitative crossover study, with cross-sectional and field procedures. The sample consisted of 10 physically active healthy male and female subjects between 18 and 30 years of age. With the cross-over design, all the volunteers participated in 3 groups: intervention with vascular occlusion, intervention without vascular occlusion and the control group. Results Overall, lactate and cholesterol remained elevated after 15 minutes of recovery and blood glucose and blood pressure did not vary among the groups. Conclusion Vascular occlusion training is an effective method for manipulating hemodynamic variables. Evidence level II; Clinical study.

EFFECTS OF BLOOD FLOW RESTRICTION TRAINING ON HANDGRIP STRENGTH AND MUSCULAR VOLUME OF YOUNG WOMEN

Background

High-intensity training methods are generally recommended to increase muscle mass and strength, with training loads of 60-70% 1RM for novice and 80-100% 1RM for advanced individuals. Blood flow restriction training, despite using lower intensities (30-50% 1RM), can provide similar improvements in muscle mass and strength. However, studies commonly investigate the effects of blood flow restriction training in large muscular groups, whereas there are few studies that investigated those effects in smaller muscle groups, such as the muscles involved in grasping (e.g, wrist flexors; finger flexors). Clinically, smaller muscular groups should also be considered in intervention programs, given that repetitive stress, such as repeated strain injuries, affects upper limbs and may lead to chronic pain and incapacity for work. The purpose of the present study was to examine the effects of blood flow restriction training in strength and anthropometric indicators of muscular volume in young women.

Hypothesis

The effect of blood flow restriction training in handgrip strength (HGS) and muscular volume of young women can be similar to traditional training, even with lower loads.

Methods

Twenty-eight university students, 18 to 25 years of age, were randomly assigned into two groups, blood flow restriction training (BFR, n = 14) and traditional training (TRAD, n = 14). The anthropometric measures and maximum handgrip strength (MHGS) test were performed before and after the intervention. The participants did three weekly sessions of dynamic concentric contraction exercises on a dynamometer for four weeks (12 sessions). Each session had a time length of five minutes and the intensity was established from a percentage of MHGS at 30-35% in the first week, 40-45% in the second and 50-55% in third/fourth weeks. Three sets of 15-25 handgrip repetitions were performed until a failure with a 30 seconds rest for BFR training and three sets of 8-12 repetitions with one-minute rest for TRAD training.

Results

A significant increase was found in the arm muscle circumference (20.6 ± 2.2 vs 21.6 ± 1.7cm) and right MHGS (32.7 ± 4.5 vs 34.3 ± 4.1 kgf) and left MHGS (28.0 ± 5.5 vs 30.9 ± 4.1 kgf) for the BFR training, and the left MHGS (27.6 ± 5.0 vs 31.0 ± 6.1 kgf) for the TRAD training.

Conclusion

Dynamometer training with blood flow restriction, performed with low to moderate loads, was more effective than the traditional training in increasing HGS and muscle volume in young women.

Level of evidence

2b.

Local and Systemic Effects of Blood Flow Restriction Therapy in an Animal Model

BACKGROUND

Blood flow restriction therapy (BFRT) has been increasingly applied to improve athletic performance and injury recovery. Validation of BFRT has lagged behind commercialization, and currently the mechanism by which this therapy acts is unknown. BFRT is one type of ischemic therapy, which involves exercising with blood flow restriction. Repetitive restriction of muscle blood flow (RRMBF) is another ischemic therapy type, which does not include exercise.

HYPOTHESIS/PURPOSE

The purpose was to develop a rat model of ischemic therapy, characterize changes to muscle contractility, and evaluate local and systemic biochemical and histologic responses of 2 ischemic therapy types. We hypothesized that ischemic therapy would improve muscle mass and strength as compared with the control group.

STUDY DESIGN

Controlled laboratory study.

METHODS

Four groups of 10 Sprague-Dawley rats were established: control, stimulation, RRMBF, and BFRT. One hindlimb of each subject underwent 8 treatment sessions over 4 weeks. To simulate exercise, the stimulation group underwent peroneal nerve stimulation for 2 minutes. The RRMBF group used a pneumatic cuff inflated to 100 mm Hg with a 48-minute protocol. The BFRT group involved 100-mm Hg pneumatic cuff inflation and peroneal nerve stimulation for a 5-minute protocol. Four methods of evaluation were performed: in vivo contractility testing, histology, immunohistochemistry, and ELISA. Analysis of variance with post hoc Tukey test and linear mixed effects modeling were used to compare the treatment groups.

