The plank (also called a front hold, hover, or abdominal bridge) is an isometric core strength exercise that involves maintaining a position similar to a push-up for the maximum possible time.
The plank strengthens the abdominals, back, and shoulders. Muscles involved in the front plank include:
Primary muscles: erector spinae, rectus abdominis (abs), and transverse abdominis.
Secondary muscles: trapezius, rhomboids, rotator cuff, the anterior, medial, and posterior deltoid muscles, pectorals, serratus anterior, gluteus maximus, quadriceps, and gastrocnemius.
Muscles involved in the side plank include:
Primary: transversus abdominis muscle, gluteus medius and gluteus minimus muscles, the adductor muscles of the hip, and the external, and internal obliques.
Secondary: gluteus maximus, quadriceps, and hamstrings.