Leg Muscles Research Articles

Age-related breakdown in networks of inter-muscular coordination.

Assessing inter-muscular coordination in older adults is crucial, as it directly impacts an individual's ability for independent functioning, injury prevention, and active engagement in daily activities. However, the precise mechanisms by which distinct muscle fiber types synchronize their activity across muscles to generate coordinated movements in older adults remain unknown. Our objective is to investigate how distinct muscle groups dynamically synchronize with each other in young and older adults during exercise. Thirty-five young adults and nine older adults performed one bodyweight squat set until exhaustion. Simultaneous surface electromyography (sEMG) recordings were taken from the left and right vastus lateralis, and left and right erector spinae. To quantify inter-muscular coordination, we first obtained ten time series of sEMG band power for each muscle, representing the dynamics of different muscle fiber types. Next, we calculated the bivariate equal-time Pearson's cross-correlation for each pair of sEMG band power time series across all leg and back muscles. The main results show (i) an overall reduction in the degree of inter-muscular coordination, and (ii) increased stratification of the inter-muscular network in older adults compared to young adults. These findings suggest that as individuals age, the global inter-muscular network becomes less flexible and adaptable, hindering its ability to reorganize effectively in response to fatigue or other stimuli. This network approach opens new avenues for developing novel network-based markers to characterize multilevel inter-muscular interactions, which can help target functional deficits and potentially reduce the risk of falls and neuro-muscular injuries in older adults.

Assessment of Age-Related Differences in Lower Leg Muscles Quality Using Radiomic Features of Magnetic Resonance Images.

Sarcopenia, characterised by a decline in muscle mass and strength, affects the health of the elderly, leading to increased falls, hospitalisation, and mortality rates. Muscle quality, reflecting microscopic and macroscopic muscle changes, is a critical determinant of physical function. To utilise radiomic features extracted from magnetic resonance (MR) images to assess age-related changes in muscle quality, a dataset of 24 adults, divided into older (male/female: 6/6, 66-79years) and younger (male/female: 6/6, 21-31years) groups, was used to investigate the radiomics features of the dorsiflexor and plantar flexor muscles of the lower leg that are critical for mobility. MR images were processed using MaZda software for feature extraction. Dimensionality reduction was performed using principal component analysis and recursive feature elimination, followed by classification using machine learning models, such as support vector machine, extreme gradient boosting, and naïve Bayes. A leave-one-out validation test was used to train and test the classifiers, and the area under the receiver operating characteristic curve (AUC) was used to evaluate the classification performance. The analysis revealed that significant differences in radiomic feature distributions were found between age groups, with older adults showing higher complexity and variability in muscle texture. The plantar flexors showed similar or higher AUC than the dorsiflexors in all models. When the dorsiflexor muscles were combined with the plantar flexor muscles, they tended to have a higher AUC than when they were used alone. Radiomic features in lower-leg MR images reflect ageing, especially in the plantar flexor muscles. Radiomic analysis can offer a deeper understanding of age-related muscle quality than traditional muscle mass assessments.

The functional role of the rabbit digastric muscle during mastication.

Muscle spindle abundance is highly variable in vertebrates, but the functional determinants of this variation are unclear. Recent work has shown that human leg muscles with the lowest abundance of muscle spindles primarily function to lengthen and absorb energy, while muscles with a greater spindle abundance perform active-stretch-shorten cycles with no net work, suggesting that muscle spindle abundance may be underpinned by muscle function. Compared with other mammalian muscles, the digastric muscle contains the lowest abundance of muscle spindles and, therefore, might be expected to generate substantial negative work. However, it is widely hypothesised that as a jaw-opener (anatomically) the digastric muscle would primarily function to depress the jaw, and consequently do positive work. Through a combination of X-ray reconstruction of moving morphology (XROMM), electromyography and fluoromicrometry, we characterised the 3D kinematics of the jaw and digastric muscle during feeding in rabbits. Subsequently, the work loop technique was used to simulate in vivo muscle behaviour in situ, enabling muscle force to be quantified in relation to muscle strain and hence determine the muscle's function during mastication. When functioning on either the working or balancing side, the digastric muscle generates a large amount of positive work during jaw opening, and a large amount of negative work during jaw closing, on average producing a relatively small amount of net negative work. Our data therefore further support the hypothesis that muscle spindle abundance is linked to muscle function; specifically, muscles that absorb a relatively large amount of negative work have a low spindle abundance.

