Push-ups are not ony the best thing to do to your upper body, it's also something you can do almost anywhere - especially when you can't make it to the gym.

Some things you can do also in your own home or apartment:

1. Buy a core ball and do various crunches and push-ups.  

2. Dance!  Sure, you'll look like a fool,  but if you live alone no one but your ego cares.  Great cardio! 

 Within 10 minutes I was soaking in sweat - just like I would in a gym.