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Exercise Redox Signalling
Published in James N. Cobley, Gareth W. Davison, Oxidative Eustress in Exercise Physiology, 2022
Ruy A. Louzada, Jessica Bouviere, Rodrigo S. Fortunato, Denise P. Carvalho
In the onset of muscle contraction, a high demand for ATP drives the cellular metabolism to provide energy for ATPases, calcium handling events, and promotion of the crossbridge interaction between actin and myosin filaments. Within milliseconds, ATP demand rapidly induces an orchestrated metabolic flow to match the demand for ATP. Initially, mitochondria were believed to be the main source of ROS following exercise based on an obvious correlation between increased oxygen consumption and increased ATP production. It has been shown that at least 11 mitochondrial sites can generate ROS in mammals that depends on the bioenergetic state (Wong et al., 2017). Remarkably, during exercise mitochondria operate in state 3 (also known as the maximal ADP stimulated respiration) and thereby reduce ROS generation, contrary to what is observed in the basal conditions, where mitochondria operate in respiration state 4 (Goncalves et al., 2015). Elegantly, when mitochondria are exposed to a condition that mimics exercise, H2O2 is considerably reduced (Goncalves et al., 2015; Jackson et al., 2016) and also confirmed using an in vivo mice model of exercise (Henríquez-Olguin et al., 2019).
Biochemistry of Buffering Capacity and Ingestion of Buffers In Exercise and Athletic Performance
Published in Peter M. Tiidus, Rebecca E. K. MacPherson, Paul J. LeBlanc, Andrea R. Josse, The Routledge Handbook on Biochemistry of Exercise, 2020
Bryan Saunders, Guilherme G. Artioli, Eimear Dolan, Rebecca L. Jones, Joseph Matthews, Craig Sale
Muscle fatigue is the loss in force or power production in response to muscle contraction (61). During exercise, this results in the inability to sustain exercise at a given intensity. It is widely accepted that exercise-induced muscle fatigue is a complex, multifactorial phenomenon caused by several mechanisms that can vary according to exercise type, intensity, and duration. Both central (i.e., arising in the central nervous system) and peripheral (i.e., arising in skeletal muscle or the neuromuscular junction) events have been implicated in fatigue development (61).
Fundamentals
Published in Clare E. Milner, Functional Anatomy for Sport and Exercise, 2019
There are two more types of muscle contraction which are special cases of concentric and eccentric contractions: isokinetic and isotonic. In an isokinetic muscle contraction, there is a constant speed of rotation of the joint. This type of movement is utilized in a rehabilitation setting, where an isokinetic dynamometer machine is used to restrict the joint motion to a fixed speed. An isotonic muscle contraction is one in which the amount of muscle tension or tone is kept constant. Since the effectiveness of a muscle in moving a joint may change depending on the angular position of the joint, the amount of muscle tension required to lift a weight may change at different stages of the movement. This is related to the line of action of the muscle across the joint and how close to the joint centre it passes. Strength training machines are often designed to create isotonic contractions during weight-lifting exercises. For example, an arm curl machine is typically designed with a cam-shaped pulley for the cable to pass over between the joint and the weight stack, rather than a round pulley. The changing curvature of the cam pulley is designed to alter the resistance of the machine at different stages of the arm curl to keep the muscle tension constant, and the contraction isotonic. The rationale for this is that muscle strength will be evenly developed throughout the range of motion of the exercise. With traditional free weights, more muscle force is required at some stages of the movement than others, and the body develops in response to this.
Dual-Task Training Effects on the Cognitive-Motor Interference in Individuals with Intellectual Disability
Published in Journal of Motor Behavior, 2023
Rihab Borji, Thoraya Fendri, Sofien Kasmi, Emna Haddar, Rabeb Laatar, Sonia Sahli, Haithem Rebai
Isometric muscle force for the quadriceps muscle group of the dominant leg was assessed before and after the 8 weeks only under ST condition. Participants were asked to perform 3 MVC of the knee extensors lasting 5 s with a 3-min rest period between trials. Strong verbal encouragements were provided to the participants during all of these MVC. In the beginning of the testing session, participants performed many (12-15) sub-maximal isometric contractions as a warm-up phase. Participants were seated comfortably on a knee extension device (leg extension machine, PANATTA SPORT ®, Italia) with the trunk-thigh angle flexed at 90°. A strap secured the hips and thighs to minimize uncontrolled movements. The force generated during the muscle contraction was assessed by a strain gauge. A leather ankle cuff was placed around the dominant leg just proximal to the malleoli and tightly attached to a load cell (range 0–2500 N; Globus Ergometer, Globus, Codogne, Italy) properly mounted on the leg extension machine. The chain was adjusted in length so that when the participant performed knee extension, the knee remained at 90° of flexion (0° corresponds to full knee extension). The signal from the load cell was amplified using a Globus amplifier (Tesys 400, Globus, Codogne, Italy) and fed through an analog-todigital converter (12 bit) and stored on computer with a sampling frequency of 1000 Hz.
Solanaceae glycoalkaloids: α-solanine and α-chaconine modify the cardioinhibitory activity of verapamil
Published in Pharmaceutical Biology, 2022
Szymon Chowański, Magdalena Winkiel, Monika Szymczak-Cendlak, Paweł Marciniak, Dominika Mańczak, Karolina Walkowiak-Nowicka, Marta Spochacz, Sabino A. Bufo, Laura Scrano, Zbigniew Adamski
Calcium ions are crucial for the contraction of all types of muscles. After influx into the cytoplasm, they interact with myofilaments and ultimately allow for interaction between myosin and actin filaments, and thus for muscle contraction. Since they are a trigger and an executor of muscle contractions, their concentration in the sarcoplasm must be strictly regulated. In striated muscles, cell membrane depolarization is a signal that initiates the cascade responsible for muscle contraction. Changes in the cell membrane potential activate and open the L-type calcium channels. Then, the local increase in Ca2+ concentration activates the ryanodine receptor, a sarcoplasmic calcium channel, which releases the next portion of calcium ions into the cytoplasm, which interacts with myofilaments.
Ergogenic Effects of Sodium Bicarbonate Supplementation on Middle-, But Not Short-Distance Swimming Tests: A Meta-Analysis
Published in Journal of Dietary Supplements, 2022
Maximum effort swimming tests may cause a considerable amount of fatigue. After a single 200-m swimming event, several studies found very high blood lactate concentrations (∼14 to 18 mmol.L−1), which is indicative of acidosis (Vescovi et al. 2011; Kachaunov 2018). Indeed, one study reported that pH is reduced from 7.4 (recorded during rest) to 7.1 after maximum effort 200-m front crawl swimming (Kapus et al. 2008). Muscle acidosis may cause fatigue because the accumulating H+ may impair muscle contractions (Lancha Junior et al. 2015). Additionally, acidosis is associated with an inhibition of phosphocreatine re-synthesis and inhibition of enzymes related to the glycolytic pathway (Lancha Junior et al. 2015). When sodium bicarbonate is ingested before an event, there is an increase in blood bicarbonate and pH levels (Bishop and Claudius 2005; Lindh et al. 2008). Parallel with these physiological changes, there is an increase in extracellular buffering during high-intensity exercise, which ultimately contributes to pH maintenance and a delay in fatigue (Lancha Junior et al. 2015). These physiological mechanisms may explain the ergogenic effect of sodium bicarbonate found in this meta-analysis.