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Muscle Physiology and Electromyography
Published in Verna Wright, Eric L. Radin, Mechanics of Human Joints, 2020
To analize the movements fully, it is necessary to know the forces acting in the muscles. The only fail-safe method of doing this is to construct a statically determinate mechanical model of the body segment under consideration and solveit according to Newton’s laws. In many studies this method is not feasible, and consequently, investigations have turned to shortcut methods for estimating muscle force. Muscle contraction is initiated by an electrical impulse, and this can be recorded using the technique of electromyography (EMG), which produces signals of varying sizes according to the intensity of the contraction. This has led to the common misunderstanding that EMG signal size is directly related to force. In fact, the relationship of EMG signal size to force is very complex, and interpretation of the signals with respect to force should be undertaken with extreme caution.
Basic Electrophysiology
Published in Joseph D. Bronzino, Donald R. Peterson, Biomedical Engineering Fundamentals, 2019
FIGURE 38.2 A modern Galvani-like experiment. An experiment similar to that of Galvani is sketched, shows a probe (a) that creates current density J around the tip. e current causes action potentials (b) to occur in the nerve. e action potentials are drawn with stylized triangular waveforms, oset horizontally to suggest the time delay arising from action potentials propagating along the nerve. Symbol θ represents the conduction velocity, usually 1 m/s or more. (θ is used in electrophysiology to be dierent from voltage V.) Neurotransmitters (indicated by small circles at (c) allow the neural excitatory signal to cross into the muscle. Action potentials in the muscle release calcium ions, which leads to muscle contraction.
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.
Groundwater quality evaluation using the water quality index (WQI), the synthetic pollution index (SPI), and geospatial tools: a case study of Sujawal district, Pakistan
Published in Human and Ecological Risk Assessment: An International Journal, 2020
Ghulam Shabir Solangi, Altaf Ali Siyal, Muhammad Munir Babar, Pirah Siyal
The permissible calcium level in drinking water as per the WHO guidelines is 75 mg/L. The observed level of calcium concentration in the groundwater samples in the study area ranged from 14.4 to 391.2 mg/L with an average level of 126.6 ± 14.58 mg/L. About 19.2% of groundwater samples had calcium levels within the permissible limit, while the remainder of the 80.8% had calcium levels above the permissible value of 75 mg/L. In the human body, calcium facilitates muscle contraction, vascular contraction, blood clotting, and nerve signal transmission. Deficiencies in calcium increase the risk of osteoporosis, nephrolithiasis, hypertension, cancer, and artery diseases in humans, whereas higher levels of calcium and magnesium in the human body are harmful, especially for those who have a tendency to produce kidney and bladder stones (Saleem et al.2016). The interpolated spatial distribution calcium map (Figure 4a) shows that calcium concentration in most of the areas of the district exceeded the safe level of 75 mg/L.
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.
Influence of type of MVC test on electromyography measures of biceps brachii and triceps brachii
Published in International Journal of Occupational Safety and Ergonomics, 2018
Danuta Roman-Liu, Paweł Bartuzi
Phenomena related to muscle contraction can be registered by electromyography (EMG) with electrodes inserted into a muscle or placed on the skin surface over the muscle. Mostly because it is non-invasive, EMG with surface electrodes is increasingly significant in various applications. Measurements of the EMG signal and analyses of the differences in EMG measures are frequently used in analysing the level of muscle contraction [1,2] or fatigue [3,4]. EMG is also applied to investigate muscle activity during physical exercises [5] or to diagnose the relationship between muscle cramp and exercise-related pain [6].