RESULTS

There was no difference in muscle mass among groups (P = .40) or between hindlimbs (P = .73). In vivo contractility testing showed no difference in maximum contractile force among groups (P = .64) or between hindlimbs (P = .30). On histology, myocyte cross-sectional area was not different among groups (P = .55) or between hindlimbs (P = .44). Pax7 immunohistochemistry demonstrated no difference in muscle satellite cell density among groups (P = .06) or between hindlimbs (P = .046). ELISA demonstrated the RRMBF group as eliciting elevated GH levels as compared with the other groups (P < .001).

CONCLUSION

Ischemic therapy did not induce gains in muscle mass, contractility strength, fiber cross-sectional area, or satellite cell density locally or systemically in this model, although the RRMBF group did have elevated GH levels on ELISA.

CLINICAL RELEVANCE

This animal model does not support ischemic therapy as a method to improve muscle mass, function, or satellite cell density.

Ischemic Therapy in Musculoskeletal Medicine

BACKGROUND

The competitive environment of athletics has promoted the exploration of any technology application that may offer an edge with performance and recovery from injury. Ischemic therapy is one such technology that has rapidly been incorporated into training rooms and physical therapy clinics worldwide. This therapy modality is reported to increase an athlete's ability to improve muscle mass, strength, and endurance.

PURPOSE

To provide the sports medicine physician with an understanding of the current state of ischemic therapy technology, including treatment specifications, known physiological effects, hypothesized mechanisms, biochemical effects, athletic applications, medical applications, animal models, and future research recommendations.

STUDY DESIGN

Literature review.

METHODS

A computer-based search of the PubMed database was used to perform a comprehensive literature review on musculoskeletal ischemic therapy.

RESULTS

The current research on ischemic therapy is largely composed of case series with varying equipment, methods, and therapy specifications. The publication of case series has value in identifying this technology for future research, but the results of these studies should not be justification for application to athletes without validation of safety and effectiveness.

CONCLUSION

To date, ischemic therapy remains unvalidated, and the mechanism by which it improves muscle performance is not clear.

A focused review of myokines as a potential contributor to muscle hypertrophy from resistance-based exercise

PURPOSE

Resistance exercise induces muscle growth and is an important treatment for age-related losses in muscle mass and strength. Myokines are hypothesized as a signal conveying physiological information to skeletal muscle, possibly to "fine-tune" other regulatory pathways. While myokines are released from skeletal muscle following contraction, their role in increasing muscle mass and strength in response to resistance exercise or training is not established. Recent research identified both local and systemic release of myokines after an acute bout of resistance exercise. However, it is not known whether myokines with putative anabolic function are mechanistically involved in producing muscle hypertrophy after resistance exercise. Further, nitric oxide (NO), an important mediator of muscle stem cell activation, upregulates the expression of certain myokine genes in skeletal muscle.

METHOD

In the systemic context of complex hypertrophic signaling, this review: (1) summarizes literature on several well-recognized, representative myokines with anabolic potential; (2) explores the potential mechanistic role of myokines in skeletal muscle hypertrophy; and (3) identifies future research required to advance our understanding of myokine anabolism specifically in skeletal muscle.

RESULT

This review establishes a link between myokines and NO production, and emphasizes the importance of considering systemic release of potential anabolic myokines during resistance exercise as complementary to other signals that promote hypertrophy.

CONCLUSION

Investigating adaptations to resistance exercise in aging opens a novel avenue of interdisciplinary research into myokines and NO metabolites during resistance exercise, with the longer-term goal to improve muscle health in daily living, aging, and rehabilitation.

