It is usually referred to as 'spinning.'
The best form of aerobic exercise is the simplest one, walking. While walking, be mindful of your posture. Walk in supportive footwear, and in loose clothing. Keep the chin down, the shoulders back...
fencing >x luv ya babes.x
No, sit ups are anaerobic
Yes you can. The contraption to which you fasten your own bike is called a "bicycle trainer". They are available for purchase.
push up to go flat down with your hands on the ground going up and down