Evidence of skeletal muscle damage following electrically stimulated isometric muscle contractions in humans

Joint angle-specific neuromuscular time course of recovery after isometric resistance exercise at shorter and longer muscle lengths

Resistance training at longer muscle lengths induces greater muscle hypertrophy and different neuromuscular functional adaptations than training at shorter muscle lengths. However, the acute time course of recovery of neuromuscular characteristics after resistance exercise at shorter and longer muscle lengths in the quadriceps has never been described. Eight healthy young participants (4 M, 4 F) were randomly assigned to perform four sets of eight maximal isometric contractions at shorter (SL; 50° knee flexion) or longer (LL; 90° knee flexion) muscle lengths in a crossover fashion. During exercise, peak torque (PT), muscle activity [electromyogram (EMG)], and internal muscle forces were assessed. PT and EMG at shorter (PT50, EMG50) and longer (PT90, EMG90) muscle lengths, creatine kinase (CK), and muscle soreness were measured at baseline, immediately after exercise (Post), after 24 h (24 h), and after 48 h (48 h). During exercise, EMG (P = 0.002) and internal muscle forces (P = 0.017) were greater in LL than in SL. During recovery, there was a main effect of exercise angle, with PT50 (P = 0.002), PT90 (P = 0.016), and EMG50 (P = 0.002) all significantly reduced to a greater degree in LL compared with SL. CK and muscle soreness increased after resistance exercise, but there were no differences between SL and LL. The present results suggest that if the preceding isometric resistance exercise is performed at longer muscle lengths, function and muscle activity at shorter and longer muscle lengths are inhibited to a larger degree in the subsequent recovery period. This information can be used by practitioners to manipulate exercise prescription.NEW & NOTEWORTHY Despite the established long-term benefits of training at longer muscle lengths for muscle size and strength, acutely performing resistance exercise at longer muscle lengths may require a longer time course of neuromuscular recovery compared with performing resistance exercises at shorter muscle lengths. Furthermore, there appear to be different joint angle-specific recovery profiles, depending on the muscle length of the preceding exercise.

Cerebral Benefits Induced by Electrical Muscle Stimulation: Evidence from a Human and Rat Study

Physical exercise (EX) is well established for its positive impact on brain health. However, conventional EX may not be feasible for certain individuals. In this regard, this study explores electromyostimulation (EMS) as a potential alternative for enhancing cognitive function. Conducted on both human participants and rats, the study involved two sessions of EMS applied to the quadriceps with a duration of 30 min at one-week intervals. The human subjects experienced assessments of cognition and mood, while the rats underwent histological and biochemical analyses on the prefrontal cortex, hippocampus, and quadriceps. Our findings indicated that EMS enhanced executive functions and reduced anxiety in humans. In parallel, our results from the animal studies revealed an elevation in brain-derived neurotrophic factor (BDNF), specifically in the hippocampus. Intriguingly, this increase was not associated with heightened neuronal activity or cerebral hemodynamics; instead, our data point towards a humoral interaction from muscle to brain. While no evidence of increased muscle and circulating BDNF or FNDC5/irisin pathways could be found, our data highlight lactate as a bridging signaling molecule of the muscle-brain crosstalk following EMS. In conclusion, our results suggest that EMS could be an effective alternative to conventional EX for enhancing both brain health and cognitive function.

Prospective study to assess the efficacy and safety of a noninvasive electro-muscular stimulation for improvement of muscle strength and muscle toning of the extremities

OBJECTIVE

We sought to evaluate the safety and efficacy of an electrical muscle stimulation (EMS) device in the improvement of muscle strength and toning of the upper extremities. This device, which is FDA-cleared as a two-channel muscle stimulator, provides up to eight electrodes with waveforms inducing muscle stimulation. Although a prior study demonstrated it is safe and effective for use in the abdomen, this system, which has electrodes specifically designed for the extremities, has not previously been evaluated in the upper extremities.

METHODS

Forty-five subjects enrolled in the study to assess improvement in arm (i.e., bicep and tricep muscle) strength, and appearance following a protocol of treatments with this bioelectric muscle activation (BMA) device. All subjects received four 30-min EMS treatment sessions in Arm mode-twice weekly for 2 weeks and at least 48 h apart. Follow up visits were also scheduled 30- and 90-days after treatment. Strength was measured with a dynamometer device at baseline, at the final treatment session, and at the posttreatment 30- and 90-day assessment. Subject satisfaction was assessed gauging overall comfort of the treatment and satisfaction including willingness to recommend to others. The changes in strength between initial treatment and final treatment, as well as 30 and 90-day assessment were evaluated. Clinical photography at these visits was also assessed for each patient. Patients were instructed to not modify their normal exercise routine while participating in this study.

RESULTS

All 45 subjects completed the treatment protocol. Most patients showed an improvement in muscle strength from the initial to final treatment (i.e., the fourth treatment). Specifically, the maximum bicep strength increased by a mean of 7.5 lbs (22.83%, p = 0.006), while the average increased by a mean of 8.2 lbs (25.76%, p = 0.001) during this period. Similarly, the maximum tricep strength from initial to final treatment increased by a mean of 10.0 lbs (23.16%, p = 0.000), while the average increased by a mean of 9.6 lbs (27.12%, p = 0.000). Thirty days after the last treatment, the maximum bicep strength increased by a mean of 13.3 lbs (34.13%, p = 0.001) while the average increased by a mean of 13.6 lbs (37.05%, p = 0.000) during this period. Similarly, the maximum tricep strength from initial to 30 days postfinal treatment increased by a mean of 10.9 lbs (24.37%, p = 0.000), while the average increased by a mean of 10.5 lbs (29.37%, p = 0.000). Finally, 90 days after the last treatment, the maximum bicep strength increased by a mean of 19.4 lbs (48.4%, p = 0.000), while the average increased by a mean of 17.4 lbs (46.53%, p = 0.000) during this period. Similarly, the maximum tricep strength from initial to 90 days postfinal treatment increased by a mean of 10.8 lbs (27.12%, p = 0.000), while the average increased by a mean of 10.0 lbs (30.94%, p = 0.001).

CONCLUSION

This device was well tolerated and resulted in increased strength measurements in the upper extremities, as assessed by a dynamometer, which were sustained at 30 and 90 days.

Effect of Lactobacillus plantarum PS128 on neuromuscular efficiency after a half-marathon

Introduction: Lactobacillus plantarum PS128 (PS128) could be considered an antioxidant supplement to reduce muscle fatigue and improve exercise capacity recovery after vigorous exercise. Purpose: The purpose of this study is to investigate the effect of PS128 on muscle fatigue and electromyography (EMG) activity after a half-marathon (HM). Methods: The experimental design used a repeated-measures design with a double-blind approach. The participants either took two capsules of PS128 for 4 weeks as the PS128 group (PSG, n = 8) or took two capsules of a placebo for 4 weeks as the placebo group (PLG, n = 8) to ensure counterbalancing. The time points of the maximal voluntary isometric contraction (MVIC) and EMG activity test were set before probiotics were taken (baseline), 48 h before HM (Pre), and immediately at 0 h, 3 h, 24 h, 48 h, 72 h, and 96 h after HM. Results: EMG activity included median power frequency (MDF), integrated EMG (iEMG), and neuromuscular efficiency (peak torque/iEMG). The MVICs of knee extensors, analyzed by using an isokinetic dynamometer, showed a decrease from the Pre to 0 h (p = 0.0001), 3 h (p < 0.0001), 24 h (p < 0.0001), 48 h (p < 0.0001), 72 h (p = 0.0002), and 96 h (p = 0.0408) time points in the PLG. Sidak's multiple comparisons tests showed that the PLG was significantly lower than the PSG at 0 h (p = 0.0173), 3 h (p < 0.0001), 24 h (p < 0.0001), 48 h (p < 0.0001), 72 h (p < 0.0001), and 96 h (p = 0.0004) time points. The MDF of vastus medialis oblique (VMO) in the PLG was significantly decreased 24 h after HM and significantly lower than that in the PSG at all times points after HM. The iEMG of VMO in the PLG was significantly decreased 48 h after HM and significantly lower than that in the PSG at 0 h, 3 h, 24 h, 48 h, and 72 h after HM. Conclusion: The PS128 supplementation may prevent the decrease in MDF, iEMG, and peak torque after vigorous exercise. Recreational runners may consider implementing a probiotic supplementation regimen as a potential strategy to mitigate muscle fatigue following HM.

