1. Overload- This involves weight lifts and high reps. This will improve his leg strength and squats, leg press and leg curls can be done for the same.
2. Progression-Now, after overload, you need to further improve your strength and flexibility. For this, addition os more weights, increase the number of reps, intensity, and duration of the workout should be increased. This will help you to make more adjustments to the health routine that you are following.
3. Specificity- Now, if you want to be an athlete, you will focus on certain specific exercise regimes, if you want to be a climber, the exercises will be different. In both these examples, leg exercises have to be followed and improved over time, as both these sport involve the strength of legs.