Spiering, BA, Kraemer, WJ, Hatfield, DL, Vingren, JL, Fragala, MS, Ho, J-Y, Thomas, GA, Häkkinen, K, and Volek, JS. Effects of L-carnitine L-tartrate supplementation on muscle oxygenation responses to resistance exercise. J Strength Cond Res 22: 1130-1135, 2008-Previous research has shown that L-carnitine L-tartrate (LCLT) supplementation beneficially affects markers of hypoxic stress following resistance exercise. However, the mechanism of this response is unclear. Therefore, the primary purpose of this study was to determine the effects of LCLT supplementation on muscle tissue oxygenation during and after multiple sets of squat exercise. Nine healthy, previously resistance-trained men (25.2 ± 6 years, 91.2 ± 10.2 kg, 180.2 ± 6.3 cm) ingested LCLT (equivalent to 2g L-Carnitine/day) or an identical placebo for 23 days using a randomized, balanced, crossover, double-blind, placebo-controlled, repeated-measures study design. On day 21, forearm muscle oxygenation was measured during and after an upper arm occlusion protocol using near infrared spectroscopy (NIRS), which measures the balance of oxygen delivery in relation to oxygen consumption. On day 22, subjects performed 5 sets of 15 to 20 repetitions of squat exercise with corresponding measures of thigh muscle oxygenation, via NIRS, and serial blood draws. Compared to the placebo trial, muscle oxygenation was reduced in the LCLT trial during upper arm occlusion and following each set of resistance exercise. Despite reduced oxygenation, plasma malondealdehyde, a marker of membrane damage, was attenuated during the LCLT trial. There were no differences between trials in the vasoactive substance prostacyclin. In conclusion, because oxygen delivery was occluded during the forearm protocol, it is proposed that enhanced oxygen consumption mediated the reduced muscle oxygenation during the LCLT trial. Enhanced oxygen consumption would explain why hypoxic stress was attenuated with LCLT supplementation.
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