Although the strength of the ki that we carry varies from individual, it's linked to the physical well-being of that individual. While not requiring the body to be stronger or better to have a stronger energy-body (and indeed, I know someone who's health is declining, but their energy is increasing because of other exercises and rituals they perform), it helps to perform regular exercises.

I don't keep to this schedule anywhere near as often as I'd want to, but whenever I am able to, I try to perform 50 bokken strikes (being watchful of how I employ my ki in the strike, so as to focus the power, and in turn, my focus, as well as noting my breathing - oddly I tend to stop breathing while I do this exercise, which is a rather bad thing), as well as 25-50 pushups and situps.

For the purposes of strength, I probably don't need to perform these daily anyway, given that I'm already stronger than my physical body should allow, however, they help to boost stamina and endurance, which are things I lack. They're also good for meditative purposes (I recommend trying them while meditating, and see what happens).