Effects of Electrical Stimulation on Delayed Onset Muscle Soreness (DOMS): Evidences from Laboratory and In-Field Studies

Intense, long exercise can increase oxidative stress, leading to higher levels of inflammatory mediators and muscle damage. At the same time, fatigue has been suggested as one of the factors giving rise to delayed-onset muscle soreness (DOMS). The aim of this study was to investigate the efficacy of a specific electrical stimulation (ES) treatment (without elicited muscular contraction) on two different scenarios: in the laboratory on eleven healthy volunteers (56.45 ± 4.87 years) after upper limbs eccentric exercise (Study 1) and in the field on fourteen ultra-endurance athletes (age 47.4 ± 10.2 year) after an ultra-running race (134 km, altitude difference of 10,970 m+) by lower exercising limbs (Study 2). Subjects were randomly assigned to two experimental tasks in cross-over: Active or Sham ES treatments. The ES efficacy was assessed by monitoring the oxy-inflammation status: Reactive Oxygen Species production, total antioxidant capacity, IL-6 cytokine levels, and lactate with micro-invasive measurements (capillary blood, urine) and scales for fatigue and recovery assessments. No significant differences (p > 0.05) were found in the time course of recovery and/or pre-post-race between Sham and Active groups in both study conditions. A subjective positive role of sham stimulation (VAS scores for muscle pain assessment) was reported. In conclusion, the effectiveness of ES in treating DOMS and its effects on muscle recovery remain still unclear.

Slow or fast: Implications of myofibre type and associated differences for manifestation of neuromuscular disorders

Many neuromuscular disorders can have a differential impact on a specific myofibre type, forming the central premise of this review. The many different skeletal muscles in mammals contain a spectrum of slow- to fast-twitch myofibres with varying levels of protein isoforms that determine their distinctive contractile, metabolic, and other properties. The variations in functional properties across the range of classic 'slow' to 'fast' myofibres are outlined, combined with exemplars of the predominantly slow-twitch soleus and fast-twitch extensor digitorum longus muscles, species comparisons, and techniques used to study these properties. Other intrinsic and extrinsic differences are discussed in the context of slow and fast myofibres. These include inherent susceptibility to damage, myonecrosis, and regeneration, plus extrinsic nerves, extracellular matrix, and vasculature, examined in the context of growth, ageing, metabolic syndrome, and sexual dimorphism. These many differences emphasise the importance of carefully considering the influence of myofibre-type composition on manifestation of various neuromuscular disorders across the lifespan for both sexes. Equally, understanding the different responses of slow and fast myofibres due to intrinsic and extrinsic factors can provide deep insight into the precise molecular mechanisms that initiate and exacerbate various neuromuscular disorders. This focus on the influence of different myofibre types is of fundamental importance to enhance translation for clinical management and therapies for many skeletal muscle disorders.

Different Impacts of Heat-Killed and Viable Lactiplantibacillus plantarum TWK10 on Exercise Performance, Fatigue, Body Composition, and Gut Microbiota in Humans

Lactiplantibacillus plantarum TWK10, a probiotic strain, has been demonstrated to improve exercise performance, regulate body composition, and ameliorate age-related declines. Here, we performed a comparative analysis of viable and heat-killed TWK10 in the regulation of exercise performance, body composition, and gut microbiota in humans. Healthy adults (n = 53) were randomly divided into three groups: Control, TWK10 (viable TWK10, 3 × 1011 colony forming units/day), and TWK10-hk (heat-killed TWK10, 3 × 1011 cells/day) groups. After six-week administration, both the TWK10 and TWK10-hk groups had significantly improved exercise performance and fatigue-associated features and reduced exercise-induced inflammation, compared with controls. Viable TWK10 significantly promoted improved body composition, by increasing muscle mass proportion and reducing fat mass. Gut microbiota analysis demonstrated significantly increasing trends in the relative abundances of Akkermansiaceae and Prevotellaceae in subjects receiving viable TWK10. Predictive metagenomic profiling revealed that heat-killed TWK10 administration significantly enhanced the signaling pathways involved in amino acid metabolisms, while glutathione metabolism, and ubiquinone and other terpenoid-quinone biosynthesis pathways were enriched by viable TWK10. In conclusion, viable and heat-killed TWK10 had similar effects in improving exercise performance and attenuating exercise-induced inflammatory responses as probiotics and postbiotics, respectively. Viable TWK10 was also highly effective in regulating body composition. The differences in efficacy between viable and heat-killed TWK10 may be due to differential impacts in shaping gut microbiota.

Effect of stimulation frequency on force, power, and fatigue of isolated mouse extensor digitorum longus muscle

This study examined the effect of stimulation frequency (140, 200, 230 and 260 Hz) on isometric force, work loop (WL) power, and the fatigue resistance of extensor digitorum longus (EDL) muscle (n=32), isolated from 8-10-week-old CD-1 female mice. Stimulation frequency had significant effects on isometric properties of isolated mouse EDL, whereby increasing stimulation frequency evoked increased isometric force, quicker activation, and prolonged relaxation (P <0.047), until 230 Hz and above, thereafter force and activation did not differ (P >0.137). Increasing stimulation frequency increased maximal WL power output (P <0.001; 140 Hz, 71.3±3.5; 200 Hz, 105.4±4.1; 230 Hz, 115.5±4.1; 260 Hz, 121.1±4.1 W.kg-1), but resulted in significantly quicker rates of fatigue during consecutive WL's (P <0.004). WL shapes indicate impaired muscle relaxation at the end of shortening and subsequent increased negative work appeared to contribute to fatigue at 230 and 260 Hz, but not at lower stimulation frequencies. Cumulative work was unaffected by stimulation frequency, except at the start of fatigue protocol where 230 and 260 Hz produced more work than 140 Hz (P <0.039). We demonstrate that stimulation frequency affects force, power, and fatigue, but effects are not uniform between different assessments of contractile performance. Therefore, future work examining contractile properties of isolated skeletal muscle should consider increasing stimulation frequency beyond that needed for maximal force when examining maximal power but utilise a sub-maximal stimulation frequency for fatigue assessments to avoid high degree of negative work atypical of in vivo function.

Isoform-specific functions of synaptopodin-2 variants in cytoskeleton stabilization and autophagy regulation in muscle under mechanical stress

Protein homeostasis (proteostasis) in multicellular organisms depends on the maintenance of force-bearing and force-generating cellular structures. Within myofibrillar Z-discs of striated muscle, isoforms of synaptopodin-2 (SYNPO2/myopodin) act as adapter proteins that are engaged in proteostasis of the actin-crosslinking protein filamin C (FLNc) under mechanical stress. SYNPO2 directly binds F-actin, FLNc and α-actinin and thus contributes to the architectural features of the actin cytoskeleton. By its association with autophagy mediating proteins, i.e. BAG3 and VPS18, SYNPO2 is also engaged in protein quality control and helps to target mechanical unfolded and damaged FLNc for degradation. Here we show that deficiency of all SYNPO2-isoforms in myotubes leads to decreased myofibrillar stability and deregulated autophagy under mechanical stress. In addition, isoform-specific proteostasis functions were revealed. The PDZ-domain containing variant SYNPO2b and the shorter, PDZ-less isoform SYNPO2e both localize to Z-discs. Yet, SYNPO2e is less stably associated with the Z-disc than SYNPO2b, and is dynamically transferred into FLNc-containing myofibrillar lesions under mechanical stress. SYNPO2e also recruits BAG3 into these lesions via interaction with the WW domain of BAG3. Our data provide evidence for a role of myofibrillar lesions as a transient quality control compartment essential to prevent and repair contraction-induced myofibril damage in muscle and indicate an important coordinating activity for SYNPO2 therein.

