Effects of Four Weeks L-Carnitine L-tartrate Ingestion on Substrate Utilization during Prolonged Exercise

In a randomized, placebo-controlled, double-blind crossover design, 15 trained males undertook exercise trials during two 4 wk supplementation periods, with either 3 g L-Carnitine L-tartrate (LCLT) or 3 g placebo (P) daily. Total carbohydrate and fat oxidation during 90 min steady state cycling were not different between 0 or 4 wk within LCLT or P trials (mean +/- standard deviation: carbohydrate oxidation P0 99 +/- 36, P4W 111 +/- 27, LCLT0 107 +/- 33, LCLT4W 112 +/- 32 g, respectively; fat oxidation P0 99 +/- 28, P4W 92 +/- 21, LCLT0 94 +/- 18, LCLT4W 90 +/- 22 g, respectively). Subsequent 20 km time trial duration was shorter after P (P0 31:29 +/- 3:50, P4W 29:55 +/- 2:58 min:s, P < 0.01), with no significant change over LCLT (LCLT0 31:46 +/- 4:06, LCLT4W 31.19 +/- 4.08 min:s). Four weeks LCLT supplementation had no effect on substrate utilization or endurance performance.