Changes In Muscle Structure Research Articles

Neuromuscular electrophysiological disorders and muscle atrophy in mechanically-ventilated traumatic brain injury patients: New insights from a prospective observational study

PurposeIt is unclear whether the muscular changes in mechanically-ventilated traumatic brain injury patients (TBI) are only associated with disuse or additionally to neuromuscular electrophysiological disorders (NED). The correlation between muscle atrophy and NED may affect functional outcomes and rehabilitation programs significantly. Material and methodsAn observational study was performed to investigate the presence of NED and muscle atrophy in TBI patients undergoing mechanical ventilation. NED was diagnosed by the stimulus electrodiagnosis test when chronaxie was ≥1000μs. The muscle structure (thickness and echogenicity) was assessed by B-mode ultrasound. Tibialis anterior (TA), rectus femoris (RF), and biceps brachialis (BB) muscles were analyzed. Patients were followed from the first day of admission in the intensive care unit (ICU) to the fourteenth day. ResultsTwenty-two patients were analyzed. An increase of 48% in NED from day 1 to day 14 was detected in TA (p=0.004). All muscles presented a significant decrease in thickness (~18%, p<0.05), but echogenicity increased only in TA (19%), p<0.01 and RF (23%), p<0.01. ConclusionsMechanically-ventilated patients with TBI developed NED in addition to changes in muscle structure during their stay in the ICU.

The training-specific adaptations resulting from resistance training, gymnastics and plyometric training, and non-training in adolescent athletes

Although previous research has investigated the training-specific adaptations to training in adults, there is a paucity of research aimed at investigating these adaptations in adolescent athletes. As such, adolescent athletes’ training-specific adaptations from three different training interventions were investigated in this study. Sixteen adolescent athletes participated in this study, whereby eight performed both training interventions and eight the non-training control. Pre- and post-testing was performed for each intervention with the testing battery: ultrasonography of the vastus lateralis and lateral gastrocnemius, countermovement jump, squat jump, and isometric mid-thigh pull. The resistance training group had large significant increases in isometric mid-thigh pull relative peak force ( p &lt; 0.01, g = 0.85 (−0.01, 1.71)) and vastus lateralis fascicle length ( p = 0.04, g = 0.94 (0.07, 1.80)). The gymnastics and plyometric group demonstrated large significant changes in vastus lateralis pennation angle ( p = 0.03, g = −0.94 (−1.81, −0.08)) and fascicle length ( p = 0.03, g = 1.07 (0.19, 1.95)), and moderate significant increases in lateral gastrocnemius thickness ( p = 0.01, g = 0.63 (−0.21, 1.47)) and eccentric leg stiffness ( p = 0.03, g = 0.60 (−0.24, 1.44)). No significant changes were observed for any variables in the non-training group. The resistance training evoked increases in lower-body force producing capabilities, whereas the gymnastics and plyometric training evoked changes in muscle structure and inherent muscle qualities.

P.468 - Are muscle volume and echo-intensity related to rate of force development in children with Duchenne muscular dystrophy?

Muscle weakness in children with Duchenne muscular dystrophy (DMD) is one of the main symptoms and is mainly caused by alterations in muscle morphology. Several studies have used muscle imaging, such as ultrasonography (US), to quantify these alterations and their association with muscle weakness. An increase in echo-intensity (EI) was found to negatively correlate with the outcomes of maximal voluntary isometric contractions (MVICs). However, to what extend muscle volume and EI are related to MVIC-outcomes and rate of force development (RFD) has not yet been established. Maximal force (Nm/kg), RFD (N/s), muscle volume (ml/kg) and EI of the knee-extensors and knee flexors were collected in 10 DMD children (median age (25–75%): 8.15 (6.77 – 9.99)). Muscle volume was acquired with a 3D freehand US technique and extracted using MeVisLab and EI was calculated according to the method described by Shkylar et al (2014). Spearmans' rank correlation coefficient was used to evaluate to what extend MVIC-outcomes and RFD-values were correlated to muscle volume and EI, and the classification of Altman was used to interpret these correlations. A decrease in RFD of the knee-flexors was related to an increase in muscle volume of that same muscle group (r = -0.43). Further, an increase in EI in the knee-flexors was associated with a decrease in knee-flexor strength (r = -0.44). A decrease in muscle strength and RFD in the knee-flexors could be attributed to an increase in EI and muscle volume respectively, most likely caused by an increment of fatty and fibrous tissue. No relationship between MVIC-outcomes and RFD-values, and muscle volume and EI was found for the knee-extensors. Because changes in muscle structure in children with DMD are known to be age- and muscle specific, the study group and number of analysed muscles should be enhanced in future studies.

