Understanding the variability of the electrophysiologic laryngeal adductor reflex.

OBJECTIVE: The laryngeal adductor reflex (LAR) is vital for airway protection and can be electrophysiologically obtained under intravenous general anesthesia (IGA). This makes the electrophysiologic LAR (eLAR) an important tool for monitoring of the vagus nerves and relevant brainstem circuitry during high-risk surgeries. We investigated the intra-class variability of normal and expected abnormal eLAR. METHODS: Repeated measures of contralateral R1 (cR1) were performed under IGA in 58 patients. Data on presence/absence of cR2 and potential confounders were also collected. Review of neuroimaging, pathology and clinical exam, allowed classification into normal and expected abnormal eLAR groups. Using univariate and multivariate analysis we studied the variability of cR1 parameters and their differences between the two groups. RESULTS: In both groups, cR1 latencies had coefficients of variation of <2%. In the abnormal group, cR1 had longer latencies, required higher activation currents and was more frequently desynchronized and unsustained; cR2 was more frequently absent. CONCLUSIONS: cR1 latencies show high analytical precision for measurements. Delayed onset, difficult to elicit, desynchronized and unsustained cR1, and absence of cR2 signal an abnormal eLAR. SIGNIFICANCE: Understanding the variability and behavior of normal and abnormal eLAR under IGA can aid in the interpretation of its changes during monitoring.

Assessing pulmonary function in ALS using electrical impedance tomography.

Objective: We sought to determine whether thoracic electrical impedance tomography (EIT) could characterize pulmonary function in amyotrophic lateral sclerosis (ALS) patients, including those with facial weakness. Thoracic EIT is a noninvasive, technology in which a multi-electrode belt is placed across the chest, producing real-time impedance imaging of the chest during breathing. Methods: We enrolled 32 ALS patients and 32 age- and sex-matched healthy controls (HCs) without underlying lung disease. All participants had EIT measurements performed simultaneously with standard pulmonary function tests (PFTs), including slow and forced vital capacity (SVC and FVC) in upright and supine positions and maximal inspiratory and expiratory pressures (MIPs and MEPs, respectively). Intraclass correlation coefficients (ICCs) were calculated to assess the immediate reproducibility of EIT measurements and Pearson's correlations were used to explore the relationships between EIT and PFT values. Results: Data from 30 ALS patients and 27 HCs were analyzed. Immediate upright SVC reproducibility was very high (ICC 0.98). Correlations were generally strongest between EIT and spirometry measures, with R values ranging from 0.64 to 0.82 (p < 0.001) in the ALS cohort. There were less robust correlations between EIT values and both MIPs and MEPs in the ALS patients, with R values ranging from 0.33 to 0.44. There was no significant difference for patients with and without facial weakness. There were no reported adverse events. Conclusion: EIT-based pulmonary measures hold the promise of providing an alternative approach for lung function assessment in ALS patients. Based on these early results, further development and study of this technology are warranted.

Rapid patient-specific FEM meshes from 3D smart-phone based scans.

Objective.The objective of this study was to describe and evaluate a smart-phone based method to rapidly generate subject-specific finite element method (FEM) meshes. More accurate FEM meshes should lead to more accurate thoracic electrical impedance tomography (EIT) images.Approach.The method was evaluated on an iPhone®that utilized an app called Heges, to obtain 3D scans (colored, surface triangulations), a custom belt, and custom open-source software developed to produce the subject-specific meshes. The approach was quantitatively validated via mannequin and volunteer tests using an infrared tracker as the gold standard, and qualitatively assessed in a series of tidal-breathing EIT images recorded from 9 subjects.Main results.The subject-specific meshes can be generated in as little as 6.3 min, which requires on average 3.4 min of user interaction. The mannequin tests yielded high levels of precision and accuracy at 3.2 ± 0.4 mm and 4.0 ± 0.3 mm root mean square error (RMSE), respectively. Errors on volunteers were only slightly larger (5.2 ± 2.1 mm RMSE precision and 7.7 ± 2.9 mm RMSE accuracy), illustrating the practical RMSE of the method.Significance.Easy-to-generate, subject-specific meshes could be utilized in the thoracic EIT community, potentially reducing geometric-based artifacts and improving the clinical utility of EIT.

