Some studies on defining what ‘just do it’ advice should mean for people with cancer. My sense is that we make this more complex than it needs to be: ‘just do it’ plus ‘listen to your body’, with gentle exercise like walking, yoga, tai chi etc., is largely sufficient. Whether or not exercise increases longevity is besides the point; the issue, at least for me, is more to improve my quality of life than prolong it (although the latter would be nice too!).
Of course, beyond these basics, people who want to do more active exercise (weight training, running marathons etc), should consult with their medical team. The general advice I received was listen to your body; if I couldn’t get out of bed the next day, I had pushed myself too much. So far, I am getting out of bed!