EMG coherence of foot and ankle muscles increases with a postural challenge in men.

BACKGROUND: The functional role of intrinsic foot muscles in the control of standing balance is often overlooked in rehabilitation, partly because the interactions with ankle muscles are poorly understood. RESEARCH QUESTION: How does coactivation of Flexor Digitorum Brevis (FDB) and soleus (SOL) vary across standing tasks of increasing difficulty. METHODS: Postural sway (Centre of Pressure, CoP) and the electromyographic (EMG) activity of FDB, SOL, Medial Gastrocnemius (MG) and Tibialis Anterior (TA) were measured during bipedal standing, tandem stance, one-legged balance, and standing on toes. Coherence of the rectified EMG signals for SOL and FDB in two bandwidths (0-5 and 10-20 Hz) was calculated as a coactivation index. RESULTS AND SIGNIFICANCE: The CoP sway and the EMG activity of all muscles was greater (P<0.05) for the three difficult tasks. Significant coherence between the SOL and FDB EMG activity was found in both frequency regions: 0-5 and 10-20 Hz. The coherence integral increased with the difficulty of the postural task, especially in the 10-20 Hz band. The findings underscore the important role of FDB in the control of standing balance across tasks and its coactivation with SOL. Clinical recommendations to improve balance control need to consider the interaction between the plantar flexor and intrinsic-foot muscles.

С60 fullerene protective effect against the rat muscle soleus trauma.

Muscle trauma is one of the most common body injuries. Severe consequences of muscle trauma are ischemic injuries of the extremities. It is known that the intensification of free radical processes takes place in almost most acute diseases and conditions, including muscle trauma. C60 fullerene (C60) with powerful antioxidant properties can be considered a potential nanoagent for developing an effective therapy for skeletal muscle trauma. Here the water-soluble C60 was prepared and its structural organization has been studied by the atomic force microscopy and dynamic light scattering techniques. The selective biomechanical parameters of muscle soleus contraction and biochemical indicators of blood in rats were evaluated after intramuscular injection of C60 1 h before the muscle trauma initiation. Analysis of the force muscle response after C60 injection (1 mg kg-1 dose) showed its protective effect against ischemia and mechanical injury at the level of 30 ± 2 % and 17 ± 1 %, accordingly, relative to the pathology group. Analysis of biomechanical parameters that are responsible for correcting precise positioning confirmed the effectiveness of C60 at a level of more than 50 ± 3 % relative to the pathology group. Moreover, a decrease in the biochemical indicators of blood by about 33 ± 2 % and 10 ± 1 % in ischemia and mechanical injury, correspondingly, relative to the pathology group occurs. The results obtained demonstrate the ability of C60 to correct the functional activity of damaged skeletal muscle.

Acute and Long-Term Effects of Stretching with Whole-Body Vibration on Young's Modulus of the Soleus Muscle Measured Using Shear Wave Elastography.

The effect of whole-body vibration (WBV) stretching on soleus (SOL) muscle stiffness remains unclear. Therefore, we aimed to investigate the acute and long-term effects of stretching with WBV on SOL muscle stiffness. This study employed a repeated-measures experimental design evaluating 20 healthy young males. SOL muscle stretching with WBV was performed for 5 min per day (1 min per set, five sets) over 4 weeks, for 4 days a week. Participants stretched the SOL muscle with ankle dorsiflexion in a loaded flexed knee position on a WBV device. Data were obtained to examine acute effects before stretching, immediately after stretching, and at 5, 10, 15, and 20 min. Moreover, data were obtained to examine the long-term effects before stretching, immediately after the completion of the 4-week stretching program, and at 2 and 4 weeks later. SOL muscle stiffness was measured using Young's modulus with shear wave elastography. The acute effect of SOL muscle stretching with WBV persisted for up to 20 min. Additionally, the long-term effect of stretching was better maintained than the acute effect, which was effective for up to 4 weeks (p < 0.001). Clinically, continuous stretching with WBV may be used to improve SOL muscle stiffness in rehabilitation programs.

Identification of porcine fast/slow myogenic exosomes and their regulatory effects on lipid accumulation in intramuscular adipocytes.