Adaptation to full weight-bearing following disuse in rats: The impact of biological sex on musculoskeletal recovery.

With the technological advances made to expand space exploration, astronauts will spend extended amounts of time in space before returning to Earth. This situation of unloading and reloading influences human physiology, and readaptation to full weight-bearing may significantly impact astronauts' health. On Earth, similar situations can be observed in patients who are bedridden or suffer from sport-related injuries. However, our knowledge of male physiology far exceeds our knowledge of female's, which creates an important gap that needs to be addressed to understand the sex-based differences regarding musculoskeletal adaptation to unloading and reloading, necessary to preserve health of both sexes. Using a ground-based model of total unloading for 14 days and reloading at full weight-bearing for 7 days rats, we aimed to compare the musculoskeletal adaptations between males and females. Our results reveal the existence of significant differences. Indeed, males experienced bone loss both during the unloading and the reloading period while females did not. During simulated microgravity, males and females showed comparable muscle deconditioning with a significant decline in rear paw grip strength. However, after 7 days of recovery, muscle strength improved. Additionally, sex-based differences in myofiber size existing at baseline are significantly reduced or eliminated following unloading and recovery.

Novel phenotype characterization utilizing electrical impedance myography signatures in murine spinal cord injury neurogenic bladder models.

Neurogenic bladder (NB) affects people of all ages. Electric impedance myography (EIM) assesses localized muscle abnormalities. Here, we sought to investigate whether unique detrusor EIM signatures are present in NB due to spinal cord injury (SCI). Twenty-eight, 8-10 weeks old, C57BL/6J female mice were studied. Twenty underwent spinal cord transection; 8 served as controls. Cohorts were euthanized at 4 and 6 weeks after spinal cord transection. Each bladder was measured in-situ with EIM with applied frequencies of 1 kHz to 10 MHz, and then processed for molecular and histologic study. SCI mice had greater bladder-to-body weight ratio (p < 0.0001), greater collagen deposition (p = 0.009), and greater smooth-muscle-myosin-heavy-chain isoform A/B ratio (p < 0.0001). Compared with the control group, the SCI group was associated with lower phase, reactance, and resistance values (p < 0.01). Significant correlations (p < 0.001) between bladder-to-body weight ratios and EIM measurements were observed across the entire frequency spectrum. A severely hypertrophied phenotype was characterized by even greater bladder-to-body weight ratios and more depressed EIM values. Our study demonstrated distinct EIM alterations in the detrusor muscle of mice with NB due to SCI. With further refinement, EIM may offer a potential point-of-care tool for the assessment of NB and its response to treatment.

Electrical impedance myography for the early detection of muscle ischemia secondary to compartment syndrome: a study in a rat model.

Acute Compartment Syndrome (ACS) is one of the most devastating orthopedic conditions, affecting any of the body's many compartments, which, if sufficiently severe, may result in disability and amputation. Currently, intra-compartmental pressure measurements serve as the gold standard for diagnosing ACS. Diagnosing limbs at risk for ACS before irreversible damage to muscle and nerve is critical. Standard approaches for diagnosing impending compartment syndrome include clinical evaluation of the limb, such as assessment for "tightness" of the overlying skin, reduced pulses distally, and degree of pain, none of which are specific or sensitive. We have proposed a novel method to detect ACS via electrical impedance myography (EIM), where a weak, high-frequency alternating current is passed between one pair of electrodes through a region of tissue, and the resulting surface voltages are measured via a second pair. We evaluated the ability of EIM to detect early muscle ischemia in an established murine model of compression-induced muscle injury, where we collected resistance, reactance, and their dimensionless product, defined as Relative Injury Index (RII) during the study. Our model generated reproducible hypoxia, confirmed by Hypoxyprobe™ staining of endothelial regions within the muscle. Under conditions of ischemia, we demonstrated a reproducible, stable, and significant escalation in resistance, reactance, and RII values, compared to uninjured control limbs. These data make a reasonable argument for additional investigations into using EIM for the early recognition of muscle hypoperfusion and ischemia. However, these findings must be considered preliminary steps, requiring further pre-clinical and clinical validation.

