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Norihide Sugisaki, Kai Kobayashi, Hiroyasu Tsuchie and Hiroaki Kanehisa

 al . Biomechanical and skeletal muscle determinants of maximum running speed with aging . Med Sci Sports Exerc . 2009 ; 41 ( 4 ): 844 – 856 . PubMed doi:10.1249/MSS.0b013e3181998366 19276848 10.1249/MSS.0b013e3181998366 19. Nakatani M , Takai Y , Akagi R , et al . Validity of muscle thickness

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Nicola Giovanelli, Lea Biasutti, Desy Salvadego, Hailu K. Alemayehu, Bruno Grassi and Stefano Lazzer

the skeletal muscle, as the exercise they analyzed was not isolated to a single muscle group (cycling at 1 and 1.5 W·kg −1 ). Thus, the purpose of the present study was to evaluate the effects of a trail-running race on muscle oxidative function by measuring pulmonary gas exchange variables and muscle

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Alif Laila Tisha, Ashley Allison Armstrong, Amy Wagoner Johnson and Citlali López-Ortiz

, we analyze the series and lateral force components separately and then return to the general conceptual model to consider the net effect of force transmission in a muscle fiber contraction. Conceptual Model The system is represented using a cross-sectional view of skeletal muscle (Figure  2A ). We

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Stephan R. Fisher, Justin H. Rigby, Joni A. Mettler and Kevin W. McCurdy

. PubMed ID: 23626925 doi:10.1515/plm-2012-0032 10.1515/plm-2012-0032 23626925 2. Alves AN , Fernandes KPS , Deana AM , Bussadori SK , Mesquita-Ferrari RA . Effects of low-level laser therapy on skeletal muscle repair: a systematic review . Am J Phys Med Rehabil . 2014 ; 93 ( 12 ): 1073

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Jeffrey J. Dueweke, Tariq M. Awan and Christopher L. Mendias

Eccentric-contraction-induced skeletal muscle injuries, included in what is clinically referred to as muscle strains, are among the most common injuries treated in the sports medicine setting. Although patients with mild injuries often fully recover to their preinjury levels, patients who suffer moderate or severe injuries can have a persistent weakness and loss of function that is refractory to rehabilitation exercises and currently available therapeutic interventions. The objectives of this review were to describe the fundamental biophysics of force transmission in muscle and the mechanism of muscle-strain injuries, as well as the cellular and molecular processes that underlie the repair and regeneration of injured muscle tissue. The review also summarizes how commonly used therapeutic modalities affect muscle regeneration and opportunities to further improve our treatment of skeletal muscle strain injuries.

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Walter Herzog, Timothy Koh, Evelyne Hasler and Tim Leonard

We hypothesize that the neuromuscular system is designed to function effectively in accomplishing everyday movement tasks. Since everyday movement tasks may vary substantially in terms of speed and resistance, we speculate that agonistic muscles contribute differently to varying movement tasks such that the mechanical, structural, and physiological properties of the system are optimized at all times. We further hypothesize that a mechanical perturbation to the musculoskeletal system, such as the loss of an important joint ligament or the change of a muscle’s line of action, causes an adaptation of the system aimed at reestablishing effective function. Here. we demonstrate how the specificity of the cat ankle extensors is used to accommodate different locomotor tasks. We then illustrate how the loss of an important ligament in the cat knee leads to neuromuscular adaptation. Finally, we discuss the adaptability of skeletal muscle following an intervention that changes a muscle’s line of action, moment arm, and excursion.

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Emily Arentson-Lantz, Elfego Galvan, Adam Wacher, Christopher S. Fry and Douglas Paddon-Jones

et al., 2011 ). To mimic the overt physical inactivity experienced during hospitalization, while separating the catabolic, disease-related effects from the intrinsic effects of skeletal muscle disuse, we subjected a cohort of healthy, community-dwelling older adults to a 7-day bed rest (BR) protocol

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David T. Corr, Ray Vanderby Jr. and Thomas M. Best

An existing rheological model of skeletal muscle (Forcinito et al., 1998) was modified with a nonlinear Maxwell fluid element to provide a phenomenological model capable of analyzing the strain-stiffening behavior typically found in passive, and occasionally observed in active, skeletal muscle. This new model describes both active and passive muscular behavior as a combination of the behavior of each model component, without requiring prior knowledge of the force-length or force-velocity characteristics of the muscle.

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Joshua N. Farr, Deepika R. Laddu and Scott B. Going

Although primarily considered a disorder of the elderly, emerging evidence suggests the antecedents of osteoporosis are established during childhood and adolescence. A complex interplay of genetic, environmental, hormonal and behavioral factors determines skeletal development, and a greater effort is needed to identify the most critical factors that establish peak bone strength. Indeed, knowledge of modifiable factors that determine skeletal development may permit optimization of skeletal health during growth and could potentially offset reductions in bone strength with aging. The peripubertal years represent a unique period when the skeleton is particularly responsive to loading exercises, and there is now overwhelming evidence that exercise can optimize skeletal development. While this is not controversial, the most effective exercise prescription and how much investment in this prescription is needed to significantly impact bone health continues to be debated. Despite considerable progress, these issues are not easy to address, and important questions remain unresolved. This review focuses on the key determinants of skeletal development, whether exercise during childhood and adolescence should be advocated as a safe and effective strategy for optimizing peak bone strength, and whether investment in exercise early in life protects against the development of osteoporosis and fractures later in life.

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Brent A. Baker

Clinical Scenario:

Even though chronological aging is an inevitable phenomenological consequence occurring in every living organism, it is biological aging that may be the most significant factor challenging our quality of life. Development of functional limitations, resulting from improper maintenance and restoration of various organ systems, ultimately leads to reduced health and independence. Skeletal muscle is an organ system that, when challenged, is often injured in response to varying stimuli. Overt muscle-strain injury can be traumatic, clinically diagnosable, properly managed, and a remarkably common event, yet our contemporary understanding of how age and environmental stressors affect the initial and subsequent induction of injury and how the biological processes resulting from this event are modifiable and, eventually, lead to functional restoration and healing of skeletal muscle and adjacent tissues is presently unclear. Even though the secondary injury response to and recovery from "contraction-induced" skeletal-muscle injury are impaired with aging, there is no scientific consensus as to the exact mechanism responsible for this event. Given the multitude of investigative approaches, particular consideration given to the appropriateness of the muscle-injury model, or research paradigm, is critical so that outcomes may be physiologically relevant and translational. In this case, methods implementing stretch-shortening contractions, the most common form of muscle movements used by all mammals during physical movement, work, and activity, are highlighted.

Clinical Relevance:

Understanding the fundamental evidence regarding how aging influences the responsivity of skeletal muscle to strain injury is vital for informing how clinicians approach and implement preventive strategies, as well as therapeutic interventions. From a practical perspective, maintaining or improving the overall health and tissue quality of skeletal muscle as one ages will positively affect skeletal muscle’s safety threshold and responsivity, which may reduce incidence of injury, improve recovery time, and lessen overall fiscal burdens.