Force re-development after shortening reveals a role for titin in stretch-shortening performance enhancement in skinned muscle fibres.

Stretch-shortening cycles (SSCs) involve muscle lengthening (eccentric contractions) instantly followed by shortening (concentric contractions). This combination enhances force, work, and power output compared to pure shortening (SHO), which is known as SSC-effect. Recent evidence indicates both cross-bridge-based (XB) and non-cross-bridge-based (non-XB, e.g., titin) structures contribute to this effect. This study analyzed force re-development following SSCs and SHO to gain further insight into the roles of XB and non-XB structures regarding the SSC-effect. Experiments were conducted on rat soleus muscle fibres (n=16) with different SSC velocities (30%, 60%, 85% of maximum shortening velocity) and constant stretch-shortening magnitudes (18% of optimum length). The XB inhibitor blebbistatin was used to distinguish between XB and non-XB contributions to force generation. Results showed SSCs led to significantly greater (1.02±.15 vs. 0.68±.09 [ΔF/Δt]; t(62)=8.61, p<.001, d=2.79) and faster (75 ms vs. 205 [ms]; t(62) = -6.37, p<.001, d=-1.48) force re-development compared to SHO in the control treatment. In the blebbistatin treatment, SSCs still resulted in greater (.11±.03 vs. .06±.01 [ΔF/Δt]; t(62) = 8.00, p<.001, d=2.24) and faster (3010±1631 vs. 7916±3230 [ms]; t(62) = -8.00, p<.001, d=-1.92) force re-development compared to SHO. These findings deepen our understanding of the SSC-effect, underscoring the involvement of non-XB structures like titin in modulating force production. This modulation likely involves complex mechanosensory coupling from stretch to signal transmission during muscle contraction.

Exploring neuronal mechanisms of osteosarcopenia in older adults.

Until recently, research on the pathogenesis and treatment of osteoporosis and sarcopenia has primarily focused on local and systemic humoral mechanisms, often overlooking neuronal mechanisms. However, there is a growing body of literature on the neuronal regulation of bone and skeletal muscle structure and function, which may provide insights into the pathogenesis of osteosarcopenia. This review aims to integrate these neuronal regulatory mechanisms to form a comprehensive understanding and inspire future research that could uncover novel strategies for preventing and treating osteosarcopenia. Specifically, the review explores the functional adaptation of weight-bearing bone to mechanical loading throughout evolutionary development, from Wolff's law and Frost's mechanostat theory to the mosaic hypothesis, which emphasizes neuronal regulation. The recently introduced bone osteoregulation reflex points to the importance of the osteocytic mechanoreceptive network as a receptor in this neuronal regulation mechanism. Finally, the review focuses on the bone myoregulation reflex, which is known as a mechanism by which bone loading regulates muscle functions neuronally. Considering the ageing-related regressive changes in the nerve fibres that provide both structural and functional regulation in bone and skeletal muscle tissue and the bone and muscle tissues they innervate, it is suggested that neuronal mechanisms might play a central role in explaining osteosarcopenia in older adults.

MyotonPRO as a new valid tool for measuring cervical muscle tension. A reliability study.

OBJECTIVE: The main objective of this study is to test the reliability of a non-invasive objective method for the measurement of biomechanical parameters of cervicofacial muscle groups, with the purpose of diagnosis and evaluation of voice disorders' treatments, especially focused on muscle tension dysphonia. STUDY DESIGN: Prospective study. METHODS: The device used is a handheld myotonometer (MyotonPRO) that measures biomechanical and viscoelastic properties in superficial soft tissues frequency, stiffness, elasticity, relaxation time and creep. It is used in the field of medicine, sport and research. This pilot study includes 10 subjects, who have been measured in the masseter, sternocleidomastoid, orbicularis oris, semispinalis capitis, suprahyoid, infrahyoid and trapezius muscles on each side. Measurements were performed by 2 evaluators to assess inter-evaluator reliability. Subsequently, one of them repeated the measurements to assess intra-evaluator reliability. RESULTS: The results revealed good to excellent inter-rater reliability for the masseter, sternocleidomastoid, trapezius and suprahyoid muscles, with lower ICCs for the stiffness and creep properties. Intra-rater reliability was good to excellent for the masseter, sternocleidomastoid, semispinalis capitis and suprahyoid muscles. The lowest ICCs were found in the stiffness and creep properties. CONCLUSION: The use of a myotonometer to measure the mechanical properties of selected cervical and orofacial muscles is a reliable and reproducible method. Future research is needed to establish an association between the properties of these muscles and their role in voice disorders, as well as to determine whether this tool can aid diagnosis with quantifiable and objectifiable indicators, and for monitoring and treatment efficacy.

