[Therese, co-creator of the world's best treadmill workout program, "Trekking: The Total Treadmill Workout", sponsored by StarTrac, offers expert tips for maximizing your workout.]

On cold, wet or humid days, retreating indoors for a walk can sound pretty appealing. After experiencing workouts both indoors and out early in my walking career, I began to wonder about the differences in muscular and cardiovascular use between linear movement over land and stationery walks on a treadmill. I already knew the indoor ones were more monotonous and left me feeling like a rat in a cage. But when the weather says "walk indoors or don't walk," you want to know if the indoor workout does the same for your health. Long story, short: Yes. Whether inside or out, walking for X amount of time, at X intensity, using identical technique, will use the same calories and give you an equivalent aerobic workout.

You do move slightly differently, though:

• The belt rotating underneath your feet means you're doing tiny little jumps up and down as you walk instead of just pushing off from behind.
• The belt will also force your forefoot to slap down quicker and perhaps harder than usual, which could cause additional shin aches. You might also discover other tiny aches in muscles that take you by surprise because of a slightly different manner of moving. Still, better to do something, than nothing.

Now come the caveats and tips:

• Walking at X intensity"

Notice (above) I didn't say "speed." When you're indoors on a treadmill, you don't have to overcome wind and air resistance to move your body forward. So you'll have to either choose a slightly faster speed indoors (about .1-.2 mph more; choose less the slower you're going) to reach the same outdoor intensity, or you'll have to walk the same speed but select a 1-percent grade. Both methods will allow you to match intensities. This general guideline applies to those moving at a brisk walk (less than 12-minute miles). The faster you go, the more you'd have to increase the speed (up to .3 more) for an equivalent pace, but the 1-percent rule holds true. Check your heart rate for the best match in intensity. Wireless heart rate monitors give the most accurate continuous reading for you to check during your workout.

• Using identical technique

Too often, treadmills seduce walkers into cranking up the speed or incline beyond what they can comfortably manage. So they hang from the front bar or side handles to be able to keep up with the rotating belt. Remember, you don't have anything to hang onto outside. If you're supporting your body weight by an object, you're using less personal energy to ambulate forward, therefore using less muscle (other than in those gripping hands) and fewer calories. Keep speed and incline under control. Stand tall and swing your arms just as you do outside. Keep your shoulders relaxed and your eyes cast outward, not down at the controls. Using mirrors in front or beside you can help you occasionally check your technique (that's an advantage over the great outdoors). Don't neglect making use of the exact control over speed and incline. Throw in occasional jaunts of hills or bursts of speed to break up the monotony of staring at a blank wall.