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Myositis is associated with reduced quality of life, which is accompanied by significant impairments in muscle endurance and strength, altogether representing cardinal traits in patients with myositis. This randomised controlled trial aimed to investigate the effect of high-intensity resistance training on quality of life in patients with myositis. Thirty-two patients with established, stable myositis were randomised to 16 weeks of high-intensity resistance training (intervention group) or 16 weeks of usual care (control group). Primary outcome was quality of life assessed as the change in the physical component summary score (PCS) of the Short Form-36 health questionnaire from baseline to post-intervention. Secondary outcomes included functional capacity measures, such as functional index 3, and International Myositis Assessment and Clinical Studies Group (IMACS) disease activity and damage core set measures, including manual muscle testing 8 (MMT8). The primary outcome PCS showed an improvement in favour of high-intensity resistance training with a between-group difference of 5.33 (95% CI 0.61; 10.05) (p = 0.03). Additionally, functional index 3 showed a between-group difference indicating greater gains with high-intensity resistance training 11.49 (95% CI 3.37; 19.60) (p = 0.04), along with a between-group improvement in MMT8 1.30 (95% CI 0.09; 2.51) (p = 0.04). High-intensity resistance training for 16 weeks effectively improved quality of life in patients with myositis. Clinical measures of muscle endurance and muscle strength were also found to improve with high-intensity resistance training, while patients stayed in disease remission. Consequently, progressively adjusted high-intensity resistance training is feasible and causes no aggravation of the disease, while benefitting patients with myositis.Clinical trial registration: Clinicaltrials.gov ID: NCT04486261- https://clinicaltrials.gov/study/NCT04486261 ., (© 2024. The Author(s).)

This paper aimed to examine the acute effect of low-load (LL) exercise with blood-flow restriction (LL-BFR) on microvascular oxygenation and muscle excitability of the vastus medialis (VM) and vastus lateralis (VL) muscles during a single bout of unilateral knee extension exercise performed to task failure. Seventeen healthy recreationally resistance-trained males were enrolled in a within-group randomized cross-over study design. Participants performed one set of unilateral knee extensions at 20% of one-repetition maximum (1RM) to task failure, using a LL-BFR or LL free-flow (LL-FF) protocol in a randomized order on separate days. Changes in microvascular oxygenation and muscle excitability in VL and VM were assessed using near-infrared spectroscopy (NIRS) and surface electromyography (sEMG), respectively. Pain measures were collected using the visual analog scale (VAS) before and following set completion. Within- and between- protocol comparisons were performed at multiple time points of set completion for each muscle. During LL-BFR, participants performed 43% fewer repetitions and reported feeling more pain compared to LL-FF ( p <0.05). Normalized to time to task failure, LL-BFR and LL-FF generally demonstrated similar progression in microvascular oxygenation and muscle excitability during exercise to task failure. The present results demonstrate that LL-BFR accelerates time to task failure, compared with LL-FF, resulting in a lower dose of mechanical work to elicit similar levels of oxygenation, blood-pooling, and muscle excitability. LL-BFR may be preferable to LL-FF in clinical settings where high workloads are contraindicated, although increased pain experienced during BFR may limit its application. Highlights Compared to free flow (FF), neuromuscular fatigue mechanisms are accelerated during blood flow restricted (BFR) training. This can be observed as changes in microvascular oxygenation and muscle excitability occurring at a ∼43% faster mean rate during BFR compared to FF.BFR exercise seems to elicit the same level of neuromuscular fatigue as FF training within a shorter timeframe. This reduces total joint load and may be especially helpful in cases where high training volumes may be contraindicated (e.g. recovering from a sports injury or orthopedic surgery).