Combining electromyographic and electrical impedance data sets through machine learning: A study in D2-mdx and wild-type mice.

INTRODUCTION/AIMS: Needle impedance-electromyography (iEMG) assesses the active and passive electrical properties of muscles concurrently by using a novel needle with six electrodes, two for EMG and four for electrical impedance myography (EIM). Here, we assessed an approach for combining multifrequency EMG and EIM data via machine learning (ML) to discriminate D2-mdx muscular dystrophy and wild-type (WT) mouse skeletal muscle. METHODS: iEMG data were obtained from quadriceps of D2-mdx mice, a muscular dystrophy model, and WT animals. EIM data were collected with the animals under deep anesthesia and EMG data collected under light anesthesia, allowing for limited spontaneous movement. Fourier transformation was performed on the EMG data to provide power spectra that were sampled across the frequency range using three different approaches. Random forest-based, nested ML was applied to the EIM and EMG data sets separately and then together to assess healthy versus disease category classification using a nested cross-validation procedure. RESULTS: Data from 20 D2-mdx and 20 WT limbs were analyzed. EIM data fared better than EMG data in differentiating healthy from disease mice with 93.1% versus 75.6% accuracy, respectively. Combining EIM and EMG data sets yielded similar performance as EIM data alone with 92.2% accuracy. DISCUSSION: We have demonstrated an ML-based approach for combining EIM and EMG data obtained with an iEMG needle. While EIM-EMG in combination fared no better than EIM alone with this data set, the approach used here demonstrates a novel method of combining the two techniques to characterize the full electrical properties of skeletal muscle.

Surface Electrical Impedance Myography Detects Skeletal Muscle Atrophy in Aged Wildtype Zebrafish and Aged gpr27 Knockout Zebrafish.

Throughout a vertebrate organism's lifespan, skeletal muscle mass and function progressively decline. This age-related condition is termed sarcopenia. In humans, sarcopenia is associated with risk of falling, cardiovascular disease, and all-cause mortality. As the world population ages, projected to reach 2 billion older adults worldwide in 2050, the economic burden on the healthcare system is also projected to increase considerably. Currently, there are no pharmacological treatments for sarcopenia, and given the long-term nature of aging studies, high-throughput chemical screens are impractical in mammalian models. Zebrafish is a promising, up-and-coming vertebrate model in the field of sarcopenia that could fill this gap. Here, we developed a surface electrical impedance myography (sEIM) platform to assess skeletal muscle health, quantitatively and noninvasively, in adult zebrafish (young, aged, and genetic mutant animals). In aged zebrafish (~85% lifespan) as compared to young zebrafish (~20% lifespan), sEIM parameters (2 kHz phase angle, 2 kHz reactance, and 2 kHz resistance) robustly detected muscle atrophy (p < 0.000001, q = 0.000002; p = 0.000004, q = 0.000006; p = 0.000867, q = 0.000683, respectively). Moreover, these same measurements exhibited strong correlations with an established morphometric parameter of muscle atrophy (myofiber cross-sectional area), as determined by histological-based morphometric analysis (r = 0.831, p = 2 × 10-12; r = 0.6959, p = 2 × 10-8; and r = 0.7220; p = 4 × 10-9, respectively). Finally, the genetic deletion of gpr27, an orphan G-protein coupled receptor (GPCR), exacerbated the atrophy of skeletal muscle in aged animals, as evidenced by both sEIM and histology. In conclusion, the data here show that surface EIM techniques can effectively discriminate between healthy young and sarcopenic aged muscle as well as the advanced atrophied muscle in the gpr27 KO animals. Moreover, these studies show how EIM values correlate with cell size across the animals, making it potentially possible to utilize sEIM as a "virtual biopsy" in zebrafish to noninvasively assess myofiber atrophy, a valuable measure for muscle and gerontology research.

A scoping review of current and emerging techniques for evaluation of peripheral nerve health, degeneration, and regeneration: part 1, neurophysiology.

