Cho-Pat's Original Knee Strap stabilizes and tightens up on the kneecap mechanism by applying pressure upon the patellar tendon below the kneecap. This compression reduces or eliminates inflammation and helps prevent knees from giving out. Sizing: Based On Circumference Below Patella. Measure leg circumference just below the kneecap. Offers symptomatic relief for acute/chronic pain associated with Patello-Femoral Syndrome and Osgood-Schlatter's Disease. In most cases jumper's and runner's knees respond well. Size Small fits 10 - 12.5 in. Medium fits 12.5 - 14.5 in. Large fits 14.5 - 16.5 and X-Large fits 16.5 - 18 in.