Originally Posted by
carpediemracing
Less energy efficient, i.e. you use more energy. But you can exert more energy too.
I suppose a really light person could stand for a long time. I used to be really light (110 lbs in the first pic above) and stood a lot on climbs.
What you described it not energy efficiency. You exert more energy standing but a considerable part of that goes to the pedals and to the road. However usually your close to your limit and therefore you will eventually just blow up or have to sit back down before you blow up. It would be hard to figure out energy efficiently compared to normal riding since often you switch to anaerobic when you stand up on a climb so even measuring O2 consumption or HR will not give you a really accurate result I would guess.