Probably not much less. Physics is physics. I'd be super sceptical of any claim about efficiency of something like running being much different from person to p

Probably not much less. Physics is physics. I'd be super sceptical of any claim about efficiency of something like running being much different from person to person (happy to see any quality research that proves my scepticism to be unfounded though). People like this are just monstrously fit compared to your average person, they still have the same thermodynamic considerations.