Figure 4.

Proposed regulation of PDH activity during sprint exercise and the early post-exercise recovery. During the sprint exercise muscle contractions elicit an immediate increase of sarcoplasmic (Ca²⁺) which activates pyruvate dehydrogenase phosphatase (PDP, mainly PDP1 which is more expressed in skeletal muscle). PDPs dephosphorylate PDH in the serines 293 and 300, regardless of F_IO₂. While PDH dephosphorylation during sprint exercise is not modified by antioxidants, antioxidants facilitate Ser²⁹³PDH-1Eα re-phosphorylation during the recovery period. This indicates that reactive nitrogen and oxygen species (RNOS) contribute maintaining PDH in its active form, or that RNOS slow-down re-phosphorylation during the recovery period. Several regulatory factors of PDKs activity are modified by sprint exercise. After the sprints, the ATP/ADP ratio is decreased to a similar extent in normoxia and hypoxia, regardless of the ingestion of antioxidants. The NAD⁺/NADH⁺ ratio is decreased to a greater extent in hypoxia than normoxia, with this effect being attenuated after the ingestion of antioxidants. Serum insulin increases after the sprint exercise, more when the sprints are performed in hypoxia than normoxia. Normoxia (red arrows), hypoxia (blue arrows), antioxidants (green arrows). The length of the arrow is representative of the magnitude of the change. ^*Indicates that Ser²³²PDH-1Eα was not measured in the present investigation and, therefore, its regulation by F_IO₂ and RNOS during sprint exercise remains unknown.