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Philosophical Transactions of the Royal... May 2011Skeletal muscles are length- and velocity-sensitive force producers, constructed of a vast array of sarcomeres. Muscles come in a variety of sizes and shapes to... (Review)
Review
Skeletal muscles are length- and velocity-sensitive force producers, constructed of a vast array of sarcomeres. Muscles come in a variety of sizes and shapes to accomplish a wide variety of tasks. How does muscle design match task performance? In this review, we outline muscle's basic properties and strategies that are used to produce movement. Several examples are provided, primarily for human muscles, in which skeletal muscle architecture and moment arms are tailored to a particular performance requirement. In addition, the concept that muscles may have a preferred sarcomere length operating range is also introduced. Taken together, the case is made that muscles can be fine-tuned to perform specific tasks that require actuators with a wide range of properties.
Topics: Biomechanical Phenomena; Humans; Magnetic Resonance Imaging; Muscle Contraction; Muscle, Skeletal; Sarcomeres
PubMed: 21502118
DOI: 10.1098/rstb.2010.0316 -
Comprehensive Physiology Apr 2012Muscle plasticity is defined as the ability of a given muscle to alter its structural and functional properties in accordance with the environmental conditions imposed... (Review)
Review
Muscle plasticity is defined as the ability of a given muscle to alter its structural and functional properties in accordance with the environmental conditions imposed on it. As such, respiratory muscle is in a constant state of remodeling, and the basis of muscle's plasticity is its ability to change protein expression and resultant protein balance in response to varying environmental conditions. Here, we will describe the changes of respiratory muscle imposed by extrinsic changes in mechanical load, activity, and innervation. Although there is a large body of literature on the structural and functional plasticity of respiratory muscles, we are only beginning to understand the molecular-scale protein changes that contribute to protein balance. We will give an overview of key mechanisms regulating protein synthesis and protein degradation, as well as the complex interactions between them. We suggest future application of a systems biology approach that would develop a mathematical model of protein balance and greatly improve treatments in a variety of clinical settings related to maintaining both muscle mass and optimal contractile function of respiratory muscles.
Topics: Adaptation, Physiological; Diaphragm; Humans; Models, Biological; Motor Neurons; Muscle Contraction; Muscle Proteins; Respiratory Muscles; Systems Biology; Weight-Bearing
PubMed: 23798306
DOI: 10.1002/cphy.c110050 -
Journal of Strength and Conditioning... Oct 2019Delgado, J, Drinkwater, EJ, Banyard, HG, Haff, GG, and Nosaka, K. Comparison between back squat, Romanian deadlift, and barbell hip thrust for leg and hip muscle... (Comparative Study)
Comparative Study
Delgado, J, Drinkwater, EJ, Banyard, HG, Haff, GG, and Nosaka, K. Comparison between back squat, Romanian deadlift, and barbell hip thrust for leg and hip muscle activities during hip extension. J Strength Cond Res 33(10): 2595-2601, 2019-This study compared muscle activities of vastus lateralis (VL), biceps femoris (BF), and gluteus maximus (GM) during the back squat (SQ), Romanian deadlift (RDL), and barbell hip thrust (BHT) exercises performed with the same load (60 kg) and at one repetition maximum (1RM). Eight men with a minimum of 1 year's lower-body strength training experience performed the exercises in randomized order. Before each exercise, surface electromyography (EMG) was recorded during a maximal voluntary isometric contraction (MVIC) and then used to normalize to each muscle's EMG during each trial. Barbell hip thrust showed higher GM activity than the SQ (effect size [ES] = 1.39, p = 0.038) but was not significantly different from RDL (ES = 0.49, p = 0.285) at 1RM. Vastus lateralis activity at 1RM during the SQ was significantly greater than RDL (ES = 1.36, p = 0.002) and BHT (ES = 2.27, p = 0.009). Gluteus maximus activity was higher during MVIC when compared with the 60 kg load for the SQ (ES = 1.29, p = 0.002) and RDL (ES = 1.16, p = 0.006) but was similar for the BHT (ES = 0.22, p = 0.523). There were no significant differences in GM (ES = 0.35, p = 0.215) and BF activities (ES = 0.16, p = 0.791) between 1RM and MVIC for the SQ. These findings show that the RDL was equally as effective as the BHT for isolating the hip extensors, while the SQ simultaneously activated the hip and knee extensors.
