Asynchronous functional, cellular and transcriptional changes after a bout of eccentric exercise in the rat

Paraspinal muscles in individuals undergoing surgery for lumbar spine pathology lack a myogenic response to an acute bout of resistance exercise

Background

Lumbar spine pathology (LSP) is a common source of low back or leg pain, and paraspinal muscle in these patients demonstrates fatty and fibrotic infiltration, and cellular degeneration that do not reverse with exercise-based rehabilitation. However, it is unclear of this lack of response is due to insufficient exercise stimulus, or an inability to mount a growth response. The purpose of this study was to compare paraspinal muscle gene expression between individuals with LSP who do and do not undergo an acute bout of resistance exercise.

Methods

Paraspinal muscle biopsies were obtained from 64 individuals with LSP undergoing spinal surgery. Eight participants performed an acute bout of machine-based lumbar extension resistance exercise preoperatively. Gene expression for 42 genes associated with adipogenic/metabolic, atrophic, fibrogenic, inflammatory, and myogenic pathways was measured, and differential expression between exercised and non-exercised groups was evaluated for (a) the full cohort, and (b) an age, gender, acuity, and etiology matched sub-cohort. Principal components analyses were used to identify gene expression clustering across clinical phenotypes.

Results

The exercised cohort demonstrated upregulation of inflammatory gene IL1B, inhibition of extracellular matrix components (increased MMP3&9, decreased TIMP1&3, COL1A1) and metabolic/adipogenic genes (FABP4, PPARD, WNT10B), and downregulation of myogenic (MYOD, ANKRD2B) and atrophic (FOXO3) genes compared to the non-exercised cohort, with similar patterns in the matched sub-analysis. There were no clinical phenotypes significantly associated with gene expression profiles.

Conclusion

An acute bout of moderate-high intensity resistance exercise did not result in upregulation of myogenic genes in individuals with LSP. The response was characterized by mixed metabolic and fibrotic gene expression, upregulation of inflammation, and downregulation of myogenesis.

Traumatic muscle injury

Traumatic muscle injury represents a collection of skeletal muscle pathologies caused by trauma to the muscle tissue and is defined as damage to the muscle tissue that can result in a functional deficit. Traumatic muscle injury can affect people across the lifespan and can result from high stresses and strains to skeletal muscle tissue, often due to muscle activation while the muscle is lengthening, resulting in indirect and non-contact muscle injuries (strains or ruptures), or from external impact, resulting in direct muscle injuries (contusion or laceration). At a microscopic level, muscle fibres can repair focal damage but must be completely regenerated after full myofibre necrosis. The diagnosis of muscle injury is based on patient history and physical examination. Imaging may be indicated to eliminate differential diagnoses. The management of muscle injury has changed within the past 5 years from initial rest, immobilization and (over)protection to early activation and progressive loading using an active approach. One challenge of muscle injury management is that numerous medical treatment options, such as medications and injections, are often used or proposed to try to accelerate muscle recovery despite very limited efficacy evidence. Another challenge is the prevention of muscle injury owing to the multifactorial and complex nature of this injury.

Regenerating Myofibers after an Acute Muscle Injury: What Do We Really Know about Them?

Injury to skeletal muscle through trauma, physical activity, or disease initiates a process called muscle regeneration. When injured myofibers undergo necrosis, muscle regeneration gives rise to myofibers that have myonuclei in a central position, which contrasts the normal, peripheral position of myonuclei. Myofibers with central myonuclei are called regenerating myofibers and are the hallmark feature of muscle regeneration. An important and underappreciated aspect of muscle regeneration is the maturation of regenerating myofibers into a normal sized myofiber with peripheral myonuclei. Strikingly, very little is known about processes that govern regenerating myofiber maturation after muscle injury. As knowledge of myofiber formation and maturation during embryonic, fetal, and postnatal development has served as a foundation for understanding muscle regeneration, this narrative review discusses similarities and differences in myofiber maturation during muscle development and regeneration. Specifically, we compare and contrast myonuclear positioning, myonuclear accretion, myofiber hypertrophy, and myofiber morphology during muscle development and regeneration. We also discuss regenerating myofibers in the context of different types of myofiber necrosis (complete and segmental) after muscle trauma and injurious contractions. The overall goal of the review is to provide a framework for identifying cellular and molecular processes of myofiber maturation that are unique to muscle regeneration.

Ryanodine receptors mediate high intracellular Ca2+ and some myocyte damage following eccentric contractions in rat fast-twitch skeletal muscle

Eccentric contractions (ECC) facilitate cytosolic calcium ion (Ca2+) release from the sarcoplasmic reticulum (SR) and Ca2+ influx from the extracellular space. Ca2+ is a vital signaling messenger that regulates multiple cellular processes via its spatial and temporal concentration ([Ca2+]i) dynamics. We hypothesized that 1) a specific pattern of spatial/temporal intramyocyte Ca2+ dynamics portends muscle damage following ECC and 2) these dynamics would be regulated by the ryanodine receptor (RyR). [Ca2+]i in the tibialis anterior muscles of anesthetized adult Wistar rats was measured by ratiometric (i.e., ratio, R, 340/380 nm excitation) in vivo bioimaging with Fura-2 pre-ECC and at 5 and 24 h post-ECC (5 × 40 contractions). Separate groups of rats received RyR inhibitor dantrolene (DAN; 10 mg/kg ip) immediately post-ECC (+DAN). Muscle damage was evaluated by histological analysis on hematoxylin-eosin stained muscle sections. Compared with control (CONT, no ECC), [Ca2+]i distribution was heterogeneous with increased percent total area of high [Ca2+]i sites (operationally defined as R ≥ 1.39, i.e., ≥1 SD of mean control) 5 h post-ECC (CONT, 14.0 ± 8.0; ECC5h: 52.0 ± 7.4%, P < 0.01). DAN substantially reduced the high [Ca2+]i area 5 h post-ECC (ECC5h + DAN: 6.4 ± 3.1%, P < 0.01) and myocyte damage (ECC24h, 63.2 ± 1.0%; ECC24h + DAN: 29.1 ± 2.2%, P < 0.01). Temporal and spatially amplified [Ca2+]i fluctuations occurred regardless of DAN (ECC vs. ECC + DAN, P > 0.05). These results suggest that the RyR-mediated local high [Ca2+]i itself is related to the magnitude of muscle damage, whereas the [Ca2+]i fluctuation is an RyR-independent phenomenon.

Does cryoneurolysis result in persistent motor deficits? A controlled study using a rat peroneal nerve injury model

BACKGROUND

Cryoneurolysis of peripheral nerves uses localised intense cold to induce a prolonged block over multiple weeks that has the promise of providing potent analgesia outlasting the duration of postoperative pain following surgery, as well as treat other acute and chronic pain states. However, it remains unclear whether persistent functional motor deficits remain following cryoneurolysis of mixed sensorimotor peripheral nerves, greatly limiting clinical application of this modality. To help inform future research, we used a rat peroneal nerve injury model to evaluate if cryoneurolysis results in persistent deficits in motor function.

METHODS

Male Lewis rats (n=30) had their common peroneal nerves exposed bilaterally at the proximal lateral margin of the knee and subsequently underwent cryoneurolysis on one limb and sham treatment on the contralateral limb. Outcomes were evaluated on days 3, 14, 30, 90 and 180. The primary end point was motor function, based on ankle dorsiflexion torque. In addition, sensory function was tested based on von Frey's filament sensitivity to the peroneal sensory distribution. A subset of animals was sacrificed following functional testing at each time point, and general tissue morphology, connective tissue deposition, and axon counts were evaluated.

