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Muscle Fatigue: A state arrived at through prolonged and strong contraction of a muscle. Studies in athletes during prolonged submaximal exercise have shown that muscle fatigue increases in almost direct proportion to the rate of muscle glycogen depletion. Muscle fatigue in short-term maximal exercise is associated with oxygen lack and an increased level of blood and muscle lactic acid, and an accompanying increase in hydrogen-ion concentration in the exercised muscle.

Cross-bridge Cycle

JoVE 10870

As muscle contracts, the overlap between the thin and thick filaments increases, decreasing the length of the sarcomere—the contractile unit of the muscle—using energy in the form of ATP. At the molecular level, this is a cyclic, multistep process that involves binding and hydrolysis of ATP, and movement of actin by myosin.

When ATP, that is attached to the myosin head, is hydrolyzed to ADP, myosin moves into a high energy state bound to actin, creating a cross-bridge. When ADP is released, the myosin head moves to a low energy state, moving actin toward the center of the sarcomere. Binding of a new ATP molecule dissociates myosin from actin. When this ATP is hydrolyzed, the myosin head will bind to actin, this time on a portion of actin closer to the end of the sarcomere. Regulatory proteins troponin and tropomyosin, along with calcium, work together to control the myosin-actin interaction. When troponin binds to calcium, tropomyosin is moved away from the myosin-binding site on actin, allowing myosin and actin to interact and muscle contraction to occur. As a regulator of muscle contraction, calcium concentration is very closely controlled in muscle fibers. Muscle fibers are in close contact with motor neurons. Action potentials in motor neurons cause the release of the neurotransmitter acetylcholine in the vicinity of muscle fibers. This ge

 Core: Musculoskeletal System

Surface Electromyographic Biofeedback as a Rehabilitation Tool for Patients with Global Brachial Plexus Injury Receiving Bionic Reconstruction

1Clinical Laboratory for Bionic Extremity Reconstruction, Medical University of Vienna, 2Department of Orthopaedics and Trauma Surgery, Medical University of Vienna, 3Department of Bioengineering, Imperial College London, 4Division of Plastic and Reconstructive Surgery, Department of Surgery, Medical University of Vienna

JoVE 59839

 Neuroscience

Using Gold-standard Gait Analysis Methods to Assess Experience Effects on Lower-limb Mechanics During Moderate High-heeled Jogging and Running

1Faculty of Sports Science, Ningbo University, 2Research Academy of Grand Health Interdisciplinary, Ningbo University, 3Department of Automation, Biomechanics and Mechatronics, The Lodz University of Technology, 4Savaria Institute of Technology, Eötvös Loránd University

JoVE 55714

 Behavior

Antigenic Liposomes for Generation of Disease-specific Antibodies

1Janssen R&D, 2Department of Microbiology and Immunology, University of North Carolina, 3UNC Food Allergy Initiative, University of North Carolina, 4Department of Pediatrics, University of North Carolina, 5Department of Chemistry, University of Alberta, 6Department of Molecular Medicine, Scripps Research Institute, 7Department of Medical Microbiology and Immunology, University of Alberta

JoVE 58285

 Immunology and Infection

Integration of Brain Tissue Saturation Monitoring in Cardiopulmonary Exercise Testing in Patients with Heart Failure

1Department of Physical Medicine and Rehabilitation, Chang Gung Memorial Hospital, Linkou, 2Healthy Aging Research Center, Chang Gung University, 3School of Medicine, College of Medicine, Chang Gung University, 4Department of Physical Medicine and Rehabilitation, Chang Gung Memorial Hospital, Keelung, 5National Quemoy University, 6Kinmen Hospital, Ministry of Health and Welfare

JoVE 60289

 Medicine

An Objective and Child-friendly Assessment of Arm Function by Using a 3-D Sensor

1Data Science, Roche Pharmaceutical Research and Early Development Informatics, Roche Innovation Center Basel, F. Hoffmann-La Roche, Ltd., 2Translational Technologies and Bioinformatics, Pharmaceutical Sciences, Roche Pharmaceutical Research and Early Development, Roche Innovation Center Basel, F. Hoffmann-La Roche, Ltd., 3Biomarker Experimental Medicine, Neuroscience, Roche Pharmaceutical Research and Early Development, Roche Innovation Center Basel, F. Hoffmann-La Roche, Ltd., 4Division of Neuropediatrics, University of Basel Children's Hospital, 5Department of Neurology, University of Basel Hospital, 6Translational Medicine, Neuroscience and Rare Diseases, Roche Pharmaceutical Research and Early Development, Roche Innovation Center Basel, F. Hoffmann-La Roche, Ltd.

JoVE 57014

 Behavior

Paradigms of Lower Extremity Electrical Stimulation Training After Spinal Cord Injury

1Spinal Cord Injury and Disorders Service, Hunter Holmes McGuire VAMC, 2Department of Physical Medicine and Rehabilitation, Virginia Commonwealth University, 3Deceased, Department of Kinesiology, The University of Georgia, 4Department of Physical Medicine and Rehabilitation, Penn State Milton S. Hershey Medical Center

JoVE 57000

 Behavior
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