Topics: Adolescent; Adult; Buttocks; Electromyography; Exercise; Hamstring Muscles; Hip; Humans; Isometric Contraction; Male; Muscle, Skeletal; Quadriceps Muscle; Random Allocation; Resistance Training; Weight Lifting; Young Adult
PubMed: 31356511
DOI: 10.1519/JSC.0000000000003290 -
Folia Morphologica 2023Knowledge of anatomical variations can be of use to clinicians and surgeons when, for example, viewing images of a patient or performing operations. Such knowledge can... (Review)
Review
Knowledge of anatomical variations can be of use to clinicians and surgeons when, for example, viewing images of a patient or performing operations. Such knowledge can minimise the risk of iatrogenic complications. Herein, we present a case of a variant atlantomastoid muscle. The muscle was identified on the left side in an adult cadaver. The muscle's measurements and anatomical relationships are presented as well as a review of salient literature. We hope that increased knowledge of anatomical variants in the suboccipital region can improve patient care.
Topics: Adult; Humans; Muscle, Skeletal; Cadaver; Anatomic Variation; Surgeons
PubMed: 34826133
DOI: 10.5603/FM.a2021.0126 -
The Journal of Experimental Biology Apr 2023Muscle function during movement is more than a simple, linear transformation of neural activity into force. The classic work loop technique has pioneered our... (Review)
Review
Muscle function during movement is more than a simple, linear transformation of neural activity into force. The classic work loop technique has pioneered our understanding of muscle, but typically only characterizes function during unperturbed movement cycles, such as those experienced during steady walking, running, swimming and flying. Yet perturbations away from steady movement often place greater demands on muscle structure and function and offer a unique window into muscle's broader capacity. Recently, studies in diverse organisms from cockroaches to humans have started to grapple with muscle function in unsteady (perturbed, transient and fluctuating) conditions, but the vast range of possible parameters and the challenge of connecting in vitro to in vivo experiments are daunting. Here, we review and organize these studies into two broad approaches that extend the classic work loop paradigm. First, in the top-down approach, researchers record length and activation patterns of natural locomotion under perturbed conditions, replay these conditions in isolated muscle work loop experiments to reveal the mechanism by which muscle mediates a change in body dynamics and, finally, generalize across conditions and scale. Second, in the bottom-up approach, researchers start with an isolated muscle work loop and then add structural complexity, simulated loads and neural feedback to ultimately emulate the muscle's neuromechanical context during perturbed movement. In isolation, each of these approaches has several limitations, but new models and experimental methods coupled with the formal language of control theory give several avenues for synthesizing an understanding of muscle function under unsteady conditions.
Topics: Humans; Biomechanical Phenomena; Locomotion; Muscles; Running; Swimming
PubMed: 37042414
DOI: 10.1242/jeb.243561 -
Annual International Conference of the... Jul 2022Smooth muscle is found extensively in the human body, including in blood vessels, airways, the gastrointestinal tract, and the urinary bladder. Although the contractile...
Smooth muscle is found extensively in the human body, including in blood vessels, airways, the gastrointestinal tract, and the urinary bladder. Although the contractile proteins of smooth muscle are very similar to those of striated muscle, smooth muscle's contractile mechanism has not been studied as extensively as those for cardiac and skeletal muscle. Previous studies developed a lumped model of muscle contraction and applied it to cardiac muscle and to skeletal muscle. In this study, this model is used to quantitatively describe the contractile properties of canine smooth muscle, using data from the literature. Results show that a single equation relating muscle force to muscle length and time, and a single set of model parameters, is able to describe smooth muscle's passive and active isometric forces, isometric twitch contractions, isotonic contractions, and an inverse force-velocity relation. The latter arises from the model without assumption of a particular force-velocity curve embodied as a contractile element. This new constitutive relation may be used to describe smooth muscle within larger physiological models, for instance to describe blood vessel constriction or urinary bladder function.
