As a child living the life of a street punk, Chen Mu suffered malnutrition for a little while. Later, after his life took a turn for the better, his health started to become stronger; although judging from his appearance, you wouldn't say he was well-built. But his health was essentially excellent, and he seldom got sick.
However, when Chen Mu attempted one of the exercises, he found it to be quite strenuous. It made high demands on his lower body strength, which wasn't his strong suit. Both of Chen Mu's legs were aching and as weak as mud after going through it a few times. While he didn't know if he was really doing the exercises, the soreness that developed in his legs was perfectly real.