Peripheral neuroregeneration research and therapeutic options are expanding exponentially. With this expansion comes an increasing need to reliably evaluate and quantify nerve health. Valid and responsive measures that can serve as biomarkers of the nerve status are essential for both clinical and research purposes for diagnosis, longitudinal follow-up, and monitoring the impact of any intervention. Furthermore, such biomarkers can elucidate regeneration mechanisms and open new avenues for research. Without these measures, clinical decision-making falls short, and research becomes more costly, time-consuming, and sometimes infeasible. As a companion to Part 2, which is focused on non-invasive imaging, Part 1 of this two-part scoping review systematically identifies and critically examines many current and emerging neurophysiological techniques that have the potential to evaluate peripheral nerve health, particularly from the perspective of regenerative therapies and research.

Electrical impedance myography method of measuring anisotropic tongue tissue.

Objective.To date, measurement of the conductivity and relative permittivity properties of anisotropic biological tissues using electrical impedance myography (EIM) has only been possible through an invasiveex vivobiopsy procedure. Here, we present a novel forward and inverse theoretical modeling framework to estimate these properties combining surface and needle EIM measurements.Methods. The framework here presented models the electrical potential distribution within a monodomain, homogeneous, and three-dimensional anisotropic tissue. Finite-element method (FEM) simulations and tongue experimental results verify the validity of our method to reverse-engineer three-dimensional conductivity and relative permittivity properties from EIM measurements.Results. FEM-based simulations confirm the validity of our analytical framework, with relative errors between analytical predictions and simulations smaller than 0.12% and 2.6% in a cuboid and tongue model, respectively. Experimental results confirm qualitative differences in the conductivity and the relative permittivity properties in thex,y, andzdirections.Conclusion. Our methodology enables EIM technology to reverse-engineer the anisotropic tongue tissue conductivity and relative permittivity properties, thus unfolding full forward and inverse EIM predictability capabilities.Significance. This new method of evaluating anisotropic tongue tissue will lead to a deeper understanding of the role of biology necessary for the development of new EIM tools and approaches for tongue health measurement and monitoring.

Electrical impedance myography detects age-related skeletal muscle atrophy in adult zebrafish.

Age-related deficits in skeletal muscle function, termed sarcopenia, are due to loss of muscle mass and changes in the intrinsic mechanisms underlying contraction. Sarcopenia is associated with falls, functional decline, and mortality. Electrical impedance myography (EIM)-a minimally invasive, rapid electrophysiological tool-can be applied to animals and humans to monitor muscle health, thereby serving as a biomarker in both preclinical and clinical studies. EIM has been successfully employed in several species; however, the application of EIM to the assessment of zebrafish-a model organism amenable to high-throughput experimentation-has not been reported. Here, we demonstrated differences in EIM measures between the skeletal muscles of young (6 months of age) and aged (33 months of age) zebrafish. For example, EIM phase angle and reactance at 2 kHz showed significantly decreased phase angle (5.3 ± 2.1 versus 10.7 ± 1.5°; p = 0.001) and reactance (89.0 ± 3.9 versus 172.2 ± 54.8 ohms; p = 0.007) in aged versus young animals. Total muscle area, in addition to other morphometric features, was also strongly correlated to EIM 2 kHz phase angle across both groups (r = 0.7133, p = 0.01). Moreover, there was a strong correlation between 2 kHz phase angle and established metrics of zebrafish swimming performance, including turn angle, angular velocity, and lateral motion (r = 0.7253, r = 0.7308, r = 0.7857, respectively, p < 0.01 for all). In addition, the technique was shown to have high reproducibility between repeated measurements with a mean percentage difference of 5.34 ± 1.17% for phase angle. These relationships were also confirmed in a separate replication cohort. Together, these findings establish EIM as a fast, sensitive method for quantifying zebrafish muscle function and quality. Moreover, identifying the abnormalities in the bioelectrical properties of sarcopenic zebrafish provides new opportunities to evaluate potential therapeutics for age-related neuromuscular disorders and to interrogate the disease mechanisms of muscle degeneration.

Influence of gonadectomy on muscle health in micro- and partial-gravity environments in rats.

