The difference between treadmill and outdoor running.

People often wonder if running on a treadmill or outdoors can make a difference in their training plan and performance. Treadmill running can be very useful when your dealing with bad weather, traveling, or just as an alternative to make a change. When running on a treadmill, the belt is moving towards you, there is less resistance and it requires less effort to push your body forward. Also, you are not exposed to any head wind, no uneven road or terrain. If you only train on a treadmill, running outdoors would feel a bit more challenging. When using a treadmill, set it at a 1% gradient to make it more similar to road running.
Treadmill running also affects your running form- you may run with a flatter foot, a shorter stride length and a more forward lean. Running on a treadmill can make you feel like you are running faster than you are, so you might not match your outdoor running pace. Also the quality of the treadmill makes a big difference. If you only use the treadmill occasionally, none of these issues are a big concern.
The positive side of running on a treadmill is that it is very good training tool, especially at setting a consistent pace when you’re doing a sustained effort. Because of the difference between treadmill and outdoor running, don’t relate your treadmill pace to your outdoor running pace, use them as separate ways of measuring your performance level. Treadmill running is also a great tool to get back to running after an injury. Running on a treadmill offers some softer impact, so combining both when you are recovering from any runner’s injury might be very beneficial. 

Treadmills are also great for interval training, you can do some speedwork, hill repeats even when you don’t have access to an outdoor running path.

Here’s a great treadmill interval training session:
10-min warm up at a steady pace
10 X 1-min at 5% gradient
Increase your speed to a pace that you find hard but not flat out. 
Do a 60-90 secs recovery jog between each effort.
10-min cool down

Train Hard, Eat Right, Feel Great!