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)
We realise that this discussion could 鈥� if you鈥檒l forgive the pun 鈥� run and run, so we are declaring the correspondence closed with reference to 快猫短视频鈥檚 recent exercise myths special: regardless of whether running on a treadmill is any easier or not, its monotony makes it seem harder (13 January, p 31) 鈥� Ed
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鈥� Readers Christopher Kimberley and Eric Kvaalen disagree with my explanation of 鈥渂elt turnover鈥� (Last Word, 10 February), and I would like to respond.
On a treadmill, the belt is driven at constant speed, while the runner remains stationary. There is no horizontal acceleration of the runner with respect to the belt, hence no work is done by the runner other than that required to move their centre of mass up and down, and move their limbs. It makes no difference which reference frame we select: it is the relative motion between belt and runner that matters.
In contrast, consider the same runner on a flat, level surface, moving with apparently constant velocity, with a tail wind to match, so we can disregard wind resistance.
Our runner must exert a horizontal force against the ground with each stride. If you doubt this, consider what happens if the runner encounters a low friction surface, such as a patch of ice, loose carpet or perhaps spilled marbles.
Why doesn鈥檛 this force cause the runner to accelerate? Well, it does. With each stride, the runner repeats a cycle of acceleration and deceleration. Those in the field of biomechanics refer to this as the gait cycle, and the acceleration and deceleration periods are known as absorption and generation, respectively. As with any physical work cycle, energy losses exceed gains, with the deficit here made up by the runner.
On the treadmill, there is altogether less work being done, and the treadmill motor is doing some of it.
Howard Bobry, Nehalem, Oregon, US
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