Which are the toughest muscles to grow and why? Longevity expert explains

Jonathan Schoeff, MD, a board-certified surgeon and longevity expert, breaks down a fitness truth in a recent Instagram post: not every muscle responds the same to training. Some build mass easily, while others resist no matter the effort. He uses a simple color code: red for the hardest, yellow for tricky, and green for responsive. This allows him to really drive home how genetics, fiber types, and daily habits all shape growth challenges. Number one in the red department: calves. Serratus ante