Side Plank

Lie on one side, forearm on the floor with the elbow under the shoulder, legs stacked. Lift the hips so the body forms a straight line from head to feet, weight on the bottom forearm and the side of the bottom foot. Brace the core and hold without letting the hips sag toward the floor. The top arm can rest on the side or reach to the ceiling.

The side plank trains anti-lateral-flexion stability (see anti-movement-concepts): gravity pulls the hips down toward side-bending, and the lateral trunk muscles — the obliques (external-oblique, internal-oblique) and quadratus lumborum — plus the lateral hip (gluteus-medius) must resist to keep the spine neutral (see spine-positioning). It is one of McGill's "big three" core exercises.

Coaching:

• Keep the supporting shoulder stable (down and back, not shrugged) and stacked over the elbow.
• The main fault is the hips sagging; stop the set when the line breaks.
• Train both sides equally; note asymmetries.

Progressions (see balance-training-progression): increase hold time → top-leg or top-arm raise → add hip dips → feet/elbow on an unstable surface → from a straight-arm (hand) position. Regression: bend the knees so weight is on the bottom knee and forearm (short-lever side plank), or perform against a bench.

• Side-lying forearm/feet hold; straight head-to-feet line; hips up.
• Trains anti-lateral-flexion stability (obliques, QL) + lateral hip (gluteus medius).
• One of McGill's "big three" core exercises.
• Fault: hips sagging; keep the supporting shoulder stable; train both sides.
• Progress: longer holds → limb raises/hip dips → instability; regress to bent-knee (short lever).

• core-stability-vs-strength — a core-stability staple.
• anti-movement-concepts — anti-lateral-flexion category.
• exercise-plank — anti-extension partner.
• external-oblique, internal-oblique, gluteus-medius — primary muscles.

See also: Side Plank — in the calisthenics plank progression is the same exercise placed in the front-plank/plank-progression track rather than the core-stability-training track covered here.