scubaozy
Contributor
Well freedivers dive 100m with 1 breath (that is 200m and have to fight against buoyancy as well in the first half), so it is clear who is more efficient based on your criterion .To comment on the side conversation, going fast is not efficient. Efficient is going the farthest on a fixed amount of gas or going the same distance using less gas. Given that force is relative to the square of velocity, going the fastest can not be the most efficient method.