Whole-Body EMS Superimposed Walking and Nordic Walking on a Treadmill-Determination of Exercise Intensity to Conventional Exercise

Electrical muscle stimulation (EMS) is an increasingly popular training method and has become the focus of research in recent years. New EMS devices offer a wide range of mobile applications for whole-body EMS (WB-EMS) training, e.g., the intensification of dynamic low-intensity endurance exercises through WB-EMS. The present study aimed to determine the differences in exercise intensity between WB-EMS-superimposed and conventional walking (EMS-CW), and CON and WB-EMS-superimposed Nordic walking (WB-EMS-NW) during a treadmill test. Eleven participants (52.0 ± years; 85.9 ± 7.4 kg, 182 ± 6 cm, BMI 25.9 ± 2.2 kg/m²) performed a 10 min treadmill test at a given velocity (6.5 km/h) in four different test situations, walking (W) and Nordic walking (NW) in both conventional and WB-EMS superimposed. Oxygen uptake in absolute (VO₂) and relative to body weight (rel. VO₂), lactate, and the rate of perceived exertion (RPE) were measured before and after the test. WB-EMS intensity was adjusted individually according to the feedback of the participant. The descriptive statistics were given in mean ± SD. For the statistical analyses, one-factorial ANOVA for repeated measures and two-factorial ANOVA [factors include EMS, W/NW, and factor combination (EMS^*W/NW)] were performed (α = 0.05). Significant effects were found for EMS and W/NW factors for the outcome variables VO₂ (EMS: p = 0.006, r = 0.736; W/NW: p < 0.001, r = 0.870), relative VO₂ (EMS: p < 0.001, r = 0.850; W/NW: p < 0.001, r = 0.937), and lactate (EMS: p = 0.003, r = 0.771; w/NW: p = 0.003, r = 0.764) and both the factors produced higher results. However, the difference in VO₂ and relative VO₂ is within the range of biological variability of ± 12%. The factor combination EMS^*W/NW is statistically non-significant for all three variables. WB-EMS resulted in the higher RPE values (p = 0.035, r = 0.613), RPE differences for W/NW and EMS^*W/NW were not significant. The current study results indicate that WB-EMS influences the parameters of exercise intensity. The impact on exercise intensity and the clinical relevance of WB-EMS-superimposed walking (WB-EMS-W) exercise is questionable because of the marginal differences in the outcome variables.

The effects of blood flow restriction resistance training on indices of delayed onset muscle soreness and peak power

BACKGROUND: Low-load resistance training with blood flow restriction (LL + BFR) attenuated delayed onset muscle soreness (DOMS) under some conditions. OBJECTIVE: The purpose of this study examined the effects of reciprocal concentric-only elbow flexion-extension muscle actions at 30% of peak torque on indices of DOMS. METHODS: Thirty untrained women (mean ± SD; 22 ± 2.4 years) were randomly assigned to 6 training days of LL + BFR (n= 10), low-load non-BFR (LL) (n= 10), or control (n= 10). Participants completed 4 sets (1 × 30, 3 × 15) of submaximal (30% of peak torque), unilateral, isokinetic (120∘s-1) muscle actions. Indices of DOMS including peak power, resting elbow joint angle (ROM), perceived muscle soreness (VAS), and pain pressure threshold (PPT) were assessed. RESULTS: There were no changes in peak power, ROM, or VAS. There was a significant interaction for PPT. Follow-up analyses indicated PPT increased for the LL + BFR condition (Day 5 > Day 2), but did not decrease below baseline. The results of the present study indicated LL + BFR and LL did not induce DOMS for the elbow extensors in previously untrained women. CONCLUSION: These findings suggested LL + BFR and LL concentric-only resistance training could be an effective training modality to elicit muscular adaptation without inducing DOMS.

Effects of Various Physical Interventions on Reducing Neuromuscular Fatigue Assessed by Electromyography: A Systematic Review and Meta-Analysis

Introduction: Various interventions have been applied to improve recovery from muscle fatigue based on evidence from subjective outcomes, such as perceived fatigue and soreness, which may partly contribute to conflicting results of reducing muscle fatigue. There is a need to assess the effectiveness of various intervention on reducing neuromuscular fatigue assessed by a quantitative outcome, such as electromyography (EMG). The objective of this review and meta-analysis was to evaluate the effectiveness of different interventions and intervention timing for reducing fatigue rates during exercise. Methods: The literature was searched from the earliest record to March 2021. Eighteen studies with a total of 87 data points involving 281 participants and seven types of interventions [i.e., active recovery (AR), compression, cooling, electrical stimulation (ES), light-emitting diode therapy (LEDT), massage, and stretching] were included in this meta-analysis. Results: The results showed that compression (SMD = 0.28; 95% CI = -0.00 to 0.56; p = 0.05; I ² = 58%) and LEDT (SMD = 0.49; 95% CI = 0.11 to 0.88; p = 0.01; I ² = 52%) have a significant recovery effect on reducing muscle fatigue. Additionally, compression, AR, and cooling have a significant effect on reducing muscle fatigue when conducted during exercise, whereas a non-effective trend when applied after exercise. Discussion: This meta-analysis suggests that compression and LEDT have a significant effect on reducing muscle fatigue. The results also suggest that there is a significant effect or an effective trend on reducing muscle fatigue when compression, AR, cooling, and ES are applied during exercise, but not after exercise.

Skeletal Muscle Damage Produced by Electrically Evoked Muscle Contractions

Understanding the physiological/mechanical mechanisms leading to skeletal muscle damage remains one of the challenges in muscle physiology. This review presents the functional, structural, and cellular consequences of electrically evoked submaximal isometric contractions that can elicit severe and localized skeletal muscle damage. Hypotheses related to underlying physiological and mechanical processes involved in severe and localized muscle damage also are discussed.

Neuromuscular electrical stimulation and protein during bed rest increases CD11b+ skeletal muscle macrophages but does not correspond to muscle size or insulin sensitivity

With this cohort, we previously demonstrated preservation of thigh lean tissue with neuromuscular electrical stimulation combined with protein supplementation (NMES+PRO) treatment during bed rest in healthy older adults. Because macrophage polarization plays a significant role in the repair and maintenance of muscle size and insulin sensitivity, we hypothesized that muscle macrophages would be induced by NMES+PRO and would correspond to an increase in lean mass and an attenuated insulin resistance response altered by bed rest. Older adults (60-80 years old; body mass index < 30 kg/m2) underwent 5 days of bed rest and were randomized to either thrice daily treatment of NMES+PRO (n = 8) or CON (n = 8). Lean mass, insulin sensitivity, and markers of muscle macrophages, inflammation, and connective tissue were determined before and after bed rest. Glucose intolerance and insulin resistance occurred after bed rest but there was not a treatment effect (p > 0.10). Proinflammatory-like macrophages (CD11b+, CD206-) increased (p < 0.05) with NMES+PRO treatment and was different than CON. Minor changes in noncontractile tissue were observed. However, changes in muscle macrophages or extracellular matrix were not related to the preservation of thigh lean mass or insulin resistance. Daily NMES+PRO treatment during bed rest induced a muscle proinflammatory-like macrophage response and was unrelated to muscle size or metabolic function. This study is listed as clinical trial NCT02566590. Novelty Neuromuscular electrical stimulation combined with protein supplementation (NMES+PRO) increased proinflammatory-like macrophages and extracellular matrix content in older adults after bed rest. NMES+PRO changes in macrophages and noncontractile tissue macrophages were not related to muscle size preservation or insulin sensitivity.