Acute Neuromuscular and Microvascular Responses to Concentric and Eccentric Exercises With Blood Flow Restriction

Lauver, JD, Cayot, TE, Rotarius, TR, and Scheuermann, BW. Acute neuromuscular and microvascular responses to concentric and eccentric exercises with blood flow restriction. J Strength Cond Res 34(10): 2725-2733, 2020-The purpose of this study was to investigate the effects of the addition of blood flow restriction (BFR) during concentric and eccentric exercises on muscle excitation and microvascular oxygenation status. Subjects (N = 17) were randomly assigned to either a concentric (CON, CON + BFR) or eccentric (ECC, ECC + BFR) group, with one leg assigned to BFR and the other to non-BFR. Surface electromyography and near-infrared spectroscopy were used to measure muscle excitation and microvascular deoxygenation (deoxy-[Hb + Mb]) and [total hemoglobin concentration] during each condition, respectively. On separate days, subjects completed 4 sets (30, 15, 15, 15) of knee extension exercise at 30% maximal torque, and 1 minute of rest was provided between the sets. Greater excitation of the vastus medialis was observed during CON + BFR (54.4 ± 13.3% maximal voluntary isometric contraction [MVIC]) and ECC + BFR (53.0 ± 18.0% MVIC) compared with CON (42.0 ± 10.8% MVIC) and ECC (46.8 ± 9.6% MVIC). Change in deoxy-[Hb + Mb] was greater during CON + BFR (10.0 ± 10.4 μM) than during CON (4.1 ± 4.0 μM; p < 0.001). ECC + BFR (7.8 ± 6.7 μM) was significantly greater than ECC (3.5 ± 4.7 μM; p = 0.001). Total hemoglobin concentration was greater for ECC + BFR (7.9 ± 4.4 μM) compared with ECC (5.5 ± 3.5 μM). The addition of BFR to eccentric and concentric exercises resulted in a significant increase in metabolic stress and muscle excitation compared with non-BFR exercise. These findings suggest that although BFR may increase the hypertrophic stimulus during both modes of contraction, BFR during concentric contractions may result in a greater stimulus.

Eccentric and concentric blood flow restriction resistance training on indices of delayed onset muscle soreness in untrained women

PURPOSE

Unaccustomed exercise can result in delayed onset muscle soreness (DOMS), particularly as a result of the eccentric phase of the muscle contraction. Resistance training combined with venous blood flow restriction (vBFR) may attenuate DOMS, but the available information in this regard is conflicting. Therefore, the purpose of this study was to examine the effects of low-load eccentric vBFR (Ecc-vBFR) and concentric vBFR (Con-vBFR) resistance training on indices of DOMS.

METHODS

Twenty-five previously untrained women completed seven days of either Ecc-vBFR (n = 12) or Con-vBFR (n = 13) forearm flexion resistance training at a velocity of 120° s^-1 on an isokinetic dynamometer. The Ecc-vBFR group used a training load that corresponded to 30% of eccentric peak torque and the Con-vBFR group used a training load that corresponded to 30% of concentric peak torque.

RESULTS

There were no differences between Ecc-vBFR and Con-vBFR at any of the seven training sessions on any of the indices of DOMS. There were no decreases in the maximal voluntary isometric contraction torque which increased at days 6 and 7. Similarly, there were no changes in perceived muscle soreness, pain pressure threshold, elbow joint angle, or edema (as assessed by echo intensity via ultrasound) across the seven training sessions.

CONCLUSIONS

The Ecc-vBFR and Con-vBFR low-load training protocols were not associated with DOMS and there were no differences between protocols when performed using the same relative training intensity. These findings suggested that both unaccustomed eccentric and concentric low-load training did not result in DOMS when combined with vBFR.

Muscle damage responses to resistance exercise performed with high-load versus low-load associated with partial blood flow restriction in young women

The aim of this study was to compare if an acute exercise session of high-load resistance training (HL-RT, e.g. 70% of 1 repetition-maximum, 1 RM) induces a higher magnitude of muscle damage compared with a RT protocol with low-loads (e.g. 20% 1 RM) associated with partial blood flow restriction (LL-BFR), and investigate the recovery in the days after the protocols. We used an unilateral crossover research design in which 10 young women (22(2) y; 162(5) cm; 66(11) kg) performed HL-RT and LL-BFR in a randomized, counterbalanced manner with a minimum interval of 2 weeks between protocols. Indirect muscle damage markers were evaluated before and once a day for 4 days into recovery. Main results showed decreases of 8-12% at 24-48 h in maximal voluntary isometric and concentric contraction torques (P < 0.03), and changes in muscle architecture markers (P < 0.03) for HL-RT and LL-BFR, with no differences between protocols (P > 0.05). Moreover, delayed onset muscle soreness increased only after LL-BFR (P < 0.001). We conclude that an acute bout of low volume HL-RT or LL-BFR to failure resulted in edema-induced muscle swelling, but do not induce major or long-lasting decrements in muscle function and the level of soreness promoted from LL-BFR was mild.