BACKGROUND: Pork quality is affected by the type of muscle fibers, which is closely related to meat color, tenderness and juiciness. Exosomes are tiny vesicles with a diameter of approximately 30-150 nm that are secreted by cells and taken up by recipient cells to mediate communication. Exosome-mediated muscle-fat tissue crosstalk is a newly discovered mechanism that may have an important effect on intramuscular fat deposition and with that on meat quality. Various of adipose tissue-derived exosomes have been discovered and identified, but the identification and function of muscle exosomes, especially porcine fast/slow myotube exosomes, remain unclear. Here, we first isolated and identified exosomes secreted from porcine extensor digitorum longus (EDL) and soleus (SOL), which represent fast and slow muscle, respectively, and further explored their effects on lipid accumulation in longissimus dorsi adipocytes. RESULTS: Porcine SOL-derived exosomes (SOL-EXO) and EDL-derived exosomes (EDL-EXO) were first identified and their average particle sizes were approximately 84 nm with double-membrane disc- shapes as observed via transmission electron microscopy and scanning electron microscopy. Moreover, the intramuscular fat content of the SOL was greater than that of the EDL at 180 days of age, because SOL intramuscular adipocytes had a stronger lipid-accumulating capacity than those of the EDL. Raman spectral analysis revealed that SOL-EXO protein content was much greater than that of EDL-EXO. Proteomic sequencing identified 72 proteins that were significantly differentially expressed between SOL-EXO and EDL-EXO, 31 of which were downregulated and 41 of which were upregulated in SOL-EXO. CONCLUSIONS: Our findings suggest that muscle-fat tissue interactions occur partly via SOL-EXO promoting adipogenic activity of intramuscular adipocytes.

Resveratrol impinges on retrograde communication without inducing mitochondrial biogenesis in aged rat soleus muscle.

The natural polyphenol resveratrol (RSV) might counteract the skeletal muscle age-related loss of muscle mass and strength/function partly acting on mitochondria. This work analysed the effects of a six-week administration of RSV (50 mg/kg/day) in the oxidative Soleus (Sol) skeletal muscle of old rats (27 months old). RSV effects on key mitochondrial biogenesis proteins led to un unchanged amount of SIRT1 protein and a marked decrease (60 %) in PGC-1α protein. In addition, Peroxyredoxin 3 (PRXIII) protein decreased by 50 %, which on overall suggested the absence of induction of mitochondrial biogenesis by RSV in old Sol. A novel direct correlation between PGC-1α and PRXIII proteins was demonstrated by correlation analysis in RSV and ad-libitum (AL) rats, supporting the reciprocally coordinated expression of the proteins. RSV supplementation led to an unexpected 50 % increase in the frequency of the oxidized base OH8dG in mtDNA. Furthermore, RSV supplementation induced a 50 % increase in the DRP1 protein of mitochondrial dynamics. In both rat groups an inverse correlation between PGC-1α and the frequency of OH8dG as well as an inverse correlation between PRXIII and the frequency of OH8dG were also found, suggestive of a relationship between oxidative damage to mtDNA and mitochondrial biogenesis activity. Such results may indicate that the antioxidant activity of RSV in aged Sol impinged on the oxidative fiber-specific, ROS-mediated, retrograde communication, thereby affecting the expression of SIRT1, PGC-1α and PRXIII, reducing the compensatory responses to the age-related mitochondrial oxidative stress and decline.

Influence of the Menstrual Cycle and Training on the Performance of a Perturbed Single-Leg Squatting Task in Female Collegiate Athletes.