Sporadic inclusion body myositis (sIBM) is characterised by skeletal muscle inflammation, progressive muscle loss and weakness, which is largely refractory to immunosuppressive treatment. Low-load blood-flow restricted (BFR) training has been shown to evoke gains in myofibre cross sectional area (mCSA) in healthy adults. This could partially be due to the activation and integration of muscle satellite cells (SC) resulting in myonuclei addition. Consequently, this study investigated the effect of 12-weeks lower limb low-load BFR resistance training in sIBM patients on SC and myonuclei content, myofibre size and capillarization. Muscle biopsies from sIBM patients randomised to 12-weeks of low-load BFR resistance training (n = 11) or non-exercising controls (CON) (n = 9) were analysed for SC and myonuclei content, myofibre size and capillarization using three-colour immunofluorescence microscopy and computerised quantification procedures. No between-group differences (time-by-group interactions) or within-groups changes were observed for resident SCs (Pax7 + /Six1 + ), proliferating SCs (Pax7 + / Ki67 + ), myonuclei (Six1 + ), type 1 mCSA or capillary number (CD31 + ). However, a time-by-group interaction for type 2 mCSA was observed (p = 0.04). Satellite cell content, myonuclei number, mCSA and capillary density remained unaffected following 12-weeks low-load BFR resistance training, indicating limited myogenic capacity and satellite cell plasticity in long-term sIBM patients., Competing Interests: Declaration of Competing Interest ANJ was employed by Orphazyme A/S, who is developing pharmaceuticals for patients affected by sporadic inclusion body myositis. Orphazyme A/S does not have any financial nor scientific interest in the data presented in this article., (Copyright © 2022 The Authors. Published by Elsevier B.V. All rights reserved.)

Sporadic inclusion body myositis (sIBM) is an idiopathic inflammatory muscle disease associated with skeletal muscle inflammation and a parallel progressive decline in muscle strength and physical function. Eventually, most sIBM patients require use of wheelchair after about 10 years of diagnosis and assistance to perform activities of daily living. This study presents data from a randomized controlled intervention trial (NCT02317094) that examined the effect of 12 weeks low-load blood-flow restricted (BFR) resistance training on maximal muscle strength, power, rate of force development (RFD), thigh lean mass (TLM), and voluntary muscle activation (VA) in sIBM patients. A time-by-group interaction in knee extensor strength was observed in the stronger leg (p ≤ 0.033) but not the weaker leg. Within-group changes were observed with BFR training (BFR) manifested by increased knee extensor strength in the strongest leg (+13.7%, p = 0.049), whereas non-exercising patients (CON) showed reduced knee extensor strength (-7.7%, p = 0.018). Maximal leg extensor power obtained for the stronger leg remained unchanged following BFR training (+9.5%, p = 0.37) while decreasing in CON (-11.1%, p = 0.05). No changes in TLM were observed. VA declined post-training (p = 0.037) in both BFR (-6.3% points) and CON (-7.5% points). The present data indicate that BFR resistance training can attenuate the rate of decline in mechanical muscle function typically experienced by sIBM patients. The preservation of muscle mass and mechanical muscle function with BFR resistance training may be considered of high clinical importance in sIBM patients to countermeasure the disease-related decline in physical function., (© 2021 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

Introduction: Idiopathic inflammatory myopathies (IIMs) are rare diseases characterised by non-suppurative inflammation of skeletal muscles and muscle weakness. Additionally, IIM is associated with a reduced quality of life. Strength training is known to promote muscle hypertrophy and increase muscle strength and physical performance in healthy young and old adults. In contrast, only a few studies have examined the effects of high intensity strength training in patients with IIM and none using a randomised controlled trial (RCT) set-up. Thus, the purpose of this study is to investigate the effects of high-intensity strength training in patients affected by the IIM subsets polymyositis (PM), dermatomyositis (DM) and immune-mediated necrotising myopathy (IMNM) using an RCT study design., Methods and Analysis: 60 patients with PM, DM or IMNM will be included and randomised into (1) high-intensity strength training or (2) Care-as-Usual. The intervention period is 16 weeks comprising two whole-body strength exercise sessions per week. The primary outcome parameter will be the changes from pre training to post training in the Physical Component Summary measure in the Short Form-36 health questionnaire. Secondary outcome measures will include maximal lower limb muscle strength, skeletal muscle mass, functional capacity, disease status (International Myositis Assessment and Clinical Studies Group core set measures) and questionnaires assessing physical activity levels and cardiovascular comorbidities. Furthermore, blood samples and muscle biopsies will be collected for subsequent analyses., Ethics and Dissemination: The study complies with the Helsinki Declaration II and is approved by The Danish Data Protection Agency (P-2020-553). The study is approved by The Danish National Committee on Health Research Ethics (H-20030409). The findings of this trial will be submitted to relevant peer-reviewed journals. Abstracts will be submitted to international conferences., Trial Registration Number: NCT04486261., Competing Interests: Competing interests: None declared., (© Author(s) (or their employer(s)) 2021. Re-use permitted under CC BY-NC. No commercial re-use. See rights and permissions. Published by BMJ.)

