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Muscle Physiology and Electromyography
Published in Verna Wright, Eric L. Radin, Mechanics of Human Joints, 2020
The interdigitating arrangement of the actin and myosin filaments has a consistent cross-sectional arrangement. Both myofilament types are arranged in a hexagonal pattern, and where there is overlap between the two, the myosin filaments are found in the center of a hexagon of actin filaments (Fig. 7).
Caffeine reverts loss of muscular performance during the early-follicular phase in resistance-trained naturally menstruating women
Published in Journal of Sports Sciences, 2022
Ottavio Santana, Victor Vieira-Cavalcante, Anderson Caetano Paulo, Cintia Rodacki, Romulo Bertuzzi, Adriano Eduardo Lima-Silva, Gislaine Cristina-Souza
Although the mechanisms by which exercise performance is lower in the early-follicular phase are not completely understood, studies in animals suggest that the low oestrogen concentration might influence intracortical excitability (Smith et al., 2002; Varshney et al., 2021) and reduce myofilament calcium sensitivity, ultimately reducing force generated by myosin cross-bridges (Boullosa, 2021; Lowe et al., 2010). On the other hand, the high oestrogen concentration in mid-luteal phase might increase muscle glycogen storage capacity, ultimately improving energy availability (Oosthuyse & Bosch, 2010), and also increase myosin function, which results in improved muscle force (Lowe et al., 2010). Thus, potential reduction of muscular performance during the early-follicular phase (Moran et al., 2007; Wattanapermpool & Reiser, 1999) is of practical relevance for women involved in resistance-based training programmes, as their training workload could be reduced during this phase of the menstrual cycle (Cristina-Souza et al., 2019). Thus, searching for strategies to attenuate this decline in muscle strength, muscle power, and muscular endurance in the early-follicular phase is required.
Acute caffeine supplementation and live match-play performance in team-sports: A systematic review (2000–2021)
Published in Journal of Sports Sciences, 2022
Adriano Arguedas-Soley, Isobel Townsend, Aaron Hengist, James Betts
Peripheral effects of caffeine on skeletal muscle contraction and fatigue also involve an interference with calcium uptake and storage in the sarcoplasmic reticulum of striated muscle, an increased calcium ion (Ca++) translocation through the plasma membrane of muscle cells and an increased myofilament Ca++ sensitivity (Nehlig et al., 1992); thus optimising myofibrillar contractions. Further, clinical studies have proposed that ingesting caffeine before exercise can enhance lipolysis via inhibition of phosphodiesterase, along with direct effects on muscle glycogen sparing via inhibition of glycogen phosphorylase (Da Silva et al., 2018). Caffeine may also increase phosphorylation of AMP-activated protein kinase (AMPK) and enhance GLUT4 translocation to the plasma membrane of muscle cells and glycogen synthase (GS) activation, which can improve AMPK-dependent glucose uptake in skeletal muscle (Jensen et al., 2007). These factors may facilitate a decreased reliance on muscle glycogen as a metabolic fuel during exercise and simultaneously increase non-esterified fatty acid (NEFA) oxidation for energy provision (Arciero et al., 1995). Together, mechanisms at the central and peripheral level may therefore culminate in greater motor unit recruitment and power output, a delayed onset of fatigue and/or a decreased perception of effort with caffeine intake before endurance or high-intensity exercise. As such, caffeine is widely used as a supplement to improve sports performance.
Optimizer Smart System for the treatment of chronic heart failure: Overview of its safety and efficacy
Published in Expert Review of Medical Devices, 2021
Habib Hymie Chera, Mohammed Al-Sadawi, Nickolaos Michelakis, Michael Spinelli
CCM has multiple cellular effects in HFrEF, including an increase in the intracellular Ca2+ cycling and improved diastolic Ca2+ levels by normalization of phospholamban phosphorylation in the sarcoplasmic reticulum. It also increases the expression of the ryanodine receptor and the sarcoplasmic reticulum Ca2+‐ATPase 2a (SERCA2a) pathway, which is known to be inhibited in patients with HF [20,21]. Furthermore, CCM increases the phosphorylation of myofilament proteins, such as troponin and myosin light chain-2, which are responsible for the sensitivity to Ca2+; as well as titin proteins, that are responsible for early and late diastolic distensibility [20,22]. CCM is also associated with reduction in oxidative stress, fibrosis and sympathetic nerve activity via activation of vagal afferent fibers in the interventricular septum [21,23,24] (Figures 6 and 7).