Factors influencing back strength and the changes due to age of the oraon agricultural labourers of jalpaiguri district, west bengal

Muscle strength is a major component of successful performance in almost every activity of daily living and it is critical to health and well-being. Anthropometric, blood pressure and strength measurements were taken from Oraon agricultural labourers of Jalpaiguri district of West Bengal. The data were analyzed to find out the differences between high and low back strength groups of both sexes in different traits of the parameters mentioned above. Secondly, identifying the peak age of muscle strength in both sex and the declining ages. Thirdly, the influencing factors which, affect the back strength. The results show that high back strength groups have higher mean values of most of the anthropometric traits compared to low back strength groups and the differences are significant in case of males, but females show significant differences in few traits. Blood pressures are relatively low in high back strength groups compared to low back strength groups in both sexes. The peak age for higher back strength seems to be within the age of 24 years for males and 20 years for females. The predictive variables for males were found to be grip strength and subscapular skinfold thickness, but females show grip strength, BMI, biceps girth, bicondylar diameter of humerus. The differences in influencing factors between males and females have been sorted out from sociocultural practice of the population.     

Age, sex, and grip strength determine architectural bone parameters assessed by peripheral quantitative computed tomography (pQCT) at the human radius

The purpose of this study was to estimate the relation of some noninvasively derived mechanical characteristics of radial bone including architectural parameters for bone strength to grip strength and muscle cross-section. Sixty-three males between 21 and 78yr of age and 101 females between 18 and 80yr of age were measured at the nondominant forearm using peripheral quantitative computed tomography (pQCT). We assessed the integral bone mineral density (BMD(I)) and content (BMC(I)) by pQCT at the distal and at the mid-shaft radius. Integral bone area (Area(I)), cortical thickness (C-th), and a newly proposed index for bone strength; the stress-strain index (SSI) were also calculated. The dynamometrically measured maximum grip strength was taken as a mechanical loading parameter and muscle cross-section as a substitute for it. Sex, grip strength, BMC(I) and BMD(I) (distal radius) were identified in a multiple regression analysis to significantly predict bone strength as expressed by SSI, after adjusting for all other independent variables, including age and sex (p<0.0001). Grip strength was closest related to age, sex, BMD(I) and SSI(p) of the distal radius. The cross-sectional area of muscle was not significantly determining the grip strength within the analysis model. In conclusion, our results suggested that architectural parameters at the distal radius were better related to grip strength than to cross-sectional muscle area in both males and females. Maximum muscle strength as estimated by grip strength might be a stronger determinant of mechanical characteristics of bones as compared with cross-sectional muscle area.     

Age and gender differences in physical capability levels from mid-life onwards: the harmonisation and meta-analysis of data from eight UK cohort studies

Using data from eight UK cohorts participating in the Healthy Ageing across the Life Course (HALCyon) research programme, with ages at physical capability assessment ranging from 50 to 90+ years, we harmonised data on objective measures of physical capability (i.e. grip strength, chair rising ability, walking speed, timed get up and go, and standing balance performance) and investigated the cross-sectional age and gender differences in these measures. Levels of physical capability were generally lower in study participants of older ages, and men performed better than women (for example, results from meta-analyses (N = 14,213 (5 studies)), found that men had 12.62 kg (11.34, 13.90) higher grip strength than women after adjustment for age and body size), although for walking speed, this gender difference was attenuated after adjustment for body size. There was also evidence that the gender difference in grip strength diminished with increasing age,whereas the gender difference in walking speed widened (p<0.01 for interactions between age and gender in both cases). This study highlights not only the presence of age and gender differences in objective measures of physical capability but provides a demonstration that harmonisation of data from several large cohort studies is possible. These harmonised data are now being used within HALCyon to understand the lifetime social and biological determinants of physical capability and its changes with age.     

Grip Strength across the Life Course: Normative Data from Twelve British Studies

Introduction

Epidemiological studies have shown that weaker grip strength in later life is associated with disability, morbidity, and mortality. Grip strength is a key component of the sarcopenia and frailty phenotypes and yet it is unclear how individual measurements should be interpreted. Our objective was to produce cross-sectional centile values for grip strength across the life course. A secondary objective was to examine the impact of different aspects of measurement protocol.