Background: Anterior cruciate ligament (ACL) injuries often occur when an athlete experiences an unexpected disruption, or perturbation, during sports. ACL injury rates may also be influenced by the menstrual cycle. Purpose: To determine whether training adaptations to knee control and muscle activity during a perturbed single-leg squatting (SLS) task depend on menstrual cycle phase in female athletes. Study Design: Controlled laboratory study. Methods: A total of 21 healthy female collegiate athletes (current or former [<3 years]) who competed in 9 different sports performed an SLS task in which they attempted to match their knee position (user signal) to a target signal. The protocol consisted of a 9-condition pretest, 5 sets of 3 training trials, and a 9-condition posttest. One perturbation was delivered in each condition by altering the resistance of the device. Sagittal knee control (absolute error between the target signal and user signal) was assessed using a potentiometer. Muscle activity during perturbed squat cycles was normalized to maximal activation and to corresponding muscle activity during unperturbed squat cycles (%unperturbed) within the same test condition. Athletes performed the protocol during a distinct menstrual cycle phase (early follicular [EF], late follicular [LF], midluteal [ML]). Two-way mixed analysis of variance was used to determine the effects of the menstrual cycle and training on knee control and muscle activity during task performance. Venous blood was collected for hormonal analysis, and a series of health questionnaires and anthropometric measures were also assessed to determine differences among the menstrual cycle groups. Results: After training, athletes demonstrated better knee control during the perturbed squat cycles (lower absolute error, P < .001) and greater soleus feedback responses to the perturbation (%unperturbed, P = .035). Better knee control was demonstrated in the ML phase versus the EF phase during unperturbed and perturbed squat cycles (P < .039 for both). Quadriceps activation was greater in the ML phase compared with the EF and LF phases, both immediately before and after the perturbation (P < .001 for all). Conclusion: Athletes learned to improve knee control during the perturbed performance regardless of menstrual cycle phase. The best knee control and greatest quadriceps activation during the perturbed squatting task was found in the ML phase. Clinical Relevance: These findings may correspond to a lower incidence of ACL injury in the luteal phase and alterations in exercise performance across the menstrual cycle.

Antagonist Activation Measurement in Triceps Surae Using High-Density and Bipolar Surface EMG in Chronic Hemiparesis.

After a stroke, antagonist muscle activation during agonist command impedes movement. This study compared measurements of antagonist muscle activation using surface bipolar EMG in the gastrocnemius medialis (GM) and high-density (HD) EMG in the GM and soleus (SO) during isometric submaximal and maximal dorsiflexion efforts, with knee flexed and extended, in 12 subjects with chronic hemiparesis. The coefficients of antagonist activation (CAN) of GM and SO were calculated according to the ratio of the RMS amplitude during dorsiflexion effort to the maximal agonist effort for the same muscle. Bipolar CAN (BipCAN) was compared to CAN from channel-specific (CsCAN) and overall (OvCAN) normalizations of HD-EMG. The location of the CAN centroid was explored in GM, and CAN was compared between the medial and lateral portions of SO. Between-EMG system differences in GM were observed in maximal efforts only, between BipCAN and CsCAN with lower values in BipCAN (p < 0.001), and between BipCAN and OvCAN with lower values in OvCAN (p < 0.05). The CAN centroid is located mid-height and medially in GM, while the CAN was similar in medial and lateral SO. In chronic hemiparesis, the estimates of GM hyperactivity differ between bipolar and HD-EMGs, with channel-specific and overall normalizations yielding, respectively, higher and lower CAN values than bipolar EMG. HD-EMG would be the way to develop personalized rehabilitation programs based on individual antagonist activations.

Transcriptomics reveals transient and dynamic muscle fibrosis and atrophy differences following spinal cord injury in rats.

