Just for fun
If you keep the muscles around your knees strong and flexible you'll reduce the chance of an injury. Below are some simple exercises you can do every day.
Note that if any of these exercises hurt, you should see a doctor before continuing with them. Pain might indicate that you've already done some damage to your knees.
EXERCISES
Keep your knees together and your back straight.
Pull one foot up towards your backside and hold for six seconds.
Make sure the foot points straight behind your body, not to one side.
Do this exercise several times. Then do the same for the other leg.
Sit on the floor with one leg outstretched and the other leg bent.
Raise the outstretched leg about 200 mm off the floor.
Point the toes towards your head and hold for six seconds.
Do this exercise several times. Then do the same for the other leg.
Sit on a chair or box to support your legs above the knee.
Raise one leg until it's fully stretched out, with your foot flexed back towards your head.
Hold for six seconds.
Then lower the leg about 30 degrees with the foot still flexed and hold for another six seconds.
Do this exercise several times. Then do the same for the other leg.
Reference
These exercises are adapted from those shown in an article called 'Preventing job-site knee injuries' written by Steven Bond, an orthopaedic surgeon.
The article appears in the members' area of the Fine Homebuilding website.
To see the full article you will need to join as a member, but you can access lots of other articles and information pages in the public areas of the site.