We have all heard of EPO and its importance for bikers and endurance athletes. It is a naturally occurring hormone that is produced by altitude exposure. It improves blood composition, but can also increase VO2 max as an acute response by letting you use more of the capacity.
Ketone supplementation may also prove to be another way. Produced by the body as you process carbs/fats and also after fasting. It may be able to increase the proportion of your physical capacity that you can use.