Electromyostimulation with blood flow restriction enhances activation of mTOR and MAPK signaling pathways in rat gastrocnemius muscles

Neuromuscular electrical stimulation (NMES) combined with blood flow restriction (BFR) induces muscle hypertrophy. However, cellular mechanisms underlying the muscle hypertrophy induced by NMES combined with BFR remain unclear. We tested the hypothesis that NMES combined with BFR would enhance the mechanistic target of rapamycin (mTOR) and mitogen-activated protein kinase (MAPK) signaling pathways. Age-matched male Wistar rats (6 months old, n = 7 per group) were assigned randomly to control, BFR alone (BFR), NMES alone (NMES), and NMES combined with BFR (NMES/BFR) groups. NMES induced 25 isometric contractions lasting 8 s with 4-s resting periods between contractions in the gastrocnemius muscle. Four sets in total were performed, with 1-min intervals between sets. A latex cuff was placed on the proximal portion of the hind limb and BFR at 200 mm Hg was conducted in 4 sets (each set 5 min) with 1-min rest intervals between sets. Venous blood was collected from the lateral tail vein to determine pH, H⁺ concentration, and lactate concentration before and immediately after the treatments. Expression levels of proteins related to muscle hypertrophy were determined by Western blot analysis. The application of NMES/BFR promoted muscle fatigue more than NMES alone. NMES/BFR induced greater changes in accumulation of metabolites and increase in gastrocnemius muscle weight. The phosphorylation of mTOR and MAPK signaling-related proteins was also enhanced following NMES/BFR, compared with other conditions. Thus, NMES enhanced the activation of mTOR and MAPK signaling pathways when combined with BFR.

The Role of Inflammation and Immune Cells in Blood Flow Restriction Training Adaptation: A Review

Blood flow restriction (BFR) combined with low-intensity strength training has been shown to increase skeletal muscle mass and strength in a variety of populations. BFR results in a robust metabolic stress which is hypothesized to induce muscle growth via increased recruitment of fast-twitch muscle fibers, a greater endocrine response, and/or enhancing the cellular swelling contribution to the hypertrophic process. Following exercise, neutrophils are the first immune cells to initiate the tissue remodeling process via several mechanisms including an increased production of cytokines and recruitment of monocytes/macrophages, which facilitate the phagocytosis of foreign particles, the differentiation of myoblasts, and the formation of new myotubes. Thus, the purpose of this review was to discuss the mechanisms through which metabolic stress and immune cell recruitment may induce skeletal muscle remodeling following BFR strength training.

Effects of blood flow restriction during moderate-intensity eccentric knee extensions

We investigated if blood flow restriction (BFR, cuff pressure 20 mmHG below individual occlusion pressure) increases metabolic stress, hormonal response, release of muscle damage markers, and muscle swelling induced by moderate-intensity eccentric contractions. In a randomized, matched-pair design, 20 male subjects (25.3 ± 3.3 years) performed four sets of unilateral eccentric knee extensions (75% 1RM) to volitional failure with (IG) or without (CG) femoral BFR. Despite significant differences of performed repetitions between IG (85.6 ± 15.4 repetitions) and CG (142.3 ± 44.1 repetitions), peak values of lactate (IG 7.0 ± 1.4 mmol l-1, CG 6.9 ± 2.7 mmol l-1), growth-hormone (IG 4.9 ± 4.8 ng ml-1, CG 5.2 ± 3.5 ng ml-1), insulin-like growth factor 1 (IG 172.1 ± 41.9 ng ml-1, CG 178.7 ± 82.1 ng ml-1), creatine-kinase (IG 625.5 ± 464.8 U l-1, CG 510.7 ± 443.5 U l-1), the absolute neutrophil count (IG 7.9 ± 1.3 103 µl-1, CG 8.7 ± 2.0 103 µl-1), induced muscle swelling of rectus femoris and vastus lateralis and perceived pain did not differ. The present data indicate that BFR is suitable to intensify eccentric exercises.