RESULTS

Motor deficits in treated limbs were observed at 3 and 14 days but had resolved at time points beyond 1 month. Bilateral sensory deficits were also observed at 3 and 14 days, and also resolved within 1 month. Consistent with motor functional deficits, axon counts trended lower in treated nerves compared with contralateral controls at 3 days; however, axon counts were not significantly different at later time points.

CONCLUSIONS

When applied to a mixed sensorimotor nerve, cryoneurolysis did not result in persistent motor deficits.

Eccentric Muscle Contractions: Risks and Benefits

Eccentric contractions, characterized by the lengthening of the muscle-tendon complex, present several unique features compared with other types of contractions, which may lead to unique adaptations. Due to its specific physiological and mechanical properties, there is an increasing interest in employing eccentric muscle work for rehabilitation and clinical purposes. However, unaccustomed eccentric exercise is known to cause muscle damage and delayed pain, commonly defined as “Delayed-Onset Muscular Soreness” (DOMS). To date, the most useful preventive strategy to avoid these adverse effects consists of repeating sessions involving submaximal eccentric contractions whose intensity is progressively increased over the training. Despite an increased number of investigations focusing on the eccentric contraction, a significant gap still remains in our understanding of the cellular and molecular mechanisms underlying the initial damage response and subsequent adaptations to eccentric exercise. Yet, unraveling the molecular basis of exercise-related muscle damage and soreness might help uncover the mechanistic basis of pathological conditions as myalgia or neuromuscular diseases. In addition, a better insight into the mechanisms governing eccentric training adaptations should provide invaluable information for designing therapeutic interventions and identifying potential therapeutic targets.

Minimal Evidence for a Secondary Loss of Strength After an Acute Muscle Injury: A Systematic Review and Meta-Analysis

BACKGROUND

An immediate loss of strength follows virtually all types of muscle injury but there is debate whether the initial strength loss is maximal or if a secondary loss of strength occurs during the first 3 days post-injury.

OBJECTIVE

The objective of this analysis was to conduct a systematic review and meta-analysis of the research literature to determine if a secondary loss of strength occurs after an injurious initiating event.

METHODS

Literature searches were performed using eight electronic databases (e.g., PubMed, Cochrane Library). Search terms included skeletal muscle AND (injur* OR damage*) AND (strength OR force OR torque). The extracted strength data were converted to a standard format by calculating the standardized mean difference, which is reported as the effect size (ES) along with its 95 % confidence interval (CI). The calculation of ES was designed so that a negative ES that was statistically less than zero would be interpreted as indicating a secondary loss of strength.

RESULTS

A total of 223 studies with over 4000 human and animal subjects yielded data on 262 independent groups and a total of 936 separate ESs. Our overall meta-analysis yielded a small-to-medium, positive overall ES that was statistically greater than zero (overall ES = +0.34, 95 % CI 0.27-0.40; P < 0.00000001). Considerable variation in ES was observed among studies (I ² = 86 %), which could be partially explained by the research group conducting the study, sex of the subject, day of post-injury strength assessment, whether fatigue was present immediately post-injury, and the muscle group injured. From the subgroup meta-analyses probing these variables, 36 subgroup ESs were calculated and none were statistically less than zero.

CONCLUSION

Overall, our findings do not support the presence of a secondary loss of strength following an acute muscle injury, and strongly suggest that strength, on average, recovers steadily over the first 3 days post-injury.

Variations of collagen-encoding genes are associated with exercise-induced muscle damage

We investigated whether single nucleotide polymorphisms (SNPs) within genes encoding the alpha-1 chain of type I (COL1A1, rs2249492; rs1800012), type II (COL2A1, rs2070739), and type V (COL5A1, rs12722) collagen were associated with the variable response to exercise-induced muscle damage (EIMD). Knee extensor muscle strength and soreness were assessed pre-, post-, and 48 h post-EIMD (120 maximal eccentric knee extensor contractions) in 65 young healthy participants, who were genotyped for the aforementioned SNPs. We found that COL1A1 (minor) T-allele carriers (rs1800012) and (major) T-allele homozygotes (rs2249492) were generally weaker (P ≤ 0.019); and (minor) A-allele carriers of COL2A1 (P = 0.002) and (major) T-allele carriers of COL5A1 (P = 0.004) SNPs reported greater muscle soreness, all compared with their respective major (rs1800012; rs2070739) and minor (rs2249492; rs12722) allele homozygote counterparts. To conclude, the risk alleles of these four SNPs appear to negatively influence muscle strength and post-EIMD recovery, possibly via a dysregulated collagen network affecting the muscle’s mechanical properties.

Effects of Streptomycin Administration on Increases in Skeletal Muscle Fiber Permeability and Size Following Eccentric Muscle Contractions

The purpose of this study was to investigate the preventive effect of streptomycin (Str) administration on changes in membrane permeability and the histomorphological characteristics of damaged muscle fibers following eccentric contraction (ECC ). Eighteen 7-week-old male Fischer 344 rats were randomly assigned to three groups: control (Cont), ECC, and ECC with Str (ECC + Str). The tibialis anterior (TA) muscles in both ECC groups were stimulated electrically and exhibited ECC. Evans blue dye (EBD), a marker of muscle fiber damage associated with increased membrane permeability, was injected 24 hr before TA muscle sampling. The number of EBD-positive fibers, muscle fiber cross-sectional area (CSA), and roundness were determined via histomorphological analysis. The ECC intervention resulted in an increased fraction of EBD-positive fibers, a larger CSA, and decreased roundness. The fraction of EBD-positive fibers was 79% lower in the ECC + Str group than in the ECC group. However, there was no difference in the CSA and roundness of the EBD-positive fibers between the two ECC groups. These results suggest that Str administration can reduce the number of myofibers that increase membrane permeability following ECC, but does not ameliorate the extent of fiber swelling in extant EBD-positive fibers. Anat Rec, 301:1096-1102, 2018. © 2018 Wiley Periodicals, Inc.

Recovery of rat muscle size but not function more than 1 year after a single botulinum toxin injection

INTRODUCTION

Neurotoxin injection is used to treat a wide variety of neuromuscular disorders. The purpose of this study was to measure the functional and structural properties of botulinum toxin-injected adult rat skeletal muscle over nearly the entire lifespan.

METHODS

Ten groups of animals were subjected to either neurotoxin injection [Botox, Type A (BT-A); Allergan, Irvine, California] or saline solution injection. Neurotoxin-injected animals (n = 90) were analyzed at different time-points: 1 week; 1 month; 3 months; 6 months; 12 months; or 18 months.

RESULTS

In spite of the recovery of structural features, such as muscle mass and fiber area, dorsiflexion torque production remained significantly depressed by 25%, even at 12 months after neurotoxin injection.

DISCUSSION

The data demonstrate that, after a single BT-A injection, although gross muscle morphology recovered over a 12-month time period, loss of contractile function did not recover. Muscle Nerve 57: 435-441, 2018.

Serum reference value of two potential doping candidates-myostatin and insulin-like growth factor-I in the healthy young male

Background

Myostatin negatively regulates muscle growth, and its inhibition by suitable proteins can increase muscle bulk and exercise performance. However, the reference values of serum myostatin in athletes performing strength training are still lacking.

Methods

A cross-sectional study recruiting28 male collegiate athletes performing strength training and 29 age-matched normal controls was conducted.