Topics: Animals; Dogs; Humans; Isometric Contraction; Muscle Contraction; Muscle, Skeletal; Muscle, Smooth; Urinary Bladder
PubMed: 36086339
DOI: 10.1109/EMBC48229.2022.9871599 -
Annals of Plastic Surgery May 1991The hypothesis presented is that a muscle, transferred to a new area for purposes of recontouring or soft-tissue coverage, may be used also to provide sensibility. I... (Review)
Review
The hypothesis presented is that a muscle, transferred to a new area for purposes of recontouring or soft-tissue coverage, may be used also to provide sensibility. I hypothesize that the muscle's sensory end-organs, the muscle spindles, can be reinnervated by regenerating sensory afferent fibers from an adjacent cutaneous nerve. The muscle spindle's neural impulses, which normally pass to a subconscious level, would instead pass to the postcentral gyrus and reach conscious perception. A mechanism exists, therefore, by adding a sural or calcaneal nerve repair to the motor nerve of a muscle flap, transferred, for example, to the foot, to restore sensibility through microneurovascular transfer of a classic motor end-organ.
Topics: Humans; Muscles; Nerve Regeneration; Neurons, Afferent; Surgical Flaps
PubMed: 1952717
DOI: 10.1097/00000637-199105000-00006 -
NMR in Biomedicine Mar 2017The mechanical functions of muscles involve the generation of force and the actuation of movement by shortening or lengthening under load. These functions are... (Review)
Review
The mechanical functions of muscles involve the generation of force and the actuation of movement by shortening or lengthening under load. These functions are influenced, in part, by the internal arrangement of muscle fibers with respect to the muscle's mechanical line of action. This property is known as muscle architecture. In this review, we describe the use of diffusion tensor (DT)-MRI muscle fiber tracking for the study of muscle architecture. In the first section, the importance of skeletal muscle architecture to function is discussed. In addition, traditional and complementary methods for the assessment of muscle architecture (brightness-mode ultrasound imaging and cadaver analysis) are presented. Next, DT-MRI is introduced and the structural basis for the reduced and anisotropic diffusion of water in muscle is discussed. The third section discusses issues related to the acquisition of skeletal muscle DT-MRI data and presents recommendations for optimal strategies. The fourth section discusses methods for the pre-processing of DT-MRI data, the available approaches for the calculation of the diffusion tensor and the seeding and propagating of fiber tracts, and the analysis of the tracking results to measure structural properties pertinent to muscle biomechanics. Lastly, examples are presented of how DT-MRI fiber tracking has been used to provide new insights into how muscles function, and important future research directions are highlighted. Copyright © 2016 John Wiley & Sons, Ltd.