Methods

We combined 60,803 observations from 49,964 participants (26,687 female) of 12 general population studies in Great Britain. We produced centile curves for ages 4 to 90 and investigated the prevalence of weak grip, defined as strength at least 2.5 SDs below the gender-specific peak mean. We carried out a series of sensitivity analyses to assess the impact of dynamometer type and measurement position (seated or standing).

Results

Our results suggested three overall periods: an increase to peak in early adult life, maintenance through to midlife, and decline from midlife onwards. Males were on average stronger than females from adolescence onwards: males’ peak median grip was 51 kg between ages 29 and 39, compared to 31 kg in females between ages 26 and 42. Weak grip strength, defined as strength at least 2.5 SDs below the gender-specific peak mean, increased sharply with age, reaching a prevalence of 23% in males and 27% in females by age 80. Sensitivity analyses suggested our findings were robust to differences in dynamometer type and measurement position.

Conclusion

This is the first study to provide normative data for grip strength across the life course. These centile values have the potential to inform the clinical assessment of grip strength which is recognised as an important part of the identification of people with sarcopenia and frailty.     

Does gender influence neuromotor control of the knee and hip?

Patellofemoral pain (PFP) is a common condition that occurs more frequently in females. Anatomical, hormonal and neuromuscular factors have been proposed to contribute to the increased incidence of PFP in females, with neuromuscular factors considered to be of particular importance. This cross-sectional study aimed to evaluate differences in the neuromotor control of the knee and hip muscles between genders and to investigate whether clinical measures of hip rotation range and strength were associated with EMG measures of hip and thigh motor control. Twenty-nine (16 female and 13 male) asymptomatic participants completed a visual choice reaction-time stair stepping task. EMG activity was recorded from vastus medialis oblique, vastus lateralis, anterior and posterior gluteus medius muscles. In addition hip rotation range of motion and hip external rotation, abduction and trunk strength were assessed. There were no differences in the timing or peak of EMG activation of the vasti or gluteus medius muscle between genders during the stepping task. There were however significant associations between EMG measures of motor control of the vasti and hip strength in both females and males. These findings are suggestive of a link between hip muscle control and vasti neuromotor control.     

中国壮侗语族人群的肌肉分布及其与年龄的关系

为了解壮侗语族族群肌肉分布特点以及探讨随年龄增长壮侗语族族群各个部位肌肉量变化的基本特点,使用人体脂肪测量仪采用生物电阻抗法在海南、贵州、广西、云南、湖南五个省、自治区测量了壮侗语族13个族群的身体肌肉量。总样本量为5098例（男性为2126例,女性为2972例）。采用握力计测量了2685例男性和3793例女性的左手、右手握力。研究发现,壮侗语族族群男性、女性肌肉量总体评价接近标准,上下肢肌肉量判断属于标准水平。男性、女性均为躯干肌肉量最大,下肢肌肉量次之,上肢肌肉量最小。男性总肌肉量、四肢肌肉量、躯干肌肉量都大于女性。男性3个年龄组间总肌肉量、躯干肌肉量、上肢肌肉量、右下肢肌肉量的差异具有统计学意义,而左下肢肌肉量彼此接近;女性3个年龄组间总肌肉量、四肢肌肉量、躯干肌肉量差异均具有统计学意义。男性除左下肢肌肉量外,其余5项肌肉量指标均与年龄呈显著负相关关系;女性总肌肉量、躯干肌肉量与年龄呈显著负相关,但四肢肌肉量与年龄无显著负相关。壮侗语族族群肌肉量少于北方族群,具有中国南方族群的特点。在南方族群中,壮侗语族族群男性肌肉量中等,女性肌肉量略多一些。     

How Aging Affects Grasping Behavior and Pull Strength in Captive Gray Mouse Lemurs (<Emphasis Type="Italic">Microcebus murinus</Emphasis>)

Prehension is essential for animal survival and fitness. It is involved in locomotion and feeding behavior and subject to physical and physiological constraints. Studies of prehension in primates have explored the importance of food properties and of the environment, but aging has rarely been studied although prehensile capacity may deteriorate with age in humans. To test the hypothesis that aging affects grasping abilities and to reveal possible behavioral adaptations to this, we quantified behavioral grasping strategies and pull strength in 10 young adult (2–3 yr old) and 10 aged (7–8 yr old) gray mouse lemurs (Microcebus murinus). We assessed grasping strategies in an experimental cage by quantifying grip types used to grasp static and mobile foods. We measured strength using a Kistler triaxial force platform. Our results show that 1) mobile and static foods affected individuals of different ages in similar ways; 2) older individuals used more mouth grasps than young ones; 3) aged individuals made twice as many attempts as young ones when grasping mobile food items but this difference was not significant; and 4) there were no differences in hand grip strength between age classes but young individuals showed a higher foot pull strength compared to old ones. These data suggest that the observed differences in behavior may be due to a decrease in foot grip strength, which in turn influences stability on narrow branches, forcing animals to use their hands to maintain stability and preventing them from using their hands for food-related tasks.     

