You should feel your heart rate getting up there now. Five more seconds. All right, that's it. 15-second break, we're going to move on to bird dog on the stability ball. You may have seen this one ...

adding 5 additional push-ups whenever you feel comfortable. Modification: To make this easier in terms of stability support, use just one hand on the ball (instead of both) and plant your other ...

which looks like an exercise ball cut in half, is a good way to incorporate more stability into your exercises. You can stand on it during squats, put your hands or feet on it during push-ups, or ...

I have a pretty strong lower body, so I breeze through a few sets of these easily as well as the 12 leg curls on the stability ball ... medicine-ball push-ups, and lateral dumbbell raises.