The serum concentration of myostatin and insulin-like growth factor 1 (IGF-1), grip strength, and body composition were the main outcome measures. We used regression models to analyze the correlation between serum markers and the physiological parameters. The athlete group had greater height, weight, body mass index (BMI), fat mass percentage, fat-free mass, muscle mass, waist girth, grip strength, and estimated daily energy expenditure.

Results

The IGF-1 concentration was higher in the athlete group (324 ± 80 vs. 263 ± 134 ng/ml), but the myostatin levels did not differ (12.1 ± 3.7 vs. 12.4 ± 3.5 ng/ml). The reference value for IGF-1 among the healthy young males was 293 ± 114 ng/ml, correlated with age and height; the value for myostatin was 12.3 ± 3.6 ng/ml, correlated negatively with BMI, fat mass percentage, and waist girth after adjustment for age.

Conclusion

Myostatin level is negatively related to fat percentage, and serum IGF-1 is positively related to height. The reference values could provide a basis for future doping-related study.

Effects of delayed NSAID administration after experimental eccentric contraction injury - A cellular and proteomics study

BACKGROUND

Acute muscle injuries are exceedingly common and non-steroidal anti-inflammatory drugs (NSAIDs) are widely consumed to reduce the associated inflammation, swelling and pain that peak 1-2 days post-injury. While prophylactic use or early administration of NSAIDs has been shown to delay muscle regeneration and contribute to loss of muscle strength after healing, little is known about the effects of delayed NSAID use. Further, NSAID use following non-penetrating injury has been associated with increased risk and severity of infection, including that due to group A streptococcus, though the mechanisms remain to be elucidated. The present study investigated the effects of delayed NSAID administration on muscle repair and sought mechanisms supporting an injury/NSAID/infection axis.

METHODS

A murine model of eccentric contraction (EC)-induced injury of the tibialis anterior muscle was used to profile the cellular and molecular changes induced by ketorolac tromethamine administered 47 hr post injury.

RESULTS

NSAID administration inhibited several important muscle regeneration processes and down-regulated multiple cytoprotective proteins known to inhibit the intrinsic pathway of programmed cell death. These activities were associated with increased caspase activity in injured muscles but were independent of any NSAID effect on macrophage influx or phenotype switching.

CONCLUSIONS

These findings provide new molecular evidence supporting the notion that NSAIDs have a direct negative influence on muscle repair after acute strain injury in mice and thus add to renewed concern about the safety and benefits of NSAIDS in both children and adults, in those with progressive loss of muscle mass such as the elderly or patients with cancer or AIDS, and those at risk of secondary infection after trauma or surgery.

Effects of GaAs laser and stretching on muscle contusion in rats

ABSTRACT Laser and stretching are used to treat skeletal muscle injuries. This study aimed to evaluate the effects of GaAs laser and stretching in the morphology of the tibialis anterior (TA) muscle after contusion. Thirty-six male rats (349±23g) were divided into six groups (n=6): control group (CG); lesion group (LG); lesion and laser group (LLG); lesion and stretching group (LSG); lesion, laser and stretching group (LLSG); and stretching group (SG). TA was wounded by a contusion apparatus. We used GaAs laser 4.5 J/cm2 dose for 32 s each, beginning 48 h after lesion, for 7 days, once a day. Manual passive stretching was applied by 10 repetitions for 1 minute, initiating on the 8th day, once a day, 3 times a week, during 3 weeks. After 4 weeks, rats were euthanized and we analyzed: muscle weight and length, cross sectional area of muscle fibers (CSAMF), serial sarcomere number (SSN), sarcomere length, and percentage of connective tissue. Comparisons among groups were made by ANOVA and post hoc Tukey tests, with the significance level set at ≤ 0.05. The serial sarcomere number of LLSG was higher than LSG. The sarcomere length of LSG was superior to LLG, LLSG, and SG. SG increased SSN compared to CG, while the percentage of connective tissue of SG decreased in comparison to LLSG. Thus, the sarcomerogenesis of injured muscles was enhanced by laser therapy, stretching, and association of both. The stretching protocol was enough to increase SSN of intact muscles.

A systems-based investigation into vitamin D and skeletal muscle repair, regeneration, and hypertrophy

Skeletal muscle is a direct target for vitamin D. Observational studies suggest that low 25[OH]D correlates with functional recovery of skeletal muscle following eccentric contractions in humans and crush injury in rats. However, a definitive association is yet to be established. To address this gap in knowledge in relation to damage repair, a randomised, placebo-controlled trial was performed in 20 males with insufficient concentrations of serum 25(OH)D (45 ± 25 nmol/l). Prior to and following 6 wk of supplemental vitamin D3 (4,000 IU/day) or placebo (50 mg of cellulose), participants performed 20 × 10 damaging eccentric contractions of the knee extensors, with peak torque measured over the following 7 days of recovery. Parallel experimentation using isolated human skeletal muscle-derived myoblast cells from biopsies of 14 males with low serum 25(OH)D (37 ± 11 nmol/l) were subjected to mechanical wound injury, which enabled corresponding in vitro studies of muscle repair, regeneration, and hypertrophy in the presence and absence of 10 or 100 nmol 1α,25(OH)2D3. Supplemental vitamin D3 increased serum 25(OH)D and improved recovery of peak torque at 48 h and 7 days postexercise. In vitro, 10 nmol 1α,25(OH)2D3 improved muscle cell migration dynamics and resulted in improved myotube fusion/differentiation at the biochemical, morphological, and molecular level together with increased myotube hypertrophy at 7 and 10 days postdamage. Together, these preliminary data are the first to characterize a role for vitamin D in human skeletal muscle regeneration and suggest that maintaining serum 25(OH)D may be beneficial for enhancing reparative processes and potentially for facilitating subsequent hypertrophy.

Protein supplementation increases postexercise plasma myostatin concentration after 8 weeks of resistance training in young physically active subjects

Myostatin (MSTN) is a negative regulator of muscle growth even if some studies have shown a counterintuitive positive correlation between MSTN and muscle mass (MM). Our aim was to investigate the influence of 2 months of resistance training (RT) and diets with different protein contents on plasma MSTN, interleukin 1 beta (IL-1β), interleukin 6 (IL-6), tumor necrosis factor alpha (TNF-α), and insulin-like growth factor 1 (IGF-1). Eighteen healthy volunteers were randomly divided in two groups: high protein (HP) and normal protein (NP) groups. Different protein diet contents were 1.8 and 0.85 g of protein·kg bw(-1)·day(-1) for HP and NP, respectively. Subjects underwent 8 weeks of standardized progressive RT. MSTN, IGF-1, IL-1β, IL-6, and TNF-α were analyzed before and after the first and the last training sessions. Lean body mass, MM, upper-limb muscle area, and strength were measured. Plasma MSTN showed a significant increase (P<.001) after the last training in the HP group compared with NP group and with starting value. IGF-1 plasma concentration showed a positive correlation with MSTN in HP after the last training (r(2)=0.6456; P=.0295). No significant differences were found between NP and HP for IL-1β, IL-6, TNF-α, and strength and MM or area. These findings suggest a "paradoxical" postexercise increase of plasma MSTN after 8 weeks of RT and HP diets. This MSTN elevation correlates positively with IGF-1 plasma level. This double increase of opposite (catabolic/anabolic) mediators could explain the substantial overlapping of MM increases in the two groups.