MRI can provide fundamental tools in decoding physiological stressors stimulated by training paradigms. Acute physiological changes induced by three diverse exercise protocols known to elicit similar levels of muscle hypertrophy were evaluated using muscle functional magnetic resonance imaging (mfMRI). The study was a cross-over study with participants ( n = 10) performing three acute unilateral knee extensor exercise protocols to failure and a work matched control exercise protocol. Participants were scanned after each exercise protocol; 70% 1 repetition maximum (RM) (FF70); 20% 1RM (FF20); 20% 1RM with blood flow restriction (BFR20); free-flow (FF) control work matched to BFR20 (FF20 WM ). Post exercise mfMRI scans were used to obtain interleaved measures of muscle R2 (indicator of edema), R2' (indicator of deoxyhemoglobin), muscle cross sectional area (CSA) blood flow, and diffusion. Both BFR20 and FF20 exercise resulted in a larger acute decrease in R2, decrease in R2', and expansion of the extracellular compartment with slower rates of recovery. BFR20 caused greater acute increases in muscle CSA than FF20 WM and FF70. Only BFR20 caused acute increases in intracellular volume. Postexercise muscle blood flow was higher after FF70 and FF20 exercise than BFR20. Acute changes in mean diffusivity were similar across all exercise protocols. This study was able to differentiate the acute physiological responses between anabolic exercise protocols. Low-load exercise protocols, known to have relatively higher energy contributions from glycolysis at task failure, elicited a higher mfMRI response. Noninvasive mfMRI represents a promising tool for decoding mechanisms of anabolic adaptation in muscle. NEW & NOTEWORTHY Using muscle functional MRI (mfMRI), this study was able to differentiate the acute physiological responses following three established hypertrophic resistance exercise strategies. Low-load exercise protocols performed to failure, with or without blood flow restriction, resulted in larger changes in R 2 (i.e. greater T 2 -shifts) with a slow rate of return to baseline indicative of myocellular fluid shifts. These data were cross evaluated with interleaved measures of macrovascular blood flow, water diffusion, muscle cross sectional area (i.e. acute macroscopic muscle swelling), and intracellular water fraction measured using MRI.

Important physiological quantities for investigating muscle hypertrophy include blood oxygenation, cell swelling, and changes in blood flow. The purpose of this study was to compare the acute changes of these parameters in human skeletal muscle induced by low-load (20% 1-RM) blood flow-restricted (BFR-20) knee extensor exercise compared with free-flow work-matched (FF-20 WM ) and free-flow 50% 1-RM (FF-50) knee extensor exercise using multimodal magnetic resonance imaging (MRI). Subjects ( n = 11) completed acute exercise sessions for each exercise mode in an MRI scanner, where interleaved measures of muscle R 2 (indicator of edema), [Formula: see text] (indicator of deoxyhemoglobin), macrovascular blood flow, and diffusion were performed before, between sets, and after the final set for each exercise protocol. BFR-20 exercise resulted in larger acute decreases in R 2 and greater increases in cross-sectional area than FF-20 WM and FF-50 ( P < 0.01). Blood oxygenation decreased between sets during BFR-20, as indicated by a 13.6% increase in [Formula: see text] values ( P < 0.01)), whereas they remained unchanged for FF-20 WM and decreased during FF-50 exercise. Quadriceps blood flow between sets was highest for the heavier load (FF-50), averaging 305 mL/min, and lowest for BFR-20 at 123 ± 73 mL/min until post-exercise cuff release, where blood flow rates in BFR-20 exceeded both FF protocols ( P < 0.01). Acute changes in diffusion rates were similar for all exercise protocols. This study was able to differentiate the acute exercise response of selected physiological factors associated with skeletal muscle hypertrophy. Marked differences in these parameters were found to exist between BFR and FF exercise conditions, which contribute to explain the anabolic potential of low-load blood flow restricted muscle exercise. NEW & NOTEWORTHY Acute changes in blood flow, diffusion, blood oxygenation, cross-sectional area, and the "T 2 shift" are evaluated in human skeletal muscle in response to blood flow-restricted (BFR) and conventional free-flow knee extensor exercise performed in an MRI scanner. The acute physiological response to exercise was dependent on the magnitude of load and the application of BFR. Physiological variables changed markedly and established a steady state rapidly after the first of four exercise sets.

