By lying on the foam roll, you can stretch out the front of your chest, the area of the pectoral muscles.
Lie along the foam roll making sure that your head is supported, knees are bent and that your arms are relaxed by your side. If this position provides minimal stretch, take your arms out to the sides until you feel a comfortable stretch through the front of your chest.
At no point should you experience any tingling or numbness in your hands. If you do then discuss the stretch with your physio. This may be a sign that the exercise is not appropriate for you or you may be able to eliminate it by propping pillows underneath your arms to reduce the intensity of the stretch.
In order to increase the intensity of the stretch, or to feel the stretch in a slightly different part of the chest, take your arms further away from your body. Stop and hold the stretch when you feel you have reached a tight point.
At any stage if you are not comfortable with the stretch, try using pillows under the backs of both arms to reduce the stretch.