Explore chapters and articles related to this topic
Bioenergetics
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 phosphagen system attains increased activation at the initiation of all exercise regardless of intensity but is primarily engaged in providing energy for short-term high-intensity activities such as weight-training exercise and sprinting. (14, 35, 50). The phosphagen system involves ATP and creatine phosphate (PCr), and three enzymes: myosin ATPase, creatine kinase (CK) and myokinase. Energy is supplied for muscle contraction by the hydrolysis of ATP, catalyzed by myosin ATPase, producing ADP and inorganic phosphate (Pi). During high-intensity work, CK catalyzes the reaction in which PCr donates its phosphate group to ADP, re-forming ATP and producing creatine (Cr). These reactions provide energy rapidly and at a high rate:
Exercise Physiology
Published in Peter Kam, Ian Power, Michael J. Cousins, Philip J. Siddal, Principles of Physiology for the Anaesthetist, 2020
Peter Kam, Ian Power, Michael J. Cousins, Philip J. Siddal
The phosphagen system consists of cellular ATP and phosphocreatine. Phosphocreatine (creatine phosphate) is the next available energy source. The phosphate moiety is connected with a high energy bond (provides 10,300 calories per mole when broken). Muscle cells contain 2–4 times more phosphocreatine than ATP. The phosphagen system can sustain maximal muscle contraction for only 8–10 seconds. Energy derived from the phosphagen system is used for maximal short bursts of muscle power. The muscle cell replenishes the creatine phosphate pool during recovery by utilizing ATP derived from oxidative phosphorylation.
Supplying Muscle Machines with Energy
Published in Peter W. Hochachka, Muscles as Molecular and Metabolic Machines, 2019
When O2 is limiting for muscle work, anaerobic glycogenolysis or glycolysis appears to be the main “back-up” mechanism for ATP replenishment after phosphagen supplies are depleted. This metabolic pathway is phylogenetically ancient, and its component enzymes are considered to be highly conservative. Their relatively constant properties are thought to be maintained by rigorous natural selection (Boiteux and Hess, 1981). The only sites where major adaptational changes are known are at the terminal step, normally catalyzed by lactate dehydrogenase (LDH), and at the PEP branchpoint. Thus, many invertebrate groups have evolved different terminal dehydrogenases; the energy yields of these modified glycolytic pathways, however, are unchanged from the classical process of fermentation to lactate. At the level of PEP, some animals possess high PEP carboxykinase activities, which allow a large flow of carbon away from mainstream glycolysis and toward succinate or propionate, as anaerobic end products. These branching pathways may or may not be coupled with simultaneous aspartate fermentation, but in all cases, they are energetically more efficient than classical glycolysis, which is presumably why they are active under extreme hypoxic or ischemic conditions, even in mammals (Hochachka, 1980). As with Phosphagens, a minimal set of criteria must be met in order for a compound to be a useful anaerobic fuel for muscle work.
Effects of Citrulline Malate Supplementation on Muscle Strength in Resistance-Trained Adults: A Systematic Review and Meta-Analysis of Randomized Controlled Trials
Published in Journal of Dietary Supplements, 2022
Andreo F. Aguiar, Juliano Casonatto
This hypothesis is consistent with previous studies that showed a beneficial effect of CM supplementation on the number of repetitions performed (Glenn et al. 2017; Pérez-Guisado and Jakeman 2010; Wax et al. 2015, 2016) but not on muscle strength (Hwang et al. 2018; Farney et al. 2019), supporting the idea that the ergogenic effects of CM supplementation are more beneficial for LME than muscle strength. A possible explanation for these findings may be the metabolic, but not neural, nature of the action mechanisms of CM. Given that short-term muscle strength gains are more associated with neural adaptation (i.e., greater recruitment of motor units) (Del Vecchio et al. 2019) and that LME performance is more associated with the phosphagen system (i.e., phosphocreatine [PCr] and ATP content) and delivery of energy substrate to active musculature, it seems logical that the beneficial effects of CM supplementation in improved PCr resynthesis and ATP production (Bendahan et al. 2002) and increased blood flow mediated by vasodilation (Rogers et al. 2020) may be more advantageous to increase LME than muscle strength. While this suggestion is clearly speculative, there is sufficient published evidence to allow for future systematic reviews and meta-analyses to confirm the effectiveness of CM supplementation and its mechanisms of action on LME gains.
Use of Creatine and Creatinine to Minimize Doxorubicin-Induced Cytotoxicity in Cardiac and Skeletal Muscle Myoblasts
Published in Nutrition and Cancer, 2021
Eric Christopher Bredahl, Wisam Najdawi, Caroline Pass, Jake Siedlik, Joan Eckerson, Kristen Drescher
Creatine (α-methyl guandino-acetic acid, Cr) is a naturally occurring substance obtained through the diet or from endogenous production in the liver and pancreas from the precursors glycine, methionine, and arginine (16). Cr is primarily stored in muscle tissue and readily combines with phosphate to form phosphocreatine (PCr), a high energy phosphagen in the adenosine triphosphate (ATP)-PCr system (17, 18). The cyclization of Cr and PCr into creatinine (CrN) is a reversible nonenzmatic temperature and pH dependent process (19). Generally speaking, Cr formation is favored at high pH and low temperature. Conversely, CrN formation is favored at high temperature and low pH (19). Once produced, CrN is nonionic and membrane permeable and can freely move into the blood where it is excreted by the kidneys into the urine (19).
Ergogenic Properties of Ketogenic Diets in Normal-Weight Individuals: A Systematic Review
Published in Journal of the American College of Nutrition, 2020
Jie Kang, Nicholas A. Ratamess, Avery D. Faigenbaum, Jill A. Bush
Much less information is available regarding the impact of a KD in athletes seeking to improve strength and power. Unlike endurance events in which an increase in fat oxidation may provide an ergogenic effect, this type of performance depends almost exclusively on phosphagen and anaerobic glycolytic systems (31). However, the potential of KDs to reduce BM and %fat can make the diet intriguing for weight-sensitive athletes who always aim to achieve a high power-to-BM ratio. This review identified 7 studies that have examined the effect of a KD on muscular strength and power and anaerobic capacity (Table 6). Three of the 7 studies found no effect on muscular strength and power as measured by 1-RM tests, pushups, and squat and countermovement jumps (33,41,45) or anaerobic capacity as measured by 400-m run (45). Two studies noted an improvement in grip strength, sit-ups, and 1-RM for back squat and bench press, but the improvement occurred in both the KD and the control groups (34,53). The remaining two studies were with mixed results following a KD. For example, by using a Wingate cycle test, Fleming et al. (40) observed a reduction in absolute power in watts, but no change in relative power in watts·kg−1. Similarly, McSwiney et al. (47) noted an increase in peak power in watts·kg−1, but no change in mean power in watts·kg−1 as measured by 6-second sprint and critical power test on a cycle ergometer.