I think your still trying to think mammalian, or warm blooded. Snakes bodies use food differently than warm blooded animals. I don't know the specifics, but it takes a simple observation to show that the weight of the snakes, fat percentage, is far more important than the exercise it gets.

Snakes are sedentary, cruise around to hunt, have excellent senses to hunt with, all to maximize their meals and metabolism to get food quickly and put it to use for digestion and growth.