Suspension training improves bilateral isometric strength asymmetry of knee muscles in people with multiple sclerosis

IntroductionMost people with multiple sclerosis are diagnosed with bilateral strength asymmetry in the lower limbs. Strength asymmetry increases muscle metabolic cost, muscle fatigability, postural instability, gait disturbance, imbalance, and risk of falling, and negatively affects the quality of life in PwMS. So far, the effects of rehabilitation exercises on reducing the asymmetric index in this population has not been studied convincingly. The purpose of this study was to investigate the effect of suspension exercise on bilateral isometric strength asymmetry of knee muscles in patients with multiple sclerosis. Materials & methodsIn this randomized controlled trial, twenty-seven female patients were purposively selected as the statistical sample and randomly divided into the control (n = 13, age: 34.72 ± 5.01 years) and exercise (n = 14, age: 37.62 ± 4.58 years) groups. The control group received routine care while the exercise group received the suspension exercise protocol. Isometric muscle strength and bilateral asymmetry were measured at baseline and after 8 weeks. The Biodex isokinetic dynamometer was used to measure the maximal voluntary isometric contraction of the flexor and extensor muscles of the knee. The analysis of covariance was used to analyze the data. ResultsThe isometric strength of the knee extensor muscles in the weak leg at the angle of 20° and in both legs at the angle of 70° in the exercise group improved significantly. Furthermore, the strength of the knee flexor muscles in the exercise group was increased. The amount of bilateral strength asymmetry in the knee flexor and extensor muscles at the angle of 70° significantly decreased in the exercise group. Discussions & conclusionsThese data suggest that suspension training is a practical approach to manage bilateral asymmetry in knee flexor and extensor muscle strength in patients with an EDSS of less than four.

Integration of multiscale fusion of residual neural network with 2-D gramian angular fields for lower limb movement recognition based on multi-channel sEMG signals

The human lower limb movements recognition (LLMR) plays a pivotal role in active lower limb exoskeleton robots. Employing surface electromyography (sEMG) signals for LLMR allows for the convenient, rapid and stable capture of signal variations, facilitating efficient identification of lower limb motion patterns. However, current sEMG-based LLMR methods face challenges such as incomplete feature extraction, limited contextual information and restricted feature extraction scales during feature extraction. This paper proposed a LLMR method based on Gramian Angular Fields (GAF) and multiscale fusion of Residual Neural Network (MS-ResNet). The denoised sEMG time series was transformed into Gramian Angular Difference Field (GADF) matrix based on GAF. The MS-ResNet model, incorporating ResNet and multiscale feature fusion concepts, was proposed to comprehensively capture global and local information through different-scale feature extraction and fusion, so as to improve recognition performance. sEMG signals from 11 muscles of the preferred leg of 15 healthy subjects were recorded during six common lower limb movements. Experimental analysis investigated the impact of the convolutional kernel size (k × k) in Stream 2 of MS-ResNet and the number of muscles involved on recognition performance. The study revealed that selecting k as 13, coupled with 11 muscles, yielded optimal model performance with the average cross-individual recognition accuracy reaching 97.62 %, demonstrating the model’s efficiency in LLMR. This method could provide a viable solution for developing more efficient and reliable LLMR systems, applicable to lower limb exoskeleton robots and intelligent prosthetics.

Acute Effects of Soft Tissue Modalities on Muscular Ultrasound Characteristics and Isometric Performance

Prior to training, many athletes perform different soft-tissue preparation protocols. Many of these protocols involve stretching, foam rolling, and/or percussion massage. Many of these modalities have been studied, but not as a group to observe muscle alterations and differences in males and females. In total, 40 (20 males, 20 females) participants performed five minutes of static stretching, foam rolling, and percussion massage. Pre- and post-isometric leg strength, muscle activation and ultrasound assessments (cross-sectional area, echo intensity, pennation angle, fascicle length, and muscle thickness) were taken. The results indicate that there is no significant difference among modalities, and that they do not significantly alter any muscle characteristic or improve performance. There is a significant difference in size between males and female, with males having larger muscle and greater pennation angles than females. This allows males to generate significantly more muscle force. However, they both respond similarly to each modality. In conclusion, the muscle response to static stretching, foam rolling, and percussion massage do not differ among modalities and do not contribute to an increase or decrease in maximal isometric knee extension with similar effects between males and females.

