The leg exercises that you choose will depend to a large extent on what you're trying to achieve. For example, are you trying to build strength, increase running endurance or improve balance and flexibility? Similarly, are you a weight-lifter, a jogger or a ballerina?
Of course there will be some overlap in the exercises selected as such things as exercises for building strength can be combine well with those for improving balance.
To begin, remember that any exercise routine should only be done after a warm-up period that includes stretching.
One excellent exercise for strengthening and toning leg muscles is 'spinning', using a stationary bike. Of course you can also use a regular bicycle, but the exercise is less controllable and involves a lot of other muscle groups.
A 15 minute spin will help tone the calves, hamstrings and quads as well as improve joint flexibility. On occasions it can also reduce cellulite and fat. As an added benefit, it's also a very good cardiovascular exercise so that you get two for the price of one when you spin.
If you're looking for something a bit less vigorous and simply want to help strengthen your knee, then here are a couple of options.
This first one is really good for people who suffer from conditions such as a roughening of the cartilage underneath the knee cap or chondromalacia patella, which sometimes results from the bones not sitting properly in the 'V' of the knee joint.
Sit in a chair with you back straight, but relaxed, and your legs bent at 90 degrees so that the thigh is parallel to the ground and the lower leg is vertical. One leg at a time, tense your thigh and hold this tension for 5 seconds before releasing. Switch legs and repeat this exercise 10 times for each leg.
This next exercise does a little bit more to build strength in the muscles that control the bending of your knee.
Sit up straight, breathe normally and cross your legs at the ankle. Push forward with the rear leg and back with the front leg. This can be a little tricky at first but, if you concentrate on it, you'll soon get the hang of things.
Switch legs by reversing the direction of the cross and repeat the exercise 10 times for each position.
Okay, we're getting a little more strenuous now.
Stand up straight (preferably on a mat or a carpeted or wooden floor) with your heels together and your toes slightly apart. Make sure you are well-balanced.
Lift your heels and balance on the balls of your feet. Hold this position for 5 seconds and then lower yourself slowly back onto your heels. Repeat this exercise 10 times to begin with and, as you build strength and balance, gradually increase the length of time you're on the balls of the feet.
You can also vary this exercise by bending slightly at the knee while you are on the balls of your feet. This will bring the thighs (hamstrings and quadriceps or 'quads') as well as the buttocks into play.
For those of us who are getting on a bit we face the problem of falls which frequently lead to broken hips and severe health problems. Keeping your legs in shape when you're younger, even if you can't particularly see a reason for doing so at the time, can have immense benefits later in life.