One of my favorite quick work outs is my ab workout that I will do when I have a long day and don't feel like being in the gym for a while. I'll run in for about a half hour and be done and feel satisfied! (you can do this at home too) -Before you start hit the treadmill or bike anything that really gets your heart pumping. I try to get my heart rate to 160 or above before I start my workout. Next hit the matt. I usually use a 10 pound weight you can use no weight or anything that fits your strength level. -Russian twists: 3 sets of 1 minute. -Hip lifts: 3 sets of 1 minute. -Planks: 3 sets of 30 second hold. -V-UPs : 3 sets of 20 reps. -Mountain climbers: 2 sets of 1 minute. -Ab bikes: 3 sets of 1 minute. I finish with cardio as well, remember to take breaks between exercises