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Electromyograms
Published in A. Bakiya, K. Kamalanand, R. L. J. De Britto, Mechano-Electric Correlations in the Human Physiological System, 2021
A. Bakiya, K. Kamalanand, R. L. J. De Britto
In the measurement of EMG signals, there are two categories of contractions, namely, isotonic contraction and isometric contraction (Nazmi et al., 2016). Isotonic contraction is often used for athletic goals, whereas isometric contractions are utilized for physical rehabilitation. The isotonic contraction is a muscle contraction that produces force with respect to the resistance in which the length of the muscle changes. Further, isotonic contraction is classified into two types, namely, the concentric contraction and eccentric contraction (Nazmi et al., 2016). The combination of concentric and eccentric contraction creates a dynamic contraction (e.g., the joint movement during dumbbell bicep curl exercise). Concentric contraction permits the muscle to reduce unstable energy but rigidity remains constant during the contraction. In eccentric contraction, the length of the contraction is longer, disturbing the muscles to stretch in response to a greater opposing force. Isometric contraction is the contraction that creates no change in muscle length but the energy and tension remain unstable (Nazmi et al., 2016).
Isokinetics
Published in Paul Grimshaw, Michael Cole, Adrian Burden, Neil Fowler, Instant Notes in Sport and Exercise Biomechanics, 2019
Isokinetic devices can be set up to examine almost any joint within the human body. Figure G6.2 shows an application on the shoulder during a flexion and extension movement. The machine, in this case, would assess the agonist and antagonist shoulder muscle function. The agonist muscle is defined as the muscle that contracts while another muscle resists or counteracts its motion. The antagonist muscle is defined as the muscle that offers a resistance during the action of the agonist muscle. This muscle contraction can be in the form of both a concentric and an eccentric type of contraction. Concentric contraction is defined as when muscle tension is developed to accelerate a lever arm or limb. In this case, the muscle contracts concentrically and the fibres of the muscle shorten (i.e. origin and insertion are drawn together). An eccentric contraction is when muscle tension is developed to decelerate a lever arm or limb. As the muscle contracts eccentrically, its fibres lengthen and the origin and insertion points are drawn apart. During the shoulder movement portrayed in Figure G6.2, the machine would assess the torque/strength possessed by both the flexor (pectoralis major and deltoid) and the extensor (latissimus dorsi and teres major) muscles of the shoulder joint.
Electrical stimulation of cells derived from muscle
Published in Ze Zhang, Mahmoud Rouabhia, Simon E. Moulton, Conductive Polymers, 2018
Anita F. Quigley, Justin L. Bourke, Robert M. I. Kapsa
The influence of electrical stimulation on myogenic behavior is best known as the force that facilitates and dictates muscle contraction, as demonstrated by Galvani, Aldini, Duchenne, and McWilliam. In the body, skeletal muscle contractile activity is controlled by the nerves where an action potential travels down the nerve to the nerve ending, resulting in the release of acetylcholine at the neuromuscular junction. This neurotransmitter binds to acetylcholine receptors on the sarcolemma of the muscle, resulting in the activation of sodium–potassium channels on the sarcolemma of muscle fibers, causing an influx of sodium ions. This influx causes an action potential that travels to the t-tubules and sarcoplasmic reticulum, where it induces calcium release to the cytoplasm. Calcium then binds to troponin on the tropomyosin complex and induces actin myosin filament sliding, resulting in muscle contraction. Direct electrical stimulation of skeletal muscle mimics the action potential induced by acetylcholine release, resulting in a release of calcium from the sarcoplasmic reticulum, leading to contraction. As such, the use of electrical stimulation for influencing myogenic behavior both in vivo and in vitro has great potential in medicine for the treatment of neuromuscular disorders, paralysis, and many other disorders involving skeletal, cardiac, and smooth muscles.
Relationship between pre-exercise muscle stiffness and muscle damage induced by eccentric exercise
Published in European Journal of Sport Science, 2019
Jingfei Xu, Siu Ngor Fu, Dong Zhou, Chen Huang, François Hug
During eccentric contraction, the muscle is forcibly lengthened leading to damage of its contractile and cytoskeletal constituents (LaStayo et al., 2003). Reduced maximal voluntary contraction (MVC) torque, delayed onset muscle soreness and increase in passive muscle stiffness are commonly used as non-invasive markers of muscle damage (Proske & Allen, 2005). Among them, the decrease in MVC is considered as one of the best indirect indicators of muscle damage in human (Paulsen, Mikkelsen, Raastad, & Peake, 2012). The magnitude of force reduction, however, is highly variable among individuals even when exposed to the same exercise protocol (Clarkson et al., 2005; Nosaka & Newton, 2002). The underlying mechanisms for these individual differences in strength loss are unclear. Muscle extensibility has been proposed as one of the factors that affect the force reduction associated with eccentric exercise (Chen, Nosaka, et al., 2011; McHugh et al., 1999).
Resistance characteristics of innovative eco-fitness equipment: a water buoyancy muscular machine
Published in Sports Biomechanics, 2018
Wei-Han Chen, Ya-Chen Liu, Hsing-Hao Tai, Chiang Liu
Muscle contractions can be divided into isometric (constant length), concentric (decrease in length) and eccentric (increase in length) patterns according to changes in muscle length during contraction. Each contraction pattern has advantages and disadvantages in terms of training gains (Berger, 1962; Colliander & Tesch, 1990; Potier, Alexander, & Seynnes, 2009) or injury risks (Moritani, Muramatsu, & Muro,1988; Okamoto, Masuhara, & Ikuta, 2006; Potier et al., 2009; Proske & Morgan, 2001), such as static (isometric) strength being improved considerably more by training statically rather than dynamically, and conversely, dynamic (concentric and eccentric) strength being improved considerably more by training dynamically rather than statically (Berger, 1962). Eccentric training can promote strength, fascicle length and range of motion by the repeated destruction and recovery of muscle fibres, and can reduce the incidence of sports injuries (Potier et al., 2009; Proske & Morgan, 2001); however, this is inconvenient and less safe. Conversely, concentric training is more safe (Moritani et al., 1988) and convenient than eccentric training, but has an adverse effect on atherosclerosis (Okamoto et al., 2006); in addition, increases in strength-related performance were greater following a programme consisting of maximum concentric and eccentric muscle actions than those in resistance training using only concentric muscle actions (Colliander & Tesch, 1990). Therefore, a muscular fitness training machine with isometric, concentric and eccentric resistances may provide users with more comprehensive training. In addition, force–length and force–velocity relationships are crucial factors in resistance training.
Shoulder muscles coordination during eccentric actions
Published in Computer Methods in Biomechanics and Biomedical Engineering, 2019
N. A. Turpin, R. Martinez, M. Begon
Eccentric (ECC) contraction corresponds to when an active muscle is stretched. This mode of contraction is commonly encountered in sports or occupational activities, for example when resisting or lowering a load or in the deceleration phase of throwing. ECC contractions have been associated with poor force control, variable motor output and with altered and variable movement kinematics. Actually, inhibitory and excitatory influences on the motoneurons and the control strategies associated with ECC contractions proved to be distinct from concentric (CON) or isometric contractions (Duchateau and Enoka 2008).