Dramatic changes in muscle contractile and structural properties after 2 botulinum toxin injections

INTRODUCTION

Botulinum toxin is frequently administered serially to maintain therapeutic muscle paralysis, but the effect of repeated doses on muscle function are largely unknown. This study characterized the muscle response to 2 onabotulinum toxin (BoNT) injections separated by 3 months.

METHODS

Animal subjects received a single toxin injection (n = 8), 2 BoNT injections separated by 3 months (n = 14), or 1 BoNT and 1 saline injection separated by 3 months (n = 8).

RESULTS

The functional effect of 2 serial injections was exponentially greater than the effect of a single injection. While both groups treated with a single BoNT injection had decreased torque in the injected leg by approximately 50% relative to contralateral legs, the double BoNT injected group had decreased torque by over 95% relative to the preinjection level. Both single and double BoNT injections produced clear signs of fiber-type grouping.

CONCLUSIONS

These experiments demonstrate a disproportionately greater effect of repeated BoNT injections.

Effects of eccentric exercise in rehabilitation of phasic and tonic muscles after leg immobilization in rats

Eccentric exercise is an essential resource for skeletal muscle rehabilitation following muscle disuse however, abnormalities linked to the tissue recuperation require further research. Our aim was analyze the adaptation ability of rehabilitated muscular tissue in rats during different periods of eccentric training after 10 days of limb immobilization. Twenty-seven Wistar rats were divided into six groups: immobilized 10 days, immobilized and eccentric trained for 10 days, immobilized and eccentric trained for 21 days, and three age-matched control groups. After sacrifice, soleus and plantaris muscles were frozen, cut and stained for general histology using hematoxylin and eosin and Gomori trichrome methods and immunohistochemical methods for fiber typing (mATPase, NADH2-TR), for capillaries (CD31) and intermediate filaments (desmin, vimentin) and high resolution microscopy of resin embedded material. Immobilization resulted in more intense morphological alterations in soleus muscles such as formation of target fibers, nuclear centralization, a reduction in the number of type I fibers, diameter of type I, IIA, IIAD fibers, and capillaries. After 10 days of eccentric training, increases in the nuclear centralization and the number of lobulated fibers were observed. This period was insufficient to reestablish the capillary/fiber (C/F) ratio and distribution of fiber types as that observed in the control group. However, 21 days of rehabilitation allowed the reversal of all morphological and quantitative abnormalities. For the plantaris muscles, 10-days of training restored their basic characteristics. Despite the fact that immobilization affected soleus and plantaris muscles, 10 days of eccentric training was insufficient to restore the morphological characteristics of soleus muscles, which was not the case observed in plantaris muscle.

Use it or lose it: multiscale skeletal muscle adaptation to mechanical stimuli

Skeletal muscle undergoes continuous turnover to adapt to changes in its mechanical environment. Overload increases muscle mass, whereas underload decreases muscle mass. These changes are correlated with, and enabled by, structural alterations across the molecular, subcellular, cellular, tissue, and organ scales. Despite extensive research on muscle adaptation at the individual scales, the interaction of the underlying mechanisms across the scales remains poorly understood. Here, we present a thorough review and a broad classification of multiscale muscle adaptation in response to a variety of mechanical stimuli. From this classification, we suggest that a mathematical model for skeletal muscle adaptation should include the four major stimuli, overstretch, understretch, overload, and underload, and the five key players in skeletal muscle adaptation, myosin heavy chain isoform, serial sarcomere number, parallel sarcomere number, pennation angle, and extracellular matrix composition. Including this information in multiscale computational models of muscle will shape our understanding of the interacting mechanisms of skeletal muscle adaptation across the scales. Ultimately, this will allow us to rationalize the design of exercise and rehabilitation programs, and improve the long-term success of interventional treatment in musculoskeletal disease.

Postnatal muscle modification by myogenic factors modulates neuropathology and survival in an ALS mouse model

MyoD and myogenin are myogenic transcription factors preferentially expressed in adult fast and slow muscles, respectively. Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disorder in which motor neuron loss is accompanied by muscle denervation and paralysis. Studies suggest that muscle phenotype may influence ALS disease progression. Here we demonstrate that myogenin gene transfer into muscle supports spinal cord motor neuron survival and muscle endplate innervation in the G93A SOD1 fALS mice. On the other hand, MyoD gene transfer decreases survival and enhances motor neuron degeneration and muscle denervation. Although an increase in motor neuron count is associated with increased succinic dehydrogenase staining in the muscle, muscle overexpression of PGC-1α does not improve survival or motor function. Our study suggests that postnatal muscle modification influences disease progression and demonstrates that the muscle expression of myogenic and metabolic regulators differentially impact neuropathology associated with disease progression in the G93A SOD1 fALS mouse model.

Effects of therapeutic massage on gait and pain after delayed onset muscle soreness

Unfamiliar or sudden exercise can induce delayed onset muscle soreness (DOMS) within 12–24 h. So, several researchers have reported various interventions to treat DOMS. Massage is generally known to eliminate muscle fatigue. However, effect of massage after DOMS is still not clear. We investigated whether the massage is effective on pain and gait after DOMS. The participants were divided into a control group (n= 10) with DOMS and an experimental group (n= 11) with the massage treated after DOMS. We induced DOMS by taking isotonic exercise with going up and down 20 times in 5-story building. We applied the massage and assessment on gastrocnemius of dominant foot. The change of gait and pain was assessed using gaitrite and algometer. In the present results, the massage on gastrocnemius after DOMS showed significant difference in pain (P< 0.05). Also, there was a significant difference in gait (P< 0.05), especially, spatial parameters (distance, step length, stride length) and temporal parameters (ambulation, heel on off time, stride velocity). Moreover, the pain relief after massage-treated in DOMS correlated with gait. These results suggest that the massage on gastrocnemius after DOMS has influence on pain and gait performance. Therefore, massage can be applied as intervention for delayed onset muscle soreness.

Systematic test of neurotoxin dose and volume on muscle function in a rat model

INTRODUCTION

Onabotulinum toxin serotype A (BT-A) is used for a variety of motor and sensory disorders related to abnormal muscle activity.

METHODS

We developed a high-resolution rodent model to allow precise determination of the effect of BT-A dose (measured in units) and injectate volume (measured in μl) on the efficacy of the injection and systemic side effects. Dorsiflexion is the best indicator of injected and contralateral muscle function.

RESULTS

One month after injection, dorsiflexion torque of BT-A-injected limbs was decreased significantly in all experimental groups compared with saline controls (P < 0.05). Torque was also compared among the BT-A groups, which demonstrated a significant effect of dose (P < 0.001), but no effect of volume (P > 0.2) and no dose × volume interaction (P > 0.3). Similar results were observed for other parameters measured.

CONCLUSIONS

These data demonstrate that injection dose and not volume or concentration is the primary determinant of neurotoxin efficacy in a rodent model.