High pH in beef longissimus thoracis reduces muscle fibre transverse shrinkage and light scattering which contributes to the dark colour

Most studies have focused on myoglobin regarding meat colour development, with little focus on the contribution of muscle structure and light scattering. Our aim was to investigate the pH-dependent changes in muscle structure, on the light scattering properties of the meat. Beef longissimus thoracis muscles were segregated into light, medium or dark colour groups (n=18). ‘Dark’ muscles had a high ultimate pH (pHu), lower lightness (L*), redness (a*), higher myoglobin concentration and deoxymyoglobin content compared to other muscles. Reflectance confocal laser scanning microscopy (rCLSM) revealed ‘dark’ muscles had decreased global brightness (indicator of light scattering) and increased fibre width. In a secondary experiment, decreasing the homogenisation buffer pH from 6.10 to 5.40 induced a 17% shrinkage in high pHu muscle fibres, which increased light scattering by ~25%. In conclusion, rCLSM demonstrated that muscle structure contributes to the magnitude of light scattering by a pH dependent mechanism.

Fysiologische effecten van verschillende soorten arbeid op de spierontwikkeling van het paard

Het is algemeen bekend dat training leidt tot chemische, metabole en structurele veranderingen in spieren. De invloed van het type van training op deze veranderingen werd echter nog onvoldoende bestudeerd in paarden vanwege een gebrek aan gestandaardiseerde onderzoeksmethoden. In dit overzichtsartikel wordt het effect van drie soorten training op de spierevolutie en metabole veranderingen onderzocht. De vereisten voor powertraining verschillen van die voor (langdurige) inspanning van lage intensiteit. Elk type training leidt tot een specifieke shift van spiervezeltypes, enzymconcentraties en (an)aerobe capaciteit. Deze fysiologische adaptaties als gevolg van training faciliteren het uitvoeren van de specifieke inspanningen en verhogen zo de prestatie. Het kennen van deze adaptaties per type training kan helpen om de training en het management van sportpaarden te optimaliseren in functie van hun discipline.

Changes in three-dimensional muscle structure of rabbit gastrocnemius, flexor digitorum longus, and tibialis anterior during growth

Muscular contraction dynamics depends on active and passive muscle properties (e.g., the force-velocity relation) as well as on the three-dimensional (3D) muscle structure (e.g., the muscle fascicle architecture and aponeurosis dimensions). Much is known about active muscle force generation and the muscle architecture at a particular age (mostly for adult specimens), but less is known about changes in muscle structure during growth. The present study analyzed growth-related changes in the muscle structure of rabbit gastrocnemius lateralis (GL), gastrocnemius medialis (GM), flexor digitorum longus (FDL), and tibialis anterior (TA). Changes in tendon length, muscle belly dimensions (length, width, thickness), as well as aponeurosis length, width, and area were determined using 55 rabbits between 18 and 108 days old. Additionally, the 3D muscle fascicle architecture of five rabbits of different ages (21, 37, 50, 70, 100 days) was determined using a manual digitizer.We found an almost linear increase over time in most of the geometrical parameters observed. GL and GM showed very similar growth characteristics. In contrast to the pronounced increase in muscle belly length of GL and GM, FDL and TA exhibited more uniform muscle belly growth in length, width, and thickness. In general, the aponeuroses of the muscles exhibited lower growth rates in width than in length, and aponeurosis areas were larger than physiological cross-sectional areas. There were almost no changes in fascicle lengths with increasing age for GL, GM, and FDL. In contrast, there was a clear increase in TA fascicle length from about 20 to over 40mm. Pennation angles of TA (11.0 ± 2.1°) and FDL (16.7 ± 3.2°) remained almost unchanged but increased for GL from 13.4 ± 3.3° to 24.3 ± 6.5° from the youngest to the oldest animal. For all muscles observed, the tendon-muscle fascicle length ratio (rTFL) changed during growth. GL and GM exhibited similar increases in rTFL from about 4–8. FDL showed the highest ratio, which increased from about 8–13, whereas TA had the lowest ratio, which decreased slightly from 2 to 1.5.The outcomes demonstrate new findings regarding changes in 3D muscle architecture and aponeurosis shape during growth, and they provide information for muscle force generation, functional relevance, and adaptation with respect to animal age. Therefore, the results help to improve understanding of muscle growth processes and can be used as input data for muscle growth modeling.