Acute effects of voluntary isometric contractions at maximal shortening vs. ballistic stretching on flexibility, strength and jump.

Background: Isometric training is used in sport, conventional physical activity and rehabilitation. Understandably, there is a great deal of research related to its effect on performance. It is known that the length of the muscle at the moment of contraction is a determinant of strength levels. In the literature we find research on isometric training in short muscle lengths, although it has not been studied in maximally shortened positions or the acute effects that occur after its application. Ballistic stretching (BS) is also popular in sport. Their execution involves actively reaching maximally shortened muscle positions. So far, isometric training has not been compared with protocols involving ballistic stretching. Considering the above, the aim of the present study was to investigate the effects of BS and voluntary isometric contraction at maximal shortening (VICAMS) on range of motion, strength and vertical jump. Methods: The study involved 60 healthy, physically active individuals (40 and 52 years old) who were randomly assigned to three groups: BS, VICAMS and a control group (CG). To assess acute effects, before and after the intervention, active range of motion (AROM), maximal voluntary isometric force (MVIF) and countermovement jump height (CMJ) were determined. Results: Time main effects and time*group interactions were found for all variables (p < 0.001). Between-group differences were shown for the VICAMS group after the intervention, with statistically significant higher AROM values compared to the other groups. MVIF values were also higher in the VICAMS group. Intra-group differences were observed for the VICAMS and Ballistic groups, as values on all variables increased from baseline. For the CMJ, intra-group differences showed that both the VICAMS and BS groups improved values compared to baseline values. Conclusions: The application of VICAMS induced acute improvements over BS in AROM, MVIF and CMJ. These results are important for coaches seeking immediate performance improvement and offer an optimal solution to the warm-up protocol.

MRI of a presumptive intracranial histiocytic sarcoma with extracranial extension in a cat.

Case summary: A 4-year-old female neutered Scottish Fold shorthair cat was presented for further investigation of circling towards the right. MRI of the brain revealed an extensive, right-sided temporal muscle lesion with associated frontotemporal bone osteolysis, intracranial, extra-axial extension along the calvarial convexity with severe pachy- and leptomeningeal thickening and contrast enhancement, and an intra-axial space-occupying lesion in the right piriform lobe. The regional lymph nodes were moderately enlarged. Cytology of the right parotid lymph node and the temporal muscle was performed and histiocytic sarcoma (HS) was diagnosed. The owners elected euthanasia. Relevance and novel information: HS of the central nervous system (CNS) is a very rare neoplastic condition in cats. Although a few case reports mention MRI, to our knowledge, the characterisation of MRI features of feline CNS HS have not been investigated in detail. Therefore, the aim of this case report was to describe the MRI characteristics in a feline HS involving not only the CNS, but also the fronto-temporal bone, temporal muscle and the regional lymph nodes. In particular, aggressive neoplastic bone invasion was a novel finding.

Gastroesophageal Junction Adenocarcinoma With Skeletal Muscle Metastases: A Case Report and Literature Review.

Esophageal and gastroesophageal junction (GEJ) malignancies are aggressive, and survival is poor once metastasis occurs. The most common sites of metastatic involvement include the liver, lymph nodes, lung, peritoneum, adrenal glands, bone, and brain, while skeletal muscle (SM) involvement is rare. We report a case of a 68-year-old female who presented with intractable emesis for one month and was found to have a primary GEJ adenocarcinoma measuring up to 6.7 cm. Endoscopic biopsy revealed poorly differentiated GEJ adenocarcinoma with positive AE1/AE3 immunostains. Positron emission tomography/computed tomography and magnetic resonance imaging revealed metastases to the omentum and left lower extremity SMs, including the proximal adductor longus, adductor magnus, and gluteus minimus. This study reviews the literature on SM metastasis in esophageal and GEJ cancer, GEJ cancer classification, incidence, treatment, and prognosis.

