Fig. 2. Metabolic processes in muscle fibers. The main biochemical processes involved in energy generation in striated muscle involve the combustion of fatty acids and carbohydrates. Carbohydrates (orange) are imported via facilitative processes from the capillary supply lines to the myofibre, where they may be stored as intramuscular triglycerides or glycogen, respectively, for later combustion. Fatty acid metabolization (green box) is an obligatory aerobic process that takes place in mitochondria via beta-oxidation and the Krebs cycle. In contrast, the `metabolic conversion' of carbohydrates via glycolysis in the cytoplasm (orange box) is oxygen-independent and is not necessarily coupled to mitochondrial respiration. This may lead to the production of the anaerobic end-product lactate. The decomposition of organic backbones in mitochondria produces reduction equivalents (and CO₂), the former of which drive the oxygen-dependent generation of ATP via coupling to respiratory chain. Boxed factors are the crucial proteins involved at successively aligned transport, storage and conversion steps of metabolic pathways in striated muscle and whose mRNA expression was investigated. Endothelial LPL is involved in transporting fatty acids (FA) from the vasculature through the interstitium into the myocellular compartment (Glatz and Storch, 2001; Jeukendrup, 2002). There H-FABP is believed to play a main role in the intramyocellular transport of free FA. HSL liberates free FA from IMCL for mitochondrial oxidation. CPT I is a key enzyme for the uptake of FA into the mitochondrial matrix. The Krebs cycle enzymes Fum and SDH and the constituents of the electron transport chain, NADH6, COX1 and COX4, are then responsible for oxygen-dependent ATP production during mitochondrial respiration. PFKM represents a main control step for entry of carbohydrates into the glycolytic pathway. For further explanation, see List of abbreviations.