

The smaller the foot, in this case, the harder the muscles have to work to create the same torque (or moment).
That’s backwards, a shorter lever arm requires less force. If you had a 10 foot long foot, you’d have to have insanely strong calf muscles to stand on your tip toes, because how far the load is from the fulcrum.
It’s totally true from a physics standpoint. A longer lever arm between the load and fulcrum requires more force to move the same weight for a type 1 lever, all else being equal.
“Harder to exercise” is poorly defined, especially when you go on to discuss endurance, speed, and force, all of which are very different terms.
I totally get what you’re saying, but I specifically narrowed it down to force for a reason. My shorter friends kick my ass in lifting due to the mechanical advantage their shorter limbs have, but I smoke them in a distance run because my longer limbs allow me to traverse a greater distance in a single step. This is complicated though because larger lungs are a factor here too.