Type 1 Muscle Fiber Hypertrophy after Blood Flow–restricted Training in Powerlifter

PURPOSE: To investigate the effects of blood flow restricted resistance exercise (BFRRE) on myofiber areas (MFA), number of myonuclei and satellite cells (SC), muscle size and strength in powerlifters. METHODS Seventeen national level powerlifters (25+/-6 yrs [mean+/-SD], 15 men) were randomly assigned to either a BFRRE group (n=9) performing two blocks (week 1 and 3) of five BFRRE front squat sessions within a 6.5-week training period, or a conventional training group (Con; n=8) performing front squats at ~70% of one-repetition maximum (1RM). The BFRRE consisted of four sets (first and last set to voluntary failure) at ~30% of 1RM. Muscle biopsies were obtained from m. vastus lateralis (VL) and analyzed for MFA, myonuclei, SC and capillaries. Cross sectional areas (CSA) of VL and m. rectus femoris (RF) were measured by ultrasonography. Strength was evaluated by maximal voluntary isokinetic torque (MVIT) in knee extension and 1RM in front squat. RESULTS: BFRRE induced selective type I fiber increases in MFA (BFRRE: 12% vs. Con: 0%, p<0.01) and myonuclear number (BFRRE: 17% vs. Con: 0%, p=0.02). Type II MFA was unaltered in both groups. BFRRE induced greater changes in VL CSA (7.7% vs. 0.5%, p=0.04), which correlated with the increases in MFA of type I fibers (r=0.81, p=0.02). No group differences were observed in SC and strength changes, although MVIT increased with BFRRE (p=0.04), whereas 1RM increased in Con (p=0.02). CONCLUSION Two blocks of low-load BFRRE in the front squat exercise resulted in increased quadriceps CSA associated with preferential hypertrophy and myonuclear addition in type 1 fibres of national level powerlifters.Type 1 Muscle Fiber Hypertrophy after Blood Flow–restricted Training in PowerlifteracceptedVersionNivå

Effects of an acute bout of low-load resistance training with blood flow restriction: -with special reference to muscle damage, hypertrophic signaling and satellite cells

Main findings: Blood flow restriction reduces muscle endurance at low exercise loads (20-40% of 1RM) but not necessarily at moderate to higher loads (>50% of 1RM) in the knee extension exercise. The intramuscular pressures in the quadriceps are probably quite high already at low-to-moderate loads in this exercise, sufficient to induce relative ischemia as long as the muscle is under tension. Fatiguing low-load dynamic knee extension exercise both with and without blood flow restriction induces DOMS. Fatiguing low-load dynamic knee extension exercise both with and without blood flow restriction induces high muscle activity in the quadriceps. Not only the concentric but also the eccentric muscle activity increases as the point of torque failure draws closer. Very likely, this indicates a high degree of muscle fiber recruitment, possibly also during eccentric muscle actions. Multiple sets of low-load resistance exercise to failure with BFR induce decrements in maximum torque capacity and signs of increased sarcolemmal permeability and damage at the muscle fiber level. These phenomena were also observed in the freeflow leg, but to a lesser degree. Multiple sets of low-load resistance exercise to failure with BFR appear to induce long-lasting (>24 hours) increases in hypertrophic signaling, and rapid increases in satellite cell numbers. These phenomena were also observed in the free-flow leg, but to a somewhat lesser degree with regard to signaling

Ischemic strength training: a low-load alternative to heavy resistance exercise?

Strength training with low loads in combination with vascular occlusion has been proposed as an alternative to heavy resistance exercise in the rehabilitation setting, especially when high forces acting upon the musculo-skeletal system are contraindicated. Several studies on low-to-moderate intensity resistance exercise combined with cuff occlusion have demonstrated increases in muscle strength and size that are comparable to those typically seen after conventional high-load strength training. However, the physiological mechanisms by which occlusion training induces increased muscle mass and strength are currently unclear, although several candidate stimuli have been proposed. Also, the long-term safety, practicality, and efficacy of this training method are still controversial. Furthermore, recent studies have demonstrated that in some instances, tourniquet cuffs may not be necessary for relative ischemia and significant training effects to occur with resistance exercise at low-to-moderate loads. The aims of the present review are to summarize current opinion and knowledge regarding the physiology of ischemic strength training and to discuss some of the training and health aspects of this type of exercise. In addition, suggestions for further research are given

Comparaison de deux protocoles d'entraînement de force par occlusion vasculaire (à l'épuisement versus sous-maximal) sur la réponse des protéines de stress

