If you only have 20 minutes to spare in a busy day, it is not excuse to skip the daily work out. A lot can be done to boost health, burn calories, and improve your overall mood with just a 20 minute workout.
The key to a successful 20 minute workout is making the most of every single second. A high impact, successful workout can be had in a small amount of time with 4, 4 minute fast and furious intervals followed each time by a one minute cool down where you still make use of the time. Start off with four minutes of high impact cardio to get your heart rate going and burn calories. Choose something you can do efficiently but is still challenging to the body. A beginner may do jumping jacks, and a pro may do burpees. Choose something that can really make you feel that burn in just four minutes. Follow it with one minute of a brisk walk in place or jog. The next two sets four minutes should be followed up by spot specific workouts. For example 4 minutes of push-ups followed by a one minute jog cool down and 4 minutes of as many sit ups as you can do followed by a 1 minute jog cool down. The last set should return to hard and fast cardio to get your heart rate back up with a quick cool down.
With just a 20 minute workout you can still fit in toning and cardio to a busy day. The key is to push yourself as hard as you can during each four minute interval. You are literally trying to squeeze a normal paced 45 minute workout into less than half the time, but it can be done if you figuratively cover as much ground (do as many sit ups/lifts/burpees) as you would have with more time.