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Muscle
Published in Laurie K. McCorry, Martin M. Zdanowicz, Cynthia Y. Gonnella, Essentials of Human Physiology and Pathophysiology for Pharmacy and Allied Health, 2019
Laurie K. McCorry, Martin M. Zdanowicz, Cynthia Y. Gonnella
Movement that decreases the angle of a joint, or bends the joint, and brings the bones toward each other is referred to as flexion. For the above example, the biceps brachii flexes the forearm. In contrast, movement that increases the angle of the joint and straightens the joint is referred to as extension. In the previously mentioned example, the triceps brachii acts as an opposing muscle to the biceps brachii. Located on the posterior surface of the arm, the triceps brachii originates on the scapula and the upper portion of the humerus (arm), and inserts on the ulna (the other bone of the forearm), and crosses the elbow joint. However, when it develops tension and shortens, the triceps extends the forearm and straightens the elbow joint. Thus, the triceps brachii causes a movement opposite to that of the biceps brachii. A muscle that works in opposition to another muscle is referred to as an antagonist muscle. An agonist muscle, or prime mover, provides the force for a specific movement. In this case, the agonist muscle is the biceps brachii. Synergist muscles work with the prime movers to achieve the movement. In this case, the synergist muscle is the brachialis muscle of the arm.
Throwing
Published in Paul Grimshaw, Michael Cole, Adrian Burden, Neil Fowler, Instant Notes in Sport and Exercise Biomechanics, 2019
As with most open chain exercises, the freedom of the distal segment allows substantial variation in the specific orientation of the various segments and the relative length of each phase during the performance of the skill. These variations give rise to various techniques that may include: i) overarm throwing; ii) round-arm throwing; iii) bowling; and iv) overhead striking, serving or smashing. Within each of these different techniques there are many more variations, which makes it impossible to define all of them. Essentially the techniques differ by the orientation of the trunk and the degree of shoulder abduction. These differences in limb orientations will lead to some differences in the prime mover muscles involved in the action. However, the general phasing and the nature of the muscle actions will be consistent across all of the variants of the throwing action.
General Anatomy
Published in Gene L. Colborn, David B. Lause, Musculoskeletal Anatomy, 2009
Gene L. Colborn, David B. Lause
When a muscle contracts, it may do so as a prime mover at a joint between two bones. It may also function as a synergistic muscle with others in movement, as is often the case. A single muscle rarely acts alone as a prime mover, and its actions are influenced by the contraction or relaxation of other muscles. A muscle may also act to stabilize a joint, rather than to produce distinct joint movement; or it may function as an antagonist to other muscles acting upon a particular joint.
Shoulder muscles coordination during eccentric actions
Published in Computer Methods in Biomechanics and Biomedical Engineering, 2019
N. A. Turpin, R. Martinez, M. Begon
The number of synergies varied between 1 and 3 across subjects with a modal value of s = 2 observed in ∼75% of the subjects. Adding intramuscular recordings (rotator cuff muscles) did not change this distribution, showing that they do not belong to specific synergies. The number of synergies did not vary between CON and ECC (p = 1). The first synergy mainly activated prime mover muscles, i.e., the anterior and medial deltoids, the trapezius superior and the serratus anterior, suggesting a role in driving the movement. The second and third synergies co-activated most of the recorded muscles, suggesting a role in stabilizing the glenohumeral joint. For reasons of statistical power, we focused the rest of the analysis on the 75% of subjects with 2 synergies. Synergy vectors were similar between CON and ECC, i.e. r = 0.96 ± 0.04 and 0.84 ± 0.14 for synergy #1 and #2, respectively. Activation of synergy #1 was lower in ECC at the lowest position on the trajectory (arms down; Figure 2). Activation of synergy #2 was greater at times corresponding to mid-range of motion (∼20–55%) and end-range of motion (∼90–100%). Mid-range and end-range of motion correspond to when the tension provided by the glenohumeral ligaments is negligible and to positions at which glenohumeral dislocations usually occur, respectively. These observations strongly support the hypothesis that synergy #2 participates in glenohumeral stabilization.
Validation of an OpenSim full-body model with detailed lumbar spine for estimating lower lumbar spine loads during symmetric and asymmetric lifting tasks
Published in Computer Methods in Biomechanics and Biomedical Engineering, 2019
Erica Beaucage-Gauvreau, William S. P. Robertson, Scott C. E. Brandon, Robert Fraser, Brian J. C. Freeman, Ryan B. Graham, Dominic Thewlis, Claire F. Jones
The poor results for the RA muscles were expected because SO (used in this analysis) penalises antagonist co-contraction (Ait-Haddou et al. 2000). Since the prime-mover muscles during lifting are the trunk extensors (Cresswell and Thorstensson 1994), the effect of the abdominal contractions on the net forces and moments is minimal (Cholewicki et al. 1999). Activation of the antagonist abdominal muscles, and the resulting intra-abdominal pressure (IAP), results in unloading of the lumbar spine during lifting tasks (Stokes et al. 2010); however, the contribution of IAP to increased lumbar spine stiffness and stability is thought to be more significant than its effects on vertebral loading (Cholewicki et al. 1999). The LFB model is not suitable to evaluate the effect of abdominal muscle activity on spine loading, and future work should consider the contributions of RA activations to IAP, and therefore to the loading, stiffness and stability of the lumbar spine.
A versatile approach to determine instantaneous co-activation: Development, implementation and comparison to existing measures
Published in Computer Methods in Biomechanics and Biomedical Engineering, 2018
Daniel Viggiani, Jeff M Barrett, Kayla M Fewster, Jack Callaghan
Firstly, these equations almost exclusively utilize muscle pairs acting in a single plane on a single hinge joint, where one muscle is the ‘prime mover’ and the other provides ‘movement control’ (Falconer and Winter 1985; Rudolph et al. 2000; Lewek et al. 2004). However, there often is no single prime mover in situations where muscles act about multiple anatomical axes (Tsuang et al. 1993) or span multiple joints (Hahn et al. 2014). There have been attempts to overcome this two-muscle limitation. Current modelling approaches (Brookham et al. 2011; Brookham and Dickerson 2014; Le et al. 2018) employ a set of equations to quantify co-contraction between multiple muscles considering the relative size of each muscle of interest. However, one limitation to these approaches is that each muscle must be specified as an agonist or antagonist and the output remains an agonist/antagonist ratio similar to the historical two-muscle equations. Ranavolo et al. (2015) proposed a series of equations determining the dissimilarities between all possible pairs of muscles, correcting for the number of muscles used, and redistributing the output using a sigmoid-shaped weighting term. While this method allows for co-activity measures of multiple muscles without specificity to a plane of motion, there are some drawbacks. In particular, inconsistencies arise at lower levels of muscle activity (<50% maximum voluntary activation (MVA)) since they are mapped to a relatively insensitive region of the sigmoidal curve (Ranavolo et al. 2015). In short, the capability of these methods to accommodate more than two muscles is a recent development.