The effect of low level laser irradiation on oxidative stress, muscle damage and function following neuromuscular electrical stimulation. A double blind, randomised, crossover trial

BACKGROUND

Low level laser therapy (LLLT) is among novel methods for preventing and treating muscle damage and soreness induced by volitional exercise, but little is known about using LLLT before neuromuscular electrical stimulation. The aim of this first randomised, double blind, crossover trial addressing this issue was to evaluate effects of LLLT on muscle damage and oxidative stress, as well as recovery of muscle function after a single session of isometric neuromuscular electrical stimulation(NMES).

METHODS

Twenty four moderately active, healthy men aged 21-22 years received 45 electrically evoked tetanic, isometric contractions of the quadriceps femoris, preceded by LLLT or sham-LLLT. Maximal isometric voluntary muscle torques, perceived soreness, and blood samples were analysed from baseline to 96 h post intervention. We measured plasma markers of muscle damage (the activity of creatine kinase), and inflammation (C-reactive protein), and evaluated redox state parameters.

RESULTS

NMES-evoked contractions induced oxidative stress, demonstrated by an increase in lipid peroxidation and impairments in enzymatic antioxidant system. LLLT irradiations had a protective effect on NMES-induced decrease in enzymatic antioxidant defence and shortened the duration of inflammation. This effect of irradiations on redox state and inflammation did not affect lipid peroxidation, muscle damage, and muscle torque.

CONCLUSIONS

LLLT may protect from impairments in enzymatic antioxidant system and may shorten inflammation induced by a single NMES session in moderately active, healthy men. However, the effects of LLLT on redox state and inflammatory processes do not seem to affect muscle damage and recovery of muscle function after NMES.

TRIAL REGISTRATION

The study was retrospectively registered in the Australian New Zealand Clinical Trials Registry (ANZCTR); The trial registration number: ACTRN12619000678190; date of registration: 6 May 2019.

Impact of transcutaneous neuromuscular electrical stimulation or resistance exercise on skeletal muscle mRNA expression in COPD

Background: Voluntary resistance exercise (RE) training increases muscle mass and strength in patients with chronic obstructive pulmonary disease (COPD). Nonvolitional transcutaneous neuromuscular electrical stimulation (NMES) may be an alternative strategy for reducing ambulatory muscle weakness in patients unable to perform RE training, but little comparative data are available. This study, therefore, investigated changes in muscle mRNA abundance of a number of gene targets in response to a single bout of NMES compared with RE. Methods: Twenty-six patients with stable COPD (15 male; FEV₁, 43±18% predicted; age, 64±8 years; fat free mass index, 16.6±1.8 kg/m²) undertook 30 minutes of quadriceps NMES (50 Hz, current at the limit of tolerance) or 5×30 maximal voluntary isokinetic knee extensions. Vastus lateralis muscle biopsies were obtained at rest immediately before and 24 hours after intervention. Expression of 384 targeted mRNA transcripts was assessed by real time TaqMan PCR. Significant change in expression from baseline was determined using the ΔΔC_T method with a false discovery rate (FDR) of <5%. Results: NMES and RE altered mRNA abundance of 18 and 68 genes, respectively (FDR <5%), of which 14 genes were common to both interventions and of the same magnitude of fold change. Biological functions of upregulated genes included inflammation, hypertrophy, muscle protein turnover, and muscle growth, whilst downregulated genes included mitochondrial and cell signaling functions. Conclusions: Compared with NMES, RE had a broader impact on mRNA abundance and, therefore, appears to be the superior intervention for maximizing transcriptional responses in the quadriceps of patients with COPD. However, if voluntary RE is not feasible in a clinical setting, NMES by modifying expression of genes known to impact upon muscle mass and strength may have a positive influence on muscle function.

Effectiveness of Grounded Sleeping on Recovery After Intensive Eccentric Muscle Loading

Purpose: We set out to investigate the effectiveness of grounded sleeping on the time course of recovery with respect to muscle soreness and athletic performance after intensive eccentric muscle loading. Methods: Twenty-two healthy participants were recruited for this study and randomly assigned to an experimental group (GRD, grounded sleeping, n = 12) or control group (UGD, sham-grounded sleeping, n = 10) to evaluate the effects of 10 days recovery with GRD vs. UGD following a single intensive downhill treadmill intervention in a triple-blinded (participant, tester, and data analyst) manner. To operationalize recovery a test battery was performed at baseline and on days 1, 2, 3, 5, 7, and 10 post-intervention: (1) perception of muscle soreness (VAS), (2) creatine kinase blood levels (CK), (3) maximum voluntary isometric contraction (MVIC) for both legs, (4) counter movement jump (CMJ) and drop jump (DJ) performance. Furthermore, in four participants blood was sampled for detailed analysis of complete blood counts and serum-derived inflammation markers. Results: The downhill treadmill running intervention led to distinct changes in all measured parameters related to fatigue. These changes were detectable already 5-min post intervention and were not fully recovered 10 days post intervention. GRD led to less pronounced decrease in performance (CMJ, MVIC) and less increase with respect to CK compared with UGD (all P < 0.05). Detailed blood samples demonstrated that grounded sleeping modulates the recovery process by (a) keeping a constant hemoconcentration, as represented by the number of erythrocytes, and the hemoglobin/hematocrit values; and (b) by the reduction of muscle damage-associated inflammation markers such as, IP-10, MIP-1α, and sP-Selectin. Conclusion: The downhill running protocol is a feasible methodology to produce long term muscle soreness and muscular fatigue. GRD was shown to result in faster recovery and/or less pronounced markers of muscle damage and inflammation. GRD might be seen as a simple methodology to enhance acute and long-term recovery after intensive eccentric exercises.

An Evidence-Based Approach for Choosing Post-exercise Recovery Techniques to Reduce Markers of Muscle Damage, Soreness, Fatigue, and Inflammation: A Systematic Review With Meta-Analysis

Introduction: The aim of the present work was to perform a meta-analysis evaluating the impact of recovery techniques on delayed onset muscle soreness (DOMS), perceived fatigue, muscle damage, and inflammatory markers after physical exercise. Method: Three databases including PubMed, Embase, and Web-of-Science were searched using the following terms: ("recovery" or "active recovery" or "cooling" or "massage" or "compression garment" or "electrostimulation" or "stretching" or "immersion" or "cryotherapy") and ("DOMS" or "perceived fatigue" or "CK" or "CRP" or "IL-6") and ("after exercise" or "post-exercise") for randomized controlled trials, crossover trials, and repeated-measure studies. Overall, 99 studies were included. Results: Active recovery, massage, compression garments, immersion, contrast water therapy, and cryotherapy induced a small to large decrease (-2.26 < g < -0.40) in the magnitude of DOMS, while there was no change for the other methods. Massage was found to be the most powerful technique for recovering from DOMS and fatigue. In terms of muscle damage and inflammatory markers, we observed an overall moderate decrease in creatine kinase [SMD (95% CI) = -0.37 (-0.58 to -0.16), I2 = 40.15%] and overall small decreases in interleukin-6 [SMD (95% CI) = -0.36 (-0.60 to -0.12), I2 = 0%] and C-reactive protein [SMD (95% CI) = -0.38 (-0.59 to-0.14), I2 = 39%]. The most powerful techniques for reducing inflammation were massage and cold exposure. Conclusion: Massage seems to be the most effective method for reducing DOMS and perceived fatigue. Perceived fatigue can be effectively managed using compression techniques, such as compression garments, massage, or water immersion.

