Do what you want I find . If I feel I'm slowing up I stand and get the speed up but I can feel ive done it so get back in the saddle . I noticed last week that I used my arms and mid body more to go up a hill , the legs just kept spinning but the rest really helped me fly up it to my standards .

Sometimes I stare at my feet & tell myself I'm on a flat surface haha.

, that could be an important factor.