Forearm electromyographic activity during the deadlift exercise is affected by grip type and sex

Muscle activation, peak velocity (PV) and perceived technical difficulty while using three grip variations and three loads during a deadlift exercise (DL) were examined. Twenty-nine resistance-trained athletes (15 males, age: 22.2 ± 2.7 years; 14 females, age: 24.8 ± 7.0 years) performed the DL with 50%, 70% and 90% of their one repetition maximum (1RM) using hook grip (HG), mixed grip (MG) and double overhand (DOH) grip. Surface electromyography (EMG) of the brachialis (BS), brachioradialis (BR) and flexor carpi ulnaris (FCU) was recorded. PV and perceived technical difficulty of each grip were also measured. Regardless of load and grip, females exhibited greater BS activation compared to males (p < 0.05; ES = 0.69) while males displayed greater BR activation, significant at 90% load (p < 0.01; ES = 1.01). MG elicited the least BR and FCU activation regardless of load and sex (p < 0.01; ES = 0.64–0.68) and was consistently ranked as the easiest grip for any load. Males achieved significantly greater PV than females at 50% and 70% (p < 0.01; ES = 1.72–1.92). Hand orientation did not significantly impact PV. A MG may be beneficial in reducing the overall perceived technical difficulty when performing a maximal DL. Athletes aiming to maximise muscle activation and potentially develop their grip strength should utilise a DOH grip or HG.     

Influence of puberty on muscle development at the forearm

Despite its fundamental importance for physical development, the growth of the muscle system has received relatively little consideration. In this study, we analyzed the relationship between cross-sectional area (CSA) of forearm muscles and maximal isometric grip force with age and pubertal stage. The study population comprised 366 children, adolescents, and young adults from 6 to 23 yr of age (185 female) and 107 adults (88 female) aged 29 to 40 yr. By use of peripheral quantitative computed tomography, muscle CSA was determined at the site of the forearm, whose distance to the ulnar styloid process corresponded to 65% of forearm length. Both muscle CSA and grip force were higher in prepubertal boys than in girls. The gender differences decreased until pubertal stage 3 and reincreased thereafter. In girls at pubertal stage 5, muscle CSA no longer increased with age (P > 0.4), whereas there was still some age-related increase in grip force (P = 0.02). In boys at pubertal stage 5, both muscle CSA and grip force continued to increase significantly with age (P < 0.005 each). Specific grip force (grip force per muscle CSA) adjusted for forearm length increased by almost one-half between 6 and 20 yr of age, with no difference between the genders. In conclusion, forearm muscle growth takes a gender-specific course during puberty, indicating that it is influenced by hormonal changes. However, the increase in specific grip force is similar in both genders and thus appears to be independent of sex hormones.     

Effect of whole body vibration frequency on neuromuscular activity in ACL-deficient and healthy males

Whole-body vibration (WBV) has been shown to enhance muscle activity via reflex pathways, thus having the potential to contrast muscle weakness in individuals with rupture of the anterior cruciate ligament (ACL). The present study aimed to compare the magnitude of neuromuscular activation during WBV over a frequency spectrum from 20 to 45 Hz between ACL-deficient and healthy individuals. Fifteen males aged 28±4 with ACL rupture and 15 age-matched healthy males were recruited. Root mean square (RMS) of the surface electromyogram from the vastus lateralis in both limbs was computed during WBV in a static half-squat position at 20, 25, 30, 35, 40 and 45 Hz, and normalized to the RMS while maintaining the half-squat position without vibration. The RMS of the vastus lateralis in the ACL-deficient limb was significantly greater than in the contralateral limb at 25, 30, 35 and 40 Hz (P<0.05) and in both limbs of the healthy participants (dominant limb at 25, 30, 35, 40 and 45 Hz, P<0.05; non dominant limb at 20, 25, 30, 35, 40 and 45 Hz, P<0.05). The greater neuromuscular activity in the injured limb compared to the uninjured limb of the ACL-deficient patients and to both limbs of the healthy participants during WBV might be due to either augmented excitatory or reduced inhibitory neural inflow to motoneurons of the vastus lateralis through the reflex pathways activated by vibratory stimuli. The study provides optimal WBV frequencies which might be used as reference values for ACL-deficient patients.     

