Runners have long debated the difference between training on a treadmill and training on solid ground. 鈥淏elt turnover鈥� is commonly cited as a factor that helps to move your foot backwards and thereby makes running on a treadmill easier than running on the road. At constant velocity, is this a real effect? If so, wouldn鈥檛 it be felt on any 鈥渕oving鈥� surface you walk on, such as a train or plane 鈥� or even Earth? (Continued)
鈥� A previous correspondent (2 December 2017) states that a runner on level ground expends more energy than one running on a level treadmill. If I understand school physics correctly, this is wrong.
As Newton informs us in his first two laws of motion: an object in an inertial frame of reference either remains at rest or continues to move at a constant velocity unless acted on by a force, and that Force = Mass x Acceleration.
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For the road runner, the frame of reference is the road and for the treadmill runner it is the moving belt, not the floor and walls of the gym, as your correspondent seems to suggest.
Both runners expend energy in their muscles accelerating and decelerating their limbs to stay on their feet. But neither applies a net force to the running surface in their direction of travel while they run at a constant speed. If they did, they would accelerate in accordance with Newton鈥檚 second law (ignoring the small force required to overcome frictional resistance such as headwind).
Your correspondent is right to say both runners work harder on uphill slopes. They both need to apply additional force to counter the downward force due to the acceleration of gravity. They are now both gaining height within their respective frames of reference and this requires work.
Christopher Kimberley, Worcester, UK
鈥� Once your body is in motion, no energy is required to keep it moving forward, except to overcome air resistance. In fact, we can say that your body is moving and Earth is staying still, or we can say the opposite. There is no way to say that one point of view is more correct than the other.
There are only two differences between running on a treadmill and running on a solid, flat surface.
One is that the treadmill may not be as solid as the ground. The other is the lack of wind or air resistance. If the belt has no more springiness than solid ground, and if you have a huge fan blowing against you at a speed equal to your speed on the belt, then there will be no difference in terms of how easy it is.
Eric Kvaalen, Les Essarts-le-Roi, France
鈥淥nce your body is in motion no energy is required to keep it moving except to overcome air resistance鈥�
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