Half Jack Exercises

Jumping jacks have long been used by exercises ranging from school age to the military. An excellent cardiovascular exercise, jumping jacks raise your heart rate and work muscles in your legs, arms and core. Standard jumping jacks aren't suitable for everyone, but you can modify them to work as a half jack.

The half jack movement is similar to that of a standard jumping jack. Start by standing with your arms by your sides and your feet together with your back straight. Jump up and spread your legs and arms, landing with your feet slightly wider than shoulder width and your arms straight out at shoulder height. Jump again to bring your feet together and your arms down. The arm position is the main difference between standard and half jacks; in standard jacks, you lift your arms over your head until they touch. Start with one set of 10 repetitions and increase to one set of 20.

Jumping jacks are often used to warm up your muscles and get your body ready for more intense aerobic or strength exercises. A half jack is useful when a person has a shoulder injury that prevents a full range of motion, such as a rotator cuff problem. It reduces the strain on the shoulders while still engaging them and your biceps as part of the lift. Half jacks make jumping jacks possible in rooms with low ceilings as well, such as a workout room or family room with a low ceiling fan.

To engage your biceps and triceps more in the movement, lift your arms with your palms up as you jump and bring your hands in toward your shoulders, keeping your upper arm parallel to the floor. Straighten and lower your arms as you jump to bring your feet together. For a more explosive movement, squat before each jump to propel yourself higher with each leap. Lift your arms out to shoulder level with a powerful movement to help balance yourself as you jump.

Water provides resistance to your body as you perform half jacks in a pool. Stand in chest-deep water and perform standard half jacks, allowing the water to create resistance for your jump and for your arms. You can modify this move by crossing your arms in front of your chest and opening them out to your sides to help them stay underwater and encounter additional resistance. Perform 10 repetitions.