We all have commitments, such as managing your household, succeeding in your profession, spending time with family and friends, and engaging in extracurricular activities.  Most of us do not have the time to spend hours on end in the gym.  Research has shown that short duration, high intensity workouts are one of the most efficient ways to lose body fat, gain lean muscle mass, and optimize health.  For example, Arthur Weltman, Ph.D., found greater reduction in abdominal adiposity with the inclusion of high intensity exercise (~75-80% of V02max) three days a week when compared to exercising five days a week at lower intensity (~50-60% of V02max).  Martin Gibala, Ph.D compared the effects of high intensity training with continuous endurance training and found remarkably similar changes in muscle oxidative capacity and exercise capacity.
The solution
Schedule four to thirty minutes in your busy day for a short duration, high intensity workout (remember, intensity is relative and should match your current level of fitness).  Then, try one of these full body workouts to get more “bang for your buck.”  Meaning, the workouts will incorporate all major muscle groups, and use all three energy systems: the phosphagen system (anaerobic), glycolysis (anaerobic), and the oxidative system (aerobic) which will eventually increase your metabolism (burn more fat and calories), strength, endurance, stamina, and quality of life.
Note: Please check with your physician before performing these workouts and always properly warm-up and cool-down before and after each workout.  Also, technique and safety is very important for performing all these movements.  If you are not comfortable with these movements, I would highly suggest seeking advice from a professional.
Workout #1: Manmakers
Select a pair of dumbbells that you know you could perform multiple movements with, without putting the weight down.  Perform one repetition of each movement five times for one round. Rest 30-60 seconds and repeat for a total of four rounds.
•    DB Push-Up x 1
•    DB Renegade Row x 1 (each arm)
•    DB Clean x 1
•    DB Push Press x 1
•    DB Overhead Lunge x 1 (each leg)
•    Reposition and start over.
Click here to see Manmakers video
Workout #2: Tabata
This high intensity intermittent training method (dubbed Tabata) belongs to Dr. Izumi Tabata and other researchers from the National Institute of Fitness and Sport in Japan.  Tabata uses a four minute interval training cycle of 20 seconds of maximum work, followed by ten seconds of rest, and repeated eight times.  You can do this workout using bodyweight exercises, such as squats, push ups, and pull ups, as well as cycling, running, rowing, and jump roping, or even the elliptical.  For the workout below, all you need is a stop watch, a pull-up bar, and a floor mat.
(20 seconds of work, 10 seconds of rest x 8 = 4 minutes for each exercise.  Rest 60 seconds and move on to the next exercise for a longer workout).
•    Row
•    Rest 60 seconds
•    Bodyweight Squats
•    Rest 60 seconds
•    Pull-Ups
•    Rest 60 seconds
•    Push-Ups
•    Rest 60 seconds
•    Sit-Ups
Time should not be an issue when you can incorporate one of these fast and efficient workouts into your daily routine.  Set aside a small amount of your day to improve your health and get the results you have always wanted.
References:
American College of Sports Medicine, 2008.  High Intensity Exercise Best For Improving Body Composition.  Retrieved by: http://www.acsm.org/AM/PrinterTemplate.cfm?Section=Home_Page&TEMPLATE=/CM/ContentDisplay.cfm&CONTENTID=11521
Gibala, Martin J., (2007). High Intensity Interval Training: A Time-efficient Strategy for Health Promotion?  Current Sports Medicine Reports, p 211-213.  Retrieved by: Gibala_CurrSportsMedRep-6_2007.pdf/C58EA28C-18C0-4a97-9AF2-036E93DDAFB3/Gibala_CurrSportsMedRep-6_2007