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Neuromuscular Physiology
Published in Michael H. Stone, Timothy J. Suchomel, W. Guy Hornsby, John P. Wagle, Aaron J. Cunanan, Strength and Conditioning in Sports, 2023
Michael H. Stone, Timothy J. Suchomel, W. Guy Hornsby, John P. Wagle, Aaron J. Cunanan
For intact whole muscles, internal tension and the resulting external force produced is a function of the interaction of a number of sarcomere lengths and the mechanical characteristics of the skeletal lever system. Although, the force-velocity characteristics of intact muscle are largely like those of isolated muscle, there can be differences during high force productions in which (particularly for single-joint exercises) force is approaching the isometric maximum, input from various mechanoreceptors (including joint receptors and golgi tendon organs) inhibit the agonist muscle force output in order to reduce tissue strain (4, 195). Thus, dynamic force can be higher near the isometric value (Figure 1.18). Resistance training can increase neural activation of the muscle and reduce the force deficit at high force outputs, thus the force-velocity relationship of isolated and intact muscle become more similar at the high force end.
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.
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.
Different cardiovascular responses to exercise training in hypertensive women receiving β-blockers or angiotensin receptor blockers: A pilot study
Published in Clinical and Experimental Hypertension, 2022
Igor M. Mariano, Ana Luiza Amaral, Victor Hugo V. Carrijo, Juliene G. Costa, Mateus de L. Rodrigues, Thulio M. Cunha, Guilherme M. Puga
In order to assess maximum strength in resistance exercises before exercise training, we initially performed 2 familiarizations with the 1 Maximum Repetition test, and then performed the test (14). The following resistance exercises were performed in the exercise sessions: Leg press 45° (hip and knee extension), Chest press in vertical machine (shoulder horizontal abduction with elbow extension), Anterior latissimus dorsi pulldown (shoulder abduction and elbow flexion), Squat with lumbar Swiss ball support (hip and knee extension), and classic abdominal crunch (spine flexion with fixed hip and flexed knee on a flat surface). Each exercise was performed in a traditional 3-series format of 8–12 repetitions with 60 seconds rest between sets and exercises. The intensity was determined through repetition zones of 8–12 complete movements until there was motor alteration that compromised the correct technique or abrupt reduction in movement speed. The order of the exercises was alternated between agonist muscle groups. The abdominal exercise was performed through maximal repetitions without external load. The load readjustment occurred daily to maintain the repetition zone.
Bipedal hopping as a new measure to detect subtle sensorimotor impairment in people with multiple sclerosis
Published in Disability and Rehabilitation, 2022
Megan C. Kirkland, Katie P. Wadden, Michelle Ploughman
Excessive co-contraction, when the antagonist muscle is concurrently contracted with the agonist muscle, reduces the efficiency of the work produced. Excessive co-contraction of extensors may be particularly problematic during the eccentric phase of hopping, when the hips, knees, and ankles flex while the extensors must appropriately relax [90]. At this key juncture, the contraction pattern must efficiently switch from eccentric to concentric [90]. Using EMG in healthy individuals, greater co-contraction ratio in the plantar flexors during concentric phase resulted in decreased jump height and reduced power [166]. Also, lower limb spasticity negatively impacted jump distance in children with HIV encephalopathy [140]. Thus, the ability to accurately relax the antagonist muscle can be interrupted by spasticity [167] and this inefficient co-contraction can hinder hopping performance. Furthermore, inefficient work and inappropriate muscle contraction may contribute to fatigue and greater variability from hop to hop, which can be measured as the coefficient of variation during BHT. Kirkland et al. found that people with MS had greater variability than control subjects. For example, the hop length differed from hop to hop in the MS group (18% variability) but was more consistent in controls (8% variability) [37].
Efficacy of proprioceptive neuromuscular facilitation on spasticity in patients with stroke: a systematic review
Published in Physical Therapy Reviews, 2021
Anas R. Alashram, Alia A. Alghwiri, Elvira Padua, Giuseppe Annino
In the study by Wang et al. [22], the authors explained that a single treatment session is not enough to reduce spasticity in patients with stroke. Moreover, the mechanism behind the reduction in spasticity by Yeole et al. [23] was explained by Dena Gardiner [31]. The explanation is, when the antagonist’s muscle is stretched using a PNF technique, this may stimulate the stretch reflex leading to a reciprocal inhibition of the agonist muscle, which indirectly increasing the range of motion of the joint [31]. The study was of fair quality on the PEDro scale. So the clinical meaning of reported effects can be established. Furthermore, Jagtap and Singaravelan [25] had explained that the PNF techniques increase the demand on the neuromuscular mechanisms. However, the improvement (reduction in spasticity) lasted for only 30 min after the intervention [25]. We propose that a single session is not enough to produce a long-term effect.