According to Zweck, there are a couple of key differences between using a cross trainer compared to a treadmill. 'Firstly, there is the impact, or lack of it, when using a cross trainer,' he explains. 'When you run, typically a force of two to three times your body weight is absorbed by the body every time your foot strikes the floor. When multiplied by the volume of steps you take when you run, this is a lot of force and can cause muscle or joint pain.