Journal Title (Medline/Pubmed accepted abbreviation): Metab Clin Exp
Page numbers: 1190-1199
doi (if applicable):
Summary of Background and Research Design
Hypothesis/purpose of study:To examine the effects of L-carnitine L-tartrate (LCLT) supplementation on markers of recovery from physical exertion in men and women between 40 and 65 years of age
Subjects:A total of 9 men and 9 women, mean age of 45 and 52 years for males and females, respectively, participated in the study. The subjects were healthy and recreationally active, but were not considered to be resistance-trained. Mean body mass index values were 26.6 kg/m2 for men and 24.2 kg/m2 for women.
Experimental design:Randomized, double-blind, placebo-controlled, crossover trial
Treatments and protocol:The subjects were randomly assigned to either LCLT supplementation or placebo for the first treatment period of 3 weeks and 3 days. The LCLT supplementation consisted of a dose of 2 g/d elementary L-carnitine as L-carnitine L-tartrate. The subjects performed a resistance training bout at the end of the 3-week period. The resistance training consisted of 4 sets of 15 repetitions of a squat/leg press exercise at 50% 1-repetition maximum. Supplementation persisted for 3 days after the resistance training bout and recovery measures were taken at 24, 48, and 96 hours after the exercise. A one-week washout period followed and then the subjects began the opposite treatment period.
Summary of research findings:
- The LCLT supplementation significantly increased serum L-carnitine measures in both men and women at pre-, during, and post-exercise measurement time points.
- Serum hypoxanthine levels were measured as an indicator of the increased oxidation of adenosine monophosphate (AMP). High glycolytic rates increase the formation of adenosine diphosphate (ADP). Two molecules of ADP are used to make one molecule of adenosine triphosphate (ATP) and one molecule of AMP. The ATP is used for energy, but the AMP is oxidized to hypoxanthine. Compared with placebo, the LCLT supplementation significantly decreased serum hypoxanthine levels immediately after starting exercise and at 15 and 30 min during exercise in men, while only the values at 15 and 30 min were significantly lower for LCLT in the women.
- The authors also measured serum xanthine oxidase concentrations. These concentrations would be expected to fall if L-carnitine supplementation was increasing cellular ATP levels. Essentially, the higher ATP levels would increase activity of calcium-ATPase pumps, which pump calcium ions out of the sarcoplasm. The reduced concentration of calcium ions in the sarcoplasm would, in turn, would result in less cleavage of the xanthine dehydrogenase enzyme to xanthine oxidase. Similar to the pattern observed with hypoxanthine, the LCLT lowered xanthine oxidase levels immediately after starting exercise and at 15 and 30 min of exercise in men. For women, only the values immediately after starting exercise and at 15 min of exercise were significantly lower for LCLT versus placebo.
- The LCLT supplementation significantly decreased plasma malondialdehyde levels versus placebo at every measurement except 120 min of exercise in men. In women, LCTL reduced malondialdehyde levels at pre-exercise and during the first 30 min of exercise relative to placebo. This finding indicates reduced oxidative stress.
- Both myoglobin levels and creatine kinase levels (indicators of muscle cell membrane damage) were reduced by LCLT supplementation versus placebo. Correspondingly, perceived muscle soreness was lower at several measurement points for LCLT compared with placebo in both men and women.
- The LCLT supplement did not alter performance during the exercise.
Interpretation of findings/Key practice applications:
This article indicates that LCLT supplementation can improve several markers of recovery from exercise, even if it does not directly impact performance, in middle-aged, untrained subjects. This finding corroborates previous studies by this group in a younger population. Key limitations of this and other carnitine studies are that carnitine intakes, biosynthesis rates, and carnitine status of subjects have generally not been evaluated.