A red flag: an experimental analysis of the function of pink colouration in males of Calopteryx haemorrhoidalis asturica (Odonata: Calopterygidae).

Males display phenotypic characteristics that may be associated with their quality, allowing non-random mating and post-copulatory female choice. In the damselfly Calopteryx haemorrhoidalis asturica, males have a conspicuous pink colouration in the underside of abdominal segments 8-10, which they exhibit during pre- and post-copulatory courtship. We hypothesized that this colouration functions to increase male mating success and/or to elicit females to oviposit. We estimated mating and oviposition success of 27 males, and on the following day, treated males had their segments 8-10 painted black and control males the seventh segment. We recorded the number of male-male fights and courtships, whether the courtship ended in copulation, and whether the female remained in the territory and laid eggs. Our results indicate that the mating success of male C. h. asturica was not significantly affected by the removal of the pink colouration of the abdominal tip, but this colouration clearly affected their success in enticing females to oviposit. Courtship frequency, fat content and muscle mass were positively correlated to male mating rate, and the number of aggressive encounters was negatively correlated. Our study yields experimental evidence for the function of pink colouration of male C. h. asturica, in the context of post-copulatory sexual selection.

Relation between soft tissue energy dissipation and leg stiffness in running at different step frequencies.

This study aims to investigate the relationship between soft tissue energy dissipation and leg stiffness during running. Eight recreational healthy male runners (age: 22.2 ± 1.0 years; height: 1.84 ± 0.03 m; mass: 73.7 ± 5.7 kg) were asked to run at different speeds and step frequencies. Their soft tissue energy dissipation was estimated by the difference between the total mechanical work of the body, measured as the work done to move the body centre of mass relative to the surroundings plus the work to move the limbs relative to the body centre of mass, and lower-limb joint work. A mass-spring model with an actuator was used to analyse the force-length curve of the bouncing mechanism of running. In this way, the stiffness and damping coefficient were assessed at each speed and step frequency. Pearson's correlations were used to describe the relationship between the deviation from the spring-mass model and soft tissue energy fluctuations. The soft tissue dissipation was found to be significantly influenced by step frequency, with both positive and negative work phases decreasing when step frequency increases. Moreover, deviation from a spring-mass model was positively associated with the amount of soft tissue dissipation (r > 0.6). The findings emphasize the substantial role of soft tissues in dissipating or returning energy during running, behaving in a damped-elastic manner. Also, we introduce a novel approach for evaluating the elastic rebound of the body during running. The insights gained may have broad implications for assessing running mechanics, with potential applications in various contexts.

Plant-derived leaf vein scaffolds for the sustainable production of dog cell-cultured meat.

Animal cell culture technology in the production of slaughter-free meat offers ethical advantages with regards to animal welfare, rendering it a more socially acceptable approach for dog meat production. In this study, edible plant-derived scaffold was used as a platform for cell expansion to construct cell-cultured dog meat slices. Primary dog skeletal muscle satellite cells (MSCs) and adipose stem cells (ASCs) were isolated and cultured as seed cells, and 3D spheroid culture in vitro promoted MSCs and ASCs myogenic and adipogenic differentiation, respectively. Natural leaf veins (NLV) were produced as edible mesh scaffolds to create 3D engineered dog muscle and fat tissues. After MSCs and ASCs adhered, proliferated and differentiated on the NLV scaffolds, and muscle and fat slices were produced with cultured dog muscle fibers and adipocytes, respectively. These findings demonstrate the potential of plant-derived NLV scaffolds in the production of cultured dog meat.

The Effect of Yoga Practice on Labor Pain: A Systematic Review and Meta-Analysis.

