Answer: Slow-twitch muscle fibers
Explanation:
Slow-twitch muscle fibers are fatigue resistant which are focused on sustained, minor movements and posture control. They contain more mitochondria and myoglobin, and are aerobic in nature. They are mostly found in the lower leg, the muscles at the back which maintains posture. Professor Atlas dull ache on his lower back is being noticed by the slow twitch muscle fiber.
