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Physical and Physiological Reponses and Adaptations
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
Muscle responds to resistance training by enlarging its cross-sectional area (i.e., hypertrophy). In this manner, additional contractile elements (myofibrils) are added to the muscle fiber. The underlying mechanisms are complex and still not completely understood. The primary stimulus for skeletal muscle hypertrophy appears to be a gain in tension and mechanical strain (26, 62). Secondarily, there may be metabolic factors as a result of repeated contractions that also stimulate the hypertrophic adaptations (7, 62). The stimulus causes a cascade of multi-level effects as illustrated in Figure 6.3. The degree to which muscle damage stimulates hypertrophy is unclear and is not likely a major factor (62).
Genetics of endurance
Published in Adam P. Sharples, James P. Morton, Henning Wackerhage, Molecular Exercise Physiology, 2022
Stephen M. Roth, Henning Wackerhage
After the VO2max, the fibre-type proportion is the second major factor which affects endurance performance. In humans, adult skeletal muscle comprises slow type I, intermediate type IIa and fast type IIx fibres, as discussed in Chapter 9. Humans carry the gene for myosin heavy chain IIb but it is not normally expressed in human skeletal muscle (10). Within individuals, the proportions of fibre types differ from muscle to muscle. They range from 15% of slow type I fibres in eye muscles to 89% in the soleus (calf) muscle (11). From a genetics perspective, the most important finding is that the fibre proportions in a given muscle differ considerably in the population. For example, a quarter of North American Caucasians have either less than 35% or more than 65% type I fibres (2). Extremes of fibre-type proportions for locomotor muscles are found in speed/power versus endurance athletes, with speed/power athletes having a high percentage of fast type II and endurance athletes having a high percentage of slow type I fibres (12, 13). In this research, Costill and Saltin already concluded that ‘these measurements confirm earlier reports which suggest that the athlete’s preference for strength, speed, and/or endurance events is in part a matter of genetic endowment’ (12). The heritability estimates for fibre types range from no significant genetic effect (14) to 92.8–99.5% for females and males, respectively (15), which highlights the limitations of such studies. Today, the consensus estimate for fibre-type proportions is ≈45% heritability (2).
Muscle and Nerve Fibers Classification
Published in Maher Kurdi, Neuromuscular Pathology Made Easy, 2021
Skeletal muscle is composed of a mixture of fibers that differ in their physiological and chemical properties. This differentiation is important in clinical practice as it is considered an early tool used in the histopathological approach. By using the enzymatic histochemistry technique, practitioners can differentiate muscle fibers into two types; type I and II fibers. Type II muscle fibers are subcategorized into IIa and IIb. This precise differentiation is established based on several factors including oxidative and glycolytic activities, as described in Table 2.1.
Effects of back extensor and hip abductor fatigue on dynamic postural stability in patients with nonspecific chronic low back pain: A case-control study
Published in Physiotherapy Theory and Practice, 2022
Shirin Tajali, Narges Roozbehfar, Mohammad Mehravar, Shahin Goharpey, Khadije Gayem
Muscle fatigue, defined as a reduction in the force output of a skeletal muscle, can happen during different submaximal daily activities (Johanson et al., 2011; Parreira et al., 2013). It is known that postural control can be negatively affected by peripheral muscle fatigue due to decreased muscle contractile efficiency and proprioceptive acuity (Gribble and Hertel, 2004a, 2004b; Parreira et al., 2013). Indeed, disruption in the afferent feedbacks due to muscle fatigue may impair joint proprioception and subsequently affects somatosensory inputs and postural control strategies (Gribble and Hertel, 2004a, 2004b). In patients with chronic LBP, reduced lumbosacral proprioception and poor lumbar extensor endurance have been frequently reported in the literature (Brumagne, Cordo, and Verschueren, 2004; Da Silva et al., 2015). Importantly, decreased back muscle endurance was associated with increased periods of sitting and lower physical activity levels in chronic LBPs who reported pain during sustained postures in their work (O’Sullivan et al., 2006). Although it is well understood that back muscles are extremely important for preserving postural stability during daily activities (Da Silva et al., 2015, 2016; Parreira et al., 2013), little is known about their fatigue effects on postural stability in patients with NSCLBP.
RIP1 Regulates Mitochondrial Fission during Skeletal Muscle Ischemia Reperfusion Injury
Published in Journal of Investigative Surgery, 2022
Yu Cao, Shunli Chen, Xiangqing Xiong, Lina Lin, Wantie Wang, Liangrong Wang
Excessive mitochondrial fission and the consequent mitochondrial fragmentation is an important factor contributing to severe damage in mitochondrial membrane structure and leading to cell death during the reperfusion phase [11–13]. On the contrary, mitochondrial fusion defending against abnormal mitochondrial cleavage is inhibited by reperfusion [14]. Mitochondrial fission is believed to be an upstream event of ROS production [15–17]. Mitochondrial fragmentation induced by mitochondrial fission is believed to disrupt respiratory chain, which induces the mitochondrial permeability transition pore opening and excessive ROS production [15–17]. To support this notion, inhibition of Drp1 can decrease mitochondria fragmentation, delay the opening of mitochondrial permeability transition pore, suppress various patterns of cell death, and finally reduce the myocardial infarction area of animals following reperfusion [17–19]. Skeletal muscle is categorized into type 1 and type 2 fibers, among which type 1 fibers are rich in mitochondria and have high oxidative capacity and increased resistance to fatigue. The soleus muscles is predominantly composed of type-1 fibers, therefore, it was sampled to investigate the participation of mitochondrial fission in IR-induced skeletal muscle damage in the current study. Here, we found that Mdivi-1 attenuated Drp1 phosphorylation, mitochondrial fragmentation, structural damage and oxidative stress in the soleus muscle subjected to IR injury, which suggested the involvement of mitochondrial fission in skeletal muscle IR.
Subchronic administration of Parastar insecticide induced behavioral changes and impaired motor coordination in male Wistar rats
Published in Drug and Chemical Toxicology, 2022
Antoine Kada Sanda, Akono Edouard Nantia, T. F. Pascal Manfo, Romi T. Toboh, Roxane Essame Abende, Sterling Adaibum, Paul Fewou Moundipa, Pierre Kamtchouing
The grip strength test is a functional method used to evaluate rat limb strength. This test has been used to investigate the effects of drug on neuromuscular disorders. In both Grid Suspension Grip-strength test and Wire Hang tests, Parastar decreased the suspension time, especially at the medium and high doses, and this suggests negative effect of the agrochemical on muscle strength and coordination in rats. Skeletal muscle contraction is mediated by acetylcholine at the neuromuscular junction. Therefore results from this study suggest a possible alteration of cholinergic neurons or acetylcholinesterase system by Parastar leading to neurotoxic effect. Khan et al. (2003) reported inhibition of brain cholinesterase following exposure of frogs to a component of Parastar, Lambda cyhalothrin. Other studies demonstrated the neurotoxic effect of another pesticide, Chlorpyrifos (Yumino et al.2002; Lee et al. 2014), which was attributed to the capacity of Chorpyrifos to enhance hydrogen peroxide levels (ROS), reduce the antioxidant potential of nervous system (Yumino et al.2002; Lee et al. 2014), and interrupt mitochondria activity in brain (Singh et al. 2013; Yamada et al. 2017). Parastar may induce neurotoxic effects through same or similar mechanism.