Genetic parameter estimation and genetic evaluation of important economic traits in white and yellow broilers

ABSTRACT 1. This study calculated descriptive statistics for the production traits of two broiler populations: 1) the Northeast Agricultural University broiler lines divergently selected for abdominal fat content (NEAUHLF white broilers), including fat and lean lines; and 2) the Guangxi yellow broilers. Their genetic parameters were estimated, including (co)variance components, heritability (h 2 ) and genetic correlations (rg), using the REML method. 2. Heritability estimates (h 2 ) for NEAUHLF white broilers ranged from 0.07 to 0.61. Traits with high heritability (h 2 >0.3) included body weight at 3, 5 and 7 weeks of age (BW3, BW5, BW7), carcass weight (CW), metatarsal circumference (MeC), liver weight (LW), gizzard weight (GW), spleen weight (SW) and testis weight (TeW), while in Guangxi yellow broilers, heritability estimates ranged from 0.18 to 0.76, with every trait exhibiting high heritability, except for SW (0.18). 3. Positive genetic correlations for NEAUHLF were found (rg >0.3, ranging from 0.31 to 0.84) between BW7 and metatarsal length (MeL), MeC, body oblique length (BoL), chest angle (ChA), LW, GW, heart weight (HW) and SW. Genetic correlations between abdominal fat weight (AFW) and BW1, BW3, BW5, CW, MeL, keel length (KeL), BoL and LW were positive (rg >0.3, ranging from 0.31 to 0.58). 4. Among the Guangxi population, BW (125 d of age) showed strong positive genetic correlations with all other traits (rg >0.3, ranging from 0.30 to 0.99), while AFW displayed strong positive genetic correlations with leg muscle weight (LeW), CW, BW and thigh diameter (TD) (rg >0.3, ranging from 0.44 to 0.51). 5. It was concluded that the characteristics of the two populations were different, which means there is a need to use different strategies when performing the breeding work to improve productivity and efficiency in both broiler populations.

Influence of incubation temperature on embryonic Days 4–7 on gene expression, M. pectoralis and M. gastrocnemius microstructure, and tibia characteristics in Ross 308 Broilers

ABSTRACT The incubation temperature can influence chicken bone and muscle development, and breast and leg muscles may respond differently to changes therein. Ross 308 broiler eggs were incubated at 36.5°C, 37.5°C (control), 38.5°C and 39.0°C on embryonic days 4–7. M. pectoralis and M. gastrocnemius were sampled at hatching and 5 weeks post-hatching, and differences in gene expression, microstructure and energy metabolism were examined. Tibia strength was tested, and gait scoring was performed. Broiler performance was similar at slaughter age, but initial growth was slowed by the 36.5°C treatment. The 38.5°C treatment reduced the M. gastrocnemius weight and shifted the M. pectoralis/M. gastrocnemius ratio. All treatments reduced M. gastrocnemius glycogen content relative to the control. The expression of single myogenesis-related genes was altered in the M. pectoralis by 36.5°C. The results indicate that the incubation temperature influences broiler muscle energy metabolism, and that the temperature of 38.5°C hampers leg muscle development.

Amyotrophic Lateral Sclerosis and swim training affect copper metabolism in skeletal muscle in a mouse model of disease.