INTRODUCTION: The stress imposed to muscle fibers during blood flow restricted resistance exercise (BFRRE) is poorly investigated. Therefore, we aimed to compare the effect of a failure (FA) vs submaximal (SU) BFRRE protocol on heat-shock protein responses in the exercising muscles. METHODS: Sixteen untrained men (18-45 yrs) completed 14 BFRRE sessions divided into 2 blocks of 7 sessions in 5 days, interspersed by 10 days of rest. Legs were randomly assigned to either FA (4 sets to voluntary failure) or SU protocol (30-, 15-, 15-, 15 reps) using unilateral knee extensions at 20% of 1 repetition maximum with 30s rest between sets. BFRRE was conducted with partial blood flow restriction (100 mmHg) induced by a 15 cm wide pressure cuff. Biopsies from the m. vastus lateralis were collected before, during and post intervention. The HSP response investigated was changes in αB-crystallin staining intensity on muscle cross sections analyzed by immunofluorescence. RESULTS: Relative to pre-exercise, a significant increase in αB-crystallin staining intensity (reflecting cytoskeletal bound proteins) was observed 2h after the first session in both legs (129 ± 18%, p<0.001 and 77 ± 10%, p<0.05; FA and SU, respectively). There were no significant difference between protocols at any time point, but these changes tended to be larger in FA legs than SU legs. During the rest period and 10 days post intervention, αB-crystallin staining intensity gradually decreased to baseline values. CONCLUSION: The αB-crystallin immunostaining analyses suggest that cytoskeletal proteins are highly stressed after the first session of both FA and SU BFRRE protocols

Frequent blood flow restricted training not to failure and to failure induces similar gains in myonuclei and muscle mass

The purpose of the present study was to compare the effects of short-term high-frequency failure vs non-failure blood flow–restricted resistance exercise (BFRRE) on changes in satellite cells (SCs), myonuclei, muscle size, and strength. Seventeen untrained men performed four sets of BFRRE to failure (Failure) with one leg and not to failure (Non-failure; 30-15-15-15 repetitions) with the other leg using knee-extensions at 20% of one repetition maximum (1RM). Fourteen sessions were distributed over two 5-day blocks, separated by a 10-day rest period. Muscle samples obtained before, at mid-training, and 10-day post-intervention (Post10) were analyzed for muscle fiber area (MFA), myonuclei, and SC. Muscle size and echo intensity of m.rectus femoris (RF) and m.vastus lateralis (VL) were measured by ultrasonography, and knee extension strength with 1RM and maximal isometric contraction (MVC) up until Post24. Both protocols increased myonuclear numbers in type-1 (12%–17%) and type-2 fibers (20%–23%), and SC in type-1 (92%–134%) and type-2 fibers (23%–48%) at Post10 (p < 0.05). RF and VL size increased by 5%–10% in both legs at Post10 to Post24, whereas the MFA of type-1 fibers in Failure was decreased at Post10 (−10 ± 16%; p = 0.02). Echo intensity increased by 20% in both legs during Block1 (p < 0.001) and was 8 to 11% below baseline at Post24 (p = 0.001–0.002). MVC and 1RM decreased by 5%–10% after Block1, but increased in both legs by 6%–11% at Post24 (p < 0.05). In conclusion, both short-term high-frequency failure and non-failure BFRRE induced increases in SCs, in myonuclei content, muscle size, and strength, concomitant with decreased echo intensity. Intriguingly, the responses were delayed and peaked 10–24 days after the training intervention. Our findings may shed light on the mechanisms involved in resistance exercise-induced overreaching and supercompensation

Frequent blood flow restricted training not to failure and to failure induces similar gains in myonuclei and muscle mass

The purpose of the present study was to compare the effects of short-term high-frequency failure vs non-failure blood flow–restricted resistance exercise (BFRRE) on changes in satellite cells (SCs), myonuclei, muscle size, and strength. Seventeen untrained men performed four sets of BFRRE to failure (Failure) with one leg and not to failure (Non-failure; 30-15-15-15 repetitions) with the other leg using knee-extensions at 20% of one repetition maximum (1RM). Fourteen sessions were distributed over two 5-day blocks, separated by a 10-day rest period. Muscle samples obtained before, at mid-training, and 10-day post-intervention (Post10) were analyzed for muscle fiber area (MFA), myonuclei, and SC. Muscle size and echo intensity of m.rectus femoris (RF) and m.vastus lateralis (VL) were measured by ultrasonography, and knee extension strength with 1RM and maximal isometric contraction (MVC) up until Post24. Both protocols increased myonuclear numbers in type-1 (12%–17%) and type-2 fibers (20%–23%), and SC in type-1 (92%–134%) and type-2 fibers (23%–48%) at Post10 (p < 0.05). RF and VL size increased by 5%–10% in both legs at Post10 to Post24, whereas the MFA of type-1 fibers in Failure was decreased at Post10 (−10 ± 16%; p = 0.02). Echo intensity increased by ~20% in both legs during Block1 (p < 0.001) and was ~8 to 11% below baseline at Post24 (p = 0.001–0.002). MVC and 1RM decreased by 5%–10% after Block1, but increased in both legs by 6%–11% at Post24 (p < 0.05). In conclusion, both short-term high-frequency failure and non-failure BFRRE induced increases in SCs, in myonuclei content, muscle size, and strength, concomitant with decreased echo intensity. Intriguingly, the responses were delayed and peaked 10–24 days after the training intervention. Our findings may shed light on the mechanisms involved in resistance exercise-induced overreaching and supercompensation