BACKGROUND: The rate and magnitude of skeletal muscle wasting after severe spinal cord injury (SCI) exceeds most other disuse conditions. Assessing the time course of molecular changes can provide insight into the progression of muscle wasting post-SCI. The goals of this study were (1) to identify potential targets that may prevent the pathologic features of SCI in soleus muscles and (2) to establish therapeutic windows for treating these pathologic changes. METHODS: Four-month-old Sprague-Dawley male rats received T9 laminectomy (SHAM surgery) or severe contusion SCI. Hindlimb locomotor function was assessed weekly, with soleus muscles obtained 1 week, 2 weeks, 1 month and 3 months post-surgery (n = 6-7 per group per timepoint). RNA was extracted from muscles for bulk RNA-sequencing analysis (n = 3-5 per group per timepoint). Differentially expressed genes (DEGs) were evaluated between age-matched SHAM and SCI animals. Myofiber size, muscle fibre type and fibrosis were assessed on contralateral muscles. RESULTS: SCI produced immediate and persistent hindlimb paralysis, with Basso-Beattie-Bresnahan locomotor scores remaining below 7 throughout the study, contributing to a progressive 25-50% lower soleus mass and myofiber atrophy versus SHAM (P < 0.05 at all timepoints). Transcriptional comparisons of SCI versus SHAM resulted in 184 DEGs (1 week), 436 DEGs (2 weeks), 133 DEGs (1 month) and 1200 DEGs (3 months). Upregulated atrophy-related genes included those associated with cell senescence, nuclear factor kappa B, ubiquitin proteasome and unfolded protein response pathways, along with upregulated genes that negatively influence muscle growth through the transforming growth factor beta pathway and inhibition of insulin-like growth factor-I/Akt/mechanistic target of rapamycin and p38/mitogen-activated protein kinase signalling. Genes associated with extracellular matrix (ECM), including collagens, collagen crosslinkers, proteoglycans and those regulating ECM integrity, were enriched within upregulated DEGs at 1 week but subsequently downregulated at 2 weeks and 3 months and were accompanied by >50% higher ECM areas and hydroxyproline levels in SCI muscles (P < 0.05). Myofiber remodelling genes were enriched in upregulated DEGs at 2 weeks and 1 month and were downregulated at 3 months. Genes that regulate neuromuscular junction remodelling were evident in muscles post-SCI, along with slow-to-fast fibre-type shifts: 1 week and 2 weeks SCI muscles were composed of 90% myosin heavy chain (MHC) type I fibres, which decreased to only 16% at 3 months and were accompanied by 50% fibres containing MHC IIX (P < 0.05). Metabolism genes were enriched in upregulated DEGs at 1 month and were further enriched at 3 months. CONCLUSIONS: Our results substantiate many known pathologic features of SCI-induced wasting in rat skeletal muscle and identify a progressive and dynamic transcriptional landscape within the post-SCI soleus. Future studies are warranted to consider these therapeutic treatment windows when countering SCI muscle pathology.

Effect of repetitive peripheral magnetic stimulation of the common fibular nerve on the soleus muscle Hoffmann reflex.

[Purpose] This study aimed to investigate the effects of repetitive peripheral magnetic stimulation of the common fibular nerve on the modification of neural circuit function as measured through the soleus muscle Hoffmann reflex. [Participants and Methods] Twenty-four healthy adult males were randomly and equally divided into the magnetic stimulation (experimental) and control groups. The Hoffmann reflex of the soleus muscle was analyzed before and after 10 min of repetitive peripheral magnetic stimulation for the experimental group and before and after 10 min of rest for the control group. The averages of the values for the maximum amplitude and latency of the Hoffman reflex across twenty repetitions were recorded and compared. [Results] The Hoffmann reflex amplitude decreased following stimulation in the experimental group, and significant variations were observed between the experimental and control groups. [Conclusion] The change in the Hoffmann reflex amplitude may have been caused by the magnetic stimulation to I-a sensory fibers on the common fibular nerve, suggesting that magnetic stimulation induces reciprocal inhibition of motor neurons through synapses in the spinal cord.

Local or regional flaps in developing country: Experience from Eastern Bhutan.

Soft tissue reconstruction plays an integral part in orthopaedic surgery. For developing country like Bhutan, where no micro-surgical or plastic surgeons are available, orthopaedic surgeons perform the local or regional flaps for the soft tissue defects. In this paper, we describe the use of different kinds of local and regional flaps and its outcome at Eastern Regional Referral Hospital, Bhutan.

Physical Therapy Intervention Effects on Alteration of Spinal Excitability in Patients With Chronic Ankle Instability: A Systematic Review and Meta-analysis.