Introduction: Heavy-load strength training (HLT) is generally considered the Gold Standard exercise modality for inducing gains in skeletal muscle strength. However, use of heavy external exercise loads may be contraindicative in frail individuals. Low-load resistance exercise combined with partial blood-flow restriction (LL-BFR exercise) may offer an effective alternative for increasing mechanical muscle strength and size. The aim of this study was to compare the effect of LL-BFR training to HLT on maximal muscle strength gains. Prospero registration-id (CRD42014013382)., Materials and Methods: A systematic search in six healthcare science databases and reference lists was conducted. Data selected for primary analysis consisted of post-intervention changes in maximal muscle strength. A random-effects meta-analysis with standardized mean differences (SMD) was used., Results: Of 1413 papers identified through systematic search routines, sixteen papers fulfilled the inclusion criteria, totalling 153 participants completing HLT and 157 completing LL-BFR training. The magnitude of training-induced gains in maximal muscle strength did not differ between LL-BFR training and HLT (SMD of -0.17 (95% CI: -0.40; 0.05)). Low between-study heterogeneity was noted (I 2  = 0.0%, Chi 2 P = 9.65)., Conclusion: Low-load blood-flow-restricted training appears equally effective of producing gains in maximal voluntary muscle strength compared to HLT in 20- to 80-year-old healthy and habitually active adults., (© 2020 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

Purpose: The aim of the present study was to investigate the effect and time course of high-frequent low-load blood flow-restricted (BFR) resistance training on rapid force capacity (i.e., rate of torque development [RTD])., Materials and Methods: Ten male subjects (22.8 ± 2.3 yr) performed four sets of knee extensor exercise (20% one-repetition maximum) to concentric failure during concurrent BFR of the thigh (100 mm Hg), and eight work-matched controls (21.9 ± 3.0 yr) trained without BFR (CON). Twenty-three training sessions were performed within 19 d. Maximal slow and fast knee joint velocity muscle strength and rapid force capacity (e.g., RTD) and evoked twitch contractile parameters were assessed before (Pre) and 5 and 12 d after (Post5 and Post12) training. Muscle biopsies were obtained Pre, after 8 d (Mid8), and 3 and 10 d after (Post3 and Post10) training to examine changes in myofiber area and expression of myocellular proteins known to be modified by cellular stress (CaMKII, annexin A6, SNO-CYS)., Results: RTD remained unchanged after BFR training at Post5, while increasing 15%-20% Post12 (P < 0.01). Evoked muscle twitch parameters showed a general decline Post5 (P < 0.01) while returning to baseline levels at Post12. All contractile parameters essentially remained unchanged in CON. Elevated CaMKII was observed with BFR training at Post3 (57%) and Post10 (71%) (P < 0.05), whereas SNO-CYS increased in CON at Mid8 (P < 0.05)., Conclusion: This study is the first to show that low-load resistance exercise performed with BFR leads to marked increases in rapid force capacity (RTD). However, a general delayed adaptive response was observed for voluntary contractile parameters (including RTD) in parallel with a decline and subsequent recovery in evoked contractile properties, suggesting the delayed gain in rapid force capacity mainly have a peripheral origin.

Introduction: Loss of lean body mass is common following radiotherapy in patients with head and neck squamous cell carcinoma (HNSCC) and may reduce maximal muscle strength and functional performance. However, the associations between lean body mass, muscle strength and functional performance are unclear and no studies in HNSCC patients have compared the levels of these variables to the levels seen in healthy individuals., Purpose: The purpose of the present study was to investigate the associations between lean body mass, maximal muscle strength and functional performance in HNSCC patients and to compare the levels of these variables after radiotherapy and after progressive resistance training with the levels in healthy individuals., Material and Methods: Lean body mass (dual energy X-ray absorptiometry), maximal muscle strength (isokinetic dynamometry) and functional performance (10 m max gait speed, 30 s chair rise, 30 s arm curl, stair climb) from HNSCC patients from the DAHANCA 25 trials and data from 24 healthy individuals were included., Results: Lean body mass and maximal muscle strength were significantly associated according to the gender and age-adjusted linear regression model (p < 0.0001). In addition, maximal muscle strength were associated with 30 s arm curl performance, 10 m max gait speed and 30 s chair rise (p < 0.0001). Multiple regression analyses showed that HNSCC patients expressed significant lower levels of the investigated variables after radiotherapy than healthy individuals (p < 0.0001), and that all differences were evened out after training., Conclusions: Significant associations were found between lean body mass, maximal muscle strength and functional performance in HNSCC patients. Patients expressed lower levels of these variables compared with healthy individuals, suggesting that lean body mass is a clinically relevant health factor in HNSCC patients.