Muscle hypertrophy following blood flow-restricted, low-force isometric electrical stimulation in rat tibialis anterior: role for muscle hypoxia

Low-force exercise training with blood flow restriction (BFR) elicits muscle hypertrophy as seen typically after higher-force exercise. We investigated the effects of microvascular hypoxia [i.e., low microvascular O2 partial pressures (P mvO2)] during contractions on muscle hypertrophic signaling, growth response, and key muscle adaptations for increasing exercise capacity. Wistar rats were fitted with a cuff placed around the upper thigh and inflated to restrict limb blood flow. Low-force isometric contractions (30 Hz) were evoked via electrical stimulation of the tibialis anterior (TA) muscle. The P mvO2 was determined by phosphorescence quenching. Rats underwent acute and chronic stimulation protocols. Whereas P mvO2 decreased transiently with 30 Hz contractions, simultaneous BFR induced severe hypoxia, reducing P mvO2 lower than present for maximal (100 Hz) contractions. Low-force electrical stimulation (EXER) induced muscle hypertrophy (6.2%, P < 0.01), whereas control group conditions or BFR alone did not. EXER+BFR also induced an increase in muscle mass (11.0%, P < 0.01) and, unique among conditions studied, significantly increased fiber cross-sectional area in the superficial TA ( P < 0.05). Phosphorylation of ribosomal protein S6 was enhanced by EXER+BFR, as were peroxisome proliferator-activated receptor gamma coactivator-1α and glucose transporter 4 protein levels. Fibronectin type III domain-containing protein 5, cytochrome c oxidase subunit 4, monocarboxylate transporter 1 (MCT1), and cluster of differentiation 147 increased with EXER alone. EXER+BFR significantly increased MCT1 expression more than EXER alone. These data demonstrate that microvascular hypoxia during contractions is not essential for hypertrophy. However, hypoxia induced via BFR may potentiate the muscle hypertrophic response (as evidenced by the increased superficial fiber cross-sectional area) with increased glucose transporter and mitochondrial biogenesis, which contributes to the pleiotropic effects of exercise training with BFR that culminate in an improved capacity for sustained exercise.

NEW & NOTEWORTHY We investigated the effects of low microvascular O2 partial pressures (P mvO2) during contractions on muscle hypertrophic signaling and key elements in the muscle adaptation for increasing exercise capacity. Although demonstrating that muscle hypoxia is not obligatory for the hypertrophic response to low-force, electrically induced muscle contractions, the reduced P mvO2 enhanced ribosomal protein S6 phosphorylation and potentiated the hypertrophic response. Furthermore, contractions with blood flow restriction increased oxidative capacity, glucose transporter, and mitochondrial biogenesis, which are key determinants of the pleiotropic effects of exercise training.

Chronic Adaptations to Eccentric Training: A Systematic Review

BACKGROUND

Resistance training is an integral component of physical preparation for athletes. A growing body of evidence indicates that eccentric strength training methods induce novel stimuli for neuromuscular adaptations.

OBJECTIVE

The purpose of this systematic review was to determine the effects of eccentric training in comparison to concentric-only or traditional (i.e. constrained by concentric strength) resistance training.

METHODS

Searches were performed using the electronic databases MEDLINE via EBSCO, PubMed and SPORTDiscus via EBSCO. Full journal articles investigating the long-term (≥4 weeks) effects of eccentric training in healthy (absence of injury or illness during the 4 weeks preceding the training intervention), adult (17-35 years), human participants were selected for the systematic review. A total of 40 studies conformed to these criteria.

RESULTS

Eccentric training elicits greater improvements in muscle strength, although in a largely mode-specific manner. Superior enhancements in power and stretch-shortening cycle (SSC) function have also been reported. Eccentric training is at least as effective as other modalities in increasing muscle cross-sectional area (CSA), while the pattern of hypertrophy appears nuanced and increased CSA may occur longitudinally within muscle (i.e. the addition of sarcomeres in series). There appears to be a preferential increase in the size of type II muscle fibres and the potential to exert a unique effect upon fibre type transitions. Qualitative and quantitative changes in tendon tissue that may be related to the magnitude of strain imposed have also been reported with eccentric training.