Activation of fast skeletal muscle troponin as a potential therapeutic approach for treating neuromuscular diseases

Limited neural input results in muscle weakness in neuromuscular disease because of a reduction in the density of muscle innervation, the rate of neuromuscular junction activation or the efficiency of synaptic transmission. We developed a small-molecule fast-skeletal-troponin activator, CK-2017357, as a means to increase muscle strength by amplifying the response of muscle when neural input is otherwise diminished secondary to neuromuscular disease. Binding selectively to the fast-skeletal-troponin complex, CK-2017357 slows the rate of calcium release from troponin C and sensitizes muscle to calcium. As a consequence, the force-calcium relationship of muscle fibers shifts leftwards, as does the force-frequency relationship of a nerve-muscle pair, so that CK-2017357 increases the production of muscle force in situ at sub-maximal nerve stimulation rates. Notably, we show that sensitization of the fast-skeletal-troponin complex to calcium improves muscle force and grip strength immediately after administration of single doses of CK-2017357 in a model of the neuromuscular disease myasthenia gravis. Troponin activation may provide a new therapeutic approach to improve physical activity in diseases where neuromuscular function is compromised.     

Cross‐sectional relations of whole‐blood miRNA expression levels and hand grip strength in a community sample

MicroRNAs (miRNAs) regulate gene expression with emerging data suggesting miRNAs play a role in skeletal muscle biology. We sought to examine the association of miRNAs with grip strength in a community‐based sample. Framingham Heart Study Offspring and Generation 3 participants (n = 5668 54% women, mean age 55 years, range 24, 90 years) underwent grip strength measurement and miRNA profiling using whole blood from fasting morning samples. Linear mixed‐effects regression modeling of grip strength (kg) versus continuous miRNA ‘Cq’ values and versus binary miRNA expression was performed. We conducted an integrative miRNA–mRNA coexpression analysis and examined the enrichment of biologic pathways for the top miRNAs associated with grip strength. Grip strength was lower in women than in men and declined with age with a mean 44.7 (10.0) kg in men and 26.5 (6.3) kg in women. Among 299 miRNAs interrogated for association with grip strength, 93 (31%) had FDR q value < 0.05, 54 (18%) had an FDR q value < 0.01, and 15 (5%) had FDR q value < 0.001. For almost all miRNA–grip strength associations, increasing miRNA concentration is associated with increasing grip strength. miR‐20a‐5p (FDR q 1.8 × 10^?6) had the most significant association and several among the top 15 miRNAs had links to skeletal muscle including miR‐126‐3p, miR‐30a‐5p, and miR‐30d‐5p. The top associated biologic pathways included metabolism, chemokine signaling, and ubiquitin‐mediated proteolysis. Our comprehensive assessment in a community‐based sample of miRNAs in blood associated with grip strength provides a framework to further our understanding of the biology of muscle strength.     

Fast Skeletal Muscle Troponin Activator tirasemtiv Increases Muscle Function and Performance in the B6SJL-SOD1G93A ALS Mouse Model

Amyotrophic Lateral Sclerosis (ALS) is a motor neuron disease characterized by progressive motor neuron loss resulting in muscle atrophy, declining muscle function, and eventual paralysis. Patients typically die from respiratory failure 3 to 5 years from the onset of symptoms. Tirasemtiv is a fast skeletal troponin activator that sensitizes the sarcomere to calcium; this mechanism of action amplifies the response of muscle to neuromuscular input producing greater force when nerve input is reduced. Here, we demonstrate that a single dose of tirasemtiv significantly increases submaximal isometric force, forelimb grip strength, grid hang time, and rotarod performance in a female transgenic mouse model (B6SJL-SOD1^G93A) of ALS with functional deficits. Additionally, diaphragm force and tidal volume are significantly higher in tirasemtiv-treated female B6SJL-SOD1^G93A mice. These results support the potential of fast skeletal troponin activators to improve muscle function in neuromuscular diseases.     