Time Course and Association of Functional and Biochemical Markers in Severe Semitendinosus Damage Following Intensive Eccentric Leg Curls: Differences between and within Subjects

Purpose: To investigate the extent and evolution of hamstring muscle damage caused by an intensive bout of eccentric leg curls (ELCs) by (1) assessing the time course and association of different indirect markers of muscle damage such as changes in the force-generating capacity (FGC), functional magnetic resonance (fMRI), and serum muscle enzyme levels and (2) analyzing differences in the degree of hamstring muscle damage between and within subjects (limb-to-limb comparison).

Methods: Thirteen male participants performed six sets of 10 repetitions of an ELC with each leg. Before and at regular intervals over 7 days after the exercise, FGC was measured with maximal isometric voluntary contraction (MVC). Serum enzyme levels, fMRI transverse relaxation time (T2) and perceived muscle soreness were also assessed and compared against the FGC.

Results: Two groups of subjects were identified according to the extent of hamstring muscle damage based on decreased FGC and increased serum enzyme levels: high responders (n = 10, severe muscle damage) and moderate responders (n = 3, moderate muscle damage). In the high responders, fMRI T2 analysis revealed that the semitendinosus (ST) muscle suffered severe damage in the three regions measured (proximal, middle, and distal). The biceps femoris short head (BFsh) muscle was also damaged and there were significant differences in the FGC within subjects in the high responders.

Conclusion: FGC and serum enzyme levels measured in 10 of the subjects from the sample were consistent with severe muscle damage. However, the results showed a wide range of peak MVC reductions, reflecting different degrees of damage between subjects (high and moderate responders). fMRI analysis confirmed that the ST was the hamstring muscle most damaged by ELCs, with uniform T2 changes across all the measured sections of this muscle. During intensive ELCs, the ST muscle could suffer an anomalous recruitment pattern due to fatigue and damage, placing an excessive load on the BFsh and causing it to perform a synergistic compensation that leads to structural damage. Finally, T2 and MVC values did not correlate for the leg with the smaller FGC decrease in the hamstring muscles, suggesting that long-lasting increases in T2 signals after FGC markers have returned to baseline values might indicate an adaptive process rather than damage.

Exercise Is an Adjuvant to Contemporary Dystrophy Treatments

Duchenne muscular dystrophy is a lethal genetic disease of muscle wasting for which there is no cure. In healthy muscle, structure and function improve dramatically with exercise. In patients with dystrophy, little is known about the effects of exercise. As contemporary therapies rapidly progress and patients become more active, there is a need to understand the effects of exercise.

Is Branched-Chain Amino Acids Supplementation an Efficient Nutritional Strategy to Alleviate Skeletal Muscle Damage? A Systematic Review

Amino acids and more precisely, branched-chain amino acids (BCAAs), are usually consumed as nutritional supplements by many athletes and people involved in regular and moderate physical activities regardless of their practice level. BCAAs have been initially shown to increase muscle mass and have also been implicated in the limitation of structural and metabolic alterations associated with exercise damage. This systematic review provides a comprehensive analysis of the literature regarding the beneficial effects of BCAAs supplementation within the context of exercise-induced muscle damage or muscle injury. The potential benefit of a BCAAs supplementation was also analyzed according to the supplementation strategy-amount of BCAAs, frequency and duration of the supplementation-and the extent of muscle damage. The review protocol was registered prospectively with Prospective Register for Systematic Reviews (registration number CRD42017073006) and followed Preferred Reporting Items for Systematic reviews and Meta-Analyses guidelines. Literature search was performed from the date of commencement until August 2017 using four online databases (Medline, Cochrane library, Web of science and ScienceDirect). Original research articles: (i) written in English; (ii) describing experiments performed in Humans who received at least one oral BCAAs supplementation composed of leucine, isoleucine and valine mixture only as a nutritional strategy and (iii) reporting a follow-up of at least one day after exercise-induced muscle damage, were included in the systematic review analysis. Quality assessment was undertaken independently using the Quality Criteria Checklist for Primary Research. Changes in indirect markers of muscle damage were considered as primary outcome measures. Secondary outcome measures were the extent of change in indirect markers of muscle damage. In total, 11 studies were included in the analysis. A high heterogeneity was found regarding the different outcomes of these studies. The risk of bias was moderate considering the quality ratings were positive for six and neutral for three. Although a small number of studies were included, BCAAs supplementation can be efficacious on outcomes of exercise-induced muscle damage, as long as the extent of muscle damage was low-to-moderate, the supplementation strategy combined a high daily BCAAs intake (>200 mg kg^-1 day^-1) for a long period of time (>10 days); it was especially effective if taken prior to the damaging exercise.

Muscle pain induced by static contraction in rats is modulated by peripheral inflammatory mechanisms

Muscle pain is an important health issue and frequently related to static force exertion. The aim of this study is to evaluate whether peripheral inflammatory mechanisms are involved with static contraction-induced muscle pain in rats. To this end, we developed a model of muscle pain induced by static contraction performed by applying electrical pulses through electrodes inserted into muscle. We also evaluated the involvement of neutrophil migration, bradykinin, sympathetic amines and prostanoids. A single session of sustained static contraction of gastrocnemius muscle induced acute mechanical muscle hyperalgesia without affecting locomotor activity and with no evidence of structural damage in muscle tissue. Static contraction increased levels of creatine kinase but not lactate dehydrogenase, and induced neutrophil migration. Dexamethasone (glucocorticoid anti-inflammatory agent), DALBK (bradykinin B1 antagonist), Atenolol (β1 adrenoceptor antagonist), ICI 118,551 (β2 adrenoceptor antagonist), indomethacin (cyclooxygenase inhibitor), and fucoidan (non-specific selectin inhibitor) all reduced static contraction-induced muscle hyperalgesia; however, the bradykinin B2 antagonist, bradyzide, did not have an effect on static contraction-induced muscle hyperalgesia. Furthermore, an increased hyperalgesic response was observed when the selective bradykinin B1 agonist des-Arg⁹-bradykinin was injected into the previously stimulated muscle. Together, these findings demonstrate that static contraction induced mechanical muscle hyperalgesia in gastrocnemius muscle of rats is modulated through peripheral inflammatory mechanisms that are dependent on neutrophil migration, bradykinin, sympathetic amines and prostanoids. Considering the clinical relevance of muscle pain, we propose the present model of static contraction-induced mechanical muscle hyperalgesia as a useful tool for the study of mechanisms underlying static contraction-induced muscle pain.

Blunted Myoglobin and Quadriceps Soreness After Electrical Stimulation During the Luteal Phase or Oral Contraception

PURPOSE

Acute muscle damage after exercise triggers subsequent regeneration, leading to hypertrophy and increased strength after repeated exercise. It has been debated whether acute exercise-induced muscle damage is altered under various premenopausal estrogen conditions. Acute contraction-induced muscle damage was compared during exogenous (oral contraceptive, OC), endogenous (luteal phase, HI), or low (menses, LO) estrogen in healthy young women aged 21 to 30 years old.

METHODS

Women (OC, n = 9; HI, n = 9; LO, n = 8; total N = 26) performed 1 neuromuscular electrical stimulation (NMES) bout. Soreness, measured via visual analog scale and the Likert Scale of Muscle Soreness for Lower Limb (LSMSLL), quadriceps strength, and plasma myoglobin (Mb), interleukin (IL)-6, IL-8, and granulocyte-colony stimulating factor were measured before and after NMES.

RESULTS

NMES performance was similar across groups. Meaningful within-group increases in Mb (effect size [ES] = 1.12) and IL-8 (ES = 0.38) occurred in LO; ES for HI and OC were trivial. ES of the between-group difference in change was moderate for Mb (LO vs. HI = 1.15) and IL-8 (LO vs. HI = 0.86; LO vs. OC = 0.73). 17-β estradiol correlated moderately and negatively with Mb relative change (r = -.52, p < .05). LO had ~5% greater strength loss than OC and HI. The mean change score for the LSMSLL 2 days post-NMES was clinically greater in LO than OC or HI.