Swim training and regulation of copper metabolism result in clinical benefits in amyotrophic lateral sclerosis (ALS) mice. Therefore, the study aimed to determine whether swim training improves copper metabolism by modifying copper metabolism in the skeletal muscles of ALS mice. SOD1G93A mice (n = 6 per group) were used as the ALS model, and wild-type B6SJL (WT) mice as controls (n = 6). Mice with ALS were analyzed before the onset of ALS (ALS BEFORE), at baseline ALS (first disease symptoms, trained and untrained, ALS ONSET), and at the end of ALS (last stage disease, trained and untrained, ALS TERMINAL). Copper concentrations and the level of copper metabolism proteins in the skeletal muscles of the lower leg were determined. ALS disease caused a reduction in the copper concentration in ALS TERMINAL untrained mice compared with the ALS BEFORE (10.43 ± 1.81 and 38.67 ± 11.50 μg/mg, respectively, p = .0213). The copper chaperon for SOD1 protein, which supplies copper to SOD1, and ATPase7a protein (copper exporter), increased at the terminal stage of disease by 57% (p = .0021) and 34% (p = .0372), while the CTR1 protein (copper importer) decreased by 45% (p = .002). Swim training moderately affected the copper concentration and the concentrations of proteins responsible for copper metabolism in skeletal muscles. The results show disturbances in skeletal muscle copper metabolism associated with ALS progression, which is moderately affected by swim training. From a clinical point of view, exercise in water for ALS patients should be an essential element of rehabilitation for maintaining quality of life.

Skeletal muscle activity affects the deformity of long bone morphology in lathyritic chick embryo.

Embryonic muscle activity is involved in various aspects of bone morphogenesis and growth. Normal mechanical stimuli of muscle contraction are important in most cases, and when the muscles are immobilized, the developing bones are abnormally shaped. In chick embryos, a characteristic curved deformity is reproducibly induced in the developing tibiotarsus using the bone-weakening agent, beta-aminopropionitrile (bAPN). In this study, we applied decamethonium bromide (DMB), a well-established neuromuscular blocking agent, to embryos treated with bAPN, to test the hypothesis that the deformity is triggered and formed depending on the balance between the decrease in stiffness of the bAPN-affected tibiotarsus and the normal physiological increase in embryonic skeletal muscle activity. The occurrence of curved morphology induced by bAPN administered at 4 or 8 days of incubation (embryonic day [ED]) was temporally consistent with the posterior displacement of the leg muscles, which occurred just before ED8. The displaced muscles were assumed to exert a contraction force comparable to that of untreated normal muscles. When treated with DMB at ED8, the muscles atrophied and exhibited degenerative changes, and the degree of curved morphology was alleviated and reduced to 50% or more in the morphometric evaluation at ED10. These findings indicated that the coordinated development of skeletal element stiffness and muscle activity must be temporally regulated, particularly during the early stages of skeletogenesis.

Blood Flow Restriction Training Improves Muscular Outcomes in Patients With Chronic Ankle Instability: A Critically Appraised Topic

Clinical Scenario: The high recurrence of lateral ankle sprains progresses to chronic ankle instability (CAI) and can affect many athletes in all sports. CAI is often associated with a decrease in muscle strength, an increase in pain, a decrease in the range of motion, and a decrease in balance or neuromuscular control. The use of blood flow restriction (BFR) with CAI can increase muscular outcomes and be used as a rehabilitation tool. Clinical Question: Is there evidence to suggest that BFR improves strength, muscle activation, and/or cross-sectional area of the lower leg musculature in those with CAI? Clinical Bottom Line: There is moderate evidence to support therapeutic exercise with low-intensity BFR in patients with CAI. The evidence concluded a significant improvement in BFR to increase muscle activation of the fibularis longus, anterior tibialis, vastus lateralis, and soleus. There is moderate evidence suggesting BFR can induce strength gains in the muscles of the lower extremity in patients with CAI. Strength of Recommendation: The comprehensive evidence is a Strength of Recommendation Taxonomy (SORT) Grade B, with a level of evidence of 2, according to the Centre for Evidence-Based Medicine (CEBM) for the studies included.

