If you are out of shape, you can expect to gain muscle by doing BJJ. Schools will have students doing activities that range from simple warm-ups like a light jog and jumping jacks to intense conditioning and circuit training routines. Sparring will be a workout too. But the main focus of BJJ is on improving technique and using less strength, so if bulking up is a goal of yours, you should be doing extra conditioning outside of normal BJJ classes.
If you are out of shape, you can expect to gain muscle by doing BJJ. Schools will have students doing activities that range from simple warm-ups like a light jog and jumping jacks to intense conditioning and circuit training routines. Sparring will be a workout too. But the main focus of BJJ is on improving technique and using less strength, so if bulking up is a goal of yours, you should be doing extra conditioning outside of normal BJJ classes.