The superset is a great way to workout if you have limited time. Each cycle should take you two minutes. If you can do ten cycles of this you will total 300 pushups and 400 crunches. Not bad for 20 minutes! No resting in between sets! You basically rest by doing crunches. The two supersets you see below are great to alternate every other day.
How much running or walking can you do in 20-30 minutes? Some people can run 3-6 miles or walk 2-3 miles in that time period. Try this one if you want to run.
4 Mile Track Work: - Jog 1 mile in 7:00-8:00 - Three sets of 1/4-mile sprints in 90-100 seconds - Jog or walk - 1/4 mile
Six sets of:
- Sprint-1/8 mile - Jog - 1/8 mile
Or you can mix the two types of exercise together and do what I call a Spartan Run.
- Run 1 mile - 100 pushups in as few sets as possible - 100 crunches - Run 1 mile - 75 pushups in as few sets as possible - 75 crunches - Run 1 mile - 50 pushups in as few sets as possible - 50 crunches
How much swimming can you do in 20-30 minutes? Some people can swim a mile in that time. Here is a great workout though if you want to mix a little PT with swimming.