Gonadal hormones, such as testosterone and estradiol, modulate muscle size and strength in males and females. However, the influence of sex hormones on muscle strength in micro- and partial-gravity environments (e.g., the Moon or Mars) is not fully understood. The purpose of this study was to determine the influence of gonadectomy (castration/ovariectomy) on progression of muscle atrophy in both micro- and partial-gravity environments in male and female rats. Male and female Fischer rats (n = 120) underwent castration/ovariectomy (CAST/OVX) or sham surgery (SHAM) at 11 wk of age. After 2 wk of recovery, rats were exposed to hindlimb unloading (0 g), partial weight bearing at 40% of normal loading (0.4 g, Martian gravity), or normal loading (1.0 g) for 28 days. In males, CAST did not exacerbate body weight loss or other metrics of musculoskeletal health. In females, OVX animals tended to have greater body weight loss and greater gastrocnemius loss. Within 7 days of exposure to either microgravity or partial gravity, females had detectable changes to estrous cycle, with greater time spent in low-estradiol phases diestrus and metestrus (∼47% in 1 g vs. 58% in 0 g and 72% in 0.4 g animals, P = 0.005). We conclude that in males testosterone deficiency at the initiation of unloading has little effect on the trajectory of muscle loss. In females, initial low estradiol status may result in greater musculoskeletal losses.NEW & NOTEWORTHY We find that removal of gonadal hormones does not exacerbate muscle loss in males or females during exposure to either simulated microgravity or partial-gravity environments. However, simulated micro- and partial gravity did affect females' estrous cycles, with more time spent in low-estrogen phases. Our findings provide important data on the influence of gonadal hormones on the trajectory of muscle loss during unloading and will help inform NASA for future crewed missions to space and other planets.

Anorexia nervosa and muscle health: A systematic review of our current understanding and future recommendations for study.

OBJECTIVE: Conduct a systematic review on muscle size and strength in individuals with anorexia nervosa (AN). METHOD: In accordance with PRISMA guidelines, we searched Pubmed for articles published between 1995 and 2022 using a combination of search terms related to AN and muscle size, strength, or metabolism. After two authors screened articles and extracted data, 30 articles met inclusion criteria. Data were coded, and a risk bias was conducted for each study. RESULTS: The majority of studies focused on muscle size/lean mass (60%, n = 18) and energy expenditure (33%, n = 9), with few studies (17%, n = 5) investigating muscle function or possible mechanisms underlying muscle size (20%, n = 6). Studies supported that individuals with AN have smaller muscle size and reduced energy expenditure relative to controls. In some studies (33%, n = 10) recovery from AN was not sufficient to restore muscle mass or function. Mechanisms underlying short and long-term musculoskeletal alterations have not been thoroughly explored. DISCUSSION: Muscle mass and strength loss may be an unexplored component of physiological deterioration during and after AN. More research is necessary to understand intramuscular alterations during AN and interventions to facilitate muscle mass and functional gain following weight restoration in AN. PUBLIC SIGNIFICANCE: Muscle health is important for optimal health and is reduced in individuals with AN. However, we do not understand how muscle is altered at the cellular level throughout the course of AN. Here we review what is currently known regarding muscle health during AN and with weight restoration.

OBJETIVO: Realizar una revisión sistemática sobre el tamaño y la fuerza muscular en individuos que padecen anorexia nerviosa (AN). MÉTODO: De acuerdo con las guías PRISMA, se realizaron búsquedas en Pubmed de artículos publicados entre 1995 y 2022 mediante una combinación de términos de búsqueda relacionados con la anorexia nerviosa y el tamaño, la fuerza o el metabolismo muscular. Después de que dos autores examinaron los artículos y extrajeron los datos, 30 artículos cumplieron los criterios de inclusión. Se codificaron los datos y se realizó un sesgo de riesgo para cada estudio. RESULTADOS: La mayoría de los estudios se enfocaron en el tamaño muscular/masa magra (60%, n=18) y el gasto energético (33%, n=9), con pocos estudios (17%, n=5) investigando la función muscular o los posibles mecanismos subyacentes al tamaño muscular (20%, n=6). Los estudios apoyaron que los individuos que padecen anorexia nerviosa tienen un tamaño muscular más pequeño y un gasto de energía reducido en relación con los controles. En algunos estudios (33%, n = 10) la recuperación de la anorexia nerviosa no fue suficiente para restaurar la masa muscular o la función. Los mecanismos subyacentes a las alteraciones musculoesqueléticas a corto y largo plazo no se han explorado a fondo. DISCUSIÓN: La pérdida de masa muscular y fuerza puede ser un componente inexplorado del deterioro fisiológico durante y después de la AN. Se necesita más investigación para comprender las alteraciones intramusculares durante la anorexia nerviosa y las intervenciones para facilitar la masa muscular y la ganancia funcional después de la restauración del peso en la anorexia nerviosa.

