The plank jack is a dynamic, full-body exercise that merges the isometric stability of the traditional plank with the plyometric, cardiovascular motion of a jumping jack. This combination elevates the movement from a static core hold to a high-intensity activity demanding coordination and strength from multiple muscle groups simultaneously. Its purpose is to challenge the body’s ability to maintain a rigid, neutral spinal position while the lower extremities are in rapid, repetitive motion.
Mastering the Basic Movement
The plank jack begins in a high plank position, which is essentially the top of a push-up. Place the hands directly beneath the shoulders, fingers spread wide to distribute the weight evenly. The body should form a straight line from the head to the heels. The feet should start together, creating a narrow base of support that challenges the core stabilizers.
From this anchored base, the movement initiates with a rapid, controlled jump of both feet outward to the sides. The feet should land softly on the balls of the feet at a width slightly wider than the hips. Immediately jump the feet back inward to return to the starting position. This continuous in-and-out motion should establish a smooth, rhythmic cadence, minimizing vertical travel or “bounce” in the hips.
Muscles Activated
The plank jack is a comprehensive exercise that engages a wide array of muscles. The core is subjected to high demand, with the rectus abdominis and obliques working intensely to resist rotation and flexion caused by the jumping action. Deeper stabilizers, such as the transverse abdominis and the erector spinae, are also activated to maintain the integrity of the neutral spine throughout the exercise.
The upper body muscles, including the anterior deltoids, triceps, and pectorals, act isometrically to keep the torso elevated and the shoulders positioned over the wrists. The dynamic portion of the movement heavily recruits the lower body. Hip abductors pull the legs outward, and hip adductors control the return phase. The glutes and quadriceps contribute power to the repetitive hopping motion.
Maintaining Proper Form
The effectiveness of the plank jack hinges on maintaining a stable torso, which requires careful attention to alignment to prevent injury and maximize muscular engagement. A common error is allowing the hips to sag toward the floor, which places excessive strain on the lumbar spine and disengages the abdominal muscles. Conversely, raising the hips too high, known as “piking,” shifts the load away from the core and onto the shoulders, reducing the exercise’s intended effect.
The body should maintain a straight line from the crown of the head down to the heels, mimicking the rigid structure of a static plank. The shoulders must remain stacked directly over the wrists, and the elbows should be soft, not locked out, to protect the joints during the impact of the jumps. Keep the neck relaxed and in a neutral position, focusing the gaze a few inches in front of the hands. Bracing the abdominal wall is necessary to keep the lower back protected and the core fully engaged against the instability created by the moving feet.
Adjusting Difficulty
The plank jack can be modified to accommodate various fitness levels by introducing either regressions to simplify the movement or progressions to increase its challenge. For those new to the exercise or needing to focus on form, a simple regression is to replace the jump with a controlled step. This modification involves stepping one foot out to the side and then bringing it back, alternating legs, which reduces the impact and instability while still engaging the core stabilizers.
To increase the intensity, accelerate the speed of the jumping motion, which elevates the heart rate and introduces more instability for the core to manage. Another progression is performing the exercise from a forearm plank position, which shortens the lever and intensifies the isometric hold. Advanced practitioners may also incorporate a light resistance band around the ankles, forcing the abductors and adductors to work against external resistance during every repetition.