It is much easier for a small animal to run uphill than

It is much easier for a small animal to run uphill than for a large animal, because

1. it is easier to carry a small body weight.
2. smaller animals have a higher metabolic rate.
3. small animals have a lower O₂ requirement.
4. the efficiency of muscles in large animals is less than in the small animals.

Basal metabolic rate is inversely proportional to body size. So smaller animals have a higher metabolic rate. Hence production of energy is more.