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Spinal Cord and Reflexes
Published in Nassir H. Sabah, Neuromuscular Fundamentals, 2020
Reciprocal inhibition involves Ia inhibitory interneurons and is illustrated in Figure 11.6. Suppose that an agonist muscle for a given movement is contracting, so that its antagonist muscle, together with the muscle spindles in this muscle, are being stretched, which activates the Ia primary afferents of these muscle spindles. These afferents make excitatory synapses on Ia-interneurons that are in turn inhibitory to the α-motoneurons of the antagonist muscle (Figure 11.6). The contraction of the agonist muscle therefore relaxes the antagonist muscle though inhibition mediated by the Ia inhibitory interneurons of the antagonist muscle. A Renshaw cell is also shown in Figure 11.6 that is excited by the α-motoneurons of the synergist muscle and which in turn inhibits the Ia interneuron that inhibits the α-motoneurons of the antagonist muscle, as may be required in some cases. This inhibition of a neuron that inhibits a target neuron is an example of disinhibition of the target neuron.
Fundamentals
Published in Clare E. Milner, Functional Anatomy for Sport and Exercise, 2019
Skeletal muscle is voluntary muscle. Its primary function is to move the body at the joints. Skeletal muscle typically makes up about 40 per cent of body weight and there are more than 600 skeletal muscles in the body. Skeletal muscle has four major functions: movement, posture, joint stabilization and heat generation. Skeletal muscle is attached to the bones of the skeleton via connective tissue (see skeletal muscle – structure). The origin and insertion of a muscle are on different bones, with the muscle (or its tendon) crossing one or more joints. When the muscle contracts and shortens, it moves the bone at the joint the muscle crosses; coordinated movement of bones by muscles moves the whole body. Muscles which cross only one joint are known as ‘monoarticular’ muscles. For example, the vasti muscles, which are part of the quadriceps femoris, are monoarticular knee extensors. Their origin is on the femur and insertion on the tibia with the muscle tendon crossing the front of the knee. Muscles which cross two joints are ‘biarticular’ and can move either one or both joints depending on the action of the surrounding muscles. For example, rectus femoris is the fourth of the quadriceps muscles and it crosses the front of both the hip and knee joints. Rectus femoris can both flex the hip and extend the knee. Either of these actions can be held in check by the antagonist muscle group. For example, if hip extensors oppose the hip flexion action of rectus femoris, it will only extend the knee during concentric contraction.
Isokinetics
Published in Paul Grimshaw, Michael Cole, Adrian Burden, Neil Fowler, Instant Notes in Sport and Exercise Biomechanics, 2019
Isokinetic devices can be set up to examine almost any joint within the human body. Figure G6.2 shows an application on the shoulder during a flexion and extension movement. The machine, in this case, would assess the agonist and antagonist shoulder muscle function. The agonist muscle is defined as the muscle that contracts while another muscle resists or counteracts its motion. The antagonist muscle is defined as the muscle that offers a resistance during the action of the agonist muscle. This muscle contraction can be in the form of both a concentric and an eccentric type of contraction. Concentric contraction is defined as when muscle tension is developed to accelerate a lever arm or limb. In this case, the muscle contracts concentrically and the fibres of the muscle shorten (i.e. origin and insertion are drawn together). An eccentric contraction is when muscle tension is developed to decelerate a lever arm or limb. As the muscle contracts eccentrically, its fibres lengthen and the origin and insertion points are drawn apart. During the shoulder movement portrayed in Figure G6.2, the machine would assess the torque/strength possessed by both the flexor (pectoralis major and deltoid) and the extensor (latissimus dorsi and teres major) muscles of the shoulder joint.
Effects of rTMS combined with rPMS on stroke patients with arm paralysis after contralateral seventh cervical nerve transfer: a case-series
Published in International Journal of Neuroscience, 2023
Ting Yang, Xueping Li, Peng Xia, Xiaoju Wang, Jianqiang Lu, Lin Wang
The protocol of rPMS is outlined in Figure 1(b). The rPMS procedure is utilized to reduce spasticity of the hemiplegic upper limb. The patient is placed in a supine position with the upper extremity naturally positioned at side of the body. Stimulation is prescribed according to Modified Ashworth Scale (MAS) classification [20]. Muscles with a MAS classification ≥ I+ were stimulated at 5 Hz for a total of 750 stimulations, with 15 stimulations per string and 3 s intervals between trains. If the antagonist muscle has a MAS classification ≥ I+, it is then stimulated with similar parameters. Otherwise, it is stimulated at 20 Hz for a total of 5100 stimulations, with 30 stimulations per train and 3 s intervals between trains. The intensity was 100% RMT. The coil was placed on the skin without pressure, which led to stimulation of two groups of muscles, the elbow flexor and extensor groups and wrist extensor and flexor groups, respectively. When stimulating, the therapist held the coil, thus moving each group of muscles from proximal to distal stimulation and moving one time at the rate of the duration of each train [21]. The rPMS was also carried out one time per day for 15 days.
Anticipatory and Compensatory Postural Adjustments in Response to Dynamic Platform Perturbation during a Forward Step
Published in Journal of Motor Behavior, 2023
Yun Wang, Kazuhiko Watanabe, Tadayoshi Asaka
In response to support surface perturbations, stepping expands the boundary of the base of support and shifts the COM away from the initial position, which requires close coordination among the trunk and leg muscles. To maintain and restore balance, the central nervous system (CNS) coordinates reciprocal and co-contraction activation in agonist-antagonist postural muscles (Lee et al., 2019; Slijper & Latash, 2004). While reciprocal activation of the trunk and leg muscles effectively move the body in the AP direction, co-contraction muscle activation patterns increase the apparent stiffness of the joints and provide body stability (Aruin & Latash, 1995; Wang et al., 2019). Within the framework of the equilibrium-point hypothesis (Feldman, 1986), R and C indices describe reciprocal and co-contraction activation of agonist-antagonist muscle pairs at a joint level. It has been showed that moving the body in space led to an increase in the R index, whereas an increase of the C index contributed to stabilization of posture (Slijper & Latash, 2004).
Gait characteristics and effects of early treadmill intervention in infants and toddlers with down syndrome: a systematic review
Published in Disability and Rehabilitation, 2022
Esra Kınacı-Biber, Kübra Önerge, Akmer Mutlu
Only one study [8] investigated muscle co-contraction indices, and the results showed an increase during the swing phase in children with DS. In order to compensate for ligament laxity and other biomechanical disadvantages, DS children may perform more co-contraction with the limb in the swing phase while performing activities that require skills beyond their abilities. DS individuals show compensatory strategies due to their disadvantages in the gait cycle. Rigoldi et al. [4] in their study, DS participants (children, teenagers and adult) reported a decrease in movement in the distal joints in the sagittal plane by increasing hip movements in the frontal plane to maintain walking. It has been shown to increase joint stiffness, agonist and antagonist muscle co-contraction. The relationship between these strategies and gait parameters such as gait kinematics and kinetics, energy consumption, number of body segments involved in gait cycle and support base should be investigated in DS toddlers.