Always toe shifted, never had a bike that could heel shift before this one and the bike is relatively new to me(27 year break in between last bike and this one). Took the bike out for a nice two hour spin today. Here are my observations and thinking from an anatomical and physiological point of few (and gut too).
1. To toe shift, the foot needs to go up against gravity and against the additional resistance of the shifter. The muscles that perform this task are the anterior lower leg muscles, smaller muscles primarily meant to lift your foot up when walking.
2. To heel shift, because my feet are big and my legs are long, I need to slightly flex my hip (power muscles-big and strong) to lift my heel up over the heel shifter, then push down with mainly my hamstrings (again, big strong power muscles) and with gravity assistance against the same shifter resistance.
so, toe shift= weaker muscle against gravity with additional shifter resistance = more work = more energy expended= ?quicker fatigue factor
vs
heel shift = big powerful muscles, with gravity assist, against same shifter resistance = less work = less energy = ?less fatigue
3. It just feels good to me to hit it with my heel. There's a satisfaction there for some reason.
Thanks for this post, you all just made my ride more enjoyable.