Imagine the stress on your knees if you supported the weight of the Space Shuttle after it has been fully loaded and prepared for liftoff.
Now, imagine the wear on your knees if you had to support that weight every day,
year after year.
If you are considered an "Active Adult",
averaging at least 10,000 steps of activity per day,
your knees are accumulating the cyclic forces equivalent to approximately 4.5 million pounds of stress, each day.