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Force Generation Mechanism of Skeletal Muscle Contraction
Published in Yuehong Yin, Biomechanical Principles on Force Generation and Control of Skeletal Muscle and their Applications in Robotic Exoskeleton, 2020
The main functions of muscle spindle are detecting and feeding back muscle length and contraction velocity. It can be divided into nuclear bag type and nuclear chain type, and the structures are illustrated in Figure 1.15a and b, respectively. It can be seen that these two types are very similar, and only differ in the response characteristics. Muscle spindle is in parallel with muscle fiber and is located in muscle belly. There are also contractile fiber tissues in muscle spindle. They are located on both ends of the muscle spindle and are called as “intra-spindle muscle”. Correspondingly, the muscle fibers are called “extra-spindle muscle”. The contractions of intra-spindle muscle and extra-spindle muscle are dominated by γ and α motoneurons, respectively.
The relation between psychosocial working conditions and work-related musculoskeletal complaints
Published in Richard Graveling, Ergonomics and Musculoskeletal Disorders (MSDs) in the Workplace, 2018
Leif W. Rydstedt, J. Paul Weston
Muscle spindles provide proprioceptive feedback control of muscle tone and co-ordination of movement. Mental stress, and subsequently, elevated sympathetic arousal, has been shown to inhibit these regulatory functions. Muscle spindle activity has been suggested to be affected by static and/or repetitive work through increased release of metabolites and inflammatory substances by the muscles, resulting in their increased stiffness and metabolic activity. It has been postulated by Johansson and Sojka (1991) that this defensive mechanism against monotonous movement is related to the stress-response system. With altered proprioception, coordination of muscular and metabolic activity can be affected, with subsequent irritation of the sympathetic nervous system. Muscle spindle populations are densest in relation to the intrinsic musculature of the spine and in muscles required for fine motor control and movement. This relates to the common sites of MSDs.
Movement Control (Muscular Physiology)
Published in Emeric Arus, Biomechanics of Human Motion, 2017
The neuromuscular spindle (muscle spindle) is a complex sensory nerve-ending organ in the muscle that is sensitive to stretch in which the afferent nerve fibers terminate. This specialized fiber is involved in the stretch (myotatic) reflexes. The contact point of this sensory nerve ending is enclosed in connective tissue sheaths also called “stretch receptors.”
Skill level and forearm muscle fatigue effects on ball speed in tennis serve
Published in Sports Biomechanics, 2021
Lin-Hwa Wang, Kuo-Cheng Lo, Fong-Chin Su
Ulnar-sided wrist pain, a common complaint reported by tennis players, is associated with the ECU and FCU tendons. To perform top-spin serves, tennis players execute double-handed backhand strokes and rapid forearm rotation, leading to acute injuries for the ECU tendon. In a relevant study, an almost constant level of tendon strain occurred under eccentric contractions for the ECRL, ECRB and EDC branches during skew-driving (Murgia, Harwin, Prakoonwit, & Brownlow, 2011). This provides implications for lateral epicondylitis during forearm pronation and supination. The non-expert group demonstrated greater tendinopathy for the extensor tendon syndromes (100%) than did the expert group (25%) in this study. This injury caused unstable performance. In such a state, muscles are stimulated to protect the joint by a reflexive arc in the capsule and edge of the muscles as the joint is subjected to unstable conditions (Guanche, Knatt, Solomonow, Lu, & Baratta, 1995). Reflex latencies refer to the duration from the joint experiencing the perturbation to the time of muscle activity onset for protection. Muscle activity promotes sensitivity of the muscle spindle to change in muscle length (Allum & Mauritz, 1984). On the basis of these theories, forearm muscle activity may be immediately induced to stabilise the medial elbow as the peak elbow valgus force occurs; moreover, pain reduces muscle strength and dysfunction in the arm during serving motions.
Tendon vibration changes perceived joint angle independent of voluntary body motion direction in virtual environments
Published in Advanced Robotics, 2021
Daiki Hagimori, Naoya Isoyama, Shunsuke Yoshimoto, Nobuchika Sakata, Kiyoshi Kiyokawa
The perceptual modulation in this study is based on a kinesthetic illusion, in which the muscles opposite the vibrating part contract or feel extended and flexed when the muscles or tendons are stimulated [10] (see Figure 1 (lower left)). However, a joint that misperceives joint motion may not be the joint closest to the stimulus [11]. It is considered that the illusion is generated by intentionally activating muscle spindles and Golgi tendon organs [16]. The muscle spindles are located in the muscle and detect muscle length. The Golgi tendon organs are located in the tendon and sense tension in the tendon.
Impact of military type footwear and load carrying workload on postural stability
Published in Ergonomics, 2019
Harish Chander, Adam C. Knight, John C. Garner, Chip Wade, Daniel Carruth, Samuel J. Wilson, Jacob R. Gdovin, Caleb C. Williams
Intrinsic or human factors such as muscular fatigue or muscular exertion as result of a physiological workload has also been associated with decreased balance performance (Vuillerme et al. 2002; Corbeil et al. 2003; Chander, Garner, and Wade 2014, Wade et al. 2014; Lepers et al. 1997). A common intrinsic factor that can be seen as a perturbation to the postural control system is localised muscular fatigue, which has been shown to result in lowered balance performance (Corbeil et al. 2003; Garner et al. 2013). Published results have supported that postural stability and equilibrium are impaired after prolonged exhausting physical exercise (Pline, Madigan, and Nussbaum 2006, Caron 2004, Yaggie and McGregor 2002, Gribble and Hertel 2004). Results from the current study support previous literature as the majority (∼62%) of the SOT postural sway parameters that include the EQ scores, COMP scores, postural sway velocities, root mean square sway and the MCT postural reaction time latencies exhibited significantly reduced balance performance post-load carriage task as compared to pre-load carriage task, which could be attributed to the muscular exertion/fatigue experienced while performing the maximal effort load carriage task. When the sensory or motor components are altered or defective due to muscular exertion, body sway generally increases and concurrently there is an increased demand on the central mechanisms and peripheral muscles to maintain postural equilibrium (Corbeil et al. 2003). Muscular fatigue may impair the proprioceptive and kinesthetic properties of joints by increasing the threshold of muscle spindle discharge, disrupting afferent feedback and ultimately altering conscious joint awareness (Gribble and Hertel 2004) thereby decreasing balance performance. Results from this study support previous literature in exhibiting decreased balance performance during the post-load carriage task conditions compared to pre-load carriage task. Hence, the increases in postural sway could be attributed to localised muscle fatigue indicating an impairment of the postural control system, which is typically associated with increases in postural instability and fall rates.