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Tissue Structure and Function
Published in Joseph W. Freeman, Debabrata Banerjee, Building Tissues, 2018
Joseph W. Freeman, Debabrata Banerjee
Each sarcomere is composed of two sets of protein filament, myosin and actin (Figure 4.4). These are the principal force-generating components in the sarcomere. Thick myosin filaments are made up of many myosin molecules and are located in the A band. Myosin has a globular head end and a tail section (Figure 4.35). The center part of the filament contains only the tail regions because the molecules are oriented oppositely in either end of the filament in a bipolar arrangement (Figure 4.35). Actin is located primarily in filaments in the I bands but extends into the A bands (Figure 4.35). The thin filaments also contain smaller amounts of two other proteins, troponin and tropomyosin (Figure 4.35). The overlap of the actin and myosin filaments causes the dark coloration of the A bands. The myofilaments are arranged in interdigitating matrices capable of sliding across each other.
Muscle Physiology and Electromyography
Published in Verna Wright, Eric L. Radin, Mechanics of Human Joints, 2020
The muscle fibers are 10–100 μm in diameter and can be as long as 150 mm (4). Muscle fibers are multinucleated cells with the nuclei embedded in the sarcolemma (cell membrane). The sarcoplasm (cytoplasm) of each nucleus is drawn out into long thin strands—myofibrils—of diameter around 1 /zm. Within a single myofibril are two types of proteins, actin and myosin; the combination of these proteins to form actomyosin and subsequent splitting into component parts is the basis of muscular contraction. Under magnification, the myofibrils appear striated, and close examination reveals the repeating arrangement of the sarcomeres, as illustrated in Figure 4. The sarcomere is the basic contractile unit; it is here that length changes and force generation occur.
Bioenergy Principles and Applications
Published in Eduardo Rincón-Mejía, Alejandro de las Heras, Sustainable Energy Technologies, 2017
Marina Islas-Espinoza, Alejandro de las Heras
All cells are capable of movement. However, skeletal muscle cells are specialized in allowing animal movement. Each muscle is made of many muscle fibers. Each fiber is a large multinuclear cell. Each of these cells has a larger number of small fibers (myofibrils). Each myofibril is made of many aligned units (sarcomeres), each of which contracts thereby shortening the muscle (Figure 20.1). Sarcomere contraction is a sliding movement of actin protein filaments sliding along myosin protein filaments, according to the 1954 Huxley–Niedergerke–Hanson model. During the shortening of the sarcomere, myosin hydrolyzes ATP (Cooper and Hausman, 2015).
Urinary N-terminal fragment of titin: A surrogate marker of serum creatine kinase activity after exercise-induced severe muscle damage
Published in Journal of Sports Sciences, 2021
Yoko Tanabe, Kazuhiro Shimizu, Hiroyuki Sagayama, Naoto Fujii, Hideyuki Takahashi
The ROM decline rate was also moderately correlated with U-titin concentration and serum CK activity (Figure (4c–g)). The titin in sarcomeres plays a role in determining the ROM of the sarcomere during muscle tension, thus contributing to passive muscle stiffness (Lindstedt et al., 2002). On the other hand, eccentric exercise may cause damage to connective tissue, which can decrease ROM (Jones et al., 1987). Unsurprisingly, ROM consequently only moderately correlates with U-titin concentration and serum CK activity in the present study.
Responses to a combined dynamic stretching and antagonist static stretching warm-up protocol on isokinetic leg extension performance
Published in Sports Biomechanics, 2021
David Cogley, Paul Byrne, Joseph Halstead, Colin Coyle
Mechanical changes may also contribute to the increase in power production associated with antagonist static stretching. These alterations include reductions in stiffness of sarcomeres and increases in length between resting sarcomeres that alter the length–tension relationship of the agonist muscle (Evetovich et al., 2003). Decreases in muscular strength commonly associated with agonist SS may be caused by mechanical factors such as plastic deformation of connective tissues, increased sarcomere length, and decreased sarcomere stiffness. Decreases in muscular strength commonly associated with agonist SS may be caused by mechanical factors such as plastic deformation of connective tissues, increased sarcomere length, and decreased sarcomere stiffness therefore (Evetovich et al., 2003; Fowles et al., 2000). Lengthening the sarcomeres beyond an optimal length for force production alters the length tension relationship and therefore limits the maximal force production capabilities of the muscle (Fowles et al., 2000). Given the evidence that AMSS facilitates increased electrical activity to the agonist muscle group (Miranda et al., 2015), it is possible that AMSS also increases sarcomere stiffness of the agonist, thereby increasing muscular performance. Methods of monitoring mechanical changes in the muscle include mechanomyography (MMG) signals which record and quantify the low-frequency lateral oscillations of active skeletal muscle fibres reflecting the mechanical counterpart of the muscle activation (Herda et al., 2008). Evetovich et al. (2003) reported mechanomyography (MMG) readings to be increased (indicating reduced sarcomere stiffness) in the agonist muscle of a SS participant group versus the non-stretch group. Given that the non-stretch group produced significantly more torque, it may have been as a result of increased sarcomere stiffness, measured by MMG. The evidence of this is unclear, however, as Cramer et al. (2005) reported no difference in MMG following SS, which is in contrast to Evetovich et al. (2003). Considering that no MMG reading was utilised by Sandberg et al. (2012) it is possible that the improvements in torque that occurred via AMSS were as a result of decreased sarcomere stiffness of the agonist muscle, therefore increasing sarcomere stiffness of the antagonist musculature. In the current study, incorporating passive stretches instead of active stretches may have improved the effectiveness of the AMSS due to a greater degree of stretch placed on the muscles therefore potentially facilitating a greater degree of the mechanical adaptations mentioned.