CONCLUSIONS

Acute NMES-induced indicators of muscle fiber damage and qualitative muscle soreness may be attenuated during the luteal phase or active OC pill consumption compared with the menstrual phase.

Effect of tendon vibration during wide-pulse neuromuscular electrical stimulation (NMES) on the decline and recovery of muscle force

BACKGROUND

Neuromuscular electrical stimulation (NMES) is commonly used to activate skeletal muscles and reverse muscle atrophy in clinical populations. Clinical recommendations for NMES suggest the use of short pulse widths (100-200 μs) and low-to-moderate pulse frequencies (30-50 Hz). However, this type of NMES causes rapid muscle fatigue due to the (non-physiological) high stimulation intensities and non-orderly recruitment of motor units. The use of both wide pulse widths (1000 μs) and tendon vibration might optimize motor unit activation through spinal reflex pathways and thus delay the onset of muscle fatigue, increasing muscle force and mass. Thus, the objective of this study was to examine the acute effects of patellar tendon vibration superimposed onto wide-pulse width (1000 μs) knee extensor electrical stimulation (NMES, 30 Hz) on peak muscle force, total impulse before "muscle fatigue", and the post-exercise recovery of muscle function.

METHODS

Tendon vibration (Vib), NMES (STIM) or NMES superimposed onto vibration (STIM + Vib) were applied in separate sessions to 16 healthy adults. Total torque-time integral (TTI), maximal voluntary contraction torque (MVIC) and indirect measures of muscle damage were tested before, immediately after, 1 h and 48 h after each stimulus.

RESULTS

TTI increased (145.0 ± 127.7%) in STIM only for "positive responders" to the tendon vibration (8/16 subjects), but decreased in "negative responders" (-43.5 ± 25.7%). MVIC (-8.7%) and rectus femoris electromyography (RF EMG) (-16.7%) decreased after STIM (group effect) for at least 1 h, but not after STIM + Vib. No changes were detected in indirect markers of muscle damage in any condition.

CONCLUSIONS

Tendon vibration superimposed onto wide-pulse width NMES increased TTI only in 8 of 16 subjects, but reduced voluntary force loss (fatigue) ubiquitously. Negative responders to tendon vibration may derive greater benefit from wide-pulse width NMES alone.

Can the Use of Neuromuscular Electrical Stimulation Be Improved to Optimize Quadriceps Strengthening?

CONTEXT

Neuromuscular electrical stimulation (NMES) is a common modality used to retrain muscles and improve muscular strength after injury or surgery, particularly for the quadriceps muscle. There are parameter adjustments that can be made to maximize the effectiveness of NMES. While NMES is often used in clinical practice, there are some limitations that clinicians should be aware of, including patient discomfort, muscle fatigue, and muscle damage.

EVIDENCE ACQUISITION

PubMed was searched through August 2014 and all articles cross-referenced.

STUDY DESIGN

Clinical review.

LEVEL OF EVIDENCE

Level 3.

RESULTS

Clinicians can optimize torque production and decrease discomfort by altering parameter selection (pulse duration, pulse frequency, duty cycle, and amplitude). Pulse duration of 400 to 600 μs and a pulse frequency of 30 to 50 Hz appear to be the most effective parameters to optimize torque output while minimizing discomfort, muscle fatigue, or muscle damage. Optimal electrode placement, conditioning programs, and stimulus pattern modulation during long-term NMES use may improve results.

CONCLUSION

Torque production can be enhanced while decreasing patient discomfort and minimizing fatigue.

Regenerative function of immune system: Modulation of muscle stem cells

Ageing is characterised by progressive deterioration of physiological systems and the loss of skeletal muscle mass is one of the most recognisable, leading to muscle weakness and mobility impairments. This review highlights interactions between the immune system and skeletal muscle stem cells (widely termed satellite cells or myoblasts) to influence satellite cell behaviour during muscle regeneration after injury, and outlines deficits associated with ageing. Resident neutrophils and macrophages in skeletal muscle become activated when muscle fibres are damaged via stimuli (e.g. contusions, strains, avulsions, hyperextensions, ruptures) and release high concentrations of cytokines, chemokines and growth factors into the microenvironment. These localised responses serve to attract additional immune cells which can reach in excess of 1×10(5) immune cell/mm(3) of skeletal muscle in order to orchestrate the repair process. T-cells have a delayed response, reaching peak activation roughly 4 days after the initial damage. The cytokines and growth factors released by activated T-cells play a key role in muscle satellite cell proliferation and migration, although the precise mechanisms of these interactions remain unclear. T-cells in older people display limited ability to activate satellite cell proliferation and migration which is likely to contribute to insufficient muscle repair and, consequently, muscle wasting and weakness. If the factors released by T-cells to activate satellite cells can be identified, it may be possible to develop therapeutic agents to enhance muscle regeneration and reduce the impact of muscle wasting during ageing and disease.

Activation of satellite cells and the regeneration of human skeletal muscle are expedited by ingestion of nonsteroidal anti-inflammatory medication

With this study we investigated the role of nonsteroidal anti-inflammatory drugs (NSAIDs) in human skeletal muscle regeneration. Young men ingested NSAID [1200 mg/d ibuprofen (IBU)] or placebo (PLA) daily for 2 wk before and 4 wk after an electrical stimulation-induced injury to the leg extensor muscles of one leg. Muscle biopsies were collected from the vastus lateralis muscles before and after stimulation (2.5 h and 2, 7, and 30 d) and were assessed for satellite cells and regeneration by immunohistochemistry and real-time RT-PCR, and we also measured telomere length. After injury, and compared with PLA, IBU was found to augment the proportion of ActiveNotch1(+) satellite cells at 2 d [IBU, 29 ± 3% vs. PLA, 19 ± 2% (means ± sem)], satellite cell content at 7 d [IBU, 0.16 ± 0.01 vs. PLA, 0.12 ± 0.01 (Pax7(+) cells/fiber)], and to expedite muscle repair at 30 d. The PLA group displayed a greater proportion of embryonic myosin(+) fibers and a residual ∼2-fold increase in mRNA levels of matrix proteins (all P < 0.05). Endomysial collagen was also elevated with PLA at 30 d. Minimum telomere length shortening was not observed. In conclusion, ingestion of NSAID has a potentiating effect on Notch activation of satellite cells and muscle remodeling during large-scale regeneration of injured human skeletal muscle.-Mackey, A. L., Rasmussen, L. K., Kadi, F., Schjerling, P., Helmark, I. C., Ponsot, E., Aagaard, P., Durigan, J. L. Q., Kjaer, M. Activation of satellite cells and the regeneration of human skeletal muscle are expedited by ingestion of nonsteroidal anti-inflammatory medication.

Impaired mitochondrial function and reduced energy cost as a result of muscle damage

PURPOSE

Although it has been largely acknowledged that isometric neuromuscular electrostimulation (NMES) exercise induces larger muscle damage than voluntary contractions, the corresponding effects on muscle energetics remain to be determined. Voluntary exercise-induced muscle damage (EIMD) has been reported to have minor slight effects on muscle metabolic response to subsequent dynamic exercise, but the magnitude of muscle energetics alterations for NMES EIMD has never been documented.

METHODS

³¹P magnetic resonance spectroscopy measurements were performed in 13 young healthy males during a standardized rest-exercise-recovery protocol before (D0) and 2 d (D2) and 4 d (D4) after NMES EIMD on knee extensor muscles. Changes in kinetics of phosphorylated metabolite concentrations (i.e., phosphocreatine [PCr], inorganic phosphate [Pi], and adenosine triphosphate [ATP]) and pH were assessed to investigate aerobic and anaerobic rates of ATP production and energy cost of contraction (Ec).