CONTEXT: Chronic ankle instability (CAI) is a common injury in athletes. Different forms of physical therapy have been applied to the population with CAI to assess their impact on spinal excitability. OBJECTIVE: The purpose of this systematic review and meta-analysis was to investigate the effectiveness of various physical therapy interventions on the alteration of spinal excitability in patients with CAI. DATA SOURCES: Four databases (EMBASE, MEDLINE, Cochrane CENTRAL, and Scopus) were searched from inception to November 2022. STUDY SELECTION: A total of 253 studies were obtained and screened; 11 studies on the effects of physical therapy intervention on the alteration of spinal excitability in patients with CAI were identified for meta-analysis. STUDY DESIGN: Systematic review and meta-analysis. LEVEL OF EVIDENCE: Level 3a. DATA EXTRACTION: A total of 11 studies that included the maximal Hoffmann reflex normalized by the maximal muscle response (H/M ratio) in the peroneus longus and soleus muscles were extracted and summarized. The quality of the studies was assessed using the PEDro scale. RESULTS: The extracted studies had an average PEDro score of 4.7 ± 1.4, indicating that most of them had fair-to-good quality. The physical therapy interventions included cryotherapy, taping, mobilization, proprioceptive training, and dry needling. The overall effects showed that the H/M ratios of the peroneus longus (P = 0.44, I2 = 0%) and soleus (P = 0.56,I2 = 22%) muscles were not changed by physical therapy in patients with CAI. CONCLUSION: The meta-analysis indicated that physical therapy interventions such as cryotherapy, taping, mobilization, proprioceptive training, and dry needling do not alter the spinal excitability in patients with CAI. Given that only 1 study reported ineffective changes in spinal excitability with dry needling, more research is essential to establish and validate its efficacy. PROSPERO REGISTRATION: CRD42022372998.

Soleus Muscle H-reflex: Reference Data of Adult Population From a Tertiary Care Center in India.

Introduction The Hoffmann reflex (H reflex) is one of the most studied reflexes in human neurophysiological literature. Detection of the H reflex is useful in the diagnosis of early polyneuropathy, S1 radiculopathy, early GBS, tibial neuropathy and sciatica, and sacral plexopathy. The H reflex is also used as a tool to measure the excitability of the nervous components of the arc, regardless of the sensitivity of the sensory organs. The monosynaptic nature of reflex circuits makes H-reflex an attractive tool for clinical neurophysiology and research. Objective The objective is to create reference data of soleus H-reflex latency in an adult population from a tertiary care center in India. Materials and methods Seven hundred eighty-four healthy volunteers underwent a physical examination and brief electrophysiological examination before elicitation of the soleus H reflex of both lower extremities using standard techniques. Reference values ​​are expressed as mean ± standard deviation as well as the third and 97th percentiles for latency as the dependent variable. Results The study population included 346 (44.1%) women and 438 (55.9%) men. The men were aged 40.46 ± 14.76 years, and the women were aged 41.63 ± 13.49 years. The average weight of the men was 73.32 ± 10.28 kilograms, and the women were 62.91 ± 7.46 kilograms. The average height of the men was 172.06 ± 4.22 cm, and the women were 159.12 ± 2.42 cm. The third and 97th percentiles for H-reflex latency on the right side were 22.86 ms to 34.22 ms and on the left side were 22.86 ms to 35.39 ms. The average right tibial H latency and left tibial H latency were 28.18 ± 2.59 ms and 28.14 ± 2.70 ms, respectively. Conclusion A sizable subject population was used to provide reference data for this study. Because of the huge sample size and nearly appropriate coverage of different age groups, reference ranges have been established for various age, height, and BMI groups.

Gastrocnemius recession: Discrepancies in the literature.

A gastrocnemius contracture is a common problem that results in decreased ankle dorsiflexion that contributes to an array of foot and ankle ailments. A common surgical treatment for this condition is a gastrocnemius recession (GR). Many adaptations of the original procedure have been described. Misinterpretations of proper GR procedures have potentially caused confusion when selecting a treatment. This paper proposes to identify errors between the use of GR and gastrocnemius-soleus recession (GSR) procedure techniques in the current literature. A systematic literature review was performed in June 2021, using the PubMed database and select orthopedic texts. Only studies that met the established criteria and either correctly or incorrectly described a GR or GSR procedure were included. After applying exclusion criteria, 108 publications were included. These articles and texts were reviewed for surgical technique and terminology errors in accordance with established parameters. The articles were classified as either: "Correct" or "Incorrect." Of the 108 publications and texts included, 18 articles incorrectly described either a GR or a GSR (16.67%). Ninety articles correctly described either a GR or a GSR (83.33%). The literature supports the use of a GR to treat a gastrocnemius contracture. Inaccurate articles create confusion as to what exactly a GR entails. Sources of ambiguity included terminology, inconsistent anatomical zone definition, and technique selection. Due to this confusion, it is suspected that patient outcomes can be impacted. Postoperative outcomes of GSR patients are worse than GR patients. Further investigation is necessary to determine if performing the incorrect procedure negatively affects patient outcomes.