Topics: Algorithms; Animals; Diffusion Tensor Imaging; Forecasting; Humans; Image Enhancement; Image Interpretation, Computer-Assisted; Muscle Fibers, Skeletal; Muscle, Skeletal; Reproducibility of Results; Sensitivity and Specificity
PubMed: 27257975
DOI: 10.1002/nbm.3563 -
Sports Medicine (Auckland, N.Z.) Jan 1991The importance of carbohydrates as a fuel source during endurance exercise has been known for 60 years. With the advent of the muscle biopsy needle in the 1960s, it was... (Review)
Review
The importance of carbohydrates as a fuel source during endurance exercise has been known for 60 years. With the advent of the muscle biopsy needle in the 1960s, it was determined that the major source of carbohydrate during exercise was the muscle glycogen stores. It was demonstrated that the capacity to exercise at intensities between 65 to 75% VO2max was related to the pre-exercise level of muscle glycogen, i.e. the greater the muscle glycogen stores, the longer the exercise time to exhaustion. Because of the paramount importance of muscle glycogen during prolonged, intense exercise, a considerable amount of research has been conducted in an attempt to design the best regimen to elevate the muscle's glycogen stores prior to competition and to determine the most effective means of rapidly replenishing the muscle glycogen stores after exercise. The rate-limiting step in glycogen synthesis is the transfer of glucose from uridine diphosphate-glucose to an amylose chain. This reaction is catalysed by the enzyme glycogen synthase which can exist in a glucose-6-phosphate-dependent, inactive form (D-form) and a glucose-6-phosphate-independent, active form (I-form). The conversion of glycogen synthase from one form to the other is controlled by phosphorylation-dephosphorylation reactions. The muscle glycogen concentration can vary greatly depending on training status, exercise routines and diet. The pattern of muscle glycogen resynthesis following exercise-induced depletion is biphasic. Following the cessation of exercise and with adequate carbohydrate consumption, muscle glycogen is rapidly resynthesised to near pre-exercise levels within 24 hours. Muscle glycogen then increases very gradually to above-normal levels over the next few days. Contributing to the rapid phase of glycogen resynthesis is an increase in the percentage of glycogen synthase I, an increase in the muscle cell membrane permeability to glucose, and an increase in the muscle's sensitivity to insulin. The slow phase of glycogen synthesis appears to be under the control of an intermediate form of glycogen synthase that is highly sensitive to glucose-6-phosphate activation. Conversion of the enzyme to this intermediate form may be due to the muscle tissue being constantly exposed to an elevated plasma insulin concentration subsequent to several days of high carbohydrate consumption. For optimal training performance, muscle glycogen stores must be replenished on a daily basis. For the average endurance athlete, a daily carbohydrate consumption of 500 to 600g is required. This results in a maximum glycogen storage of 80 to 100 mumol/g wet weight.(ABSTRACT TRUNCATED AT 400 WORDS)
Topics: Dietary Carbohydrates; Exercise; Glycogen; Humans; Muscles; Physical Endurance
PubMed: 2011684
DOI: 10.2165/00007256-199111010-00002 -
European Journal of Applied Physiology Oct 2015Non-local muscle fatigue (NLMF) is characterized by muscle performance impairments in a contralateral or remote non-exercised muscle(s) following a fatiguing protocol of... (Review)
Review
INTRODUCTION
Non-local muscle fatigue (NLMF) is characterized by muscle performance impairments in a contralateral or remote non-exercised muscle(s) following a fatiguing protocol of a different muscle group(s). This topic is of interest as it affords insights into physiological determinants of muscle fatigue and may provide practical applications concerning the order of exercises in training and rehabilitation programs.
METHODS
A literature review was conducted using Web of Science, PubMed, and Google Scholar databases to evaluate the NLMF effects and possible underlying mechanisms. Overall, 35 studies with 58 outcome measures that met the inclusion criteria were identified.
RESULTS
The literature is conflicting with approximately half of the studies reporting NLMF effects (32 of 58 measurements). However, on closer examination 76% of outcome measures of the lower limbs reported NLMF effects (23 of 30 measurements) compared to only 32% in the upper body (9 of 28 measurements). Thus, it appears that NLMF effects may be muscle group dependent. Also, tests that involve prolonged or repetitive contractions provide clearer evidence of NLMF. Other variables potentially influencing the size of the NLMF effect include the fatigued muscle groups, the protocols used to elicit the fatigue, gender and training background of participants.
CONCLUSION
While the NLMF literature is conflicting, certain variables appear to affect NLMF responses which can account for some of the discrepancies. Furthermore, the NLMF effects may be attributed to four different but interconnected pathways: neurological, biochemical, biomechanical and psychological.
Topics: Evoked Potentials, Motor; Humans; Muscle Contraction; Muscle Fatigue; Muscle, Skeletal; Physical Exertion
PubMed: 26330274
DOI: 10.1007/s00421-015-3249-y