The Spanish squat is a rehab or prehab exercise that allows loading of the quads with reduced force on the knee joint, and is commonly used as part of patellar tendinopathy rehab.
 
Stand in front of a power rack or similar, and wrap a heavy band anchored to the rack around the backs of your knees—either a single loop, or an individual loop for each leg. Step back far enough to create some initial band tension—you should be able to lean your body backward slightly and be held up.
 
Squat by sitting back, keeping both the shins and trunk as close to vertical as possible until the knee is at about a 90-degree angle, then stand again, maintaining a slight backward lean of the body.
 
Purpose
The Spanish squat allows loading of the quads with minimal force on the knee joint and limited contribution by the posterior chain to build quad and/or patellar strength, particularly when coming back from injury, or help rehab patellar tendinopathy.
 
Programming
The Spanish squat can be introduced as isometric holds for 15-45 seconds as needed early on in a rehab process, and built to sets of 8-15 reps of actual squats as pain and strength allow. Slow eccentrics can be used in the initial squatting phase as well to encourage greater tendon strengthening.