CONCLUSIONS

Eccentric training is a potent stimulus for enhancements in muscle mechanical function, and muscle-tendon unit (MTU) morphological and architectural adaptations. The inclusion of eccentric loads not constrained by concentric strength appears to be superior to traditional resistance training in improving variables associated with strength, power and speed performance.

The effects of RSR13 on microvascular Po2 kinetics and muscle contractile performance in the rat arterial ligation model of peripheral arterial disease

Exercise intolerance and claudication are symptomatic of peripheral arterial disease. There is a close relationship between muscle O2 delivery, microvascular oxygen partial pressure (P mvO2), and contractile performance. We therefore hypothesized that a reduction of hemoglobin-oxygen affinity via RSR13 would maintain a higher P mvO2 and enhance blood-muscle O2 transport and contractile function. In male Wistar rats (12 wk of age), we created hindlimb ischemia via right-side iliac artery ligation (AL). The contralateral (left) muscle served as control (CONT). Seven days after AL, phosphorescence-quenching techniques were used to measure P mvO2 at rest and during contractions (electrical stimulation; 1 Hz, 300 s) in tibialis anterior muscle (TA) under saline ( n = 10) or RSR13 ( n = 10) conditions. RSR13 at rest increased TA P mvO2 in CONT (13.9 ± 1.6 to 19.3 ± 1.9 Torr, P < 0.05) and AL (9.0 ± 0.5 to 9.9 ± 0.7 Torr, P < 0.05). Furthermore, RSR13 extended maintenance of the initial TA force (i.e., improved contractile performance) such that force was not decreased significantly until contraction 240 vs. 150 in CONT and 80 vs. 20 in AL. This improved muscle endurance with RSR13 was accompanied by a greater ΔP mvO2 (P mvO2 decrease from baseline) (CONT, 7.4 ± 1.0 to 11.2 ± 1.3; AL, 6.9 ± 0.5 to 8.6 ± 0.6 Torr, both P < 0.05). Whereas RSR13 did not alter the kinetics profile of P mvO2 (i.e., mean response time) substantially during contractions, muscle force was elevated, and the ratio of muscle force to P mvO2 increased. In conclusion, reduction of hemoglobin-oxygen affinity via RSR13 in AL increased P mvO2 and improved muscle contractile performance most likely via enhanced blood-muscle O2 diffusion.

NEW & NOTEWORTHY This is the first investigation to examine the effect of RSR13 (erythrocyte allosteric effector) on skeletal muscle microvascular oxygen partial pressure kinetics and contractile function using an arterial ligation model of peripheral arterial disease in experimental animals. The present results provide strong support for the concept that reducing hemoglobin-O2 affinity via RSR13 improved tibialis anterior muscle contractile performance most likely via enhanced blood-muscle O2 diffusion.

Blood flow restriction attenuates eccentric exercise-induced muscle damage without perceptual and cardiovascular overload

The aim of this study was to evaluate the acute effects of high-intensity eccentric exercise (HI-ECC) combined with blood flow restriction (BFR) on muscle damage markers, and perceptual and cardiovascular responses. Nine healthy men (26 ± 1 years, BMI 24 ± 1 kg m^- ²) underwent unilateral elbow extension in two conditions: without (HI-ECC) and with BFR (HI-ECC+BFR). The HI-ECC protocol corresponded to three sets of 10 repetitions with 130% of maximal strength (1RM). The ratings of perceived exertion (RPE) and pain (RPP) were measured after each set. Muscle damage was evaluated by range of motion (ROM), upper arm circumference (CIR) and muscle soreness using a visual analogue scale at different moments (pre-exercise, immediately after, 24 and 48 h postexercise). Systolic (SBP), diastolic (DBP), mean blood pressure (MBP) and heart rate (HR) were measured before exercise and after each set. RPP was higher in HI-ECC+BFR than in HI-ECC after each set. Range of motion decreased postexercise in both conditions; however, in HI-ECC+BFR group, it returned to pre-exercise condition earlier (post-24 h) than HI-ECC (post-48 h). CIR increased only in HI-ECC, while no difference was observed in HI-ECC+BFR condition. Regarding cardiovascular responses, MBP and SBP did not change at any moment. HR showed similar increases in both conditions during exercise while DBP decreased only in HI-ECC condition. Thus, BFR attenuated HI-ECC-induced muscle damage and there was no increase in cardiovascular responses.