Effectiveness of instrument assisted soft tissue mobilization versus foam rolling on trigger point release in calf muscles.

BACKGROUND: Instrument assisted soft tissue mobilization and foam rolling are two techniques that have been proven effective in treating Myofascial Trigger Points, irrespective of the type of trigger point. However, little is known about the comparative effectiveness of Instrument assisted soft tissue mobilization and foam rolling. This study proposed to evaluate the effectiveness of either technique on plantar flexors trigger points, ankle dorsiflexion, and lower limb power present in the calf muscles in non-symptomatic patients. METHOD: Forty-two subjects with bilateral calf muscle tightness, at least one trigger point in the calf muscle, and fulfilling the inclusion criteria were randomly assigned to either of the groups. Group A was treated for gastrocnemius and soleus trigger points using Instrument assisted soft tissue mobilization and Group B was treated using the Foam Rolling method. Treatment was given every alternate day, a total of 3 sessions. Subjects were evaluated on 1st and 3rd sessions for pre-post differences of ankle dorsiflexion Range of motion in weight bearing and non-weight bearing position, pressure pain threshold for gastrocnemius trigger point 1(G1), 2(G2), and soleus point 1(S1) on both sides, and lower limb power. RESULT: Within group analyses, both groups had shown statistically significant results for all parameters except gastrocnemius trigger point 2 of foam rolling. For between group comparison foam rolling had a statistically significant result in non-weight bearing ankle dorsiflexion range of motion. CONCLUSION: Both Instrument assisted soft tissue mobilization and Foam rolling were equally effective for treating calf trigger points. But foam rolling was more effective in improving ankle dorsiflexion range of motion.

Assessment and modelling of the activation-dependent shift in optimal length of the human soleus muscle in vivo.

Previous in vitro and in situ studies have reported a shift in optimal muscle fibre length for force generation (L0) towards longer length at decreasing activation levels (also referred to as length-dependent activation), yet the relevance for in vivo human muscle contractions with a variable activation pattern remains largely unclear. By a combination of dynamometry, ultrasound and electromyography (EMG), we experimentally obtained muscle force-fascicle length curves of the human soleus at 100%, 60% and 30% EMGmax levels from 15 participants aiming to investigate activation-dependent shifts in L0 in vivo. The results showed a significant increase in L0 of 6.5 ± 6.0% from 100% to 60% EMGmax and of 9.1 ± 7.2% from 100% to 30% EMGmax (both P < 0.001), respectively, providing evidence of a moderate in vivo activation dependence of the soleus force-length relationship. Based on the experimental results, an approximation model of an activation-dependent force-length relationship was defined for each individual separately and for the collective data of all participants, both with sufficiently high accuracy (R2 of 0.899 ± 0.056 and R2 = 0.858). This individual approximation approach and the general approximation model outcome are freely accessible and may be used to integrate activation-dependent shifts in L0 in experimental and musculoskeletal modelling studies to improve muscle force predictions. KEY POINTS: The phenomenon of the activation-dependent shift in optimal muscle fibre length for force generation (length-dependent activation) is poorly understood for human muscle in vivo dynamic contractions. We experimentally observed a moderate shift in optimal fascicle length towards longer length at decreasing electromyographic activity levels for the human soleus muscle in vivo. Based on the experimental results, we developed a freely accessible approximation model that allows the consideration of activation-dependent shifts in optimal length in future experimental and musculoskeletal modelling studies to improve muscle force predictions.

Fatty infiltration of gastrocnemius-soleus muscle complex: Considerations for myosteatosis rehabilitation.

