If you're like most people, you've been doing the usual set of workouts and exercises to get into shape. Push-ups, sit ups, crunches and lunges are great exercises when you're first starting out, but your body will adapt to the routine fairly quickly. The result? Fewer calories burned and little or no results with your workout routine.

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Fortunately, there are a number of exercises designed to target key muscle groups and really help you get in shape fast. The American Council of Exercise encourages people of all fitness levels to try a variety of exercises that help build strength, stamina and endurance by challenging key muscle groups and maximizing the range of motion. Here are a few effective exercises and routines to get you started:

Overhead Press

The overhead press targets your middle deltoids and triceps for firm shoulders and arms; you'll need to lift dumbbells or a barbell over your head and hold for a few seconds during each rep. This exercise is best performed with your feet standing shoulder width apart and knees slightly bent; slowly raise the weights over your head and bring them back down to ear level before repeating the sequence. You'll need to maintain good form throughout the sequence.