After total knee replacement, your surgeon will give you a series of exercises to perform to meet the expected recovery rate. It is always important to follow your doctor's orders. Once your recovery has reached the point that your doctor says you can increase your physical activity, you may wish to include aquatic activities, including aquatic exercise, which can help to strengthen muscles and get them back in shape.
Walking waist-deep in a pool is a simple exercise that will strengthen all your leg muscles, including those supporting the knee joint. Walking in water provides more of a muscle workout because the water offers more resistance than air. At the same time, the buoyancy factor of water means that you are putting less strain on your joints. As such, aquatic exercise can help with total knee replacement recovery.
An easy strategy is to employ many of your doctor-ordered exercises, adapted for the water (of course, ask your doctor about this first). Instead of doing knee extensions while sitting in a chair, sit on the edge of the pool and dangle your legs in the water. Using the water for added resistance, do your knee extensions, slowly raising one leg at a time, straightening out the knee. While standing in the water, against the side of the pool, so you can use the pool's edge for support, you can do leg extensions. Slowly raise one leg straight up as high as you can, hold it a moment, then let it sink back down.
As well, you can do a version of the heel slide. Again standing against the side the pool, place one foot against the pool's side wall. Now slide the foot up the wall toward your buttocks as far as the knee will bend. Hold then release. While floating on your back, hanging onto the side of the pool, scissor kick your legs slowly as if swimming. And, of course, once you are able to, simply swim laps across the pool. See if the gym offers an aquatic exercise class.
Some gyms may offer aquatic exercise equipment. Once your knees are stronger, you might consider adding in walking on an aquatic treadmill, or sit and use an aquatic treadcycle, or working out on an aquatic stepper and twister. Start with the aquatic treadmill or treadcyle then work your way toward the aquatic stepper and twister. Both the treadmill and treadcycle use a treadmill base. The treadcycle is simply the sitting down version. The stepper and twister provides exercise similar to climbing stairs with abdominal twisting action.