Background: Labor pain management is a critical aspect of midwifery care and an essential purpose of childbirth-related care. There is a need for comprehensive results on relevant non-therapeutic methods of reducing labor pain. This systematic review and meta-analysis study was conducted to investigate the effect of yoga practice on labor pain. Material and Methods: We performed a systematic literature search from SCOPUS, PubMed, Web of Science, and Science Direct for relevant studies from January 1, 1990 to June 2, 2022. We selected published quasi-randomized and randomized controlled trial studies that evaluated the effect of yoga practice on labor pain. Quality research was applied. We pooled the Standardized Mean Dfference (SMD) of labor pain in pregnant women with and without yoga practice during pregnancy using a random-effects model at 95% Confidence Intervals (CIs). Results: Nine studies including 660 women were included in the meta-analysis. Pregnant women in the yoga practice group experienced statistically significantly low labor pain at the beginning of the active phase compared to the control group (SMD: -1.10, 95% CI: -1.61, -0.58, p < 0.001; I2 = 89%). Yoga interventions also reduced the intensity of labor pain in active (SMD: -1.32, 95% CI: -2.03, -0.60, p < 0.001; I2 = 92%) and transition (SMD: -1.93, 95% CI: -2.87, -0.99, p < 0.001; I2 = 92%) phases compared to the control group, respectively. Conclusions: The results of the study showed that yoga practice during pregnancy reduces the intensity of labor pain in different labor phases. However, these findings should be considered cautiously due to the substantial heterogeneity between studies.

Incidence of Lateral Femoral Cutaneous Nerve Dysfunction After Total Hip Arthroplasty Through the Anterior-Based Muscle-Sparing Surgical Approach.

Background: The anterior-based muscle-sparing (ABMS) approach, using the intramuscular interval between the tensor fascia lata and gluteus medius, is an increasingly popular total hip arthroplasty (THA) approach. Its incidence of lateral femoral cutaneous nerve (LFCN) numbness has not been defined. The incidence of LFCN symptoms in direct anterior THA ranges from 7%-32% at 1-year follow-up. The purpose of this study is to determine the incidence of LFCN symptoms in patients who underwent ABMS THA at 1-year follow-up. Methods: This was a single-center, multisurgeon retrospective study of ABMS THAs with minimum 1-year follow-up data between January 2014 and September 2021. Eight hundred sixty-nine THAs were included. Mean age of the patients was 67.2 years, with 43.4% male and 56.5% female. Mean body mass index was 26.8, and mean American Society of Anesthesiologists was 2.3. Statistical analysis included chi-square tests, 2-sample t-test, and binomial logistic regression. A P-value of .05 was considered statistically significant for all tests. Results: Nine patients (1%) reported LFCN-associated symptoms at 1-year follow-up. The most common complaint was numbness (n = 5, 55.6%), followed by diminished sensation (n = 2, 22.2%), burning (n = 1, 11.1%), and generalized pain (11.1%). There was no difference in age, sex, body mass index, or American Society of Anesthesiologists between the group that experienced symptoms and the group that did not (P = 1.00, P = .34, P = .74, P = .80). Conclusions: The incidence of LFCN dysfunction is 1% at 1 year after surgery with the ABMS approach. Additional studies may elucidate all risks and benefits of the ABMS approach with respect to LFCN injuries.

Dietary Patterns and Geriatric Syndromes in older Mexican adults: Analysis of the 2018-19 National Health and Nutrition Survey.

BACKGROUND: The study of dietary patterns in older adults (OA) and their association with geriatric syndromes (GS) is scarce in Latin America. OBJECTIVE: To describe the association of dietary patterns with GS in the Mexican older adult population, using data from the 2018-19 National Health and Nutrition Survey. METHODS: Dietary data were collected from 3,511 adults (≥60 years of age, both sexes) using a semi-quantitative food frequency questionnaire. Dietary patterns were derived by principal component analysis based on the consumption of 162 foods from 24 food groups. The GS studied were: frailty, depressive symptoms (DS), low appendicular skeletal muscle mass (ASMM); additionally, we studied inflammation (serum CRP>5 mg/L). Logistic regression models were used. RESULTS: Four major dietary patterns were identified: a) "Western", b) "Prudent", c) "Soups", and d) "Traditional". The middle and higher tertiles of the "Prudent" pattern were associated with lower odds of DS (OR 0.71, p = 0.04; and OR 0.61, p = 0.008), respectively. The second tertile of the "Soups" pattern was associated with lower odds of low ASMM (OR 0.68, p = 0031) and inflammation (OR 0.58, p = 0.022). The highest tertile of the "Traditional" pattern was associated with low ASMM (OR 1.55, p = 0.008) and lower odds of inflammation (OR 0.69, p = 0.044). No association was found between the "Western" dietary pattern and GS. CONCLUSIONS: Three of four major dietary patterns were associated with GS in older Mexican adults. Further studies are needed to address strategies to improve diet quality in this age group and its association with health and functional outcomes.

