Impact of creatine on muscle performance and phosphagen stores after immobilization

Creatine Supplementation for Muscle Growth: A Scoping Review of Randomized Clinical Trials from 2012 to 2021

Creatine supplementation is the most popular ergonomic aid for athletes in recent years and is used for improving sport performance and muscle growth. However, creatine supplementation is not always effective in all populations. To address these discrepancies, numerous studies have examined the use of creatine supplementation for muscle growth. This scoping review aimed to investigate the effects of creatine supplementation for muscle growth in various populations, in which Arksey and O'Malley's scoping review framework is used to present the findings. For this study, we performed a systematic search of the PubMed, Embase, and Web of Science databases for theses and articles published between 2012 and 2021. A manual search of the reference lists of the uncovered studies was conducted and an expert panel was consulted. Two reviewers screened the articles for eligibility according to the inclusion criteria. Methodological quality was assessed using the National Heart, Lung and Blood Institute's (NHLBI's) quality assessment tool. A total of 16 randomized controlled trials (RCTs) were finally included. All the authors extracted key data and descriptively analyzed the data. Thematic analysis was used to categorize the results into themes. Three major themes related to muscle growth were generated: (i) subjects of creatine supplementation-muscle growth is more effective in healthy young subjects than others; (ii) training of subjects-sufficient training is important in all populations; (iii) future direction and recommendation of creatine supplementation for muscle growth-injury prevention and utilization in medical practice. Overall, creatine is an efficient form of supplementation for muscle growth in the healthy young population with adequate training in a variety of dosage strategies and athletic activities. However, more well-designed, long-term RCTs with larger sample sizes are needed in older and muscular disease-related populations to definitively determine the effects of creatine supplementation on muscle growth in these other populations.

The Application of Creatine Supplementation in Medical Rehabilitation

Numerous health conditions affecting the musculoskeletal, cardiopulmonary, and nervous systems can result in physical dysfunction, impaired performance, muscle weakness, and disuse-induced atrophy. Due to its well-documented anabolic potential, creatine monohydrate has been investigated as a supplemental agent to mitigate the loss of muscle mass and function in a variety of acute and chronic conditions. A review of the literature was conducted to assess the current state of knowledge regarding the effects of creatine supplementation on rehabilitation from immobilization and injury, neurodegenerative diseases, cardiopulmonary disease, and other muscular disorders. Several of the findings are encouraging, showcasing creatine's potential efficacy as a supplemental agent via preservation of muscle mass, strength, and physical function; however, the results are not consistent. For multiple diseases, only a few creatine studies with small sample sizes have been published, making it difficult to draw definitive conclusions. Rationale for discordant findings is further complicated by differences in disease pathologies, intervention protocols, creatine dosing and duration, and patient population. While creatine supplementation demonstrates promise as a therapeutic aid, more research is needed to fill gaps in knowledge within medical rehabilitation.

Immobilization leads to alterations in intracellular phosphagen and creatine transporter content in human skeletal muscle

The role of dysregulated intracellular creatine (Cr) metabolism in disuse atrophy is unknown. In this study, skeletal muscle biopsy samples were obtained after 7 days of unilateral leg immobilization (IMMOB) and from the nonimmobilized control limb (CTRL) of 15 healthy men (23.1 ± 3.5 yr). Samples were analyzed for fiber type cross-sectional area (CSA) and creatine transporter (CreaT) at the cell membrane periphery (MEM) or intracellular (INT) areas, via immunofluorescence microscopy. Creatine kinase (CK) and AMP-activated protein kinase (AMPK) were determined via immunoblot. Phosphocreatine (PCr), Cr, and ATP were measured via enzymatic analysis. Body composition and maximal isometric knee extensor strength were assessed before and after disuse. Leg strength and fat-free mass were reduced in IMMOB (~32% and 4%, respectively; P < 0.01 for both). Type II fiber CSA was smaller (~12%; P = 0.028) and intramuscular PCr lower (~13%; P = 0.015) in IMMOB vs. CTRL. CreaT protein was greater in type I fibers in both limbs (P < 0.01). CreaT was greater in IMMOB vs. CTRL (P < 0.01) and inversely associated with PCr concentration in both limbs (P < 0.05). MEM CreaT was greater than INT CreaT in type I and II fibers of both limbs (~14% for both; P < 0.01 for both). Type I fiber CreaT tended to be greater in IMMOB vs. CTRL (P = 0.074). CK was greater and phospho-to-total AMPKThr172 tended to be greater, in IMMOB vs. CTRL (P = 0.013 and 0.051, respectively). These findings suggest that modulation of intracellular Cr metabolism is an adaptive response to immobilization in young healthy skeletal muscle.

Severe Hyperhomocysteinemia Decreases Respiratory Enzyme and Na(+)-K(+) ATPase Activities, and Leads to Mitochondrial Alterations in Rat Amygdala

Severe hyperhomocysteinemia is caused by increased plasma levels of homocysteine (Hcy), a methionine derivative, and is associated with cerebral disorders. Creatine supplementation has emerged as an adjuvant to protect against neurodegenerative diseases, due to its potential antioxidant role. Here, we examined the effects of severe hyperhomocysteinemia on brain metabolism, and evaluated a possible neuroprotective role of creatine in hyperhomocysteinemia, by concomitant treatment with Hcy and creatine (50 mg/Kg body weight). Hyperhomocysteinemia was induced in young rats (6-day-old) by treatment with homocysteine (0.3-0.6 µmol/g body weight) for 23 days, and then the following parameters of rat amygdala were evaluated: (1) the activity of the respiratory chain complexes succinate dehydrogenase, complex II and cytochrome c oxidase; (2) mitochondrial mass and membrane potential; (3) the levels of necrosis and apoptosis; and (4) the activity and immunocontent of Na(+),K(+)-ATPase. Hcy treatment decreased the activities of succinate dehydrogenase and cytochrome c oxidase, but did not alter complex II activity. Hcy treatment also increased the number of cells with high mitochondrial mass, high mitochondrial membrane potential, and in late apoptosis. Importantly, creatine administration prevented some of the key effects of Hcy administration on the amygdala. We also observed a decrease in the activity and immunocontent of the α1 subunit of the Na(+),K(+)-ATPase in amygdala after Hcy- treatment. Our findings support the notion that Hcy modulates mitochondrial function and bioenergetics in the brain, as well as Na(+),K(+)-ATPase activity, and suggest that creatine might represent an effective adjuvant to protect against the effects of high Hcy plasma levels.