Planks primarily work the core muscles, which include:

• Rectus abdominis : The "six-pack" muscles on the front of your abdomen.
• Transversus abdominis : The deep "corset" muscle that stabilizes your waist and back.
• Internal and external obliques : Side abdominal muscles that help stabilize the spine and torso and assist with twisting motions

In addition to the core, planks engage several other muscle groups throughout the body to maintain proper form and stability:

• Upper body muscles : Shoulders (deltoids), chest (pectorals), upper back (rhomboids, trapezius, latissimus dorsi), arms (biceps, triceps), and serratus anterior.
• Lower body muscles : Glutes, quadriceps, hamstrings, calves, and foot muscles help stabilize the hips and legs during the plank

Thus, planks are considered a full-body exercise with a strong emphasis on core strength, helping support the spine and maintain posture while also activating muscles in the shoulders, arms, back, and legs