A study of flex miniaturized coils for focal nerve magnetic stimulation.

BACKGROUND: Peripheral magnetic stimulation (PMS) is emerging as a complement to standard electrical stimulation (ES) of the peripheral nervous system (PNS). PMS may stimulate sensory and motor nerve fibers without the discomfort associated with the ES used for standard nerve conduction studies. The PMS coils are the same ones used in transcranial magnetic stimulation (TMS) and lack focality and selectiveness in the stimulation. PURPOSE: This study presents a novel coil for PMS, developed using Flexible technologies, and characterized by reduced dimensions for a precise and controlled targeting of peripheral nerves. METHODS: We performed hybrid electromagnetic (EM) and electrophysiological simulations to study the EM exposure induced by a novel miniaturized coil (or mcoil) in and around the radial nerve of the neuro-functionalized virtual human body model Yoon-Sun, and to estimate the current threshold to induce magnetic stimulation (MS) of the radial nerve. Eleven healthy subjects were studied with the mcoil, which consisted of two 15 mm diameter coils in a figure-of-eight configuration, each with a hundred turns of a 25 µm copper-clad four-layer foil. Sensory nerve action potentials (SNAPs) were measured in each subject using two electrodes and compared with those obtained from standard ES. The SNAPs conduction velocities were estimated as a performance metric. RESULTS: The induced electric field was estimated numerically to peak at a maximum intensity of 39 V/m underneath the mcoil fed by 70 A currents. In such conditions, the electrophysiological simulations suggested that the mcoil elicits SNAPs originating at 7 mm from the center of the mcoil. Furthermore, the numerically estimated latencies and waveforms agreed with those obtained during the PMS experiments on healthy subjects, confirming the ability of the mcoil to stimulate the radial nerve sensory fibers. CONCLUSION: Hybrid EM-electrophysiological simulations assisted the development of a miniaturized coil with a small diameter and a high number of turns using flexible electronics. The numerical dosimetric analysis predicted the threshold current amplitudes required for a suprathreshold peripheral nerve sensory stimulation, which was experimentally confirmed. The developed and now validated computational pipeline will be used to improve the performances (e.g., focality and minimal currents) of new generations of mcoil designs.

Electrical Impedance Myography Correlates with Functional Measures of Disease Progression in D2-mdx Mice and Boys with Duchenne Muscular Dystrophy.

BACKGROUND: Sensitive, objective, and longitudinal outcome measures applicable to both pre-clinical and clinical interventions are needed to assess muscle health in Duchenne muscular dystrophy (DMD). Electrical impedance myography (EIM) has the potential to non-invasively measure disease progression in mice and boys with DMD. OBJECTIVE: We sought to evaluate how electrical impedance values (i.e., phase, reactance, and resistance) correlate to established measures of disease in both D2-mdx and wild type (WT) mice and boys with and without DMD. METHODS: Histological, functional, and EIM data collected from previous studies of WT and D2-mdx mice at 6, 13, 21 and 43 weeks of age were reanalyzed. In parallel, previously collected functional outcome measures and EIM values were reanalyzed from boys with and without DMD at four different age groups from 2 to 14 years old. RESULTS: In mice, disease progression as detected by histological, functional, and EIM measures, was appreciable over this time period and grip strength best correlated to longitudinal phase and reactance impedance values. In boys, disease progression quantified through commonly utilized functional outcome measures was significant and longitudinal phase demonstrated the strongest correlation with functional outcome measures. CONCLUSION: Similar changes in EIM values, specifically in longitudinal reactance and phase, were found to show significant correlations to functional measures in both mice and boys. Thus, EIM demonstrates applicability in both pre-clinical and clinical settings and can be used as a safe, non-invasive, and longitudinal proxy biomarker to assess muscle health in DMD.

Sex differences in muscle health in simulated micro- and partial-gravity environments in rats.