Envejecimiento: Cambios Estructurales y Papel De La Facilitación Neuromuscular Propioceptiva

En el mundo, el porcentaje de adultos mayores se encuentra en aumento, obligando al desarrollo continuo de políticas en salud. En razón a los cambios morfológicos y estructurales propios del músculo esquelético durante el envejecimiento, que llevan a su deterioro, varios modelos de ejercicio han sido puestos a prueba, incluyendo el entrenamiento de la fuerza explosiva y la flexibilidad. La Facilitación Neuromuscular Propioceptiva, ha surgido como una alternativa de entrenamiento, gracias a los resultados positivos demostrados en el área de la prevención y la rehabilitación; sin embargo en el adulto mayor sano no ha sido posible demostrar dichos beneficios, presentándose por el contrario dificultades en la aplicación de los programas, dados por los tiempos necesarios para hacer tangibles los resultados y los riesgos que con su implementación se puedan presentar. Es necesario desarrollar nuevas investigaciones que involucren técnicas combinadas de entrenamiento, con el fin de comprender y optimizar la respuesta al ejercicio físico en el adulto mayor.

Two-dimensional and shear wave elastography ultrasound: A reliable method to analyse spastic muscles?

Few data exist on the feasibility and reliability of measuring muscular atrophy in 2 dimensions (2D) by ultrasonography (US) and elasticity with shear wave elastography (SWE) in spastic muscles. Fourteen patients with chronic stroke took part in 2 intersession reliability experiments performed with 1-week intervals between sessions. Pennation angle (PA), muscle thickness (MT), and shear elastic modulus (µ) were measured in spastic gastrocnemius medialis (GM) muscles at rest and at maximal passive stretching in paretic and nonparetic legs. On the paretic side, the coefficient of variation (CV) in GM was 6.30% for MT and 6.40% for PA at rest and was 7.53% and 8.26% for MT and PA, respectively, at maximal passive stretching. The reliability of the µ measurement was good only for GM at rest on the paretic side (CV = 9.86%). 2D US associated with SWE shows promise for assessing structural changes in muscles. With some methodological adaptations, this approach could help guide spasticity treatment. Muscle Nerve 57: 222-228, 2018.

Age-related differences in twitch properties and muscle activation of the first dorsal interosseous.

To examine twitch force potentiation and twitch contraction duration, as well as electromyographic amplitude (EMGRMS) and motor unit mean firing rates (MFR) at targeted forces between young and old individuals in the first dorsal interosseous (FDI). Ultrasonography was used to assess muscle quality. Twenty-two young (YG) (age=22.6±2.7years) and 14 older (OD) (age=62.1±4.7years) individuals completed conditioning contractions at 10% and 50% maximal voluntary contraction, (MVC) during which EMGRMS and MFRs were assessed. Evoked twitches preceded and followed the conditioning contractions. Ultrasound images were taken to quantify muscle quality (cross-sectional area [CSA] and echo intensity [EI]). No differences were found between young and old for CSA, pre-conditioning contraction twitch force, or MFRs (P>0.05). However, OD individuals exhibited greater EI and contraction duration (P<0.05), and EMGRMS (YG=35.4±8.7%, OD=43.4±13.2%; P=0.034). Twitch force potentiation was lower for OD (0.311±0.15N) than YG (0.619±0.26N) from pre- to post-50% conditioning contraction (P<0.001). Lower levels of potentiation with elongated contraction durations likely contributed to greater muscle activation during the conditioning contractions in the OD rather than altered MFRs. Ultrasonography suggested age-related changes in muscle structure contributed to altered contractile properties in the OD. Greater muscle activation requirements can have negative implications on fatigue resistance at low to moderate intensities in older individuals.

