Neuromuscular Physiology
Michael H. Stone, Timothy J. Suchomel, W. Guy Hornsby, John P. Wagle, Aaron J. Cunanan in Strength and Conditioning in Sports, 2023
From a gross anatomical aspect, muscle fibers are arranged into two basic structural patterns: fusiform or pennate (also spelled pinnate). The fusiform arrangement makes up most human muscle, with the fibers largely arranged in parallel arrays along the muscle’s longitudinal axis with tendons at the proximal and distal ends. In many of the larger muscles the fibers (and the fascicles) are inserted obliquely into the tendon, and this arrangement resembles a feather (i.e., pennation). Pennate muscle fibers are typically shorter than those of a fusiform muscle and insert on their tendons in several different manners forming uni-, bi-, and multipennate muscles. Fusiform fibers can largely run parallel, converge or form a circular arrangement; the various arrangements of human fusiform and pennate muscle fibers are shown in Figure 1.1.
The movement systems: skeletal and muscular
Nick Draper, Helen Marshall in Exercise Physiology, 2014
A pennate muscle has fascicles that attach obliquely, at a common angle, to the tendon. Due to the angular arrangement, and hence direction of pull of the muscle fibres, contraction of a pennate muscle is unable to reduce its length to the same degree as a parallel muscle. A greater number of myofibrils, however, are found in pennate muscles allowing for a greater development of muscular tension. Pennate muscles, therefore, generally allow a higher force production but a smaller range of movement. Depending on the location of the fascicles in relation to the tendon, a pennate muscle may be classified as unipennate, bipennate or multipennate. A muscle is unipennate when all muscle fibres are on one side of the tendon and bipennate when on both sides of the tendon. Bipennate muscles are much more common, with the rectus femoris muscle of the thigh being a well-known example. In some cases the tendon branches within a pennate muscle and is known as multi-pennate, for example the deltoid muscle of the shoulder.
Functional Properties of Muscle
Nassir H. Sabah in Neuromuscular Fundamentals, 2020
where the function is assumed to be some power law. It would seem logical to assume, as has been the case in most of the literature, that the force developed by a muscle fiber is directly proportional to the cross-sectional area of the fiber. However, more recent work on chemically skinned human muscle fibers has indicated that the force is more nearly proportional to fiber diameter rather than cross-sectional area, the force per unit diameter being approximately 6.5 N/m for both type I and type IIA fibers. Thus, n = 1 in Equation 10.21 if the force is directly proportional to the cross-sectional area, and n = 1/2 if the force is proportional to a linear dimension of the cross-sectional area. In either case, the term sinnϕcosϕ is always less than 1. But the ratio (L/w)n can be large, so that the ratio (Fpen/Fpar) > 1. The force developed by a pennate muscle is therefore larger than that developed by a parallel muscle of the same volume, but the excursion in the line of action of the muscle will be smaller. In human limb muscles, the mean pennation angles are usually between 5° and 15°. On the other hand, the lateral gastrocnemius muscle of the wild turkey is a unipennate muscle having an average pennation angle of 25°.
Modeling of muscular activation of the muscle-tendon complex using discrete element method
Published in Computer Methods in Biomechanics and Biomedical Engineering, 2021
Anthony Roux, Jennyfer Lecompte, Ivan Iordanoff, Sébastien Laporte
With a maximal isometric force of a muscle fiber fixed at Fmax fiber = 0.3 N, a pack of 400 muscle fibers create a maximal isometric force of 400 × 0.3 = 120 N. However, a parallelepiped of 400 muscle fibers gives a maximal isometric force of 104.2 N and a parallelepiped of 400 muscle fibers oriented by 20° gives a maximal isometric force of 68.8 N. The decrease in force is due to the parallelepiped structure, the pennation angle and the influence of the ECM on the mechanical behavior. For a cylindrical structure with the same dimensions (pennation angle = 20°), the maximal isometric force is 37.3 N. This new decrease is linked to the cylindrical geometry and shorter muscle fibers at the external surface of this specific shape. The relationship between the maximal isometric force of the muscle fiber alone and the equivalent MTC of 400 pennate muscle fibers is not obvious; it depends on the behavior of the ECM, the shape of the equivalent MTC and the value of the pennation angle (Winters and Stark 1988; Winter and Challis 2010; Sànchez et al. 2014; Todros et al. 2020).