Development of selected performance, dressing and meat quality traits of Pekin ducks in relation to genotype and phytogenic feed additives

Abstract The aim of this study was to determine the effect of the genetic origin of ducks and the use of phytogenic additives in their feeding on performance indices, slaughter value and dressing percentage, as well as meat quality. The experimental material consisted of three genetic groups of Pekin ducks: Polish Pekin P-33 (P), Dworka D-11 (D) and Star 53 H.Y. (S). A 7-week experimental rearing of 216 commercial hybrids (3 × 72 animals) was carried out. Within each genetic line, three feeding groups were established, differing in the use of plant-based additives in the feed mixture (5% herb mixture or 5% black cumin seed). To assess slaughter value and meat quality of the ducks, 18 birds from each group were selected, including 9 males and 9 females. It was shown that the basic performance and slaughter value traits of Pekin ducks depend (p≤0.05) on their genetic origin. The most favourable (p≤0.05) rearing efficiency and slaughter value (body, carcass and meat weight) were found for commercial Star 53 HY ducks. Their breast muscles were characterized by higher (p≤0.05) cooking loss and lower (p≤0.05) collagen content. The genetic origin of the ducks was shown to influence (p≤0.05) economic efficiency of rearing, dressing percentage and chemical indicators of meat (except for water content in breast muscles) and some physical characteristics (pH24, cooking loss, colour lightness of leg muscles and electrical conductivity in breast muscles). Supplementation of the standard diet of ducks with phytogenic additives (mixture of herbs, black cumin seeds) at a level of 5% had (p≤0.05) a negative effect on body, carcass and meat weight, and a positive effect on the physical characteristics of meat related to water loss (pH24 and cooking loss).

The contribution of lower leg muscles during vertical jump: An electromyographic study

The contribution of lower leg muscles during vertical jump: An electromyographic study

The Effect of Going Up and Down the Stairs to the Explosive Power of Leg Muscles in Pencak Silat Catching Snake Rolls

The problem in this research is the lack of explosive power of the leg muscles of pencak silat leg pencak silat catch snake roll in Lintau. For this reason, pencak silat leg pencak silat catch snake roll in Lintau needs to be trained programmatically through training principles that can be carried out both theoretically and practically in achieving maximum explosive power. There are several forms of exercise that can increase leg muscle explosive power, including an exercise program by going up and down stairs. This type of research is a quasi-experimental research. The population is the Pencak Silat College of tungkai pencak silat tangkap gulung ular in Lintau. Samples were taken by total sampling technique so that the sample amounted to 15 people. The research instrument uses a vertical jump test and the data analysis technique used is the t test hypothesis testing. As a result of research and hypothesis testing, it can be concluded that "There is an effect of going up and down stairs on the explosiveness of leg muscles in Pencak Silat Tangkap Snake Roll, which is evidenced by the tcount > ttable with a value of (3,310> 1,761).

Tracking perching behavior of cage-free laying hens with deep learning technologies

Providing perches in cage-free (CF) housing offers significant benefits for laying hens, such as improved leg muscle development, bone health, reduced abdominal fat, and decreased fear and aggression. A precise detection method is essential to ensure that hens engage in perching behavior from an early age, as manual observation is often labor-intensive and sometimes inaccurate. The objectives of this study were to (1) develop and test a deep learning model for detecting perching behavior; and (2) evaluate the optimal model's performance on detecting perching behavior of laying hens of different ages. In this study, recent deep learning models, that is, YOLOv8s-PB, YOLOv8x-PB, YOLOv7-PB, and YOLOv7x-PB, were developed, trained and compared in detecting perching behavior in 4 CF rooms (200 hens/room). Perch height was up to 1.8 m from the litter floor and situated 1.5 m below the cameras. A total of 3,000 images were used, with each image featuring at least 1 hen perching. The models' detection accuracies and their performance across different age groups of hens were compared using 1-way ANOVA at a 5% significance level. The results showed that the YOLOv8x-PB model outperform all other models used, achieving the precision of 94.80%, recall of 95.10%, and mean average precision (mAP@0.50) of 97.60%. While all models proved over 94% detection precision. With optimal model, PB detection precision was highest (97.40%) for peaking phase followed by prelay (95.20%), grower (94.80%), developer (94.70%) and layers (92.70%) phases while the lowest detection precision (88.80%) was for starter phase. Detection performance was somewhat reduced by the overlapping of birds during perching and occlusion. Overall, the YOLOv8x-PB model was the most optimal in detecting perching behavior, proposing a valuable tool for CF producers to monitor the perching activities of laying hens automatically.

Task difficulty of visually guided gait modifications involves differences in central drive to spinal motor neurons.

