Over the years of working in my clinic I've noticed that when a person has had a painful knee, hip or lower back, one of the things that becomes a problem for them is the ability to get down on the floor and get back up.
In fact, getting on the floor becomes a fear. Fear perpetuates into avoidance. Avoidance creates more difficulty for that task in the future. In this case, the floor becomes a great obstacle.
"Always do what you are afraid to do." Ralph Waldo Emmerson.
Most of these painful areas aren't from a major accident. Years of abuse and avoidance has manifested in this "painful area." I started thinking about a typical day and realized that without effort, you can indeed go a very long time with out ever getting down on the floor.
Wake up in a bed, usually several feet off the floor. Go to the bathroom on a toilet. Walk to the kitchen and sit at a counter or chair. Go to work in a car. Sit at a desk. Drive home. Eat dinner at a table. Perhaps they go to the gym and workout, typically on a machine, bench, bike, elliptical, ect. Go back to bed. Repeat.
It takes concerted effort to physically get down on the floor. Which is why I believe some of the best exercises are done on the ground.
Turkish get ups. Most of the time I just try to get my patients to get to the half way point of getting their hips off the floor. A baby get up.
Primal Rolling. Rolling from the stomach to the back, left and right. This is a core based exercise. Surprisingly how many people can't do this at first.
Foam Rolling. One of the big benefits I believe with the foam roller is not only the roller but how you are on the ground moving on top of it. Pushing and pulling using their hands and feet.
In the book "Muscles and Meridians", author Philip Beach takes it a step further and recommends some floor based postures that aren't exercises per say, but are simple postures that benefit the myofascial system.
Full Squat. Now this is probably unrealistic for most people to be able to relax into a full squat, like a toddler. But, when hanging onto a poll or door jam, leaning away, this becomes a very nice way to get the hips below the knees. Not exactly a floor based posture, but if you can do a full squat with ease, You're not going to have to many mobility issues.
Sitting on the toes. Knees on the ground, feet under your butt, with toes in extension. Keeps mobility in your big toe.
Drinking posture. Same as sitting with toes under the butt, but now you bend forward so that your forearms are on the floor.
Kneeling. Same as sitting, but now the tops of the feet are flat on the floor.
Cowboy Posture. This is a combo. One knee in Kneeling, one knee up so the foot is flat on the ground.
Long sitting. Sitting with legs straight out in front of you.
Cross Legged. Sometimes this has been called sitting Indian Style.
Side Saddle. Sitting, one leg is externally rotated and bent the other leg is internally rotated, both knees are bent.
Tailors Posture. Sitting, bottoms of the feet are pushed together and brought as close to the body as possible. As my track coach used to shout, "Put you're soles together and give me an Amen!"
These postures should be entered with care, but can be done while watching commercials for example. The idea is to simply bring back whats called floor based living. Those with knee pain will probably find the kneeling postures to aggressive. I would suggest not to spend more then a minute in each posture and slowly transition form one to the next as part of your cool down from exercise or just pick a few during your evening to reclaim the floor.