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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
The smallest unit containing the necessary contractile and regulatory components is the sarcomere; thus, the sarcomere serves as the functional unit of the muscular system. Muscle fibers contain thousands of sarcomeres, and whole muscles contain many muscle fibers. Motor units are made up of a MN and all the muscle fibers it innervates and represent the functional unit of the neuromuscular system. Motor units can have different sizes, contractile, and metabolic characteristics, and their activation patterns are compatible with these profiles. Motor units and whole muscles activated by groups of task-specific nuclei in the cortex result in task-specific voluntary movements. Information on how these systems operate is fundamental to the development of the understanding necessary to plan and design logical and efficient training processes and programs.
Thermography by Specialty
Published in James Stewart Campbell, M. Nathaniel Mead, Human Medical Thermography, 2023
James Stewart Campbell, M. Nathaniel Mead
Myopathy refers to disorders with muscle weakness due to dysfunction of muscle fiber. Muscle cramps, stiffness, and muscle spasms can also occur. Pain is not a typical symptom of myopathy. Upon thermal imaging, flaccid myopathies with weakness and muscle disuse appear cool over the involved muscles, while muscular cramps or “tight” myopathies will appear warm due to the heat produced by prolonged, intense muscular contraction. This heat is conducted to overlying skin where it can be viewed thermographically (Figure 11.14). White blood cells and macrophages are generally absent in non-inflammatory myopathy, thus production of NO is not a major feature. The muscular dystrophies, mitochondrial myopathies, and glycogen storage diseases are non-inflammatory myopathies.64
Molecular adaptation to resistance exercise
Published in Adam P. Sharples, James P. Morton, Henning Wackerhage, Molecular Exercise Physiology, 2022
The first question is: does resistance exercise increase the number of muscle fibres within a muscle, a process known as hyperplasia? As discussed in Chapter 2, generally, hyperplasia is thought to contribute little towards the overall increase in muscle mass after resistance training in adult human muscle. However, in response to extreme growth stimuli, muscle fibre number can increase. A meta-analysis of animal studies suggested that in models where muscle fibre mass increases dramatically (by over 50%) such as following synergist ablation (where the gastrocnemius and soleus muscles are removed from the hind limb and the plantaris muscle must take on the extra load, and as a result undergoes significant muscle hypertrophy), approximately ~7% of that increase in muscle mass was due to an increase in fibre number as a result of fibre splitting. This number was later confirmed in a study by Goodman et al., where they demonstrated that synergist ablation in rodents resulted in a ~60% increase in fibre number, which accounted for only ~6% of the increase in muscle mass (9). The use of synergist ablation in contributing to our understanding in molecular exercise physiology was covered in Chapter 1 and the role of hyperplasia in muscle regeneration is also covered in more detail in Chapter 13.
A comparison of CrossFit and concurrent training on myonectin, insulin resistance and physical performance in healthy young women
Published in Archives of Physiology and Biochemistry, 2023
Masoomeh Bahremand, Elham Hakak Dokht, Mahtab Moazzami
Another important finding of our investigation was that VO2max increased significantly in response to both CrossFit and CT interventions. There is little agreement in previous studies regarding the impacts of CrossFit workout on aerobic fitness. For example, Brisebois et al. reported an increase in absolute and relative VO2max after 8-week HIFT in inactive adults (Brisebois et al. 2018). On the other hand, Sobrero et al. observed no change in VO2max in recreationally active women after HIFT of similar length (Sobrero et al. 2017). Differences in the conducting of a HIFT regimen could describe these findings. Although our participants were primarily active, recently in elite endurance athletes, strong evidence reported that resistance training can lead to improved long-term (more than 30 min) and short-term (less than 15 min) endurance capability (Aagaard and Andersen 2010). These findings indicated that resistance training might enhance endurance performance through an elevated type IIA muscle fibers’ proportion, increased maximal muscle strength, and raised rate of force development, whereas also likely involving improvements in neuromuscular function. Concerning the mechanisms responsible for CT-induced raises in VO2max, it is hypothesised that increases in VO2max among subjects are due to central nervous system adaptation and stimulation of the oxidative enzyme citrate synthase causing by this regimen (Sale et al. 1990).
The ultrastructure of muscle fibers and satellite cells in experimental autoimmune encephalomyelitis after treatment with transcranial magnetic stimulation
Published in Ultrastructural Pathology, 2022
María Angeles Peña-Toledo, Evelio Luque, Manuel LaTorre, Ignacio Jimena, Fernando Leiva-Cepas, Ignacio Ruz-Caracuel, Eduardo Agüera, J. Peña-Amaro, Isaac Tunez
The repercussions of muscle fiber innervation loss or damage on muscle ultrastructure are well known,1–4 although these histological changes may be determined by the type of lesion and/or degree of damage to the nerve. In experimental autoimmune encephalomyelitis (EAE), a common experimental model of multiple sclerosis (MS),5 and spinal cord and peripheral nerve injuries occurs that results in muscle damage.6,7 We have previously described skeletal muscle neurogenic involvement in these models, consisting of atrophy and the presence of characteristic muscle fiber lesions.8 At the ultrastructural level, these lesions included mitochondrial and myofibrillar alterations and the presence of autophagic vacuoles, which could explain the increase in oxidative stress that occurs in this model.8 In other models, muscle denervation atrophy has also been associated with increased generation of reactive oxygen species (ROS),9 which could be related to the involvement of different organelles.10
Spinal automaticity of movement control and its role in recovering function after spinal injury
Published in Expert Review of Neurotherapeutics, 2022
According to the size principle, the order of recruitment of motor neurons within a given motor pool starts from small to large. The number of muscle fibers innervated by a single motor neuron provides an accurate estimate of the size of a motor unit and the order of recruitment within each motor pool ([7] and (Figure 1(a,b)). Furthermore, the number of motor units activated within a motor pool determines the force, speed, and power generated by the muscle. The orderly recruitment of muscle fibers of a muscle unit confers biochemical and physiological benefits. The slow oxidative motor unit can perform the most work and has the highest resistance to fatigue (Figure 1(a)). Thus, smaller units tend to be recruited more often compared to larger, more easily fatigable motor units. The size principle assumes that recruiting the slow (S) motor units with a high oxidative capacity, is a more effective strategy for generating movements requiring low force and power. In contrast, the fast fatigable (FF) units relying primarily on glycolytic metabolism generate higher forces, speed, and power, but are needed less often (Figure 1(b,c)). The fast fatigue-resistant (FR) units are more intermediate in force and fatigability.