Role of the cytoskeleton in muscle transcriptional responses to altered use

In this work, the interaction between the loss of a primary component of the skeletal muscle cytoskeleton, desmin, and two common physiological stressors, acute mechanical injury and aging, were investigated at the transcriptional, protein, and whole muscle levels. The transcriptional response of desmin knockout (des(-/-)) plantarflexors to a bout of 50 eccentric contractions (ECCs) showed substantial overlap with the response in wild-type (wt) muscle. However, changes in the expression of genes involved in muscle response to injury were blunted in adult des(-/-) muscle compared with wt (fold change with ECC in des(-/-) and wt, respectively: Mybph, 1.4 and 2.9; Xirp1, 2.2 and 5.7; Csrp3, 1.8 and 4.3), similar to the observed blunted mechanical response (torque drop: des(-/-) 30.3% and wt 55.5%). Interestingly, in the absence of stressors, des(-/-) muscle exhibited elevated expression of many these genes compared with wt. The largest transcriptional changes were observed in the interaction between aging and the absence of desmin, including many genes related to slow fiber pathway (Myh7, Myl3, Atp2a2, and Casq2) and insulin sensitivity (Tlr4, Trib3, Pdk3, and Pdk4). Consistent with these transcriptional changes, adult des(-/-) muscle exhibited a significant fiber type shift from fast to slow isoforms of myosin heavy chain (wt, 5.3% IIa and 71.7% IIb; des(-/-), 8.4% IIa and 61.4% IIb) and a decreased insulin-stimulated glucose uptake (wt, 0.188 μmol/g muscle/20 min; des(-/-), 0.085 μmol/g muscle/20 min). This work points to novel areas of influence of this cytoskeletal protein and directs future work to elucidate its function.

Human alpha-actinin-3 genotype association with exercise-induced muscle damage and the repeated-bout effect

Alpha-actinin-3 (ACTN3) is an integral part of the Z line of the sarcomere. The ACTN3 R577X (rs1815739) polymorphism determines the presence or absence of functional ACTN3, which may influence the extent of exercise-induced muscle damage. This study aimed to compare the impact of, and recovery from, muscle-damaging eccentric exercise on subjects with or without functional ACTN3. Seventeen young men (20-33 years old), homozygous for the R (n = 9) or X (n = 8) alleles, performed two bouts of stretch-shortening exercise (50 drop jumps) two weeks apart. Muscle soreness, plasma creatine kinase (CK) activity, jump height, maximal voluntary isometric torque (MVC), peak concentric isokinetic torque (IT), and electrically stimulated knee extension torques at 20 and 100 Hz were measured at baseline and at a number of time points up to 14 days after each bout. There were no significant baseline differences between the groups. However, significant time point × genotype interactions were observed for MVC (p = 0.021) and IT (p = 0.011) for the immediate effect of eccentric exercise in bout 1. The RR group showed greater voluntary force decrements (RR vs. XX: MVC, -33.3% vs. -24.5%; IT, -35.9% vs. -23.2%) and slower recovery. A repeated-bout effect was clearly observed, but there were no differences by genotype group. The ACTN3 genotype modulates the response of muscle function to plyometric jumping exercise, although the differences are modest. The ACTN3 genotype does not influence the clearly observed repeated-bout effect; however, XX homozygotes recover baseline voluntary torque values faster and thus may be able to undertake more frequent training sessions.

The central role of myostatin in skeletal muscle and whole body homeostasis

Myostatin is a powerful negative regulator of skeletal muscle mass in mammalian species. It plays a key role in skeletal muscle homeostasis and has now been well described since its discovery. Myostatin is capable of inducing muscle atrophy via its inhibition of myoblast proliferation, increasing ubiquitin-proteasomal activity and downregulating activity of the IGF-Akt pathway. These well-recognized effects are seen in multiple atrophy causing situations, including injury, diseases such as cachexia, disuse and space flight, demonstrating the importance of the myostatin signalling mechanism. Based on this central role, significant work has been pursued to inhibit myostatin's actions in vivo. Importantly, several new studies have uncovered roles for myostatin distinct from skeletal muscle size. Myostatin has been suggested to play a role in cardiomyocyte homeostasis, glucose metabolism and adipocyte proliferation, all of which are examined in detail below. Based on these effects, myostatin inhibition has potential to be widely utilized in many Western diseases such as chronic obstructive pulmonary disease, type II diabetes and obesity. However, if myostatin inhibitors are to successfully translate from bench-top to bedside in the near future, awareness must be raised on these non-traditional effects of myostatin away from skeletal muscle. Indeed, further research into these novel areas is required.

Expression of extracellular matrix components and related growth factors in human tendon and muscle after acute exercise

Acute kicking exercise induces collagen synthesis in both tendon and muscle in humans, but it is not known if this relates to increased collagen transcription and if other matrix genes are regulated. Young men performed 1 h of one-leg kicking at 67% of max workload. Biopsies were taken from the patellar tendon and vastus lateralis muscle of each leg at 2 (n = 10), 6 (n = 11), or 26 h (n = 10) after exercise. Levels of messenger ribonucleic acid mRNA for collagens, noncollagenous matrix proteins, and growth factors were measured with real-time reverse transcription polymerase chain reaction. In tendon, gene expression was unchanged except for a decrease in insulin-like growth factor-IEa (IGF-IEa; P < 0.05). In muscle, collagen expression was not significantly altered, while levels of connective tissue growth factor (CTGF), IGF-IEa, transforming growth factor-β1, -2 (TGF-β), and the TGF-β receptor II mRNA were increased (P < 0.05). Matrix components tenascin-C, fibronectin, and decorin were also induced in loaded muscle (P < 0.05), while fibromodulin was unaffected. In conclusion, the relatively robust changes in matrix components and related growth factors in muscle indicate a stimulation of extracellular matrix even with moderate exercise. However, in tendon tissue, this exercise model does not appear to induce any anabolic response on the transcriptional level.

Effects of a single bout of isometric neuromuscular electrical stimulation on rat gastrocnemius muscle: a combined functional, biochemical and MRI investigation

While muscle damage resulting from electrically-induced muscle isometric contractions has been reported in humans, animal studies have failed to illustrate similar deleterious effects and it remains to be determined whether these conflicting results are related to differences regarding experimental procedures or to species. We have investigated in vivo, in rat gastrocnemius muscles, using experimental conditions as close as possible to those used in humans (i.e., muscle length, number of contractions, stimulated muscle), the effects of a single bout of neuromuscular electrical stimulation (NMES). Maximal tetanic force was measured before, immediately after and 1h and 1, 2, 3, 7 and 14 days after NMES. Magnetic resonance imaging measurements, including volume of gastrocnemius muscles and proton transverse relaxation time (T(2)) were performed at baseline and 3, 7, and 14 days after the NMES session. Control animals did not perform any exercise and measurements were recorded at the same time points. For both groups, blood creatine kinase (CK) activity was measured within the first 3 days that followed the initial evaluation. Maximal tetanic force decreased immediately after NMES whereas measurements performed 1h and the days afterwards were similar to the baseline values. CK activity, muscle volume and T(2) values were similar throughout the experimental protocol between the two groups. Under carefully controlled experimental conditions, isometric NMES per se did not induce muscle damage in rat gastrocnemius muscles on the contrary to what has been repeatedly reported in humans. Further experiments would then be warranted in order to clearly delineate these differences and to better understand the physiological events associated with muscle damage resulting from NMES-induced isometric contractions.

Fiber-type dependence of stretch-induced force enhancement in rat skeletal muscle

When an active muscle is stretched, the force increases due to strain of contractile and noncontractile proteins. We examined this force enhancement in rat extensor digitorum longus (EDL) and soleus muscles, which differ in their composition of these proteins, and their susceptibility to damage. Small stretches were applied at different velocities during isometric contractions from which we quantified the velocity-dependent contractile and velocity-independent noncontractile contributions to force enhancement. Whereas the contractile contribution was significantly greater in soleus than EDL, the noncontractile force enhancement was significantly greater in EDL than soleus, and increased ≈6-fold after damaging eccentric contractions. The increased contractile stiffness may be functionally beneficial in slow muscle, as resistance to lengthening is fundamental to maintaining posture. Following stretch-induced muscle damage this capacity is compromised, leading to increased strain of noncontractile proteins that may facilitate the activation of signaling pathways involved in muscle adaptation to injury.

