1. Specific resistance to locomotion will remain constant if changes in the amount of force produced or in the cost of force production are directly proportional to changes in gravitational acceleration. 2. If changes in gravitational acceleration result in a disproportionate decrease of the effective mechanical advantage of limbs or reduction in contact time for developing force, then specific resistance may increase. 3. If changes in gravitational acceleration disproportionately increase effective mechanical advantage or the contact time for developing force, then specific resistance may decrease. 4. Finally, changes in the direction and magnitude of gravitational acceleration will affect the energetics and mechanics of animal motility even for small runners that appear to defy gravity.