If you have time for just one exercise and want a full body workout, try 8-Count Bodybuilders, which work the pectorals, triceps, shoulders, core, lats and hip flexors, said military physical training specialist Mark Lauren, who advocates using nothing but your own bodyweight.
Here's how to do one:
Kick your feet back so that you're in the push-up position (count 2).
Do a push-up (counts 3 and 4).
Kick your feet apart and back together (counts 5 and 6).
Kick your feet up to your hands (count 7).
Stand up (count 8).
To make this even harder, try kicking your feet apart while at the bottom of the push up. "The tighter and more perfect your form is, the harder and more productive this exercise becomes," Lauren wrote in his book, “You Are Your Own Gym.”
When Lauren is crunched for time, he'll often do 50 or 100 of these in a row. (Good luck with that. You might want to start with 25.)
Several weeks ago, his "Weekly Fitness Challenge” consisted of 50 8-Count Bodybuilders for time. He finished in just over four minutes. Keep in mind Lauren isn't a regular Joe. He broke and still holds the military’s Pararescue/ Combat Control Indoctrination Course's long standing "underwater record.” Taking one breath, Lauren swam 133 meters below the surface for 2 minutes and 23 seconds, until losing consciousness. (Don't try this at home.)
For slightly longer workouts from Lauren, try some of his 20-minute workouts.