Structural changes in skeletal muscles in hypokinesia and physical loading in the posthypokinetic period of recovery of rats’ organisms

This article reports the study of histo-ultrastructural changes of different structural components of the direct muscle of the thigh of sexually mature male rats over a prolonged period of hypokinesia and subsequent application of physical loading of average aerobic power. Using a light optical, electron microscope (for the exposure of structural transformations of muscle components) and histochemical (for determination of activity of succinate dehydrogenase according to the Nahlas method to identify muscle fibers with different phenotypes) methods, we studied the structural manifestations of adaptation of muscle fibres under prolonged (240 day) hypokinesia and 15–30 episodes of physical loading of average aerobic power in the posthypokinetic period among 55 sexually mature rats. Under prolonged hypokinesis we primarily observed changes in the intramuscular network and morphometric changes in the blood vessels. These data closely correlate with the progression of changes of the subcellular components responsible for energetic and flexible balance of muscle fibres. We found that fast oxygen-glycolytic muscle fibers and their peripheral nervous apparatus are the most sensitive to prolonged hypokinesia. As a result of application of physical loading of average aerobic power, reparative regeneration is intensified, which substantially shortens the period of recovery of structural-functional properties of skeletal muscles in the conditions of hypokinetic disorders. Thus, in prolonged hypokinesia, changes primarily affect the sources of blood supply to skeletal muscles, with the secondary development of reverse processes in muscle fibers and peripheral nervous apparatus with certain morphometric signs.

Effects of eccentric overload training on patellar tendon and vastus lateralis in three days of consecutive running

BackgroundThe analysis of structural changes in patellar tendon and muscle of healthy subjects in response to mechanical loads provides useful insight into the mechanism underlying overuse injuries. MethodsChanges produced in tendon and muscles structures after eccentric overload training and three consecutive running days were examined. Twenty healthy subjects were recruited and divided into two groups. One group (ECC) performed eccentric overload squat training (six weeks). After such training, the ECC group performed three running sessions on consecutive days, as did the control group (CONT). The structure of their patellar tendons and vastus lateralis muscles was quantified using ultrasound and Doppler imaging. Images were obtained before and after eccentric training for the ECC group and on every day of running performance for both groups. ResultsAfter eccentric training, the ECC group experienced an increase in cross-sectional area (CSA) of patellar tendon (P=0.012). After every day of running, the ECC group experienced a decrease in CSA (P=0.027). In the CONT group, after one day of running a significant increase was observed in anteroposterior width of their patellar tendon (P=0.028), as well as a decrease in pennation angle of vastus lateralis muscle (P=0.028) within three days of running sessions. ConclusionsEccentric overload training brought about changes in the patellar tendon consistent with an improvement in the quality of the tissue. The ECC group in our study showed a more normalised pattern than the CONT group in the running performance, in agreement with previous research. Level of evidenceLevel 3, controlled trial.

Bilateral Changes in Deep Tissue Environment After Manual Lymphatic Drainage in Patients with Breast Cancer Treatment-Related Lymphedema.

Breast cancer treatment-related lymphedema (BCRL) arises from a mechanical insufficiency following cancer therapies. Early BCRL detection and personalized intervention require an improved understanding of the physiological processes that initiate lymphatic impairment. Here, internal magnetic resonance imaging (MRI) measures of the tissue microenvironment were paired with clinical measures of tissue structure to test fundamental hypotheses regarding structural tissue and muscle changes after the commonly used therapeutic intervention of manual lymphatic drainage (MLD). Measurements to identify lymphatic dysfunction in healthy volunteers (n = 29) and patients with BCRL (n = 16) consisted of (1) limb volume, tissue dielectric constant, and bioelectrical impedance (i.e., non-MRI measures); (2) qualitative 3 Tesla diffusion-weighted, T1-weighted and T2-weighted MRI; and (3) quantitative multi-echo T2 MRI of the axilla. Measurements were repeated in patients immediately following MLD. Normative control and BCRL T2 values were quantified and a signed Wilcoxon Rank-Sum test was applied (significance: two-sided p < 0.05). Non-MRI measures yielded significant capacity for discriminating between arms with versus without clinical signs of BCRL, yet yielded no change in response to MLD. Alternatively, a significant increase in deep tissue T2 on the involved (pre T2 = 0.0371 ± 0.003 seconds; post T2 = 0.0389 ± 0.003; p = 0.029) and contralateral (pre T2 = 0.0365 ± 0.002; post T2 = 0.0395 ± 0.002; p < 0.01) arms was observed. Trends for larger T2 increases on the involved side after MLD in patients with stage 2 BCRL relative to earlier stages 0 and 1 BCRL were observed, consistent with tissue composition changes in later stages of BCRL manifesting as breakdown of fibrotic tissue after MLD in the involved arm. Contrast consistent with relocation of fluid to the contralateral quadrant was observed in all stages. Quantitative deep tissue T2 MRI values yielded significant changes following MLD treatment, whereas non-MRI measurements did not vary. These findings highlight that internal imaging measures of tissue composition may be useful for evaluating how current and emerging therapies impact tissue function.

