Place a foam roller just above the back of the knee joint, hands at hips with fingers facing out. To increase compression, cross one leg over the other. To decrease compression, keep other leg on the ground. Lift the hips off the ground, keeping the chest up and shoulders down and back. Slowly roll up the medial hamstring from just above the back of the knee joint to the start of the glutes. Hold any tender spots for 30-90 seconds (try to relax and breathe deeply). Slowly roll back down to starting position.
Repeat with left leg.