I go to my local community center to lift and stretch out almost every day.

Even in the spring and summer, there are always at least a few people pounding away on the treadmill.

I can’t help but wonder;

“With such beautiful weather outside, why are they stuck inside on the treadmill going nowhere?”

It was partially that question that spurred me to look into todays topic:

What is the difference between running outside vs treadmill when it comes to the scientific research. When it comes to running for you, is treadmill running better or worse for you?

At first glance, they seem the same.

A physicist might even argue that there shouldn’t be any differences, since it’s just a matter of frames of references.

But it turns out that, because ground is moving, instead of the runner on top of it, there are a few key differences in your biomechanics running on a treadmill, your perception of your own running, and the physiological demands placed on your body.

Biomechanical Differences Between Treadmill Running and Outside Running

The first study we’ll look at, published in 1995 by Nigg, De Boer, and Fischer at the University of Calgary,1 examined the biomechanical differences between treadmill and overground running.

Using two high-speed cameras to capture a front and rear view of a group of runners, first running on a treadmill and then running on a road, the researchers tracked the motion of their joints throughout their gait cycle.

While a number of variables changed, the only one that was consistent across all subjects was foot angle at touchdown.

On a treadmill, the runners all landed with flatter feet (less ankle dorsiflexion) than when they were running on land.

Many other variables changed in a “subject specific” manner, but the changes were not consistent across all subjects.

This probably indicates that we all adapt to treadmill running in our own way, and may find that it stresses our body in slightly different but unpredictable ways.

Another study done two years later by Wank, Frick, and Schmidtbleicher in Germany did a similar study of the biomechanics of treadmill running,2 but extended their research by using electromyography equipment, sensors that can identify when your body activates your leg muscles and how strongly.

Like Nigg, De Boer, and Fischer, this study found flatter foot placement at footstrike.

Researchers found runners have a more pronounced forward body lean, shorter stride length, and a higher stride frequency.

They also spent less time on the ground.

Wank et al. proposed that the treadmill gait was a response to a feeling of instability on the treadmill—the runners quickened their stride, plantarflexed their ankles more, and spent less time on the ground since their body sensed that the treadmill was an unstable surface.

Some researchers have also suggested that there is an inherent instability on many treadmills because the belt momentarily stops when the foot lands on it, pinching it between the shoe and the steel plate below the belt.

The electromyography studies, however, found little difference between treadmill and overground running, leaving the instability hypothesis unproven.

Why Does Running on a Treadmill Feel Harder (or Easier)?

A much more recent study, published by Kong et al. in February of this year, further examined the brain’s perception of running on a treadmill.

In a very clever design, a group of runners first ran at a self-selected pace on a track for a few minutes, then immediately hopped on a treadmill and were told to adjust the speed of the treadmill to the pace they were running on the track.

The only catch was that the runners were not allowed to see the pace indicator on the treadmill!

After running for a few minutes on the treadmill, they again hopped onto the track and were told to run the same speed again.

Interestingly, though the runners managed to run the same pace on both occasions on the track, their perceived speed on the treadmill was drastically different.

While the runners averaged about 6:50 pace on the track, when they adjusted the treadmill to what felt like the same pace, it was actually two minutes per mile slower!

Now:

I have some doubts about whether this effect applies to everyone.

The researchers don’t say whether the runners were adapted to treadmill running or not—this could make a big difference in how they perceived their effort.

But this confirms what a lot of runners already know:

Running on a treadmill can feel a lot harder than it is.

Physiological Differences Between Running on a Treadmill and Running Outside

What’s worse, in terms of physiological demand, it turns out treadmill running is easier!

Because of the lack of wind resistance, your oxygen consumption for a given pace on a treadmill will be lower than it would be overground.

Fortunately, this can be counteracted by adding a small incline to the treadmill, as demonstrated in a 1996 study by Jones and Doust.4

These researchers compared oxygen consumption levels in a group of runners at a range of paces both overground and on a treadmill at a variety of inclines.

They found that a 1% incline offsets the lack of air resistance most accurately, leaving the physiological demands between overground running and 1% incline treadmill running similar. (click to tweet)

The only problem with this is that is exaggerates the changes in biomechanics we observed earlier! If the ground is at an incline, your foot placement automatically becomes flatter, and your body lean increases as well.

Is Treadmill Running Better or Worse for Runners?

There really aren’t too many advantages to treadmill running, at least during the sunny months of summer.

Treadmill running has a double-whammy of feeling harder, but being easier.

The difference in physiological demand can be offset by setting the treadmill to a 1% incline, but there’s no guarantee the incline measurement on a health club treadmill is accurate!

If there’s one redeeming quality in treadmill running, it’s from the changes in biomechanics. If you’ve got an injury that’s bothering you, there’s a chance treadmill running might not be as stressful. I’ve had bouts of tendonitis of the extensor tendons, on the top of the foot, which control the ankle’s dorsiflexion.

Since foot placement is flatter on a treadmill, these tendons don’t have to work as hard, which enabled me to get back into running a few days earlier.

But, these special cases aside, there’s really no reason not to “hit the road” and ditch the treadmill if the weather’s nice outside!