Frequent blood flow restricted training not to failure and to failure induces similar gains in myonuclei and muscle mass

The purpose of the present study was to compare the effects of short-term high-frequency failure vs non-failure blood flow–restricted resistance exercise (BFRRE) on changes in satellite cells (SCs), myonuclei, muscle size, and strength. Seventeen untrained men performed four sets of BFRRE to failure (Failure) with one leg and not to failure (Non-failure; 30-15-15-15 repetitions) with the other leg using knee-extensions at 20% of one repetition maximum (1RM). Fourteen sessions were distributed over two 5-day blocks, separated by a 10-day rest period. Muscle samples obtained before, at mid-training, and 10-day post-intervention (Post10) were analyzed for muscle fiber area (MFA), myonuclei, and SC. Muscle size and echo intensity of m.rectus femoris (RF) and m.vastus lateralis (VL) were measured by ultrasonography, and knee extension strength with 1RM and maximal isometric contraction (MVC) up until Post24. Both protocols increased myonuclear numbers in type-1 (12%–17%) and type-2 fibers (20%–23%), and SC in type-1 (92%–134%) and type-2 fibers (23%–48%) at Post10 (p < 0.05). RF and VL size increased by 5%–10% in both legs at Post10 to Post24, whereas the MFA of type-1 fibers in Failure was decreased at Post10 (−10 ± 16%; p = 0.02). Echo intensity increased by 20% in both legs during Block1 (p < 0.001) and was 8 to 11% below baseline at Post24 (p = 0.001–0.002). MVC and 1RM decreased by 5%–10% after Block1, but increased in both legs by 6%–11% at Post24 (p < 0.05). In conclusion, both short-term high-frequency failure and non-failure BFRRE induced increases in SCs, in myonuclei content, muscle size, and strength, concomitant with decreased echo intensity. Intriguingly, the responses were delayed and peaked 10–24 days after the training intervention. Our findings may shed light on the mechanisms involved in resistance exercise-induced overreaching and supercompensation

Comparison of knee flexor strength recovery between semitendinosus alone versus semitendinosus with gracilis autograft for ACL reconstruction: a systematic review and meta-analysis

Abstract Background Whether there is a difference in harvesting the semitendinosus tendon alone (S) or in combination with the gracilis tendon (SG) for the recovery of knee flexor strength after anterior cruciate ligament (ACL) reconstruction remains inconclusive. Therefore, this study aimed to assess the recovery of knee flexor strength based on the autograft composition, S or SG autograft at 6, 12, and ≥ 24 months after ACL reconstruction. Methods A systematic review and meta-analysis was conducted following the PRISMA guidelines. A comprehensive search was performed encompassing the Cochrane Library, Embase, Medline, PEDRo and AMED databases from inception to January 2023. Inclusion criteria were human clinical trials published in English, comprised of randomized controlled trials (RCTs), longitudinal cohort-, cross-sectional and case–control studies that compared knee flexor strength recovery between S and SG autografts in patients undergoing primary ACL reconstruction. Isokinetic peak torques were summarized for angular velocities of 60°/s, 180°/s, and across all angular velocities, assessed at 6, 12, and ≥ 24 months after ACL reconstruction. A random-effects model was used with standardized mean differences and 95% confidence intervals. Risk of bias was assessed with the RoBANS for non-randomized studies and the Cochrane RoB 2 tool for RCTs. Certainty of evidence was appraised using the GRADE working group methodology. Results Among the 1,227 patients from the 15 included studies, 604 patients received treatment with S autograft (49%), and 623 received SG autograft (51%). Patients treated with S autograft displayed lesser strength deficits at 6 months across all angular velocities d = -0.25, (95% CI -0.40; -0.10, p = 0.001). Beyond 6 months after ACL reconstruction, no significant difference was observed between autograft compositions. Conclusion The harvest of S autograft for ACL reconstruction yields superior knee flexor strength recovery compared to SG autograft 6 months after ACL reconstruction, irrespective of angular velocity at isokinetic testing. However, the clinical significance of the observed difference in knee flexor strength between autograft compositions at 6 months is questionable, given the very low certainty of evidence and small effect size. There was no significant difference in knee flexor strength recovery between autograft compositions beyond 6 months after ACL reconstruction. Trial registration CRD42022286773