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Skeletal Muscle
Published in Nassir H. Sabah, Neuromuscular Fundamentals, 2020
Aponeuroses are similar in composition to tendon but are flat and broad. They are associated with sheet-like muscles having a wide area of attachment rather than the restricted area of attachment of tendons (Figure 9.1). Examples are abdominal muscles, as well as intercostal muscles of the ribs, and muscles of the hand and foot. Tendons and aponeuroses convey muscular activity, whether it is mainly force or movement, to the body parts acted upon by the muscles. They contribute to the viscoelastic properties of muscle, as discussed in Section 10.3.2, and allow skeletal muscle to: be conveniently located some distance away from its point of action; for example, some of the muscles that move the fingers are located in the forearm, not the hand, and act on the fingers through long tendons;apply force along a line that is different from the muscle axis by plying around a bone acting as a pulley; for example, the knee acts as a simple pulley by means of which the quadriceps femoris muscle in the thigh extends the leg. The muscle attachment nearer to the center of the body, or which is fixed or moves least when the muscle contracts, is the origin, whereas the attachment that is farther away from the center of the body, or which moves more, is the insertion.
Muscle Physiology and Electromyography
Published in Verna Wright, Eric L. Radin, Mechanics of Human Joints, 2020
The main bulk of the muscle is belly, which is composed of muscle fibers, the functional part of the muscle. During acontraction in vivo, the muscle belly can often be seen or palpated below the skin as a pronounced, hard bulge. The tendons anchor the muscle to the skeleton at the origin (most proximal attachment) and the insertion (more distal attachment). The tendons are composed of tough collagen fibers, which abut the ends of the muscle fibers to form a continuous structure. The size and shape of the tendon can vary enormously, in some cases being completely absent. For example in the vastus medialis, one of the quadriceps group of muscles, the fibers attach directly to the anterior surface of the femur. At the other extreme, a tendon may be 250 mm or even longer, for example in the semitendinosus of the hamstring group. Most muscles have tendons that are slim and round in cross section, but in some broad, flat muscles, the tendons are flattened accordingly. In these cases the tendon is given a specific name, the aponeurosis.
Effects of barbell load on kinematics, kinetics, and myoelectric activity in back squats
Published in Sports Biomechanics, 2022
Stian Larsen, Eirik Kristiansen, Hallvard Nygaard Falch, Markus Estifanos Haugen, Marius Steiro Fimland, Roland van den Tillaar
In addition, with the 102% load, lower vastus lateralis activity was observed in all regions compared to the other loads, which also could be a factor that the lift was not successful (Figure 6), since the external knee moment increases over the first two phases. When in the first ascending region lateral vastus activity was less this results in lower knee extension at different events (Figure 3), thereby sticking at heights with less force capacity (van den Tillaar et al., 2021). Another surprising observation was greater erector spinae iliocostalis activity for 100% compared to other loads (Figure 7), as the erector spinae is responsible for maintaining a rigid torso during lifts (Schoenfeld, 2010). Its activity was expected to be the same or higher between the 100 and 102% load due to the increasing load on the trunk. However, This finding can be explained by an intricate coordinating mechanism as suggested by Toussaint et al. (1995) who found that the thoracic part of the erector spinae takes over activity of the lumbar part when demand of erector spinae increases during lifts. The thoraral part of the erector spinae has through the aponeurosis attachement at L5S1 more posterior than lumbar part of the erector spinae. Thereby it has a longer moment arm around the lumbar sacral joint and in that way it is more effective to use this part of the erector spinae to withstand the extra load (Potvin et al., 1991; Toussaint et al., 1995).
Increased toe-flexor muscle strength does not alter metatarsophalangeal and ankle joint mechanics or running economy
Published in Journal of Sports Sciences, 2019
One potential method for intrinsically altering MTPJ mechanics could be stiffening of the plantar aponeurosis or IFM tendons. Greater MTPJ passive stiffness has been shown to correlate with improved submaximal RE (Man, Lam, Lee, Capio, & Leung, 2016). Kelly, Farris, et al. (2018) demonstrated that the flexor digitorum brevis contracts isometrically during arch compression, suggesting that energy storage and return in the IFM is primarily a function of the tendon structures and not muscle tissue. If the other IFM behave similarly, then perhaps increasing IFM strength is not an effective mechanism to alter MTPJ mechanics. Increasing Achilles tendon stiffness has also been shown to improve submaximal RE (Albracht & Arampatzis, 2013), suggesting that tendon remodelling may be as or more important than muscle strengthening. At a minimum, tendon stiffness must increase with increased muscle strength, or else a faster, less efficient shortening of the muscle fascicles may occur (Albracht & Arampatzis, 2013; Lichtwark & Wilson, 2008). The IFM have a low fibre-length-to-muscle-length ratio, effectively reducing their natural excursion (Kura et al., 1997). Thus, the interplay between IFM tendon and plantar aponeurosis stiffness and the potential to passively alter MTPJ mechanics requires further investigation.
Aponeurosis behaviour during muscular contraction: A narrative review
Published in European Journal of Sport Science, 2018
Understanding whether aponeurosis stiffness can be altered at different muscle lengths and forces is crucial for understanding how this tissue contributes to elastic energy savings and power amplification during animal and human locomotion (Roberts & Azizi, 2011), as well as for determining how this tissue contributes to mechanisms of muscle damage and injury. The studies outlined in this narrative review challenge the idea that the aponeurosis and tendon have similar roles during muscular contraction and highlight that our knowledge of aponeurosis function is quite limited. Previous studies using animal preparations (Ettema & Huijing, 1989; Huijing & Ettema, 1988; Scott & Loeb, 1995) and one recent human study (Raiteri et al., 2018) have shown that the aponeurosis force–length relationship can be modulated by both muscle force and muscle length. However, it remains to be determined if a variable aponeurosis stiffness is useful for maximising muscle performance and versatility under a range of different conditions, such as walking and running at different speeds. Future work should investigate the aponeurosis contributions to mechanical work in stretch-shortening cycles in lower limb muscles that produce substantial power during walking and running, such as the triceps surae. The subsequent benefits of a variable aponeurosis stiffness on the muscle fascicle length changes should also be investigated in different species, to examine if muscle efficiency is optimised by a tuneable aponeurosis stiffness and whether this is partly responsible for the favoured pennate design of lower limb muscles in animals that have low costs of transport.