A 23-year study of mortality and development of co-morbidities in patients with obesity undergoing bariatric surgery (laparoscopic gastric banding) in comparison with medical treatment of obesity

Although obesity-related type 2 diabetes mellitus (T2DM) and sarcopenia in the elderly have been increasing worldwide, the associations among visceral fat accumulation, skeletal muscle indices (mass, strength, and quality) and cardiovascular diseases in T2DM remain poorly investigated. We enrolled 183 Japanese T2DM inpatients (126 men, 57 women; mean age 64.7 ± 12.6 years, ± SD). The estimated-visceral fat area (eVFA) and skeletal muscle mass were measured by each device using bioelectrical impedance analysis method. We also measured grip strength by dynamometer and motor nerve conduction velocity (MCV). We analyzed the difference in skeletal muscle indices between T2DM patients with and without visceral fat accumulation, and examined the impact of skeletal muscle indices on cardiovascular diseases in patients with visceral fat accumulation. The prevalence of sarcopenia defined by the Consensus of Asian Working Group for Sarcopenia and low skeletal muscle mass were both lower in the visceral fat accumulation (+) group than in (−) group. However, the prevalence of weak hand grip strength was similar in the visceral fat accumulation (−) and (+) groups, indicating that considerable patients with visceral fat accumulation had weak grip strength in spite of fair skeletal muscle mass. Muscle quality [grip strength (kg)/arm muscle mass (kg)] was significantly lower in patients with visceral fat accumulation. Multiple regression analysis identified eVFA, MCV and sex as significant and independent determinants of muscle quality. In visceral fat accumulation (+) group, the patients with low muscle quality had longer duration of diabetes, lower eGFR, higher serum adiponectin, lower MCV and higher prevalence of cardiovascular diseases, compared to the patients with high muscle quality. Finally, sex- and age-adjusted models showed significant association between low muscle quality and cardiovascular diseases in all subjects (odds ratio 2.28, p = 0.012), especially in patients with visceral fat accumulation (odds ratio 2.72, p = 0.018). T2DM patients with visceral fat accumulation had low muscle quality, and patients with low muscle quality were more affected with cardiovascular diseases.     

Neuromuscular performance characteristics of open-wheel and rally drivers

The purpose of the present study was to investigate neuromuscular performance characteristics in open-wheel and rally drivers using the cross-sectional study design. The subjects (N = 28) consisted of experienced international-level open-wheel drivers (n = 9), experienced international-level rally drivers (n = 9) and a physically active nondriving male control group (n = 10). In 3 separate test sessions, speed, muscle strength, and endurance tests were performed. The rally drivers had higher (p < 0.05) grip, shoulder flexion, and ankle plantar flexion strength, as compared to the control group. The open-wheel drivers showed higher strengths (p < 0.05) than the controls in neck forces, grip, shoulder flexion, and leg extension. The rally drivers were stronger (p < 0.05) than the open-wheel drivers in grip, plantar flexion, and trunk extension forces, whereas the open-wheel drivers were stronger (p < 0.01) than the rally drivers in neck lateral flexions and extension forces. Thus, competitive long-term open-wheel and rally drivers differ specifically in neuromuscular performance. For practice, these findings suggest that rally drivers should concentrate on training hand, ankle, and trunk muscles, whereas open-wheel drivers should train neck muscles, especially, and all other muscle groups rather equally.     

Growth and anabolic hormones,leptin, and neuromuscular performance in moderately trained prepubescent athletes and untrained boys

We investigated hormonal regulators of growth and development, leptin levels, body composition, neuromuscular performance, and the associations among them in trained prepubertal athletes (experimental group [EG]) and an untrained control group (CG). Informed consent was obtained from the children and their parents. Their maturation stage was evaluated according to Tanner's criteria. There were no differences between EG and CG in physical characteristics, body mass index (BMI), lean body mass, testosterone (T), sex hormone-binding globulin, free androgen index, growth hormone (GH), hand grip strength, and jumping performance. Leptin levels and percent fat of the EG were significantly lower than those of the CG (p < 0.05-0.005). Leptin levels were significantly correlated to body fat and BMI for both the EG and the CG (r = 0.51-0.79). There is little evidence that leptin has a positive effect on growth and anabolic factors. Sex hormone-binding globulin and GH may explain the variation of leptin in athletes with low T (R(2) = 0.43) and in CG (R(2) = 0.35), respectively. Leptin seems to be a permissive factor for the onset of puberty, and the training background needs an optimal biological maturation to produce significant differences in muscle and power performance.     