Although previous studies have reported fatty infiltration of the gastrocnemius-soleus complex, little is known about the volumetric distribution and patterns of fatty infiltration. The purpose of this anatomical study was to document and quantify the frequency, distribution, and pattern of fatty infiltration of the gastrocnemius-soleus complex. One hundred formalin-embalmed specimens (mean age 78.1 ± 12.3 years; 48F/52M) were serially dissected to document the frequency, distribution, and pattern of fatty infiltration in the medial and lateral heads of gastrocnemius and soleus muscles. Fatty infiltration was found in 23% of specimens, 13 unilaterally (8F/5M) and 10 (5M/5F) bilaterally. The fatty infiltration process was observed to begin medially from the medial aspect of the medial head of gastrocnemius and medial margin of soleus and then progressed laterally throughout the medial head of gastrocnemius and the marginal, anterior, and posterior soleus. The lateral head of gastrocnemius remained primarily muscular in all specimens. Microscopically, the pattern of infiltration was demonstrated as intramuscular with intact aponeuroses, and septa. The remaining endo-, peri-, and epimysium preserved the overall contour of the gastrocnemius-soleus complex, even in cases of significant fatty replacement. Since the external contour of the calf is preserved, the presence of fatty infiltration may be underdiagnosed in the clinic without imaging. Myosteatosis is associated with gait and balance challenges in the elderly, which can impact quality of life and result in increased risk of falling. The findings of the study have implications in the rehabilitation management of elderly patients with sarcopenia and myosteatosis.

Soleus H-reflex amplitude modulation during walking remains physiological during transspinal stimulation in humans.

The soleus H-reflex modulation pattern was investigated during stepping following transspinal stimulation over the thoracolumbar region at 15, 30, and 50 Hz with 10 kHz carry-over frequency above and below the paresthesia threshold. The soleus H-reflex was elicited by posterior tibial nerve stimulation with a single 1 ms pulse at an intensity that the M-wave amplitudes ranged from 0 to 15% of the maximal M-wave evoked 80 ms after the test stimulus, and the soleus H-reflex was half the size of the maximal H-reflex evoked on the ascending portion of the recruitment curve. During treadmill walking, the soleus H-reflex was elicited every 2 or 3 steps, and stimuli were randomly dispersed across the step cycle which was divided in 16 equal bins. For each subject and condition, the soleus M-wave and H-reflex were normalized to the maximal M-wave. The soleus background electromyographic (EMG) activity was estimated as the linear envelope for 50 ms duration starting at 100 ms before posterior tibial nerve stimulation for each bin. The gain was determined as the slope of the relationship between the soleus H-reflex and the soleus background EMG activity. The soleus H-reflex phase-dependent amplitude modulation remained unaltered during transspinal stimulation, regardless frequency, or intensity. Similarly, the H-reflex slope and intercept remained the same for all transspinal stimulation conditions tested. Locomotor EMG activity was increased in knee extensor muscles during transspinal stimulation at 30 and 50 Hz throughout the step cycle while no effects were observed in flexor muscles. These findings suggest that transspinal stimulation above and below the paresthesia threshold at 15, 30, and 50 Hz does not block or impair spinal integration of proprioceptive inputs and increases activity of thigh muscles that affect both hip and knee joint movement. Transspinal stimulation may serve as a neurorecovery strategy to augment standing or walking ability in upper motoneuron lesions.

Neuromuscular Electrical Stimulation Does Not Influence Spinal Excitability in Multiple Sclerosis Patients.