Pharmacological inhibition of myostatin protects against skeletal muscle atrophy and weakness after anterior cruciate ligament tear.

Anterior cruciate ligament (ACL) tears are among the most frequent knee injuries in sports medicine, with tear rates in the US up to 250,000 per year. Many patients who suffer from ACL tears have persistent atrophy and weakness even after considerable rehabilitation. Myostatin is a cytokine that directly induces muscle atrophy, and previous studies rodent models and patients have demonstrated an upregulation of myostatin after ACL tear. Using a preclinical rat model, our objective was to determine if the use of a bioneutralizing antibody against myostatin could prevent muscle atrophy and weakness after ACL tear. Rats underwent a surgically induced ACL tear and were treated with either a bioneutralizing antibody against myostatin (10B3, GlaxoSmithKline) or a sham antibody (E1-82.15, GlaxoSmithKline). Muscles were harvested at either 7 or 21 days after induction of a tear to measure changes in contractile function, fiber size, and genes involved in muscle atrophy and hypertrophy. These time points were selected to evaluate early and later changes in muscle structure and function. Compared to the sham antibody group, 7 days after ACL tear, myostatin inhibition reduced the expression of proteolytic genes and induced the expression of hypertrophy genes. These early changes in gene expression lead to a 22% increase in muscle fiber cross-sectional area and a 10% improvement in maximum isometric force production that were observed 21 days after ACL tear. Overall, myostatin inhibition lead to several favorable, although modest, changes in molecular biomarkers of muscle regeneration and reduced muscle atrophy and weakness following ACL tear. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:2499-2505, 2017.

Skeletal muscle aging: influence of oxidative stress and physical exercise.

Skeletal muscle abnormalities are responsible for significant disability in the elderly. Sarcopenia is the main alteration occurring during senescence and a key public health issue as it predicts frailty, poor quality of life, and mortality. Several factors such as reduced physical activity, hormonal changes, insulin resistance, genetic susceptibility, appetite loss, and nutritional deficiencies are involved in the physiopathology of muscle changes. Sarcopenia is characterized by structural, biochemical, molecular and functional muscle changes. An imbalance between anabolic and catabolic intracellular signaling pathways and an increase in oxidative stress both play important roles in muscle abnormalities. Currently, despite the discovery of new targets and development of new drugs, nonpharmacological therapies such as physical exercise and nutritional support are considered the basis for prevention and treatment of age-associated muscle abnormalities. There has been an increase in information on signaling pathways beneficially modulated by exercise; nonetheless, studies are needed to establish the best type, intensity, and frequency of exercise to prevent or treat age-induced skeletal muscle alterations.

Utjecaj strukturnih i biokemijskih promjena mi�ica post mortem na mekocu mesa

The aim of this paper was to describe the main structural and biochemical changes of muscles during post-mortem process implicated with meat tenderness. Taking into account complexity of biochemical and structural changes in muscles, meat tenderness is associated with the amount and quality of connective tissue, intramuscular lipid content (marbling), sarcomere length, and myofibrillar protein degradation. In short, more tender meat is associated with lower connective tissue content, higher collagen solubility, greater intramuscular lipid content, longer sarcomeres and greater myofibrillar protein degradation. However, it must be considered that the interactions among the listed factors are complex and dependent on numerous processes during post-mortem such as chilling regime, electrical stimulation, carcass suspension, aging, mechanical tenderization, different marinades, and thermal processing conditions.