Skeletal muscle size and strength are important for overall health for astronauts. However, how male and female muscle may respond differently to micro- and partial-gravity environments is not fully understood. The purpose of this study was to determine how biological sex and sex steroid hormones influence the progression of muscle atrophy after long term exposure to micro and partial gravity environments in male and female rats. Male and female Fisher rats (n â€‹= â€‹120) underwent either castration/ovariectomy or sham surgeries. After two weeks recovery, animals were divided into microgravity (0g), partial-gravity (40% of weight bearing, 0.4g), or full weight bearing (1g) interventions for 28 days. Measurements of muscle size and strength were evaluated prior to and after interventions. At 0g, females lost more dorsiflexion strength, plantar flexion strength, and other metrics of muscle size compared to males; castration/ovariectomy did not influence these differences. Additionally, at 0.4g, females lost more dorsiflexion strength, plantar flexion strength, and other metrics of muscle strength compared to males; castration/ovariectomy did not influence these differences. Females have greater musculoskeletal aberrations during exposure to both microgravity and partial-gravity environments; these differences are not dependent on the presence of sex steroid hormones. Correspondingly, additional interventions may be necessary to mitigate musculoskeletal loss in female astronauts to protect occupational and overall health.

Diminished muscle integrity in patients with fibrodysplasia ossificans progressiva assessed with at-home electrical impedance myography.

Fibrodysplasia ossificans progressiva (FOP) is an ultra-rare disorder involving skeletal dysplasia and heterotopic ossification (HO) of muscle and connective tissue. We aimed to define a novel biomarker in FOP that enables reliable assessment of musculoskeletal tissue integrity. Considering logistical difficulties that FOP patients often face, our goal was to identify an at-home biomarker technique. Electrical impedance myography (EIM) is a non-invasive, portable method that can inform on muscle health. 15 FOP patients (age 10-52) and 13 healthy controls were assessed. Using EIM, multiple muscle groups were characterized per participant in a 45-min period. The Cumulative Analogue Joint Involvement Scale (CAJIS) was implemented to determine mobility burden severity. We additionally evaluated physical activity levels via a Patient-Reported Outcomes Measurement Information System (PROMIS)-based questionnaire. Relative to controls, FOP patients demonstrated significantly lower regional and whole-body phase values at 50 kHz and 100 kHz, indicating more diseased muscle tissue. Lower whole-body phase and reactance values, and higher resistance values, were associated with greater FOP burden (CAJIS score range: 4-30) and lower physical activity levels at 50 kHz and 100 kHz. This study points to the potential utility of EIM as a clinical biomarker tool capable of characterizing muscle integrity in FOP.

Effect of Athletic Training on Fatigue During Neuromuscular Electrical Stimulation.

The purpose of this study was to explore the effect an individual's exercise training type will have on muscle fatigability during repetitive contractions induced by Neuromuscular Electrical Stimulation (NMES). Thirty-four subjects comprising of competitive athletes and controls were recruited into three cohorts: Endurance (runners/cyclists) n = 13; nine male, four female; 27 ± 8 years old, Explosive (Lifters/Sprinters) n = 11; nine male, two female; 30 ± 7 years old, and controls n = 10, six male, four female, 26 ± 4 years old. Subjects were placed in a custom-made leg extension rig, and received NMES against a fixed resistance (NMES-FR), to the Vastus Medialis muscle resulting in isometric leg extensions, at a duty cycle of 1 s on/3 s rest, for 20 min. The force of the isometric contractions was recorded using a Hogan MicroFet2 dynamometer, and three separate fatigue metrics were calculated to compare the different cohorts, sports within each cohort, and gender within each cohort. For every fatigue metric, the endurance group fatigued significantly less than both the explosive and control cohorts, with no difference observed between the explosive and the controls. Within each cohort, no significant difference was observed in any fatigue metric between sport or gender, but these comparisons lacked power. The results show that only high capacity endurance activity will have any effect on reducing one's fatigability during repetitive NMES. The implications of this conclusion can aid in the development of NMES regimens for use in healthy populations, such as athletic training or astronaut musculoskeletal countermeasures, as well as clinical applications when fatigue is to be minimized.