When measuring total energy used there was a study done on horses
This found there was an optimum pace that used the least calories. It was a steady pace but not the slowest pace which might have been anticipated
Fast pace uses the most energy
Slowest pace uses considerably less
But there is an optimum pace inbetween the two where the least energy is used. This ties in with experience of running where running really slow can feel harder than at a still relaxed but faster pace.
^ This and I am sure it applied to all animals including humans.