Tricarboxylic-acid-cycle intermediates and cycle endurance capacity.

The purpose of this study was to determine whether ingestion of a multinutrient supplement containing 3 tricarboxylic-acid-cycle intermediates (TCAIs; pyridoxine-alpha-ketoglutarate, malate, and succinate) and other substances potentially supporting the TCA cycle (such as aspartate and glutamate) would improve cyclists' time to exhaustion during a submaximal endurance-exercise test (approximately 70 % to 75 % VO2peak) and rate of recovery. Seven well-trained male cyclists (VO2max 67.4 2.1 mL x kg(-1) x in(-1), 28.6 +/- 2.4 y) participated in a randomized, double-blind crossover study for 7 wk. Each took either the treatment or a placebo 30 min before and after their normal training sessions for 3 wk and before submaximal exercise tests. There were no significant differences between the TCAI group (KI) and placebo group (P) in time to exhaustion during cycling (KI = 105 +/- 18, P = 113 +/- 11 min); respiratory-exchange ratio at 20-min intervals; blood lactate and plasma glucose before, after, and at 30-min intervals during exercise; perceived exertion at 20-min intervals during exercise; or time to fatigue after the 30-min recovery (KI = 16.1 +/- 3.2, P = 15 +/- 2 min). Taking a dietary sport supplement containing several TCAIs and supporting substances for 3 wk does not improve cycling performance at 75 % VO2peak or speed recovery from previously fatiguing exercise.