Achieving maximal voluntary contraction of paraspinal muscles requires two tasks: Insight from an EMG study of females with and without adolescent idiopathic scoliosis.

An accurate estimation of maximal voluntary muscle activation is critical for normalisation in scientific studies. Only a handful of studies appropriately normalise muscle activation data when investigating paraspinal muscle activity in populations such as adolescent idiopathic scoliosis (AIS). This neglect compromises the ability to interpret data. The aim of this study was to determine the type of trunk extension task that reliably achieves peak paraspinal muscle activation in participants with and without AIS. Adolescent females with typically developing spines (controls: n = 20, mean[SD] age 13.1[1.8]years), or primary right thoracic AIS (n = 24, age: 13.8[1.5]years, Cobb angle thoracic: 39.5[16.4]°, lumbar: 28.0[11.6]°) performed a series of 3x unresisted and 3x resisted maximal voluntary trunk extensions in prone. Paraspinal muscle activation was recorded bilaterally at two thoracic levels and one lumbar level using surface electromyography (EMG). Muscle activation was highly repeatable within task [ICC 0.77-0.95, all p < 0.01]. At group level, there were no differences in peak muscle activation between tasks irrespective of side (left/right) or vertebral level (Estimate 0.98, 95%CI 0.36 to 2.65, p=0.97). Peak activation was achieved with the unresisted task in 40.5%, and resisted task in 59.5% of the total outcomes (6 recording locations, 44 participants). Individual participant maximum amplitude varied up to 64% (mean[SD]:18[13]%) between the unresisted and resisted tasks. We recommend that both the resisted and unresisted trunk extension tasks are used to increase confidence that a maximum voluntary activation of paraspinal muscles is achieved. Failure to do so could introduce large error in the estimations of muscle activation.

In ovo betaine injection improves breast muscle growth in newly hatched goslings through FXR/IGF-2 pathway.

Betaine has been shown to enhance growth performance and increase breast muscle yield in ducks and broilers through various mechanisms, including the modification of DNA methylation. However, the impact of in ovo betaine injection on muscle growth in newly hatched goslings remains unclear. In this study, fifty eggs were injected with saline or betaine at 7.5 mg/egg prior to incubation, and the subsequent effects on breast muscle growth in the newly hatched goslings were investigated. Betaine significantly increased (P < 0.05) the hatch weight, breast muscle weight, and breast muscle index, accompanied by an augmentation in muscle bundle cross-sectional area. Concurrently, betaine significantly upregulated (P < 0.05) the expression levels of myogenic regulatory factors, including myogenin (MyoG) and paired box 7 (Pax7) both mRNA and protein, while downregulating (P < 0.05) the mRNA and protein levels of myostatin (MSTN). Histological analysis revealed a higher abundance of proliferating cell nuclear antigen (PCNA) and Pax7 immune-positive cells in the breast muscle of the betaine group, consistent with elevated PCNA and Pax7 mRNA and protein levels. Additionally, significantly increased (P < 0.05) contents of insulin-like growth factor 1 (IGF-1) and insulin-like growth factor 2 (IGF-2) were observed in the breast muscle of the betaine group, so was mRNA expression of IGF-1, IGF-2, and insulin-like growth factor 1 receptor (IGF-1R). Betaine also significantly in8creased (P < 0.05) global DNA methylation of the breast muscle, accompanied by enhanced mRNA and protein levels of methionine cycle and DNA methylation-related enzymes, Interestingly, the promoter regions of IGF-1, IGF-2, and IGF-1R genes were significantly hypomethylated (P < 0.05). Moreover, in ovo betaine injection significantly upregulated (P < 0.05) the protein level of farnesoid X receptor (FXR) in breast muscle and FXR binding to the promoter of IGF-2 gene. These findings suggest that in ovo betaine injection promotes breast muscle growth during embryonic development in goslings through the FXR-mediated IGF-2 pathway, ultimately improving hatch weight and breast muscle weight.

Low psoas muscle index has a negative impact on survival after minimal invasive esophagectomy for cancer in European men.

