During mountain stages of the Tour de France you’ll often hear Phil Liggett use the term “oxygen debt” – when the muscles lack an adequate amount of oxygen due to high-intensity anaerobic efforts. Oxygen debt is more formally known as hypoxemia.
The most important mediators of the cellular response to hypoxia are “transcription factors” (proteins which influence which genes are used in which cell) called HIFs (or hypoxia-inducible factors).
HIF activates the genes that influence adaptive responses to hypoxia, including:
– the production of EPO
– the way the cells generate energy
– the creation of veins and blood vessels (called VEGF: vascular endothelial growth factor)
– the supply of iron (important for red cell production).
From this list, it is clear that the HIFs have the potential to improve the performance of an athlete. Does that mean administering HIFs will have an immediate effect on performance?
The short answer is no, because the HIFs are targeted for degradation in the absence of sustained blood hypoxia, so providing an external source isn’t the best way to increase their activity. Instead HIF stabilisers can be used to prolong the activity of the HIFs and provide ongoing production of natural EPO when there is no biological need for it (i.e. when oxygen levels are normal in the blood).
HIF stabilisers
As mentioned above, HIFs also stimulate the formation of new blood vessels (a process called angiogenesis) and therefore HIF stabilisers will improve this process. For an endurance athlete, this means more blood vessels supplying the muscle, which are normally generated over time in response to training.
By using HIF stabilisers, an athlete may be able to decrease the training period required to improve the blood supply to the muscles from weeks or months to a matter of days. Think about this: More oxygen-rich blood being delivered to more blood vessels generated within new muscle tissue. Add to this an improvement in carbohydrate metabolism and you have a very attractive performance-enhancing drug. You can quickly see the consequences (or benefits) here.
HIF stabilisers are still being developed for routine use in humans but they are being tested in clinical trials now. These drugs are small chemical compounds that can be delivered in an oral pill and they are difficult to detect in blood and urine samples.