Excitation-transcription coupling in skeletal muscle: the molecular pathways of exercise

Muscle fibres have different properties with respect to force, contraction speed, endurance, oxidative/glycolytic capacity etc. Although adult muscle fibres are normally post-mitotic with little turnover of cells, the physiological properties of the pre-existing fibres can be changed in the adult animal upon changes in usage such as after exercise. The signal to change is mainly conveyed by alterations in the patterns of nerve-evoked electrical activity, and is to a large extent due to switches in the expression of genes. Thus, an excitation-transcription coupling must exist. It is suggested that changes in nerve-evoked muscle activity lead to a variety of activity correlates such as increases in free intracellular Ca²⁺ levels caused by influx across the cell membrane and/or release from the sarcoplasmatic reticulum, concentrations of metabolites such as lipids and ADP, hypoxia and mechanical stress. Such correlates are detected by sensors such as protein kinase C (PKC), calmodulin, AMP-activated kinase (AMPK), peroxisome proliferator-activated receptor δ (PPARδ), and oxygen dependent prolyl hydroxylases that trigger intracellular signaling cascades. These complex cascades involve several transcription factors such as nuclear factor of activated T-cells (NFAT), myocyte enhancer factor 2 (MEF2), myogenic differentiation factor (myoD), myogenin, PPARδ, and sine oculis homeobox 1/eyes absent 1 (Six1/Eya1). These factors might act indirectly by inducing gene products that act back on the cascade, or as ultimate transcription factors binding to and transactivating/repressing genes for the fast and slow isoforms of various contractile proteins and of metabolic enzymes. The determination of size and force is even more complex as this involves not only intracellular signaling within the muscle fibres, but also muscle stem cells called satellite cells. Intercellular signaling substances such as myostatin and insulin-like growth factor 1 (IGF-1) seem to act in a paracrine fashion. Induction of hypertrophy is accompanied by the satellite cells fusing to myofibres and thereby increasing the capacity for protein synthesis. These extra nuclei seem to remain part of the fibre even during subsequent atrophy as a form of muscle memory facilitating retraining. In addition to changes in myonuclear number during hypertrophy, changes in muscle fibre size seem to be caused by alterations in transcription, translation (per nucleus) and protein degradation.

Effect of N-acetylcysteine on markers of skeletal muscle injury after fatiguing contractile activity

The effects of N-Acetylcysteine (NAC), an unspecific antioxidant, on fatiguing contractile activity-induced injury were investigated. Twenty-four male Wistar rats were randomly assigned to two groups. The placebo group (N=12) received one injection of phosphate buffer (PBS) 1 h prior to contractile activity induced by electrical stimulation. The NAC group (NAC; N=12) received electrical stimulation for the same time period and NAC (500 mg/kg, i.p.) dissolved in PBS 1 h prior to electrical stimulation. The contralateral hindlimb was used as a control, except in the analysis of plasma enzyme activities, when a control group (rats placebo group not electrically stimulated and not treated) was included. The following parameters were measured: tetanic force, muscle fatigue, plasma activities of creatine kinase (CK) and lactate dehydrogenase (LDH), changes in muscle vascular permeability using Evans blue dye (EBD), muscle content of reactive oxygen species (ROS) and thiobarbituric acid-reactive substances (TBARS) and myeloperoxidase (MPO) activity. Muscle fatigue was delayed and tetanic force was preserved in NAC-treated rats. NAC treatment decreased plasma CK and LDH activities. The content of muscle-derived ROS, TBARS, EBD and MPO activity in both gastrocnemius and soleus muscles were also decreased by NAC pre-treatment. Thus, NAC has a protective effect against injury induced by fatiguing contractile activity in skeletal muscle.

Eccentric exercise in vivo: strain-induced muscle damage and adaptation in a stable system

The muscle tendon unit is a stable system, designed to operate eccentrically with efficiency and resiliency. Fiber strains, although minimized by tendon compliance during exercise, are essential components to decoding the mechanical and chemical signals during exercise. Subsequent cellular adaptations minimize the subsequent "dose" of stress and strain and serve to limit the exacerbation of damage into injury.

Exercise does not influence myostatin and follistatin messenger RNA expression in young women

We evaluated changes in myostatin, follistatin, and MyoD messenger RNA (mRNA) gene expression using eccentric exercise (EE) and concentric exercise (CE) as probes to better understand the mechanisms of muscle hypertrophy in young women. Twelve women performed single-leg maximal eccentric (n = 6, 25 +/- 1 years, 59 +/- 7 kg) or concentric (n = 6, 24 +/- 1 years, 65 +/- 7 kg) isokinetic knee extension exercise for 7 sessions. Muscle biopsies were taken from the vastus lateralis at baseline, 8 hours after the first exercise session, and 8 hours after the seventh exercise session. In the EE group, there were no changes in myostatin and follistatin (p > or = 0.17); however, MyoD expression increased after 1 exercise bout (p = 0.02). In the CE group, there were no changes in myostatin, follistatin, or MyoD mRNA gene expression (p > or = 0.07). Differences between the EE and CE groups were not significant (p > or = 0.05). These data suggest that a single bout or multiple bouts of maximal EE or CE may not significantly alter myostatin or follistatin mRNA gene expression in young women. However, MyoD mRNA expression seems to increase only after EE.

Forward lunge: a training study of eccentric exercises of the lower limbs

A few studies have shown that eccentric exercise is effective for prevention and treatment of muscle injuries. Most earlier studies on eccentric exercises have used training with advanced equipment. Forward lunges are considered eccentric exercises, and they may be performed without any equipment. These exercises are commonly used by sprint runners. We performed a prospective, randomized, 6-week training study comparing the effects of walking or jumping forward lunges on hamstring and quadriceps strength and function. Thirty-two soccer players were included in the study. The forward lunge training was done as an addition to ordinary soccer training twice a week for 6 weeks. The outcome was measured by the maximal hamstring and quadriceps strength tests and by functional tests with 1-leg hop tests and 30-m sprint runs. Overall muscle pain was evaluated using a visual analogue scale score, and local pain was estimated with an algometer. Whereas the walking lunge improved hamstring strength, the jumping lunge resulted in sprint running improvements. Algometer testing showed a general increase in the pain detection thresholds of all subjects, including the controls. Thus, precautions should be taken when algometers are used for temporal studies of pain. Walking and jumping forward lunges can be used for improving hamstring strength and running speed in young soccer player. The findings may have relevance when designing protocols for prevention and rehabilitation of muscle injuries.

Stretch-activated ion channel blockade attenuates adaptations to eccentric exercise

PURPOSE

The purpose of this study was to test the hypothesis that stretch-activated ion channel (SAC) function is essential for the repeated bout effect (RBE) in skeletal muscle. Specifically, we investigated if daily injections of streptomycin (a known SAC blocker) would abrogate the muscle's adaptive resistance to the damaging effects of eccentric exercise over a 4-wk period. Furthermore, we hypothesized that the lack of an RBE would be due to the lack of functional adaptations that typically result from repeated bouts of eccentric exercise, including increased peak isometric torque, muscle hypertrophy, and rightward shift of the torque-angle relationship.

