Creatine supplementation has also been shown to have a positive effect on exercise tolerance in chronic heart failure patients. Reduced creatine availability has been implicated in the metabolic abnormalities of failing myocardial tissue, and creatine supplementation has been shown to attenuate pharmacologically induced metabolic stress in rat myocardium, although the contribution of PCr to energy delivery in myocardial tissue is normally negligible. However, no research to date indicates whether creatine exerts its effects in cardiac patients via improving heart or skeletal muscle energetics. Alternatively, PCr has been proposed to stabilize membranes under conditions of cellular damage and the creatine-like compound, cyclocreatine, has been suggested to maintain ATP production in heart and skeletal muscle long after PCr stores have been depleted which may be more fruitful areas of future research. Two early studies have begun this examination with what appear to be favorable preliminary results.
To assess the effects of dietary creatine supplementation on skeletal muscle metabolism and endurance in patients suffering from chronic heart failure, Andrews et al. used a forearm model of muscle metabolism. Maximal voluntary contractions were measured using handgrip dynamometry as subjects performed handgrip exercise of 5-seconds’ contraction followed by 5 seconds of rest for 5 minutes at 25%, 50%, and 75% of maximum voluntary contraction or until exhaustion. Blood was sampled at rest and 0 and 2 minutes after exercise for measurement of lactate and ammonia.
After 30 minutes, the procedure was repeated with fixed workloads of 7 kg, 14 kg, and 21 kg. Patients were assigned to creatine at 20 g daily or matching placebo for 5 days and returned after 6 days for repeat study. During post-testing, contractions until exhaustion at 75% of maximum voluntary contraction increased after creatine treatment with no significant placebo effect. Ammonia and lactate per contraction at 75% maximum voluntary contraction fell significantly after creatine but not after placebo.
In a complementary study, Gordon et al. noted that cardiac creatine levels are depressed in chronic heart failure and thus evaluated the effects of creatine supplementation on ejection fraction, symptom-limited physical endurance, and skeletal muscle strength in patients with chronic heart failure. In a double-blind, placebo-controlled design, 17 patients were supplemented with creatine, 20 g/daily for 10 days. Before and on the last day of supplementation ejection fraction was determined by radionuclide angiography, as was symptom-limited 1-legged knee extensor and 2-legged exercise performance on the cycle ergometer. Muscle strength as unilateral concentric knee extensor performance was also evaluated. Skeletal muscle biopsies were performed to determine the amount of energy-rich phosphagens. Although no change in ejection fraction was seen in either group compared with baseline, creatine supplementation increased skeletal muscle total creatine and PCr by 17% and 12%, respectively. More specifically, however, increments were seen only in patients with less than 140 mmol total creatine/kg. Additionally, 1-legged performance (21 %), 2-legged performance 00%), and peak torque (5%) also increased. Both peak torque and 1-legged performance increased linearly with increased skeletal muscle PCr. The increments in 1-legged, 2-legged, and peak torque were significant compared with the placebo group. One week of creatine supplementation to patients who suffered from chronic heart failure did not increase ejection fraction but increased skeletal muscle energy-rich phosphagens and performance regarding both strength and endurance. Therefore, it appears that creatine supplementation in chronic heart failure may favorably augment skeletal muscle endurance; it attenuates the abnormal skeletal muscle metabolic response to exercise and thus provides a new and novel therapeutic approach to treatment that merits further attention.
Tags:cyclocreatine, During post testing., myocardium Skeletal Muscle Metabolism
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