Exogenous ketones is a legal way to essentially increase VO2max.

Esters (e.g. KetoneAid) for big, quick hit must use with bicarbonate.. most research says good for 3rd or 4th hour of ride.. NOTE: no effect to can actually impair short performance of an hour or so though! Ketone diols (e.g. KetoneIQ) for less of a ketone hit, but don't require bicarbonate since work a little slower.. need to go through liver first.