(1) Background: Neuromuscular electrical stimulation (NMES) has beneficial effects on physical functions in Multiple sclerosis (MS) patients. However, the neurophysiological mechanisms underlying these functional improvements are still unclear. This study aims at comparing acute responses in spinal excitability, as measured by soleus Hoffmann reflex (H-reflex), between MS patients and healthy individuals, under three experimental conditions involving the ankle planta flexor muscles: (1) passive NMES (pNMES); (2) NMES superimposed onto isometric voluntary contraction (NMES+); and (3) isometric voluntary contraction (ISO). (2) Methods: In total, 20 MS patients (MS) and 20 healthy individuals as the control group (CG) took part in a single experimental session. Under each condition, participants performed 15 repetitions of 6 s at 20% of maximal voluntary isometric contraction, with 6 s of recovery between repetitions. Before and after each condition, H-reflex amplitudes were recorded. (3) Results: In MS, H-reflex amplitude did not change under any experimental condition (ISO: p = 0.506; pNMES: p = 0.068; NMES+: p = 0.126). In CG, H-reflex amplitude significantly increased under NMES+ (p = 0.01), decreased under pNMES (p < 0.000) and was unaltered under ISO (p = 0.829). (4) Conclusions: The different H-reflex responses between MS and CG might reflect a reduced ability of MS patients in modulating spinal excitability.

The effects of residual dipolar coupling on carnosine in proton muscle spectra.

Carnosine, an MR-visible dipeptide in human muscle, is well characterized by two peaks at ~8 and ~7 ppm from C2 and C4 imidazole protons. Like creatine and other metabolites, carnosine is subject to residual dipolar coupling in the anisotropic environment of muscle fibers, but the effects have not been studied extensively. Single-voxel TE 30-32 PRESS spectra from three different 3T studies were acquired from gastrocnemius medialis and soleus muscles in the human lower leg. In these studies, carnosine T2 values were measured, and spectra were obtained at three different foot angles. LCModel was used to fit the carnosine peaks with a basis set that was generated using shaped RF pulses and included a range of dipolar couplings affecting the C4 peak. A seven-parameter analytic expression was used to fit the CH2 doublets of creatine. It incorporated an optimized "effective TE" value to model the effect of shaped RF pulses. The fits confirm that the triplet C4 peak of carnosine is dipolar coupled to a pair of CH2 protons, with no need to include a contribution from a separate pool of freely rotating uncoupled carnosine. Moreover, the couplings experienced by carnosine C4 protons and creatine CH2 protons are strongly correlated (R2 = 0.88, P<0.001), exhibiting a similar 3cos2 θ - 1 dependence on the angle θ between fiber orientation and B0. T2 values for the singlet C2 peak of gastrocnemius carnosine are inversely proportional to the C4 dipolar coupling strength (R2 = 0.97, P < 0.001), which in turn is a function of foot orientation. This dependence indicates that careful positioning of the foot while acquiring lower leg muscle spectra is important to obtain reproducible carnosine concentrations. As proton magnetic resonance spectroscopy of carnosine is currently used to non-invasively estimate the muscle fiber typology, these results have important implications in sport science.

Comparison of acute responses in spinal excitability between older and young people after neuromuscular electrical stimulation.

PURPOSE: This study aims at comparing acute responses in spinal excitability, as measured by H-reflex, between older and young individuals, following a single session of NMES superimposed onto voluntary isometric contractions of the ankle plantar-flexor muscles (NMES+), with respect to passive NMES (pNMES) and voluntary isometric contractions only (ISO). METHODS: Thirty-two volunteers, 16 older (OLDER) and 16 young (YOUNG), were asked to sustain a constant force at 20% of maximal voluntary isometric contraction (MVIC) of the ankle plantar-flexor muscles in the dominant limb during each of the 3 conditions (NMES+ , pNMES and ISO). Fifteen repetitions of 6 s were performed, with a resting interval of 6 s between repetitions. Before and after each condition, soleus H-reflexes were elicited by percutaneous electrical stimulation of the posterior tibial nerve and H-reflex amplitudes recorded by surface EMG. RESULTS: In OLDER, H-reflex amplitude did not change following any experimental condition (ISO: p = 0.203; pNMES: p = 0.542; NMES+: p = 0.431) compared to baseline. On the contrary, in YOUNG, H-reflex amplitudes significantly increased (p < 0.000) and decreased (p = 0.001) following NMES+ and pNMES, respectively, while there was no significant change in reflex responses following ISO (p = 0.772). CONCLUSION: The lack of change in H-reflex responses following either NMES+ or pNMES might reflect a reduced ability of older people in modulating spinal excitability after the conditions. Specifically, an age-related alteration in controlling mechanisms at presynaptic level was suggested.