Science: Direct and indirect lactate oxidation in trained and untrained men

Lactate has been shown to be an important oxidative fuel. We aimed to quantify total lactate oxidation rate (Rox) and its direct versus indirect (glucose that is gluconeogenically derived from lactate and subsequently oxidized) components (mg·kg(-1)·min(-1)) during rest and exercise in humans. We also investigated the effects of endurance training, exercise intensity, and blood lactate concentration ([lactate]b) on direct and indirect lactate oxidation. Six untrained (UT) and six trained (T) men completed 60 min of constant load exercise at power outputs (PO) corresponding to their lactate threshold (LT). Trained subjects completed two additional 60-min sessions of constant load exercise at 10% below the LT workload (LT-10%), one of which included a lactate clamp (LT-10%+LC). Rox was higher at LT in T (22.7 ± 2.9, 75% VO2peak) compared to UT (13.4 ± 2.5, 68% VO2peak, P < 0.05). Increasing [lactate]b (LT-10%+LC, 67% VO2peak) significantly increased lactate Rox (27.9 ± 3.0) compared to its corresponding LT-10% control (15.9 ± 2.2, P < 0.05). Direct and indirect lactate oxidation rates increased significantly from rest to exercise and their relative partitioning remained relatively constant in all trials, but differed between T and UT: direct oxidation comprised 75% of total lactate oxidation in UT and 90% in T suggesting the presence of training-induced adaptations. Partitioning of total carbohydrate (CHO) utilization showed that subjects derived one-third of CHO energy from blood lactate, and exogenous lactate infusion significantly increased lactate oxidation, causing a glycogen sparing effect in exercising muscle.

• http://www.ncbi.nlm.nih.gov/m/pubmed/23788576/