METHODS

Twelve New Zealand white rabbits were each subjected to 12 bouts of eccentric exercise over a 4-wk period while receiving either daily injections of streptomycin or sham injections.

RESULTS

Although blocking the SAC function completely eliminated the expected adaptive response in biomechanical parameters during the exercise regimen, there remained evidence of an acquired RBE, albeit with an attenuated response when compared with the muscles with intact SAC function.

CONCLUSION

Blocking sarcolemmal SAC eliminates functional adaptations of muscle after eccentric exercise. In the absence of SAC function, muscles subjected to chronic eccentric exercise still exhibit some degree of the RBE. As such, it appears that the signaling cascade that results in functional, biomechanical adaptations associated with the RBE during eccentric exercise is dependent upon intact SAC function.

Muscle injury, vimentin expression, and nonsteroidal anti-inflammatory drugs predispose to cryptic group A streptococcal necrotizing infection

BACKGROUND

Myonecrosis due to group A streptococci (GAS) often develops at sites of nonpenetrating muscle injury, and nonsteroidal anti-inflammatory drugs (NSAIDs) may increase the severity of these cryptic infections. We have previously shown that GAS bind to vimentin on injured skeletal muscles in vitro. The present study investigated whether vimentin up-regulation in injured muscles in vivo is associated with homing of circulating GAS to the injured site and whether NSAIDs facilitate this process.

METHODS

M type 3 GAS were delivered intravenously 48 h after eccentric contraction (EC)-induced injury of murine hind-limb muscles. Vimentin gene expression and homing of GAS were followed by real-time reverse-transcriptase polymerase chain reaction and quantitative bacteriology of muscle homogenates, respectively. In separate experiments, ketorolac tromethamine (Toradol) was given 1 h before GAS infusion.

RESULTS

Vimentin was up-regulated approximately 8-fold 48 h after EC. Significantly more GAS were found in moderately injured muscles than in noninjured controls. NSAIDs greatly augmented the number of GAS in injured muscles.

CONCLUSIONS

Vimentin may tether circulating GAS to injured muscle, and NSAIDs enhance this process. Strategies targeting the vimentin-GAS interaction may prevent or attenuate GAS myonecrosis. Use of NSAIDs should increase suspicion of cryptic GAS infection in patients with increasing pain at sites of nonpenetrating muscle injury.

Role of MyoD in denervated, disused, and exercised muscle

The myogenic regulatory factor MyoD plays an important role in embryonic and adult skeletal muscle growth. Even though it is best known as a marker for activated satellite cells, it is also expressed in myonuclei, and its expression can be induced by a variety of different conditions. Several model systems have been used to study the mechanisms behind MyoD regulation, such as exercise, stretch, disuse, and denervation. Since MyoD reacts in a highly muscle-specific manner, and its expression varies over time and between species, universally valid predictions and explanations for changes in MyoD expression are not possible. This review explores the complex role of MyoD in muscle plasticity by evaluating the induction of MyoD expression in the context of muscle composition and electrical and mechanical stimulation.

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

It is unknown whether muscle damage at the level of the sarcomere can be induced without lengthening contractions. To investigate this, we designed a study where seven young, healthy men underwent 30 min of repeated electrical stimulated contraction of m. gastrocnemius medialis, with the ankle and leg locked in a fixed position. Two muscle biopsies were collected 48 h later: one from the stimulated muscle and one from the contralateral leg as a control. The biopsies were analyzed immunohistochemically for inflammatory cell infiltration and intermediate filament disruption. Ultrastructural changes at the level of the z-lines were investigated by transmission electron microscopy. Blood samples were collected for measurement of creatine kinase activity, and muscle soreness was assessed in the days following stimulation. The biopsies from the stimulated muscle revealed macrophage infiltration and desmin-negative staining in a small percentage of myofibers in five and four individuals, respectively. z-Line disruption was evident at varying magnitudes in all subjects and displayed a trend toward a positive correlation ( r = 0.73, P = 0.0663) with the force produced by stimulation. Increased muscle soreness in all subjects, combined with a significant increase in creatine kinase activity ( P < 0.05), is indirectly suggestive of muscle damage, and the novel findings of the present study, i.e., 1) macrophages infiltration, 2) lack of desmin staining, and 3) z-line disruption, provide direct evidence of damage at the myofiber and sarcomere levels. These data support the hypothesis that muscle damage at the level of the sarcomere can be induced without lengthening muscle contractions.

Gene expression profiling in human skeletal muscle during recovery from eccentric exercise

We used cDNA microarrays to screen for differentially expressed genes during recovery from exercise-induced muscle damage in humans. Male subjects (n = 4) performed 300 maximal eccentric contractions, and skeletal muscle biopsy samples were analyzed at 3 h and 48 h after exercise. In total, 113 genes increased 3 h postexercise, and 34 decreased. At 48 h postexercise, 59 genes increased and 29 decreased. On the basis of these data, we chose 19 gene changes and conducted secondary analyses using real-time RT-PCR from muscle biopsy samples taken from 11 additional subjects who performed an identical bout of exercise. Real-time RT-PCR analyses confirmed that exercise-induced muscle damage led to a rapid (3 h) increase in sterol response element binding protein 2 (SREBP-2), followed by a delayed (48 h) increase in the SREBP-2 gene targets Acyl CoA:cholesterol acyltransferase (ACAT)-2 and insulin-induced gene 1 (insig-1). The expression of the IL-1 receptor, a known regulator of SREBP-2, was also elevated after exercise. Taken together, these expression changes suggest a transcriptional program for increasing cholesterol and lipid synthesis and/or modification. Additionally, damaging exercise induced the expression of protein kinase H11, capping protein Z alpha (capZalpha), and modulatory calcineurin-interacting protein 1 (MCIP1), as well as cardiac ankryin repeat protein 1 (CARP1), DNAJB2, c-myc, and junD, each of which are likely involved in skeletal muscle growth, remodeling, and stress management. In summary, using DNA microarrays and RT-PCR, we have identified novel genes that respond to skeletal muscle damage, which, given the known biological functions, are likely involved in recovery from and/or adaptation to damaging exercise.

Increased efficacy and decreased systemic-effects of botulinum toxin A injection after active or passive muscle manipulation

The effect of physical manipulation on the outcome of neurotoxin (NT) injection was studied in a rat tibialis anterior (TA) model system where dorsiflexion torque could be measured precisely. After determination of initial torque, all rats received a one-time botulinum toxin A (BTX-A) injection (dose 6.0 units/kg in a volume of 100 microL) into the TA midbelly. Four experimental groups were studied: one group was subjected to BTX-A injection alone (BTX-A only, n=8), one was subjected to BTX-A injection followed immediately by 10 isometric contractions (ISO; n=9), and the third was subjected to BTX-A followed immediately by 10 muscle passive stretch/release cycles (PS; n=10). After 1 month, maximum dorsiflexion torque of the injected and contralateral legs was determined followed by quantification of TA fiber area. Post-injection torque was significantly reduced by around 80% in all NT-treated extremities 1 month after injection (p<0.05). While all NT-treated extremities demonstrated a significant torque decrease relative to their pre-injection levels, ISO and PS groups demonstrated significantly lower torques compared with the BTX-A only group which received no physical manipulation (p<0.05) indicating greater efficacy. Perhaps even more surprising was that the ISO and PS groups both demonstrated a significantly smaller contralateral effect compared with the BTX-A only group that received no manipulation (p<0.05) indicating a decreased systemic-effect. Muscle fiber size generally correlated with dorsiflexion torque. These data demonstrate that both neuromuscular activity (seen in the ISO group) and muscle movement (seen in the PS group) increased the efficacy of BTX-A and decreased the systemic side effects.