Measurement of Gender Differences of Gastrocnemius Muscle and Tendon Using Sonomyography during Calf Raises: A Pilot Study.

Skeletal muscles are essential to the gender-specific characteristics of human movements. Sonomyography, a new signal for quantifying muscle activation, is of great benefit to understand muscle function through monitoring the real-time muscle architectural changes. The purpose of this pilot study was to investigate gender differences in the architectural changes of gastronomies muscle and tendon by using sonomyography during performing two-legged calf raising exercises. A motion analysis system was developed to extract sonomyography from ultrasound images together with kinematic and kinetic measurements. Tiny fascicle length changes among seven male subjects were observed at the initial part of calf raising, whereas the fascicle of seven female subjects shortened immediately. This result suggested that men would generate higher mechanical power output of plantar flexors to regulate their heavier body mass. In addition, the larger regression coefficient between the fascicle length and muscle force for the male subjects implied that higher muscle stiffness for the men was required in demand of maintaining their heavier body economically. The findings from the current study suggested that the body mass might play a factor in the gender difference in structural changes of muscle and tendon during motion. The sonomyography may provide valuable information in the understanding of the gender difference in human movements.

Characteristics of soft tissues at the apex of the deformity in patients with kyphoscoliosis with underlying type 1 neurofibromatosis

Objective. Evaluation of skin sensitivity and analysis of morphological changes in paravertebral muscles and back skin in kyphoscoliotic deformity projection in patients with type 1 neurofibromatosis (NF-1). Materials and methods. Ten NF-1 patients who underwent surgery to treat kyphoscoliosis were examined. Using an electrical esthesiometer thermal pain sensitivity before the surgery was studied in dermatomes corresponding to the apex of the deformity. Skin and muscle biopsy samples were collected intraoperatively in the projection of the apex of the deformity curve and were subsequently analyzed by light and scanning electron microscopy. Results. Patients with kyphoscoliosis with underlying NF-1 were characterized by abnormal thermal pain sensitivity, pathological structural changes in skin and muscles accompanied by disrupted innervation and blood supply. Discussion . The observed changes may be responsible for lowered postoperative reparative potential of tissues and they must be considered in prevention and prognosis of treatment and rehabilitation efficacy.

Myofibril Changes in the Copepod Pseudodiaptomus marinus Exposed to Haline and Thermal Stresses.

Copepods are small crustaceans capable to survive in various aquatic environments. Their responses to changes in different external factors such as salinity and temperature can be observed at different integration levels from copepod genes to copepod communities. Until now, no thorough observation of the temperature or salinity effect stresses on copepods has been done by optical microscopy. In this study, we used autofluorescence to visualize these effects on the morphology of the calanoid copepod Pseudodiaptomus marinus maintained during several generations in the laboratory at favorable and stable conditions of salinity (30 psu) and temperature (18°C). Four different stress experiments were conducted: at a sharp decrease in temperature (18 to 4°C), a moderate decrease in salinity (from 30 to 15 psu), a major decrease in salinity (from 30 to 0 psu), and finally a combined stress with a decrease in both temperature and salinity (from 18°C and 30 psu to 4°C and 0 psu). After these stresses, images acquired by confocal laser scanning microscopy (CLSM) revealed changes in copepod cuticle and muscle structure. Low salinity and/or temperature stresses affected both the detection of fluorescence emitted by muscle sarcomeres and the distance between them. In the remaining paper we will use the term sarcomeres to describe the elements located within sarcomeres and emitted autofluorescence signals. Quantitative study showed an increase in the average distance between two consecutive sarcomeres from 2.06 +/- 0.11 μm to 2.44 +/- 0.42 μm and 2.88 +/- 0.45μm after the exposure to major haline stress (18°C, 0 psu) and the combined stress (4°C, 0 psu), respectively. These stresses also caused cuticle cracks which often occurred at the same location, suggesting the cuticle as a sensitive area for osmoregulation. Our results suggest the use of cuticular and muscle autofluorescence as new biomarkers of stress detectable in formalin-preserved P. marinus individuals. Our label-free method can be easily applied to a large number of other copepod species or invertebrates with striated musculature.

