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Spinal Cord and Reflexes
Published in Nassir H. Sabah, Neuromuscular Fundamentals, 2020
In Figure 11.7b, IN1 and IN2 are both inhibitory interneuron populations that mutually inhibit one another. These could be, for example, a population of Renshaw cells and a population of Ia inhibitory interneurons considered in the preceding sections. Activation of I1 reduces the excitation of α-MN1 and increases the excitation of α-MN2 through disinhibition. Conversely, activation of I2 reduces the excitation of α-MN2 and increases the excitation of α-MN1. Controlling the levels of excitation of α-MN1 and α-MN2 allows controlling the force developed by each of the two sets of antagonist muscles and their degree of coactivation (Section 13.1.2).
Lifestyle factors
Published in Jane Hanley, Mark Williams, Fathers and Perinatal Mental Health, 2019
Exercise can lower both anxiety levels and depressive symptoms and improve the quality of sleep; however, the irony of depressive symptomology is the inability to be motivated to do any exercise. Although there is little known about the underlying mechanisms, a molecular link has been found between exercise and resistance to depression. Exercise induces expression of the transcriptional coactivator PGC-1a in muscle (Agudelo et al. 2014). A mechanism was identified by which skeletal muscle induced by exercise training changes tryptophan—kynurenine metabolism and protects from stress-induced depression. Tryptophan is converted to kynurenine and is linked to neuroinflammation, considered to be one of the causes of depression, thus explaining the beneficial effects of exercise for those with depressive symptomology. The suggestion is that moderate levels of activity for twenty–thirty minutes a day can also help to prevent depressive symptoms. There is significant evidence to demonstrate that physical activity can improve depressive symptoms (WHO 2010). One of the key benefits of being active is that it can reduce stress.
Pubertal Development and Menarche
Published in Jane M. Ussher, Joan C. Chrisler, Janette Perz, Routledge International Handbook of Women’s Sexual and Reproductive Health, 2019
While adrenarche and gonadarche are thought to be distinct processes, research continues to explore their timing as sequential, oppositional, or coactivated (Shirtcliff et al., 2015). Some have noted that, in addition to its function in advancing pubertal changes, the HPA axis also regulates the stress response. To maximize the body’s capacity to perceive and defend against a threat, the stress response has been found to suppress other physiological systems, including reproductive function (Chrousos & Gold, 1992). Although this oppositional relationship between the stress response and reproductive function has been demonstrated in adults, Ruttle, Shirtcliff, Armstrong, Klein, and Essex (2013) suggested that it may not occur in adolescence. They argue that it makes more sense that coactivation, or positive coupling, would advance the development of both axes during adolescence, as opposed to the suppression of one by the other. As Shirtcliff et al. (2015) pointed out, “Stress and puberty can, and frequently do, co-occur” (p. 646), certainly an understatement.
Effects of progressive neuromuscular training on pain, function, and balance in patients with knee osteoarthritis: a randomised controlled trial
Published in European Journal of Physiotherapy, 2023
The neuromuscular training (NMT) is a form of sensorimotor training which is hypothesised to enhance unconscious motor response by stimulating both afferent signals and central mechanisms responsible for dynamic joint control; thus utilising both neuromuscular and biomechanical principles [12,13]. NMT takes into account all the 3 levels of motor activation and control; including a) cognitive awareness of the higher cortical centres, b) the vestibular and mechanoreceptor-mediated brainstem control as well as the c) reflex-mediated spinal cord control [14]. NMT exercise is an individualised treatment program that is performed in functional-loaded positions with focus on efficiency, ease and quality of movement [8]. They incorporate closed kinematic exercises of multiple joints, leading to coactivation of muscle groups that are active in movement synergies, resulting in lowering the stresses to the articular surfaces [15]. Ageberg E. et al analysed NMT in a longitudinal study (15 years) on 100 patients of ACL tear with sensorimotor deficits and found the affected knee having similar strength and functional gains as the uninjured limb [16–18]. Later the same author investigated the feasibility of NMT (coined as NEMEX-TJR) in patients with severe hip or knee OA (2010) and [19] then analysed its effects on the same group of patients (2013) with all 4 components of sensorimotor training - a) strength, b) coordination, c) balance and d) proprioception - and found improved patient-reported outcomes and physical function along with pain reduction [20].
Characteristics of the severely impaired hand in survivors of stroke with chronic impairments
Published in Topics in Stroke Rehabilitation, 2022
Alexander J. Barry, Derek G. Kamper, Mary Ellen Stoykov, Kristen Triandafilou, Elliot Roth
Substantial coactivation of antagonist muscles during voluntary task performance was also present. During attempted MCP extension torque production with the paretic hand, participants created an average of 30% MVC activation of FDS, a value almost 4 times as great as that created by neurologically intact individuals during this task.14 The more impaired participants (CMSA-H2 group) created 50% MVC activation of FDS. As with the spasticity measure, FDS coactivation was significantly negatively correlated with voluntary MCP flexion torque generation. Thus, the hypertonicity did not lead to greater voluntary force production. EDC coactivation was also observed during attempted MCP flexion, with numerous subjects creating greater EDC activation during flexion than during extension, potentially contributing to the force deficits in grip and MCP flexion torque. Diminished reciprocal inhibition, specifically in participants with spastic hemiplegia, is thought to contribute to this excessive coactivation.38 In support of the diminished reciprocal inhibition hypothesis, we also observed EDC activation of greater than 10% of maximum activation coincident with an evocation of a spastic FDS reflex.
Biomechanics of Vertical Posture and Control with Referent Joint Configurations
Published in Journal of Motor Behavior, 2021
Momoko Yamagata, Kreg Gruben, Ali Falaki, Wendy L. Ochs, Mark L. Latash
We used SPSS to perform all statistical tests (IBM Corp., Armonk, NY, USA). Data are presented in the text and figures as means ± standard errors. To test whether muscle co-activation affected zIP (Hypothesis 2), a two-way repeated-measure ANOVA was performed to evaluate the effects of Coactivation (No-C, Low-C, and High-C) and Frequency-Interval (Interval-1, Interval-2, and Interval-3). For parametric statistics, the assumptions of normality and sphericity were checked. In cases of violations of normality, log-transformation to satisfy the normality assumptions was used, and in case of violations of sphericity, the Greenhouse-Geisser procedure was used. Pairwise contrasts with Bonferroni corrections were used to explore significant effects. The significance level was set at p = 0.05.