First, with treadmills you never have to worry about the weather or time of day. Whether it's raining, snowing, blazing hot, or icy, you don't care because you don't have to run outside. You have the pleasure of running in a temperature controlled environment. You can run in any season, at any time of day. If you're a woman, you may worry about being attacked if you run outside at night. With a treadmill, that worry is gone. You're safe and sound inside. If you like running in the early hours of the morning, but hate running in the dark, you don't have to worry about it with a treadmill- it's never dark with a treadmill. So basically, a treadmill gives you freedom of choosing when you would like to run, regardless of external conditions.

Next, a treadmill gives you the opportunity to monitor your vitals. Yes, you can buy a hand-held heart monitor, but they can be a pain to lug around with you. With a treadmill, all the equipment is right there at your finger tips. All you have to do is attach the heart monitor to your finger or ear (or wherever it measures from) and you're good to go.

Third, a treadmill can record your progress and your preferred programs. You can choose from a wide variety of running "routines" that will help build strength or endurance, depending on what you'd like to focus on that day. Or you can do a mixture of both. For example, you might decide to do a high intensity run one day, alternating the difficulty and grade on the treadmill, and then an easier run the next day.

Fourth, a treadmill allows you to change your altitude or difficulty at a whim. One day you may decide you want to go through "rolling hills" while the next day, you might prefer "hill climbs." Or maybe you'd like to do both in one day. If you're outside, you might have to run a very far distance in order to get both types of hill training in one workout. But with a treadmill, you can create that environment whenever you like. Here's one example of a workout that you could do on a treadmill, but might have a hard time finding the right location outside:

Hill blasters
This is an intense hill workout that uses short runs up a steep grade. After your warm-up set the treadmill at 10 to 12 percent elevation, or the highest elevation available on your treadmill. Run for 1/10th of a mile at a strong but maintainable pace. You should run at a pace that you can maintain for the entire workout, not just one repetition. After running for 1/10th of a mile, decrease the elevation to 2 percent and decrease your speed to an easy pace for one minute of recovery. Then increase the elevation back to 12 percent for another 1/10th of a mile before decreasing again to 2 percent for one minute of recovery. Keep up this pattern of 1/10th of a mile at 12 percent elevation/ one minute at 2 percent elevation for 3 to 10 repetitions. For your first workout, stop at 3 repetitions.

However, the important thing to remember is that it's really up to you. Your personal preference might be to run outside- maybe you don't care about the weather or monitoring your vitals. Or maybe you have always hated running outdoors and will always prefer a treadmill. The important thing is that you are out there exercising.