Structural and physiological muscle changes after post-stroke hemiplegia: A systematic review

Corticospinal tract damage is responsible for motor function impairment after stroke. However, many processes seem to induce muscle damage, which may limit rehabilitation achievement. To achieve a systematic literature review of human muscular modifications due to post-strike hemiplegia. This review considers structural (histological, biochemical) and physiological modifications and their functional consequences over 1 year after stroke. Literature search on PubMed , Embase and Cochrane databases for papers published before February 2016 combining the following keywords cerebral stroke, hemiplegic, atrophy, muscle structure, paresis, skeletal muscle fiber type, motor unit, oxidative stress, strength, motor control led to select forty articles. Literature reports atrophy (20–25%), fatty replacement (17–30,6%), and decrease in fibers size and type (43% of type I fibers) as well as capillary density (38%) in spastic-paretic muscle. Enzymatic activity reduction was observed (decrease in citrate synthase and 3-hydroxyacyl-coenzymeA-deshydrogenase concentrations). A physiological reduction in the motor unit number estimate occurs very early (starting from 4 h post-stoke). At a chronic stage, an increase of motor unit firing rate and motor unit activity at “rest” were reported. These global changes have an additional effect on motor command impairments and increase the motor deficiency, even at a chronic stage. The initial dysfunction of motor command in post-stroke hemiplegia induces structural and physiological muscular changes. These changes are hardly reversible, and plead for an improvement in muscular training in these patients.

The Differential Hormonal Milieu of Morning versus Evening May Have an Impact on Muscle Hypertrophic Potential.

Substantial gains in muscle strength and hypertrophy are clearly associated with the routine performance of resistance training. What is less evident is the optimal timing of the resistance training stimulus to elicit these significant functional and structural skeletal muscle changes. Therefore, this investigation determined the impact of a single bout of resistance training performed either in the morning or evening upon acute anabolic signalling (insulin-like growth factor-binding protein-3 (IGFBP-3), myogenic index and differentiation) and catabolic processes (cortisol). Twenty-four male participants (age 21.4±1.9yrs, mass 83.7±13.7kg) with no sustained resistance training experience were allocated to a resistance exercise group (REP). Sixteen of the 24 participants were randomly selected to perform an additional non-exercising control group (CP) protocol. REP performed two bouts of resistance exercise (80% 1RM) in the morning (AM: 0800 hrs) and evening (PM: 1800 hrs), with the sessions separated by a minimum of 72 hours. Venous blood was collected immediately prior to, and 5 min after, each resistance exercise and control sessions. Serum cortisol and IGFBP-3 levels, myogenic index, myotube width, were determined at each sampling period. All data are reported as mean ± SEM, statistical significance was set at P≤0.05. As expected a significant reduction in evening cortisol concentration was observed at pre (AM: 98.4±10.5, PM: 49.8±4.4 ng/ml, P<0.001) and post (AM: 98.0±9.0, PM: 52.7±6.0 ng/ml, P<0.001) exercise. Interestingly, individual cortisol differences pre vs post exercise indicate a time-of-day effect (AM difference: -2±2.6%, PM difference: 14.0±6.7%, P = 0.03). A time-of-day related elevation in serum IGFBP-3 (AM: 3274.9 ± 345.2, PM: 3605.1 ± 367.5, p = 0.032) was also evident. Pre exercise myogenic index (AM: 8.0±0.6%, PM: 16.8±1.1%) and myotube width (AM: 48.0±3.0, PM: 71.6±1.9 μm) were significantly elevated (P<0.001) in the evening. Post exercise myogenic index was greater AM (11.5±1.6%) compared with PM (4.6±0.9%). No difference was observed in myotube width (AM: 48.5±1.5, PM: 47.8±1.8 μm) (P>0.05). Timing of resistance training regimen in the evening appears to augment some markers of hypertrophic potential, with elevated IGFBP-3, suppressed cortisol and a superior cellular environment. Further investigation, to further elucidate the time course of peak anabolic signalling in morning vs evening training conditions, are timely.