Purpose: The critical weight loss observed in head and neck squamous cell carcinoma (HNSCC) patients following radiotherapy is mainly due to loss of lean body mass. This is associated with decreases in muscle strength, functional performance and Quality of Life (QoL). The present study investigated the effect of progressive resistance training (PRT) on lean body mass, muscle strength and functional performance in HNSCC patients following radiotherapy., Patients and Methods: Following radiotherapy HNSCC patients were randomized into two groups: Early Exercise (EE, n=20) initiated 12 weeks of PRT followed by 12 weeks of self-chosen physical activity. Delayed Exercise (DE, n=21) initiated 12 weeks of self-chosen physical activity followed by 12 weeks of PRT. Lean body mass, muscle strength, functional performance and QoL were evaluated at baseline and after week 12 and 24., Results: In the first 12 weeks lean body mass increased by 4.3% in EE after PRT and in the last 12 weeks by 4.2% in DE after PRT. These increases were significantly larger than the changes after self-chosen physical activity (p ≤ 0.005). Regardless of PRT start-up time, the odds ratio of increasing lean body mass by more than 4% after PRT was 6.26 (p<0.05). PRT significantly increased muscle strength, whereas functional performance increased significantly more than after self-chosen physical activity only after delayed onset of PRT. Overall QoL improved significantly more in EE than DE from baseline to week 12., Conclusion: PRT effectively increased lean body mass and muscle strength in HNSCC patients following radiotherapy, irrespectively of early or delayed start-up., (Copyright © 2013 Elsevier Ireland Ltd. All rights reserved.)

Objectives: To examine the effect of strength training and testosterone therapy on mechanical muscle function and lean body mass (LBM) in aging men with low-normal testosterone levels in a randomized, double-blind, placebo-controlled 24-week study., Design: Randomized, double-blind, placebo-controlled., Setting: Odense, Denmark., Participants: Men aged 60 to 78, with bioavailable testosterone levels of less than 7.3 nmol/L and a waist circumference greater than 94 cm were randomized to testosterone (50-100 mg/d, n = 22) placebo (n = 23) or strength training (n = 23) for 24 weeks. The strength training group was randomized to addition of testosterone or placebo after 12 weeks. Subjects performed supervised strength training (2-3 sets with 6- to 10-repetition maximum loads, 3 times per week)., Measurements: Testosterone levels, maximal voluntary contraction and rate of force development, and LBM were obtained at 0 and at Weeks 12 and 24 of the intervention., Results: No changes in any variables were recorded with placebo. In the strength training group, maximal voluntary contraction increased 8% after 12 weeks (P = .005). During the following 12 weeks of strength training rate of force development increased by 10% (P = .04) and maximal voluntary contraction further increased (P < .001). Mechanical muscle function was unchanged in men receiving only testosterone for 24 weeks. LBM increased only in men receiving testosterone (P = .004)., Conclusion: Strength training in aging men with low-normal testosterone levels may improve mechanical muscle function, but this effect occurs without a significant increase in LBM. Clinically, only the combination of testosterone therapy and strength training resulted in an increase in mechanical muscle function and LBM., (© 2013, Copyright the Authors Journal compilation © 2013, The American Geriatrics Society.)

Low-load resistance training with blood flow restriction has been shown to elicit substantial increases in muscle mass and muscle strength; however, the effect on myogenic stem cells (MSCs) and myonuclei number remains unexplored. Ten male subjects (22.8 ± 2.3 years)performed four sets of knee extensor exercise (20% 1RM) to concentric failure during bloodflow restriction (BFR) of the proximal thigh (100 mmHg), while eight work-matched controls(21.9 ± 3.0 years) trained without BFR (control, CON). Twenty-three training sessions were performed within 19 days. Maximal isometric knee extensor strength (MVC) was examined pre- and post-training, while muscle biopsies were obtained at baseline (Pre), after 8 days intervention(Mid8) and 3 (Post3) and 10 days (Post10) post training to examine changes in myofibre area (MFA), MSC and myonuclei number. MVC increased by 7.1% (Post5) and 10.6% (Post12)(P <0.001) with BFR training, while type I and II MFA increased by 38% (Mid8), 35 – 37%(Post3) and 31 – 32% (Post10) (P <0.001). MSCs per myofibre increased with BFR training from 0.10 ± 0.01 (Pre) to 0.38 ± 0.02 (Mid8), 0.36 ± 0.04 (Post3) and 0.25 ± 0.02 (Post10) (P <0.001). Likewise, myonuclei per myofibre increased from 2.49 ± 0.07 (Pre) to 3.30 ± 0.22(Mid8), 3.20 ± 0.16 (Post3) and 3.11 ± 0.11 (Post10), (P<0.01). Although MFA increased in CON at Mid8, it returned to baseline at Post3. No changes in MSC or myonuclei number were observed in CON. This study is the first to show that short-term low-load resistance exercise performed with partial blood flow restriction leads to marked proliferation of myogenic stem cells and resulting myonuclei addition in human skeletal muscle, which is accompanied by substantial myofibre hypertrophy.