Walking in natural environments requires visually guided modifications, which can be more challenging when involving sideways steps rather than longer steps. This exploratory study investigated whether these two types of modifications involve different changes in the central drive to spinal motor neurons of leg muscles. Fifteen adults [age: 36 ± 6 (SD) years] walked on a treadmill (4 km/h) while observing a screen displaying the real-time position of their toes. At the beginning of the swing phase, a visual target appeared in front (forward) or medial-lateral (sideways) of the ground contact in random step cycles (approximately every third step). We measured three-dimensional kinematics and electromyographic activity from leg muscles bilaterally. Intermuscular coherence was calculated in the alpha (5-15 Hz), beta (15-30 Hz), and gamma bands (30-45 Hz) approximately 230 ms before and after ground contact in control and target steps. Results showed that adjustments toward sideways targets were associated with significantly higher error, lower foot lift, and higher cocontraction between antagonist ankle muscles. Movements toward sideways targets were associated with larger beta-band soleus (SOL): medial gastrocnemius (MG) coherence and a more narrow and larger peak of synchronization in the cumulant density before ground contact. In contrast, movements toward forward targets showed no significant differences in coherence or synchronization compared with control steps. Larger SOL:MG beta-band coherence and short-term synchronization were observed during sideways, but not forward, gait modifications. This suggests that visually guided gait modifications may involve differences in the central drive to spinal ankle motor neurons dependent on the level of task difficulty.NEW & NOTEWORTHY This exploratory study suggests a specific and temporally restricted increase of central (likely corticospinal) drive to ankle muscles in relation to visually guided gait modifications. The findings indicate that a high level of visual attention to control the position of the ankle joint precisely before ground contact may involve increased central drive to ankle muscles. These findings are important for understanding the neural mechanisms underlying visually guided gait and may help develop rehabilitation interventions.

Hubungan Daya Tahan Kekuatan Otot Tungkai dengan Laju Lari 100 M pada siswa Kelas VII-3 SMP Negeri 1 Bonepantai

In an effort to improve running ability, muscle strength endurance is very important. The aim of this research is to explain the relationship between the strength endurance of body movements, especially the leg or leg muscles, and the extent to which the ability to withstand the strength of the leg or leg muscles affects 100 meter running speed. junior high school students in grades VII�3. In this research, the correlation method is used simultaneously with a quantitative approach. To collect data, a Leg Dynamometer and a Stop Watch were used. Data is analyzed using simple methods and multiple correlations, along with the Product Moment formula. The results showed that (1) there was a significant relationship between leg muscle strength and running speed for 100 meters, with a correlation value of 0.449. The results show that (1) leg muscle endurance influences 100 m running speed because the calculated value is 2.510 > table is 2.008, and (2) variable X influences variable Y. The determination coefficient of 0.201 from this output shows that the influence of the independent variable ( leg muscle endurance) in the dependent variable (100 m running speed) is 20.1% and the significance value is 0.001<0.005

Comparison of selenium-mediated regulation of heat shock protein and inflammation in-vitro and in-ovo for heat resistance enhancement in broiler

Selenium is a heat-stress-reducing substance that improves heat resistance and is being studied for its effective application in the broiler industry. However, research on feed additives is labor-intensive and time-consuming because of the need for feeding experiments. We aimed to compare the effects of selenium under heat stress in vitro and in ovo, specifically examining the gene expression of heat shock proteins (HSP) and inflammatory markers. Two groups were included in the in-vitro study: in-vitro control (TC; selenium 0 μg/ml) and in-vitro selenium (TS; selenium 5 μg/ml). The satellite cells were cultured at 42°C for 48 h after selenium treatment. The in-ovo study comprised 4 groups: in-ovo control and in-ovo selenium 1-3 (OC, OS1, OS2, and OS3; selenium 2.5, 5, and 10 μg/egg, respectively). Selenium was injected on the 18th day after hatching, and heat treatment was performed at 32-34°C from the 14th to the 21st day after hatching, and the leg muscles of the chicks were collected on the 21st day. The gene expression of heat shock proteins (HSP), caspase3, nuclear factor kappa light-chain enhancer of activated B cells (NF-kB), and IL-8 was analyzed in in-vitro and in-ovo experiments, respectively. In-vitro results showed significant increases in HSP90, HSP60, and HSP40 in TS compared to TC, with a significant decrease in HSP70. In the in-ovo study, HSP70, caspase3, NF-kB and IL-8 were significantly increased in OS1. HSP90, HSP60, HSP40, HSP27 and NF-kB were significantly decreased in in-ovo OS2 compared to in-vitro TS, implying a trend in ratio compared to control. Selenium appeared to enhance heat resistance in-vitro and in-ovo by modulating HSPs and inflammation. However, differences in mRNA expression were observed depending on the concentration of selenium. These findings suggest that selenium modulates heat resistance through different mechanisms in-vitro and in-ovo, likely due to the complexity of whole-organism interactions in-ovo compared to the single-cell-type environment in-vitro. Therefore, to directly apply in-vitro results to in-ovo, a concentration comparison study for each additive is necessary.

