The important thing to remember when cross training is: only running improves your running. However, if you are just looking to lose weight or keep fit like many other beginners, participating in any activity will help. I haven't inlcluded walking in the following list. Walking is good to lose weight, but not for getting fit. In the obesity crisis we are facing in both the UK and USA, experts are misleading the public. Walking is not strenuous enough to push your heart rate through to training levels and so no training effect can take place. Don't be fooled into thinking walking alone can get you fit.

The main muscles used in running are the calves, hamstrings and buttocks. The main leg muscles not used are the quadriceps. If you want to gain all round strength, a weight training program will be necessary, but remember that bulk will slow your pace down. Many serious runners will cross train to prevent injury, and to prevent muscle imbalances. Cross training can also be used to improve flexibility, and burn calories on a recovery day. I would recommend cross training whilst injuried if possible to decrease the rate of detraining. I will cover biking and swimming in further detail here, however, dancing, skating and most other sports will all improve your fitness as long as they raise your heart rate.

Cycling: The main problem I hold with cycling is that you have to stop and start, you can't go as fast as you want, and you can't work as hard as you want, especially when going downhills. Unless you already have a bike, it can be rather expensive too. An indoor bike can help combat the above factors but generally speaking, 3 to 4 miles of biking is worth 1 mile of running terms of fitness. Cycling works the quads, which is good news for runners as this will help prevent knee injuries because it helps stabilise the knee. It will also increase flexibility in the knee and hips which in turn contributes to a healthy lifestyle. If you are fit from running, cycling can still be difficult, as I have learnt the hard way. I have noticed that my legs tire quicker and I run out of breath quicker when cycling than when running. This is mainly good news, as it means that you are most likely in your training heart rate range. When you start a new activity, remember to ease into it like you would with running, otherwise you risk injury all the same.

Swimming: This is a great exercise for recovery days or for coming back from injury - because it involves little impact. Some people know it as the only sport which exercises every muscle in the body, I am not fully aware of the extent to which this statement is true, but it does do a lot for a wide range of muscles in the body. However, as soon as you begin swimming, your heart rate will drop by 10 beats a minute. This is due to the cold nature of most baths and the fact that your body is now horizontal. This means you will have to work harder to reach your training heart rate. If I go swimming, I try to go as fast as possible, and that way I know I am in my training heart range. I find swimming very boring and to make it a habit can be quite expensive, but some find that it is the sport for them, even more so than running. Swimming will improve flexibility in many parts of the body, and will work many muscles, however the workload will be shared out between these muscles, so don't expect extra strength in every muscle used whilst swimming. 1 mile of swimming equals around 4 to 5 miles running. But swimming 1 mile will take a long time... don't be fooled.

Cross training is good to prevent muscle imbalances, and therefore injury. If variation keeps you enthusiastic, then by all means do it. Staying fit and active is important, it doesn't matter how you do it.