The best exercises are the ones that work multiple muscle groups at once. Who has hours to spend at the gym, focusing on one muscle at a time? Instead, do the following exercises to get a better workout in less time:

1. Bent Over Rows

Want to do an exercise that will work your glutes, lower back and your biceps, all while targeting your back muscles? Bent over rows are excellent for developing your "pull-ups" muscles, and you can use dumbbells for a better workout. Keep your shoulders back, your stomach clenched, and your hips loose as you bend over, and you'll see great results no time.

2. Incline Bench Press

This workout focuses on the upper chest muscles, but it also targets your shoulders and triceps. You'll find that doing more of these bench presses will help sculpt your upper torso, as well as get rid of a lot of the fat on the back of your arms.

3. Planks

Instead of wasting your time doing crunches, add planks to your routine. Holding yourself in place may seem easy, but it gets hard after 20 to 30 seconds. Hold it for a minute and you'll feel the shake in your abs and back. You can mix things up with the side plank for a full core workout.

4. Side Step Ups

Instead of sticking with the classic Step-Up, work out your inner thighs and oblique muscles as well as your thighs, calves and glutes. This is an exercise that will improve your balance drastically, and it will even give you a nice cardio workout.

5. Burpees

We all love to hate burpees, but it's one of the best full-body exercises you can do. The only muscles that don't get worked are your biceps, but every other muscle in your body will be straining by the time you're done with your set of 30 to 50. Plus, it brings in the cardio element to your workout and your heart will be thudding like a jackhammer for a great stamina boost.

6. Lunge Curl Presses

Mixing upper-body workouts with lower-body workouts not only promotes better muscle building, but also increases your stamina. To do this exercise, curl dumbbells as you step forward into a lunge. Stay in the lunge as you press the weights over your head, and step forward as you lower the dumbbells. It's a great compound exercise that works on your legs, shoulders and biceps.

7. Mountain Climbers

This is another tough exercise that combines cardio and full body training. Holding your upper body in place with your core, arms and shoulders will have those muscles quaking in no time, but your legs will be constantly in motion. You'll be breathing hard, and by the time you've finished 50, you'll be exhausted.

8. Reverse Wood Chops

With this exercise, you work your legs, core, biceps and shoulders all in one. You can use any kind of weight (dumbbell, medicine ball, kettlebell, etc.) for this exercise, and you'll find that the squatting, twisting and lifting motions will give you an excellent full-body workout.