12:00 AM
@MartinSleziak given they ask about both efficiency and (il)legality, this seems to be a sports question.
Efficiency is important in the use of energy to achieve the result, either speed for a given distance or distance covered for a given time, which are sporting aspects rather than fitness aspects.
(Il)legality is only relevant in following rules of competition, which are a sporting aspect especially for a stated stroke, rather than fitness aspect.
