Participants in this study will be randomly assigned to receive either L-carnitine or placebo for 2 weeks. To reduce the possibility of side effects, the doses of L-carnitine and placebo will be titrated over 6 days to the desired study dose. After 2 weeks, participants receiving placebo will be switched over to receive L-carnitine. All participants will continue on L-carnitine for an additional 2 weeks.