INTRODUCTION: Sarcopenia, a key component of frailty in cancer patients, is associated with complicated procedures and worse survival after esophageal resection. The psoas muscle index (PMI) has been implicated as a possible sarcopenia imaging marker. This retrospective study aims to elucidate the effect of PMI and BMI in a cohort in Europe after totally minimally invasive esophagectomy for cancer. METHODS: The study included 318 consecutive adult patients (261 men and 57 women) who underwent minimally invasive esophagectomy for cancer between January 2016 and April 2021 in a German University Hospital. The PMI was measured at the third lumbar vertebra in the preoperative CT scan. The endpoints postoperative complication rates and survival rates were analysed and correlated with PMI and BMI according to gender. RESULTS: Male patients with low PMI (< 5.3 cm2/ m2) had a significantly higher rate of postoperative pulmonary and cardiac complications (p = 0.016, respectively p = 0.018). Low PMI and low BMI (<25 kg/m2) were associated with decreased survival rates in the univariate (p < 0.001) and multivariate analysis in male patients (p = 0.024, respectively 0.004). Having a low PMI (< 5.3 cm2/ m2) was significantly associated with worse overall survival in normal and underweight men (p < 0.001), but not in obese men with a BMI ≥ 25kg/m2 (p = 0.476). CONCLUSION: Preoperative PMI and BMI are valid risk factors regarding postoperative survival after minimal invasive esophagectomy for cancer especially in a male European cohort.

Insulin sensitivity and insulin secretion in adults with Friedreich's Ataxia: the role of skeletal muscle.

INTRODUCTION: Friedreich's Ataxia (FRDA) is a multi-system disorder caused by frataxin deficiency. FRDA-related diabetes mellitus (DM) is common. Frataxin supports skeletal muscle mitochondrial oxidative phosphorylation (OXPHOS) capacity, a mediator of insulin sensitivity. Our objective was to test the association between skeletal muscle health and insulin sensitivity and secretion in adults with FRDA without DM. METHODS: Case-control study (NCT02920671). Glucose and insulin metabolism (stable-isotope oral glucose tolerance tests), body composition (dual-energy x-ray absorptiometry), physical activity (self-report), and skeletal muscle OXPHOS capacity (creatine chemical exchange saturation transfer MRI) were assessed. RESULTS: Participants included 11 individuals with FRDA (4 female), median age 27y (IQR 23, 39), BMI 26.9kg/m2 (24.1, 29.4), and 24 controls (11 female), 29y (26, 39), 24.4kg/m2 (21.8, 27.0). Fasting glucose was higher in FRDA (91 vs. 83mg/dL (5.0 vs. 4.6mmol/L), p<0.05). Individuals with FRDA had lower insulin sensitivity (WBISI 2.8 vs. 5.3, p<0.01), higher post-prandial insulin secretion (insulin secretory rate iAUC 30-180 minutes, 24,652 vs. 17,858, p<0.05), and more suppressed post-prandial endogenous glucose production (-0.9% vs. 26.9% of fasting EGP, p<0.05). In regression analyses, lower OXPHOS and inactivity explained some of the difference in insulin sensitivity. More visceral fat contributed to lower insulin sensitivity independent of FRDA. Insulin secretion accounting for sensitivity (disposition index) was not different. CONCLUSIONS: Lower mitochondrial OXPHOS capacity, inactivity, and visceral adiposity contribute to lower insulin sensitivity in FRDA. Higher insulin secretion appears compensatory, and when inadequate, could herald DM. Further studies are needed to determine if muscle- or adipose-focused interventions could delay FRDA-related DM.

Immediate effect of local vibration on motor unit firing behavior and muscle strength in healthy young adult males.

PURPOSE: The aim of this study was to examine the effect of vibration on motor unit (MU) firing behavior and physical performance of antagonist muscles in healthy young adult males. METHODS: Fourteen males (age = 24.3 ± 3.6 years) were included in this study. There were two conditions, one in which participants received 80 Hz vibration in the distal tendon of the hamstring for 30 s and the control condition (no vibration). High-density surface electromyography (HD-SEMG) signals and maximal voluntary contraction (MVC) of knee extensor muscles were evaluated before and after the respective conditions and recorded from the vastus lateralis muscle during submaximal ramp-up and sustained contractions at 30% MVC. Convolution blind source separation was used to decompose the HD-SEMG signals into individual MU firing behaviors. RESULTS: In total, 739 MUs were detected (control; 360 MUs and vibration; 379 MUs), and a total of 312 matched MUs were identified across both submaximal contraction conditions (control: 150 MUs; vibration: 162 MUs). Vibration significantly increased the discharge rate (p = 0.047) and decreased the recruitment threshold before and after intervention (p = 0.001) but not in the control condition. Furthermore, the recruitment threshold is a factor that influences discharge rate. Significant correlations were observed between the recruitment threshold and both the ∆ discharge rate and the ∆ recruitment threshold under the vibration condition (p < 0.001). CONCLUSION: Vibration increased in the discharge rate and decreased the recruitment threshold of the antagonist muscle. These findings suggested that vibration contributes to immediate changes in the neural control of antagonist muscles.

