You'd be surprised. A lot of people who suffer from mental health conditions to his level are surprisingly strong and well to do in terms of physique. It's something to do with the metabolism more than physical exercise, which, let's face it, is more often than not running away from protectors and caretakers.
Like fast metabolism don't make your muscle grow? People with fast metabolism are slim and their muscles aren't so well defined.
And they are strong because of high levels of adrenaline.
seungho literally dont do shit besides smoke and have sex yet he's built like michaelangelo's david lmfao
You're right. Fast metabolism keeps you slim. But don't forget the earlier chapters: Seongho is a trained man of nobility, including martial arts and horsemanship. It might not be shown throughout but let's assume the man is vain enough to know what happens when you live a life of smoking, sake (I think), and only sex. Let's assume. Lord knows all our hopes are going down the mental drain.
P.s: Honestly, I'm also doubting the man knows anything but abusing Nakyum.
So how is Seungho built like that when let's be real he doesn't do much exercise? No amount of sex will help you grow these muscles.