The Wall Sit can be done using a medicine ball or without.
Start with your back against the wall, feet should width apart and about two feet away from the wall.
Next, lower your back down the wall until your legs are parallel to the ground.
Adjust feet if you need to so that your knees are right above your ankles.
Place hands flat against the wall or stretch arms out in front of you. (For an additional challenge, hold weights in each hand)
Hold the position for 20 to 60 seconds, rest for 30 seconds and then perform the exercise three additional times.