Have a (Swiss) ball!

As part of my current weight training and flexibility regimen, I’m incorporating several Swiss Ball exercises into the mix.  These are killers! You can take any number of regular exercises like pushups, sit-ups, or leg lifts, but introduce the Swiss ball into it, and it instantly makes the move a lot tougher. This is due to the fact that the ball introduces instability into the routine - your body has to use additional muscles to maintain balance while you’re performing the exercise - muscles that would normally not be challenged (or challenged to this degree) in the regular exercise. This instability really helps work your core, which in turn helps all the rest of your lifting.

A couple of my favorite (or not favorite, depending on how you look at it) are the Swiss Ball Pushup and the Hip Extension and Leg Curl. Also on the same page is the Swiss Ball Jackknife - if the Devil uses exercise as punishment in Hell, this one would be high on his list.