Effects of unilateral and bilateral lower extremity fatigue on static stance and postural adjustments response to the externally initiated perturbation

The study investigated the effects of unilateral and bilateral lower extremity fatigue on both postural stability and postural adjustments. Fourteen young male subjects performed unilateral and bilateral dynamic lower extremity pedaling exercises with 5 sets of 20 times at 50 % maximum voluntary contraction. Center of pressure (COP) signals were recorded before and after the fatigue exercise. Electromyography activities of six trunk and leg muscles were recorded and analyzed during the anticipatory (APAs) and compensatory (CPAs) postural adjustments. The results showed that both fatiguing exercises caused an increase in COP and larger APAs and CPAs in the rectus femoris and tibialis anterior during externally initiated perturbation. However, the observed indicators showed no clear difference between unilateral and bilateral fatigue. These results validated that when enlarged APAs were not sufficient to resist the external perturbation, the central nervous system increased the strength of CPAs to maintain the stability of the body. These findings provided a perspective on the association between APAs and CPAs, which may apply to the athletic training or rehabilitation on postural control.

Exploring the utility of ultrasound to assess disuse atrophy in different muscles of the lower leg.

Skeletal muscle is a highly plastic tissue crucial for many functions associated with whole-body health across the life course. Magnetic resonance imaging (MRI) is the current gold standard for measuring skeletal muscle size. However, MRI is expensive, and access to facilities is often limited. B-mode ultrasonography (U/S) has been proposed as a potential alternative to MRI for the assessment of muscle size. However, to date, no work has explored the utility of U/S to assess disuse muscle atrophy (DMA) across muscles with different atrophy susceptibility profiles, an omission which may limit the clinical application of previous work. To address this significant knowledge gap, 10 young men (22±years, 24.1±2.3kg/m2) underwent 15-day unilateral leg immobilization using a knee-brace and air boot. Cross-sectional area (CSA) and muscle thickness (MT) of the tibialis anterior (TA) and medial gastrocnemius (MG) were assessed via U/S before and after immobilization, with CSA and muscle volume assessed via MRI. With both muscles combined, there were good correlations between each U/S and MRI measure, both before (e.g., CSAMRI vs. MTU/S and CSAU/S: r=0.88 and 0.94, respectively, both P<0.0001) and after (e.g., VOLMRI vs. MTU/S and CSAU/S: r=0.90 and 0.96, respectively, both P<0.0001) immobilization. The relationship between the methods was notably stronger for MG than TA at each time-point (e.g., CSAMRI vs. MTU/S: MG, r=0.70, P=0.0006; TA, r=0.37, P=0.10). There was no relationship between the degree of DMA determined by the two methods in either muscle (e.g., TA pre- vs. post-immobilization, VOLMRI: 136±6 vs. 133±5, P=0.08; CSAU/S: 6.05±0.3 vs. 5.92±0.4, P=0.70; relationship between methods: r=0.12, P=0.75). Both MTU/S and CSAU/S provide comparable static measures of lower leg muscle size compared with MRI, albeit with weaker agreement in TA compared to MG. Although both MTU/S and CSAU/S can discern differences in DMA susceptibility between muscles, neither can reliably assess degree of DMA. Based on the growing recognition of heterogeneous atrophy profiles between muscles, and the topical importance of less commonly studied muscles (i.e., TA for falls prevention in older adults), future research should aim to optimize accessible methods to determine muscle losses across the body.