RESULTS

Resting [Pi]/[PCr] ratio increased at D2 (+39%) and D4 (+29%), mainly owing to the increased [Pi] (+43% and +32%, respectively), whereas a significant decrease in resting pH was determined (-0.04 pH unit and -0.03 pH unit, respectively). PCr recovery rate decreased at D2 (-21%) and D4 (-23%) in conjunction with a significantly decreased total rate of ATP production at D4 (-18%) mainly owing to an altered aerobic ATP production (-19%). Paradoxically, Ec was decreased at D4 (-21%).

CONCLUSION

Overall, NMES EIMD led to intramuscular acidosis in resting muscle and mitochondrial impairment in exercising muscle. Alterations of noncontractile processes and/or adaptive mechanisms to muscle damage might account for the decreased Ec during the dynamic exercise.

Breaking sarcomeres by in vitro exercise

Eccentric exercise leads to focal disruptions in the myofibrils, referred to as “lesions”. These structures are thought to contribute to the post-exercise muscle weakness, and to represent areas of mechanical damage and/or remodelling. Lesions have been investigated in human biopsies and animal samples after exercise. However, this approach does not examine the mechanisms behind lesion formation, or their behaviour during contraction. To circumvent this, we used electrical pulse stimulation (EPS) to simulate exercise in C2C12 myotubes, combined with live microscopy. EPS application led to the formation of sarcomeric lesions in the myotubes, resembling those seen in exercised mice, increasing in number with the time of application or stimulation intensity. Furthermore, transfection with an EGFP-tagged version of the lesion and Z-disc marker filamin-C allowed us to observe the formation of lesions using live cell imaging. Finally, using the same technique we studied the behaviour of these structures during contraction, and observed them to be passively stretching. This passive behaviour supports the hypothesis that lesions contribute to the post-exercise muscle weakness, protecting against further damage. We conclude that EPS can be reliably used as a model for the induction and study of sarcomeric lesions in myotubes in vitro.

Skeletal Muscle Inflammation Following Repeated Bouts of Lengthening Contractions in Humans

Skeletal muscle responds to exercise-induced damage by orchestrating an adaptive process that protects the muscle from damage by subsequent bouts of exercise, a phenomenon called the repeated bout effect (RBE). The mechanisms underlying the RBE are not understood. We hypothesized that an attenuated inflammation response following a repeated bout of lengthening contractions (LC) would be coincidental with a RBE, suggesting a potential relationship. Fourteen men (n = 7) and women (n = 7) completed two bouts of lengthening contractions (LC) separated by 28 days. Muscle biopsies were taken before the first bout (B1) from the non-exercised leg, and from the exercised leg 2- and 27-d post-B1 and 2-d following the second bout (B2). A 29-plex cytokine array identified alterations in inflammatory cytokines. Immunohistochemistry quantified inflammatory cell infiltration and major histocompatibility complex class 1 (MHC-1). Muscle soreness was attenuated in the days following B2 relative to B1, indicating a RBE. Intramuscular monocyte chemoattractant protein (MCP1) and interferon gamma-induced protein 10 (IP10) increased following B2 relative to the pre-exercise sample (7–52 and 11–36 pg/ml, respectively p < 0.05). Interleukin 4 (IL4) decreased (26–13 pg/ml, p < 0.05) following B2 relative to the pre-exercise sample. Infiltration of CD68⁺ macrophages and CD8⁺ T-cells were evident following B2, but not B1. Moreover, CD8⁺ T-cells were observed infiltrating apparently necrotic muscle fibers. No changes in MHC-1 were found. We conclude that inflammation is not attenuated following a repeated bout of LC and that CD8⁺ T-cells may play a role in muscle adaptation following LC. Moreover, it appears that the muscle or the immune system becomes sensitized to an initial bout of damaging exercise such that inflammatory cell infiltration into the muscle is enhanced upon a repeated bout of damaging exercise.

The integrin-adhesome is required to maintain muscle structure, mitochondrial ATP production, and movement forces in Caenorhabditis elegans

The integrin-adhesome network, which contains >150 proteins, is mechano-transducing and located at discreet positions along the cell-cell and cell-extracellular matrix interface. A small subset of the integrin-adhesome is known to maintain normal muscle morphology. However, the importance of the entire adhesome for muscle structure and function is unknown. We used RNA interference to knock down 113 putative Caenorhabditis elegans homologs constituting most of the mammalian adhesome and 48 proteins known to localize to attachment sites in C. elegans muscle. In both cases, we found >90% of components were required for normal muscle mitochondrial structure and/or proteostasis vs. empty vector controls. Approximately half of these, mainly proteins that physically interact with each other, were also required for normal sarcomere and/or adhesome structure. Next we confirmed that the dystrophy observed in adhesome mutants associates with impaired maximal mitochondrial ATP production (P < 0.01), as well as reduced probability distribution of muscle movement forces compared with wild-type animals. Our results show that the integrin-adhesome network as a whole is required for maintaining both muscle structure and function and extend the current understanding of the full complexities of the functional adhesome in vivo.—Etheridge, T., Rahman, M., Gaffney, C. J., Shaw, D., Shephard, F., Magudia, J., Solomon, D. E., Milne, T., Blawzdziewicz, J., Constantin-Teodosiu, D., Greenhaff, P. L., Vanapalli, S. A., Szewczyk, N. J. The integrin-adhesome is required to maintain muscle structure, mitochondrial ATP production, and movement forces in Caenorhabditis elegans.

Time course of central and peripheral alterations after isometric neuromuscular electrical stimulation-induced muscle damage

Isometric contractions induced by neuromuscular electrostimulation (NMES) have been shown to result in a prolonged force decrease but the time course of the potential central and peripheral factors have never been investigated. This study examined the specific time course of central and peripheral factors after isometric NMES-induced muscle damage. Twenty-five young healthy men were subjected to an NMES exercise consisting of 40 contractions for both legs. Changes in maximal voluntary contraction force of the knee extensors (MVC), peak evoked force during double stimulations at 10 Hz (Db₁₀) and 100 Hz (Db₁₀₀), its ratio (10∶100), voluntary activation, muscle soreness and plasma creatine kinase activity were assessed before, immediately after and throughout four days after NMES session. Changes in knee extensors volume and T₂ relaxation time were also assessed at two (D2) and four (D4) days post-exercise. MVC decreased by 29% immediately after NMES session and was still 19% lower than the baseline value at D4. The decrease in Db₁₀ was higher than in Db₁₀₀ immediately and one day post-exercise resulting in a decrease (−12%) in the 10∶100 ratio. On the contrary, voluntary activation significantly decreased at D2 (−5%) and was still depressed at D4 (−5%). Muscle soreness and plasma creatine kinase activity increased after NMES and peaked at D2 and D4, respectively. T₂ was also increased at D2 (6%) and D4 (9%). Additionally, changes in MVC and peripheral factors (e.g., Db₁₀₀) were correlated on the full recovery period, while a significant correlation was found between changes in MVC and VA only from D2 to D4. The decrease in MVC recorded immediately after the NMES session was mainly due to peripheral changes while both central and peripheral contributions were involved in the prolonged force reduction. Interestingly, the chronological events differ from what has been reported so far for voluntary exercise-induced muscle damage.

Protection against muscle damage induced by electrical stimulation: efficiency of a preconditioning programme

PURPOSE

The aim of this study was to explore the efficiency of a preconditioning programme composed of neuromuscular electrical stimulation (NMES) in the protection against muscle damage induced by a subsequent bout of NMES.

