The squat is a foundational movement pattern used in exercise and daily life, yet the question of how low to descend remains a persistent source of conflicting advice. Many people wonder if reaching maximum depth, often called “ass to grass” (ATG), is necessary for optimal results or if it increases the risk of joint injury. Understanding the biomechanics of this movement is key to determining a safe and effective range of motion. This involves balancing muscle recruitment with respecting individual anatomical limits.
Defining Depth and Joint Stress
Squat depth is commonly categorized by the angle of the bend in the knee joint. A shallow or partial squat involves less than 90 degrees of knee flexion, while a parallel squat reaches about 90 degrees, where the thigh is parallel to the floor. A full or deep squat extends beyond 90 degrees, with the hips dropping below the level of the knees. A long-standing myth suggests that squatting below parallel is inherently dangerous for joint structures.
Scientific analysis of joint mechanics indicates that shear forces on the internal ligaments peak near the 90-degree position and decrease as the squat deepens further. Shear forces, which create a sliding motion between the bones, are often considered problematic for ligaments. As depth increases past parallel, the forces shift from shear to more direct compression on the articulating surfaces.
Healthy cartilage within the joints is designed to manage these compressive forces, which increase linearly with greater depth. For individuals with healthy joints, deeper squatting does not increase the risk of injury and may improve joint stability by strengthening the surrounding connective tissues. The hip joint’s required flexion moment also increases with depth, meaning proper positioning of the hips must be maintained to avoid exceeding the available range of motion.
Muscle Activation Differences Based on Depth
The degree of squat depth directly influences which muscles are challenged and recruited. The activation of the quadriceps muscles remains high across all depths, as they are the primary movers in knee extension. Full quadriceps activation is maximized when the knee is fully flexed, meaning greater depth results in a more complete quadriceps workout. This increased range of motion is beneficial for maximizing the growth of the thigh muscles.
A benefit of squatting below parallel is the substantial increase in the recruitment of the gluteal muscles. The gluteus maximus must work harder to drive hip extension from the lowest position of a deep squat. Studies show that full-depth squats promote greater increases in gluteal muscle volume compared to shallower squats. Activation of the hamstring muscles, which aid in stability and hip extension, tends to remain consistent regardless of depth. For those aiming to maximize strength or hypertrophy in the gluteal muscles, prioritizing depth is an effective strategy.
Anatomical and Mobility Factors Determining Your Limit
While deep squatting is generally safe and effective, the true limit of a person’s depth is individualized and determined by physical structure and flexibility. Anatomical variations, such as the depth of the hip socket or the length of the thigh bone, can limit how far the hip can flex before bone-on-bone contact occurs. This structural limitation can manifest as a sharp, pinching sensation in the hip joint, which serves as a natural endpoint for the movement.
Mobility restrictions in the ankle and hip are common limiting factors. Sufficient ankle dorsiflexion is necessary to allow the shin to travel forward over the foot while keeping the heel grounded. If ankle mobility is restricted, the body compensates by excessively leaning the torso forward, which can compromise the lifting position. Limited hip flexibility can cause the pelvis to tuck under at the bottom of the movement, known as a “butt wink,” which signals the end of the comfortable range of motion. The safest and most productive depth is the deepest position that can be maintained without pain or compromising the spine’s natural curve.