Figure 1. Pathways and sources of substrates entering the TCA cycle.

Carbohydrates and fats are the primary substrates of muscle (Gollnick & Saltin, 1988; Saltin & Gollnick, 1988) and contribute to oxidative metabolism via oxidation through acetyl-CoA. Other biochemical pathways that can be used to increase TCA cycle intermediates in skeletal muscle are depicted and include pyruvate carboxylation and the alanine aminotransferase reaction. α-kg, α-ketoglutarate.