MUSCLE TRICARBOXYLIC ACID CYCLE INTERMEDIATES IN TRAINED FEMALES AFTER EXHAUSTIVE CYCLE EXERCISE 1406:

Our purpose was to quantify changes in tricarboxylic acid cycle intermediates (TCAI) in skeletal muscle from endurance-trained women after exhaustive, submaximal exercise. Following a 7 d glycogen super-compensation period, 9 subjects (27.1 ± 1.0 yr; 56.4 ± 1.5 ml·kg-1·min-1) cycled at ≈80% VO2max until volitional fatigue (114 ± 12 min) during the luteal phase of the menstrual cycle. Needle biopsies from vastus lateralis were obtained at rest and exhaustion (Exh). Muscle glycogen content decreased (P≤0.05) from 661± 58 at rest to 85 ± 39 mmol·kg-1 dry wt (dw) at Exh. The total concentration of the 7 measured TCAI (succinyl CoA was not determined) was higher (P≤0.05) at Exh (2.91 ± 0.30) compared to rest (1.46 ± 0.13 mmol·kg-1 dw). Citrate, isocitrate, succinate, fumarate and malate were higher (P≤0.05) at Exh compared to rest, while oxaloacetate was not different between rest and Exh. 2-oxoglutarate (2-OG) was the only TCAI which was lower (P≤0.05) at Exh (26± 9) compared to rest (55 ± 5 μmol·kg-1 dw). We conclude that (1) the TCAI profile at Exh in trained females following intense aerobic cycling is qualitatively similar to that seen in trained males [Gibala et al, Am. J. Physiol. 272 (Endocrinol. & Metab.), in press], and (2) the decrease in 2-OG at Exh is consistent with the theory of Wagemakers et al. (Int. J. Sports Med. 11:S101, 1990) that a decline in this intermediate may hasten fatigue by reducing ambient levels of TCAI.