Starting Position: Stand with your feet together. Depress and retract your scapulae (pull your shoulders down and back) without arching your low back, and "brace" (engage your abdominal/core muscles) to stiffen your spine. Hold a light-to-moderate weight medicine ball in front of your chest with both hands firmly holding on to the ball.
Step forward slowly lift the right foot off the floor, stabilizing your body on the left (stance / supporting) leg. Maintain the abdominal bracing in order to avoid any sideways tilting or swaying in your upper body and press the left (stance / supporting) foot firmly into the ground to reduce any unwanted movement and maintain stability. Hold this position momentarily before stepping forward. The right (swing) leg should initiate contact with a heel strike first, slowly transferring your body weight into the right (forward) leg with the foot placed firmly on the floor, think about lowering yourself into your hips by allowing your weight to shift downwards towards the floor instead of forward. As you load your bodyweight into the right leg, avoid any sideways tilting or swaying in your upper body and try not to move the left (supporting) foot. While simultaneously lowering yourself into your right leg and hip, lift your hands holding the medicine ball straight overhead while continuing to maintain the abdominal bracing.
While in the bottom (downward) phase of the lunge, pull the medicine ball back down towards your chest, continue to maintain a stiff core and drive your right foot into the ground to extend the right knee and straighten the leg to return to the original (starting) position of standing with both feet under the hips and the ball held in front of the chest. Repeat for a specific number of repetitions or a certain period of time.
Exercise Variation: Begin with a light-weight medicine ball in order to learn how to maintain stability all of the way through the movement. To increase the level of difficulty and to improve core and shoulder strength, once you can perform 8-12 repetitions on each leg, increase the weight of the medicine ball. Another option is to hold one dumbbell in each hand, start with the elbows bent at ninety degrees and tucked in to the side, at the bottom of the lunge, bend the elbows to bring the weight up to the shoulders and press it directly overhead.
Forward Lunge, Forward Lunge with arm drivers, Dumbbell Step-ups