Calisthenics or the gym

Yup you can build muscle with both.

Hate to sound cliche but both are effective, just depends on your goals.

High rep set circuits of push ups, pull ups, dips, and air squats / burpees can help you get strong and help with your gas tank. You may not get as big as you would weight lifting but youll shed fat and get cut.

Weight lifting gets you big and strong quicker cause its easier to load the muscles with heavier weight each session, especially leg strength. Youll probably end up with a bigger frame then you would with only calisthenics but may be stiff and not as mobile / agile depending on your stretching routine.

Both have pros and cons and is good to incorporate both if you can.

/r/Fitness Thread