Treadmill Speed Vs. Track Speed

Some who run on treadmills are more casual about their workouts than others.
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Running outside offers fresh air, a range of scenery and a variety of environments in which to do the deed. Running on a treadmill guarantees a soft surface, protection from the elements and the ability to set your pace with exquisite precision. Whether you choose one, the other or a combination of both is largely a matter of personal taste. When it comes to running fast, however, situations exist in which one method may be clearly superior to the other.

Top-End Speed

If you are an above-average runner and regularly do competition-oriented speed workouts, the treadmill may limit your ability to reach your desired pace. Many motorized treadmills have a top speed of 10 miles per hour, which translates to six minutes a mile -- fast by most standards, but not by those of genuine sprinters. Even models that reach 12 mph, which are fairly common, or even 15 mph, which are rare in public gym settings, don't allow you to run a pace any faster than 60 seconds per 400 meters. Furthermore, the faster you run on a treadmill, the more hazardous the exercise becomes because you cannot decide to stop quickly or else you'll fly off the back of the machine and possibly injure yourself. So save those sprint workouts for a track or level stretch of measured roadway.

Air Resistance vs. Still Air

When you run outside, even on a perfectly calm day, you have to overcome a slight but non-negligible effect of air resistance, which creates drag on your body in a way that increases exponentially with increasing speed. When you run on a treadmill, this effect is absent. As a result, when you run on a treadmill at a speed at or greater than about 8 miles per hour, you need to set the grade of the treadmill belt to 1 percent to duplicate the oxygen cost of running outside on level ground at the same speed. If you're a true speed demon who exceeds 11 mph or about 5:25 per mile, this grade value rises to 2 percent.

Interval Workouts

This type of speed workout involves running repetitions of a set distance at or below the pace of your target race distance, punctuated by intervals of slow jogging or walking to recover. An example for a runner hoping to run under 20 minutes for a 5K, which is 6:26 per mile or 96 seconds per 400 meters, would be 10 times 400 meters in 90 seconds each with a 90-second recovery jog or walk.

While a treadmill offers the advantage of being able to set your desired speed precisely, it also has a drawback in variable-pace sessions compared to running outdoors -- you have to manually slow or stop the belt by pushing a button, often repeatedly, and speeding it back up requires the same thing. In addition, interval workouts are often easier when done in a group. So, unless the weather is unfavorable, consider making an outdoor track your first choice of venues for these sessions.

Tempo Runs

Tempo runs offer a training stimulus similar to that of interval workouts, but they are geared toward runners specializing in longer road distances rather than track events -- for example, 10Ks, half-marathons and marathons. These are continuous efforts of about 20 minutes run at a pace you could hold for approximately an hour in a race. This speed correlates well with the pace at which you begin to accumulate lactic acid faster than you can clear it, so running at this pace trains you to become more metabolically efficient at a higher gear.

Tempo-run pace for most runners is about 25 to 30 seconds per mile slower than 5K race pace. Because you don't want to go too fast or too slow and want to maintain a specific speed for a predetermined length of time, the treadmill may be a perfect choice as long as the ennui of running inside doesn't deter you.

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