Answer:
The correct answer would be - leg action of treading water
Explanation:
As we know that air is less thick or dense than water which makes treading water more difficult for leg action as it required more muscle action harder than air and has to work more.
In leg action of treading water requires more time and hard work than air so it is a more difficult aquatic exercise.
Thus, The correct answer would be - leg action of treading water
