Your Workout Time Can Create Better Results
The metabolic demand is much higher than simply running a treadmill or lifting weights on your own. With an instructor pushing you and holding you accountable will help you push past the last rep or the final second.
It isn't just lifting weights to get big, it's giving the body a stimulus it isn't used to and forcing it adapt to the stimulus improving overall fitness and cardiovascular function. Similar to lifting heavy objects hitting objects have a positive hormonal response, specifically with serotonin and cortisol creating a balanced cocktail for stress relief.
Striking the punching bag positively affects your bone mineral density and overall fortitude.