METHODS

Sixteen male volunteers were split up into a control group (CG; n = 8) and a preconditioned group (PCG; n = 8). Both groups attended two NMES bouts (test 1 and test 2) spaced 5 weeks apart. Each one consisted in 100 quadriceps contractions and 100 hamstrings contractions. PCG attended five additional progressive NMES sessions between test 1 and test 2. The outcome measures were the changes in muscle soreness [0-10 pain score on visual analogue pain scale (VAS)], muscle flexibility and serum creatine kinase (CK) activity; they were assessed before (pre-T1) and after (post-T1) test 1 and before (pre-T2) and after (post-T2) test 2.

RESULTS

Damage markers increased similarly in both groups after test 1 (at post-T1, VAS scores = 4·18 ± 2 and 4·43 ± 1·56 cm in CG and PCG, respectively; CK activity = 2307 ± 3774 and 1671 ± 1790 IU l(-1) in CG and PCG, respectively). Compared with test 1, these damage markers were reduced after test 2 in CG (at post-T2, VAS score = 2·68 ± 1·27 cm and CK activity = 218 ± 72 IU l(-1) ). Muscle soreness was further reduced after test 2 in PCG (VAS score = 0·37 ± 0·74 cm).

CONCLUSIONS

A protective effect against muscle damage can be obtained after only one NMES bout, and an additional protective effect can be induced by a preconditioning programme.

Electrical Muscle Stimulation in the Intensive Care Unit: An Integrative Review

Following a period of critical illness, physical function and health-related quality of life are slow to recover, both in the short and long term. Muscle wasting and weakness during the intensive care unit (ICU) admission is a recognised contributory factor. Enhanced rehabilitation programmes are advocated to improve outcomes, and electrical muscle stimulation (EMS) has been recommended during the early critical illness trajectory. This technique is fairly new to the ICU, and limited efficacy data exists for its use in this setting. This integrative review will examine published and on-going ICU studies with the purpose of reporting on the characteristics of EMS study participants; content of EMS treatment protocols; safety of EMS in the ICU setting; effects on EMS on muscle wasting; effects of EMS on muscle strength; and future research.

Contrast water therapy and exercise induced muscle damage: a systematic review and meta-analysis

The aim of this systematic review was to examine the effect of Contrast Water Therapy (CWT) on recovery following exercise induced muscle damage. Controlled trials were identified from computerized literature searching and citation tracking performed up to February 2013. Eighteen trials met the inclusion criteria; all had a high risk of bias. Pooled data from 13 studies showed that CWT resulted in significantly greater improvements in muscle soreness at the five follow-up time points (<6, 24, 48, 72 and 96 hours) in comparison to passive recovery. Pooled data also showed that CWT significantly reduced muscle strength loss at each follow-up time (<6, 24, 48, 72 and 96 hours) in comparison to passive recovery. Despite comparing CWT to a large number of other recovery interventions, including cold water immersion, warm water immersion, compression, active recovery and stretching, there was little evidence for a superior treatment intervention. The current evidence base shows that CWT is superior to using passive recovery or rest after exercise; the magnitudes of these effects may be most relevant to an elite sporting population. There seems to be little difference in recovery outcome between CWT and other popular recovery interventions.

Extensive inflammatory cell infiltration in human skeletal muscle in response to an ultraendurance exercise bout in experienced athletes

The impact of a 24-h ultraendurance exercise bout on systemic and local muscle inflammatory reactions was investigated in nine experienced athletes. Blood and muscle biopsies were collected before (Pre), immediately after the exercise bout (Post), and after 28 h of recovery (Post28). Circulating blood levels of leukocytes, creatine kinase (CK), C-reactive protein (CRP), and selected inflammatory cytokines were assessed together with the evaluation of the occurrence of inflammatory cells (CD3(+), CD8(+), CD68(+)) and the expression of major histocompatibility complex class I (MHC class I) in skeletal muscle. An extensive inflammatory cell infiltration occurred in all athletes, and the number of CD3(+), CD8(+), and CD68(+) cells were two- to threefold higher at Post28 compared with Pre (P < 0.05). The inflammatory cell infiltration was associated with a significant increase in the expression of MHC class I in muscle fibers. There was a significant increase in blood leukocyte count, IL-6, IL-8, CRP, and CK at Post. At Post28, total leukocytes, IL-6, and CK had declined, whereas IL-8 and CRP continued to increase. Increases in IL-1β and TNF-α were not significant. There were no significant associations between the magnitude of the systemic and local muscle inflammatory reactions. Signs of muscle degenerative and regenerative events were observed in all athletes with various degrees of severity and were not affected by the 24-h ultraendurance exercise bout. In conclusion, a low-intensity but very prolonged single-endurance exercise bout can generate a strong inflammatory cell infiltration in skeletal muscle of well-trained experienced ultraendurance athletes, and the amplitude of the local reaction is not proportional to the systemic inflammatory response.

Telomere length and regulatory proteins in human skeletal muscle with and without ongoing regenerative cycles

New insights suggest the existence of telomere regulatory mechanisms in several adult tissues. In this study, we aimed to assess in vivo telomere length and the presence of specific proteins involved in telomere regulation in a model of human skeletal muscle with (patients with dermatomyosis or polymyositis) and without ongoing regenerative events (healthy subjects). Mean (meanTRF) and minimal telomere (miniTRF) lengths and the expression of telomerase, tankyrase 1, TRF2 (telomeric repeat binding factor 2) and POT1 (protection of telomeres 1) were investigated in skeletal muscle samples from 12 patients (MYO) and 13 healthy subjects (CON). There was no significant shortening of telomeres in skeletal muscle from patients compared with control subjects (MYO, meanTRF length 11.0 ± 1.8 kbp and miniTRF length 4.7 ± 0.8 kbp; CON, meanTRF length 10.4 ± 1.1 kbp and miniTRF length 4.6 ± 0.5 kbp). Theoretically, telomere length can be controlled by endogenous mechanisms. Here, we show for the first time that expression levels of telomerase, tankyrase 1, TRF2 and POT1 were, respectively, six-, seven-, three- and fivefold higher in the nuclear fraction of skeletal muscle of MYO compared with CON (P < 0.05). This suggests the existence of endogenous mechanisms allowing for telomere regulation in skeletal muscle with ongoing cycles of degeneration and regeneration and a model where regulatory factors are possibly involved in the protection of skeletal muscle telomeres.

Comparison in muscle damage between maximal voluntary and electrically evoked isometric contractions of the elbow flexors

This study compared between maximal voluntary (VOL) and electrically stimulated (ES) isometric contractions of the elbow flexors for changes in indirect markers of muscle damage to investigate whether ES would induce greater muscle damage than VOL. Twelve non-resistance-trained men (23-39 years) performed VOL with one arm and ES with the contralateral arm separated by 2 weeks in a randomised, counterbalanced order. Both VOL and ES (frequency 75 Hz, pulse duration 250 μs, maximally tolerated intensity) exercises consisted of 50 maximal isometric contractions (4-s on, 15-s off) of the elbow flexors at a long muscle length (160°). Changes in maximal voluntary isometric contraction torque (MVC), range of motion, muscle soreness, pressure pain threshold and serum creatine kinase (CK) activity were measured before, immediately after and 1, 24, 48, 72 and 96 h following exercise. The average peak torque over the 50 isometric contractions was greater (P < 0.05) for VOL (32.9 ± 9.8 N m) than ES (16.9 ± 6.3 N m). MVC decreased greater and recovered slower (P < 0.05) after ES (15% lower than baseline at 96 h) than VOL (full recovery). Serum CK activity increased (P < 0.05) only after ES, and the muscles became more sore and tender after ES than VOL (P < 0.05). These results showed that ES induced greater muscle damage than VOL despite the lower torque output during ES. It seems likely that higher mechanical stress imposed on the activated muscle fibres, due to the specificity of motor unit recruitment in ES, resulted in greater muscle damage.