The squat is a foundational movement in exercise, fitness, and daily life, yet it is often the subject of intense debate regarding proper technique. Among the most common points of confusion is the movement known as the “pelvic tuck,” often referred to in gyms as the “butt wink.” This phenomenon occurs at the deepest point of the squat and causes many people to question the safety and effectiveness of their form. Understanding this movement is the first step toward optimizing the squat for both performance and long-term joint health.
Understanding the Pelvic Tuck
The pelvic tuck is an involuntary movement where the pelvis rolls backward (posterior pelvic tilt) at the bottom of the squat descent. This rotation is coupled with a slight rounding, or flexion, of the lumbar spine. The tuck is a compensatory movement, not an intentional part of the squat pattern.
When a lifter descends into a deep squat, the hip joint eventually runs out of its available range of motion, often due to anatomical or mobility restrictions. To continue lowering and achieve greater depth, the body steals motion from the next available joint: the lumbar spine. This creates the visual effect of the tailbone tucking underneath the body as the lower back loses its neutral curve.
The Biomechanical Impact of Lumbar Flexion
While a small degree of spinal motion is normal, performing a squat with pronounced lumbar flexion under load is not recommended. Rounding the lower back shifts the burden of the weight from the strong muscles of the hips and legs to the passive structures of the spine.
The intervertebral discs and ligaments are most vulnerable to injury when simultaneously compressed and bent. Flexing the spine under a heavy barbell increases the shear and compressive forces placed on the intervertebral discs. Repeated cycles of bending the spine under load can lead to disc deformation and increase the risk of herniation over time.
Allowing the pelvis to tuck and the spine to round compromises the efficiency of the lift, as the spine’s stabilizing muscles become less effective. Passive structures, such as the posterior longitudinal ligament, provide resistance to this flexion moment. Relying on these passive structures rather than active muscle contraction is a less stable strategy for heavy lifting.
Common Physical Causes of the Tuck
The pelvic tuck is often a mobility issue rather than a conscious error in technique, indicating the body has reached its limit of motion. One common cause is limited ankle dorsiflexion, which is the ability of the shin to move forward over the foot. If the ankles cannot move enough, the hips and pelvis must compensate by rolling backward to maintain balance and allow for greater depth.
Tightness in the hip flexors or a lack of range of motion in the hip joint itself can prematurely limit the squat descent. Once the femur reaches the end of its rotation within the hip socket, the pelvis must tilt posteriorly for the movement to continue. Individual anatomical differences, such as the depth of the hip socket, also restrict hip motion and lead to a tuck sooner in the descent.
Another factor is poor lumbopelvic control, relating to the torso’s inability to maintain rigidity throughout the movement. A lack of core stability means the lifter cannot effectively maintain intra-abdominal pressure to support a neutral spine position. This motor control deficit allows the spine to collapse into flexion even if the person possesses adequate joint mobility.
Adjusting Your Form to Eliminate the Tuck
The most immediate correction for the pelvic tuck is controlling the depth of the squat. You should only descend as deep as you can maintain a neutral spine, halting the movement just before the pelvis begins to roll backward. Squatting to parallel—where the thighs are parallel to the floor—provides sufficient muscle activation without forcing excessive depth.
Adjusting your stance can provide a simple, effective solution by accommodating your individual hip structure. Widening the distance between the feet or pointing the toes slightly outward can create more space in the hip joint. Experimentation with foot position helps find a stance that allows for greater hip mobility before the tuck occurs.
Mastering proper core bracing is a strategy for maintaining spinal neutrality during the squat. This technique involves taking a deep, three-dimensional breath that expands the abdominal cavity, followed by a forceful contraction of the core muscles. This action increases intra-abdominal pressure, which acts like an internal support belt to stabilize the spine throughout the lift.