Sex differences in human performance.

Sex as a biological variable is an underappreciated aspect of biomedical research, with its importance emerging in more recent years. This review assesses the current understanding of sex differences in human physical performance. Males outperform females in many physical capacities because they are faster, stronger and more powerful, particularly after male puberty. This review highlights key sex differences in physiological and anatomical systems (generally conferred via sex steroids and puberty) that contribute to these sex differences in human physical performance. Specifically, we address the effects of the primary sex steroids that affect human physical development, discuss insight gained from an observational study of 'real-world data' and elite athletes, and highlight the key physiological mechanisms that contribute to sex differences in several aspects of physical performance. Physiological mechanisms discussed include those for the varying magnitude of the sex differences in performance involving: (1) absolute muscular strength and power; (2) fatigability of limb muscles as a measure of relative performance; and (3) maximal aerobic power and endurance. The profound sex-based differences in human performance involving strength, power, speed and endurance, and that are largely attributable to the direct and indirect effects of sex-steroid hormones, sex chromosomes and epigenetics, provide a scientific rationale and framework for policy decisions on sex-based categories in sports during puberty and adulthood. Finally, we highlight the sex bias and problem in human performance research of insufficient studies and information on females across many areas of biology and physiology, creating knowledge gaps and opportunities for high-impact studies.

Is there a relationship between knee crepitus with quadriceps muscle thickness and strength in individuals with patellofemoral pain? A cross-sectional study.

OBJECTIVE: To explore the relationship between knee crepitus, quadriceps muscle thickness and isometric strength in individuals with patellofemoral pain (PFP). DESIGN: Cross-sectional. PARTICIPANTS: Individuals with PFP. MAIN OUTCOME MEASURES: Participants with PFP underwent assessments for presence, frequency and severity of knee crepitus. Real-time ultrasound images of the quadriceps muscles (rectus femoris, vastus medialis and lateralis) at rest and during contraction were obtained, muscle thickness was measured in both conditions. Maximal voluntary isometric contraction tests were performed to measure knee extensor strength. The relationship between knee crepitus and quadriceps muscle thickness and knee extensor strength was explored using logistic and linear regressions. RESULTS: Sixty individuals with PFP were included (age: 24; 60% women; 38% with crepitus). Knee crepitus severity was related to rectus femoris and vastus medialis thickness during rest (R2 = 0.19 and 0.09, respectively) and contraction (R2 = 0.16 and 0.07, respectively) and with vastus lateralis during contraction (R2 = 0.08). Isometric knee extensor strength was not related to knee crepitus presence, frequency, or severity. CONCLUSION: Higher severity of knee crepitus is related to lower quadriceps muscle thickness in individuals with PFP. There is no relationship between the presence and frequency of knee crepitus with quadriceps muscle thickness or knee extensor strength.

Investigation on synergistic inhibition of protein-bound heterocyclic amines in sarcoplasmic and myofibrillar model systems by amino acid combinations.

The inhibition of amino acids on the formation of protein-bound HAs was assessed in both model systems and roast beef patties, and the synergism between these amino acids was also investigated. The amino acids can promote the formation of protein-bound HAs at low addition amount, and the total content of protein-bound HAs increased from 444.05 ± 4.98 ng/g of the control group to 517.36 ± 16.51 ng/g when 0.05 % cysteine was added. Amino acid combinations exhibited stable inhibitory effects, with the maximum inhibitory rate of 64 % in the treatment with histidine-proline combination (1:4). The synergistic inhibition may be caused by simultaneously scavenging intermediates and competing for the binding sites of muscle proteins, and the reaction with protein-bound HAs to form adduct can serve as supporting factors to co-mitigate the promotion in protein-bound HAs from increased protein solubility. These findings proposed the potential mitigation strategies against protein-bound HAs formation.