Plank

The plank is an isometric anti-extension core exercise performed in a prone-supported position on the forearms and toes. The goal is to resist lumbar extension and maintain a rigid, straight line from heels to crown. It is the foundational movement for anti-extension core training and a prerequisite for more demanding progressions.

Execution

1. Place the forearms flat on the floor, elbows directly below the shoulders, forearms parallel or hands clasped
2. Extend the legs back, supporting only on the toes; feet hip-width apart
3. Brace the entire midsection — contract the glutes, squeeze the quads, and create tension through the torso
4. Align the body from heels to ears in a single plane; do not let the hips sag or pike up
5. Breathe steadily; do not hold the breath, which dramatically increases spinal compressive load
6. Hold the position; terminate the set when lumbar neutral cannot be maintained

What the EMG Data Shows

McGill's laboratory work shows the forearm plank produces moderate bilateral activation across the core musculature: rectus abdominis (~50% MVC), external oblique (~49% MVC), and lumbar erector spinae (~35% MVC). These values are lower than many dynamic exercises but are produced simultaneously and held continuously — the cumulative spinal stability demand is the training stimulus, not peak activation.

The transverse abdominis and multifidus contribute to segmental stiffness but are not captured by surface EMG in these studies; their contribution is inferred from spinal stability models.

Common Faults and Corrections

Fault	Effect	Fix
Hips sagging	Lumbar hyperextension; compressive stress	Drive hips up until the body is flat; squeeze glutes harder
Hips piked up	Reduces core demand; becomes a shoulder exercise	Lower hips until heels, hips, and shoulders are level
Breath holding	Spikes intra-abdominal pressure; increases lumbar compression	Breathe slowly throughout the hold
Protracted scapulae	Shoulder impingement risk	Depress and slightly retract the shoulder blades; "pull shoulders away from ears"

Progressions

The plank is not made harder by simply holding longer — once 60 seconds can be maintained with perfect form, progression should increase the mechanical demand:

1. Feet-elevated plank — elevating the feet increases the lever arm and shifts more load anteriorly
2. Single-arm or single-leg plank — reduces the base of support, creating rotational demand
3. RKC (Hardstyle) Plank — maximal full-body co-contraction superimposed on the hold; dramatically increases core activation at shorter durations
4. Ab Wheel Rollout — transforms the anti-extension demand from static to dynamic

For system-specific training applications, see each system's lens entry.