Sporadic inclusion body myositis (sIBM) is an idiopathic inflammatory muscle disease associated with skeletal muscle inflammation and a parallel progressive decline in muscle strength and physical function. Eventually, most sIBM patients require use of wheelchair after about 10 years of diagnosis and assistance to perform activities of daily living. This study presents data from a randomized controlled intervention trial (NCT02317094) that examined the effect of 12 weeks low‐load blood‐flow restricted (BFR) resistance training on maximal muscle strength, power, rate of force development (RFD), thigh lean mass (TLM), and voluntary muscle activation (VA) in sIBM patients. A time‐by‐group interaction in knee extensor strength was observed in the stronger leg (p ≤ 0.033) but not the weaker leg. Within‐group changes were observed with BFR training (BFR) manifested by increased knee extensor strength in the strongest leg (+13.7%, p = 0.049), whereas non‐exercising patients (CON) showed reduced knee extensor strength (−7.7%, p = 0.018). Maximal leg extensor power obtained for the stronger leg remained unchanged following BFR training (+9.5%, p = 0.37) while decreasing in CON (−11.1%, p = 0.05). No changes in TLM were observed. VA declined post‐training (p = 0.037) in both BFR (−6.3% points) and CON (−7.5% points). The present data indicate that BFR resistance training can attenuate the rate of decline in mechanical muscle function typically experienced by sIBM patients. The preservation of muscle mass and mechanical muscle function with BFR resistance training may be considered of high clinical importance in sIBM patients to countermeasure the disease‐related decline in physical function. [ABSTRACT FROM AUTHOR]

The current manuscript sets out a position stand for blood flow restriction (BFR) exercise, focusing on the methodology, application and safety of this mode of training. With the emergence of this technique and the wide variety of applications within the literature, the aim of this position stand is to set out a current research informed guide to BFR training to practitioners. This covers the use of BFR to enhance muscular strength and hypertrophy via training with resistance and aerobic exercise and preventing muscle atrophy using the technique passively. The authorship team for this article was selected from the researchers focused in BFR training research with expertise in exercise science, strength and conditioning and sports medicine. [ABSTRACT FROM AUTHOR]

Purpose: The aim of the present study was to investigate the effect and time course of high-frequent low-load blood flow--restricted (BFR) resistance training on rapid force capacity (i.e., rate of torque development [RTD]). Materials and Methods: Ten male subjects (22.8 ± 2.3 yr) performed four sets of knee extensor exercise (20% one-repetition maximum) to concentric failure during concurrent BFR of the thigh (100 mm Hg), and eight work-matched controls (21.9 ± 3.0 yr) trained without BFR (CON). Twenty-three training sessions were performed within 19 d. Maximal slow and fast knee joint velocity muscle strength and rapid force capacity (e.g., RTD) and evoked twitch contractile parameters were assessed before (Pre) and 5 and 12 d after (Post5 and Post12) training. Muscle biopsies were obtained Pre, after 8 d (Mid8), and 3 and 10 d after (Post3 and Post10) training to examine changes in myofiber area and expression of myocellular proteins known to be modified by cellular stress (CaMKII, annexin A6, SNO-CYS). Results: RTD remained unchanged after BFR training at Post5, while increasing 15%-20% Post12 (P < 0.01). Evoked muscle twitch parameters showed a general decline Post5 (P < 0.01) while returning to baseline levels at Post12. All contractile parameters essentially remained unchanged in CON. Elevated CaMKII was observed with BFR training at Post3 (57%) and Post10 (71%) (P < 0.05), whereas SNO-CYS increased in CON at Mid8 (P < 0.05). Conclusion: This study is the first to show that low-load resistance exercise performed with BFR leads to marked increases in rapid force capacity (RTD). However, a general delayed adaptive response was observed for voluntary contractile parameters (including RTD) in parallel with a decline and subsequent recovery in evoked contractile properties, suggesting the delayed gain in rapid force capacity mainly have a peripheral origin. [ABSTRACT FROM AUTHOR]