Humans love to run. We're the only species that does it for fun, and we've even built machines that let us run as long as we want. But when it comes to training, new research shows the best workout is the one you do outside.
Researchers wanted to find out how much a body works when running on a treadmill versus running outdoors.
They discovered that treadmills require users to run 15% faster than they would outside to get the same workout.
The scientists said this is due to the machine's belts, which return energy with every step taken.
So if you're looking to up your fitness level, it's probably best to do as your ancestors have done for 2 million years and get outdoors.