Impact of repeated bouts of eccentric exercise on myogenic gene expression

Evidence indicates that repeated-bouts of eccentric exercise (EE) do not exacerbate the extent of muscle damage indices, as compared to a single-bout. We hypothesized that molecular adaptations, under repeated-bouts of EE, would include suppression of muscle repair inhibitory factors such as myostatin and up-regulation of muscle repair positive regulatory factors such as myogenic regulatory factors (MRFs). Fifteen males were recruited for this study. The exercise group (n=9) successfully completed six sets of 15 reps of maximum voluntary eccentric contractions, for six consecutive days, using a dynamometer (Multicont-II). Blood and muscle biopsy samples were obtained from each subject 1 week prior to exercise, 2 days post the first training session, and 24 h after the last training session. Gene expression levels were determined using real-time RT-PCR. Blood samples were analyzed for creatine kinase (CK) and lactate-dehydrogenase (LDH) activity. Repeated-bouts of EE induced a large down-regulation of myostatin mRNA (-73%) which persisted throughout the study. The responses of MRFs were mild. At day 3 only myogenin increased significantly (1.9 fold) while MyoD decreased by 45%. Surprisingly, at day 7, despite the presence of muscle damage indices, all MRFs returned to the pre-exercise levels. The results of the present study showed that repeated-bouts of EE, for six consecutive days, dramatically decreased Myostatin mRNA expression but impaired the expression patterns of MRFs such that, with the exception of myogenin that showed a moderate non-sustained increase, MyoD and MYf5 response was minimal.

Myofibre damage in human skeletal muscle: effects of electrical stimulation versus voluntary contraction

Disruption to proteins within the myofibre after a single bout of unaccustomed eccentric exercise is hypothesized to induce delayed onset of muscle soreness and to be associated with an activation of satellite cells. This has been shown in animal models using electrical stimulation but not in humans using voluntary exercise. Untrained males (n=8, range 22-27 years) performed 210 maximal eccentric contractions with each leg on an isokinetic dynamometer, voluntarily (VOL) with one leg and electrically induced (ES) with the other leg. Assessments from the skeletal muscle were obtained prior to exercise and at 5, 24, 96 and 192 h postexercise. Muscle tenderness rose in VOL and ES after 24 h, and did not differ between groups. Maximal isometric contraction strength, rate of force development and impulse declined in the VOL leg from 4 h after exercise, but not in ES (except at 24 h). In contrast, a significant disruption of cytoskeletal proteins (desmin) and a rise of myogenic growth factors (myogenin) occurred only in ES. Intracellular disruption and destroyed Z-lines were markedly more pronounced in ES (40%) compared with VOL (10%). Likewise, the increase in satellite cell markers [neural cell adhesion molecule (N-CAM) and paired-box transcription factor (Pax-7)] was more pronounced in ES versus VOL. Finally, staining of the intramuscular connective tissue (tenascin C) was increased equally in ES and VOL after exercise. The present study demonstrates that in human muscle, the delayed onset of muscle soreness was not significantly different between the two treatments despite marked differences in intramuscular histological markers, in particular myofibre proteins and satellite cell markers. An increase in tenascin C expression in the midbelly of the skeletal muscle in both legs provides further evidence of a potential role for the extracellular matrix in the phenomenon of delayed onset of muscle soreness.

Repeated bout effect on the cytoskeletal proteins titin, desmin, and dystrophin in rat skeletal muscle

The aim of this study was to evaluate the effect of repeated bouts of exercise on the cytoskeletal proteins titin, desmin, and dystrophin. Rats were made to run downhill for 90 min 1 or 5 times separated by 14 days. Samples were taken from quadriceps femoris muscle 3, 48, 96 h and 50 days after the last exercise session and detected by quantitative PCR, histochemical stainings, and western blot analyses. Histopathological changes in titin, desmin, and dystophin stainings, an increase in beta-glucuronidase activity (a quantitative indicator of muscle damage), a significant decrease in the relative content of dystrophin, and intramyocellular Evans blue staining (signs of changes in sarcolemmal permeability) observed after one exercise session were attenuated after 5 exercise sessions. Titin mRNA level was not increased after the initial exercise session but was increased after the fifth session. Desmin and dystrophin mRNA levels were increased after the first and fifth sessions with desmin showing a smaller increase after the fifth session compared to the first session. Prior exercise induces adaptation that protects the sarcolemma as well as subsarcolemmal, intermediate filament, and sarcomeric proteins against disruption. Changes in mRNA levels of titin, desmin, and dystophin after an acute exercise session obviously reflect the need of these proteins in the repair process following damage. After five sessions increase in mRNA of studied proteins suggest a strong involvement in continuing adaptation to the increased exercise.

Progressive resistance training temporarily alters hamstring torque-angle relationship

To examine the effects of eccentric and concentric progressive resistance training on muscle torque-angle relationship, 30 young adults were randomly allocated into three groups of 10, control (CTL), eccentric training (ECC) and concentric training (CON). The ECC and CON groups performed seven sessions over 3 weeks of progressive resistance training of the right hamstrings muscle, using a standard barbell and a leg curl machine. Torque-angle relationship was measured before and 4, 11 and 18 days after the end of training. Voluntary isometric torque was recorded at seven test angles, with the subject prone (20-80 degrees; 0 degrees is full extension). In the CON group, the angle of peak isometric torque increased from 46.0 +/- 5.2 degrees pre-training to 53.0 +/- 14.9 degrees on day 4 following training (P<0.05). In the ECC group, peak torque was increased over baseline on days 4 and 11 post-training, particularly at extended knee angles (P<0.05). The angle at which peak torque occurred was decreased on day 4 (50.0 +/- 8.2 degrees pre-training, 29.0 +/- 7.4 degrees on day 4) and on day 11 (both P<0.01), but was similar to baseline 18 days after training. ECC therefore induced a temporary change in torque-angle relationship.

Structural and regulatory roles of muscle ankyrin repeat protein family in skeletal muscle

The biological response of muscle to eccentric contractions (ECs) results in strengthening and protection from further injury. However, the cellular basis for this response remains unclear. Previous studies identified the muscle ankyrin repeat protein (MARP) family, consisting of cardiac ankyrin repeat protein (CARP), ankyrin repeat domain 2/ankyrin repeat protein with PEST and proline-rich region (Ankrd2/Arpp), and diabetes-associated ankyrin repeat protein (DARP), as rapidly and specifically upregulated in mice after a single bout of EC. To determine the role of these genes in skeletal muscle, a survey of skeletal muscle structural and functional characteristics was performed on mice lacking all three MARP family members (MKO). There was a slight trend toward MKO muscles having a slower fiber type distribution but no differences in muscle fiber size. Single MKO fibers were less stiff, tended to have longer resting sarcomere lengths, and expressed a longer isoform of titin than their wild-type counterparts, indicating that these proteins may play a role in the passive mechanical behavior of muscle. Finally, MKO mice showed a greater degree of torque loss after a bout of ECs compared with wild-type mice, although they recovered from the injury with the same or even improved time course. This recovery was associated with enhanced expression of the muscle regulatory genes MyoD and muscle LIM protein (MLP), suggesting that the MARP family may play both important structural and gene regulatory roles in skeletal muscle.