Two hundred years ago, the treadmill was invented in England as a prison rehabilitation device. It was meant to cause the incarcerated to suffer and learn from their sweat. It would mill a bit of corn or pump some water as a bonus.
Today, the treadmill is used as an exercise rehabilitation or training device. It helps athletes and fitness enthusiasts and runners suffer and learn from their sweat, like rate, tempo and volume.
Not much has changed really. A torture device is still a torture device. Perception vs Reality :-)