Longitudinal changes in muscle power compared to muscle strength and mass

Objectives:The study reports longitudinal changes in grip strength, muscle mass and muscle power of lower extremities. The aim is to identify early muscular changes to improve the diagnosis and treatment of sarcopenia.Methods:Grip strength was measured by hand dynamometer, muscle mass by dual-energy X-ray absorptiometry and muscle power by performing a chair rise test and two-leg jumps (2LJP) on the Leonardo Mechanograph®. Longitudinal changes were analysed using paired t-tests by age group and sex. Differences between groups in terms of the annual change were tested by Analysis of Variance and the Dunnett’s test. Comparisons between the variables were performed using one sample t-tests.Results:Six-year changes were determined in 318 randomly selected healthy participants aged 20-90 years from Berlin. 2LJP declined significantly earlier in 20-39 years old women (-3.70 W/kg) and men (-5.97 W/kg, both p<0.001). This is an absolute annual decline of -0.46 W/kg in females and -0.75 W/kg in males. In the oldest age group, 2LJP showed the highest absolute annual loss with -0.99 W/kg in women and -0.88 W/kg in men. 2LJP was significantly different compared to all variables of muscle mass and strength (p<0.01).Conclusions:The results underline the importance of assessing muscle power using 2LJP during aging.     

Insulin-like growth factor-2 genotype, fat-free mass, and muscle performance across the adult life span.

The influence of insulin-like growth factor-2 (IGF2) genotype on total body fat-free mass (FFM), muscle strength, and sustained power (SP) was evaluated repeatedly at approximately 2-yr intervals in two cohorts from the Baltimore Longitudinal Study of Aging. Cohort 1 was comprised of 94 men tested for isometric grip strength and SP. Cohort 2 was comprised of 246 men and 239 women tested for total body FFM and isokinetic peak torque. Subjects were retrospectively genotyped for the IGF2 gene's ApaI polymorphism. Differences between genotype groups for total FFM, strength, and SP at first visit, at peak age (35 yr), at age 65, and across the adult age span were analyzed using either two-sample t-tests or mixed-effects models, depending on the specific comparisons made. Isokinetic arm strength at the time of first visit was lower in A/A men than in G/G men (P < 0.05). Compared with G/G women, A/A women had lower total body FFM, lower isokinetic arm and leg strength at the time of first visit, and lower values at age 35 (all P < 0.05) for these muscle phenotypes. Furthermore, this difference between the genotype groups was maintained at age 65 and across the adult age span (P < 0.05). No genotype-associated differences in rates of loss of grip strength or SP were found in cohort 1. These results from cohort 2 support the hypothesis that variation within a gene known to influence developing muscle affects muscle mass and muscle function in later life.     

Sexual dimorphism in neuromuscular junction size on a muscle used in courtship by green anole lizards.

The green anole lizard exhibits seasonal courtship behavior that is sexually dimorphic. This courtship consists of the extension of a bright red throat fan (dewlap) associated with head-bobbing display behavior. While males extend their dewlaps in aggressive encounters as well as in courtship, females use their considerably smaller dewlaps much less frequently and mainly in agonistic encounters. In parallel, a number of components of the neuromuscular system controlling dewlap extension are greater in males than in females during the breeding season, including dewlap motoneuron soma size and muscle fiber size and number. These features do not seem to change substantially in adulthood, despite a dramatic decline in dewlap use during the nonbreeding season. We explored the morphology of this neuromuscular system in more detail in the present experiment in males and females during both the breeding and nonbreeding seasons. Fiber and whole muscle length (approximately perpendicular to the fibers) were measured. Acetylcholinesterase histochemistry was used to visualize neuromuscular junctions (NMJs), and the surface area and density of NMJs were assessed for each animal. During the breeding season, NMJ size was larger in males than in females, but NMJ density along each fiber was equivalent between the sexes. In addition, whole muscle length and that of individual muscle fibers, was larger in males than in females. However, when corrected for body size, the sex difference in muscle fiber length disappeared. In the nonbreeding season, the sexual dimorphisms were maintained, suggesting that these features do not change substantially due to differences in circulating testosterone or a difference in use across seasons. Overall, these results are consistent with the idea that enhanced NMJ size is a relatively stable feature of the dewlap muscle in adulthood that either facilitates or is a consequence of using a larger muscle to extend a bigger dewlap in males compared to females.