The effect of dry needling on spasticity, gait and muscle architecture in patients with chronic stroke: A case series study
Published in Topics in Stroke Rehabilitation, 2018
Sarafraz Hadi, Otadi Khadijeh, Mohammadreza Hadian, Ayoobi Yazdi Niloofar, Gholamreza Olyaei, Bagheri Hossein, Sandra Calvo, Pablo Herrero
Muscle forces and morphometric parameters of the lower limb skeletal muscles have proven to be good determinants for balance and functional mobility (i.e. gait) after a stroke.6 Consequently, changes in morphometric parameters could alter the muscle force generation.7 Gastrocnemius and soleus are among the prime muscles in the lower limb with main role in standing and walking at all speeds,8 and their contributions increase as gait speeds up in stroke patients.9 Besides, gastrocnemius medialis (GM) is the most common pennate muscle affected by spasticity after stroke,10 and therefore, gait function might be disturbed in this group of patients.9 In pennate muscles, fascicles are arranged in parallel and attach with oblique angles to the tendon, and the resultant forces are transmitted at these angles.11 As mentioned in the literature, muscle architecture (i.e. pennation angle and fascicle length measures) affects the muscle function12 and these measures are often used to estimate the amount of force-generating capability in the muscles.13 Due to spasticity, stroke patients tend to hold their ankle joint in plantar flexion (i.e. in the direction of gravity force). Furthermore, immobilization in this position may cause changes in muscle architecture such as shorter fascicle length and larger pennation angle in comparison with normal individual. Changes in muscle fascicle lengths and their pennation angles will affect the physiologic cross-section, and consequently, force generation potential may reduce14,15 in gait cycles. Using ultrasonography imaging is the most useful, feasible and cheap tool for assessing the muscle architecture parameter, and it is possible to detect some.16,17
A comprehensive and volumetric musculoskeletal model for the dynamic simulation of the shoulder function
Published in Computer Methods in Biomechanics and Biomedical Engineering, 2019
Fabien Péan, Christine Tanner, Christian Gerber, Philipp Fürnstahl, Orcun Goksel
The shoulder is a complex biomechanical system involving many interactions between each structure. To be able to fully express the range-of-motion in a functional way, and to output clinically acceptable results, one needs to take into account many muscles and their constraints. This requires to have a complete set of muscles interacting with the humerus and the scapula, to handle the constraints such as bone-muscle or muscle-muscle contacts. Moreover, it is necessary to consider the muscle as a volumetric object to properly represent internal material and stress variations. This has the advantage of a more realistic transfer of the forces through shear, which has been described as a major effect in muscular tissues (Maas and Sandercock 2010). The presented model lacks anatomical features, such as fascia, is nonetheless more complete than the previous FE model of the same kind (Röhrle et al. 2017; Webb et al. 2014; Büchler et al. 2002; Terrier et al. 2007). As a result of using volumetric muscles, modelling pathologies such as a partial tendon tear is applicable, which is impossible to reproduce in line-segment models. Additionally, this geometric representation allows to adapt more naturally the fiber orientations inside the muscles. It has been shown that fiber direction varies substantially in the supraspinatus between the anterior and posterior part (Kim et al. 2007). The middle part of the deltoid has often been reported as a multi-pennate muscle (Klepps et al. 2004). The model here presented does not include all of these muscle specific fiber architecture. However, given our model, such different fiber directions can be accommodated and varied easily. With the current version, we focused on the completeness of muscle sets and bone-muscle interactions, while the analysis of the internal fibers architecture and of intricate pathologies on the motion are left for a future study.
Related Knowledge Centers
- Deltoid Muscle
- Epimysium
- Hand
- Rectus Femoris Muscle
- Endomysium
- Skeletal Muscle
- Muscle Fascicle
- Muscle Architecture
- Perimysium
- Quadriceps