Hi Lauren - here's an answer from Steve in our Facebook group:

'Complicated really. Personally I'd reverse engineer it a bit. Heel down, recruits more gluteals and hamstrings, neutral foot recruits more of a balance quads and hamstrings, toe down more calf muscles. So if sprinting up a short hill maybe ...an argument for a bit more toe down as there are good short burst muscles in the deeper calf muscles. They fatigue quickly though and tend to cramp if used in this way in the de-conditioned.

Personally, I tend to suggest sitting slightly back in the saddle thinking of recruiting the push phase at about 1 o'clock position, pressuring the handlebars with about 20% effort downwards to recruit the transverse abs this with your hands as close to the stem as you can to reduce excess steering. This stabilies the lower back allowing the gluteals to be recruited better. (A strong set of muscles that don't fatigue so readily.)

The sensible thing to do is try it yourself and see what happens. As you'll find the most efficient way to do it for you may not be the text book answer. What I do know though is get as light as you can safely and ride up hills! This normally has the best effect upon hill climbing.'