It really depends on what you want to achieve by getting your athlete into a running training programme, and how well the athlete tolerates it. I have a treadmill at home and have personally found it much harder to keep to a 12kph pace on the treadmill compared with overground running (which I can do quite comfortably).

I find running overground much easier than running on a treadmill for many reasons, including:
- Unable to get into a 'natural' rhythm on a treadmill as it is very hard to find a 'comfortable' speed and incline on a machine.
- No wind-chill which often increases sweating and dehydration (or so I have found).
- Completely boring. I love looking at scenery as I run, or I run with others to keep myself occupied, which tends to be difficult running on a treadmill.

As I said before it really depends on the person's own opinions and preferences, but I will try to provide some biomechanical research that compares the two in relation to tibial stress.

I stumbled across an article in the 'British Journal of Sports Medicine' that measured tibial stress in a sample of runners on both asphalt and a treadmill. Essentially the researchers found that: 'tension strain rates were 48-285% higher during overground running than during treadmill running'. This tends to predispose overground runners to tibial stress fractures.

So essentially:
- Running on a treadmill reduces tibial stress, which should theoretically reduce the incidence of tibial stress fractures, but will not lead to the increased bone density that occurs naturally as a result of that same increased stress.

According to this I would be inclined to suggest a programme that incorporates both treadmill and overground running. This way the athlete should get the benefits of both.

If anyone wants to have a closer look at this article, they can find it <a href="http://proquest.umi.com/pqdweb?index=0&did=332666941&SrchMode=1&sid=3&Fmt= 4&VInst=PROD&VType=PQD&RQT=309&VName=PQD&TS=115381 7743&clientId=20906" target="_new">here</a>