ATG squats, short for “ass-to-grass” squats, are squats performed to the absolute lowest depth your body can reach, with your hamstrings resting against your calves at the bottom. Unlike a standard parallel squat, where your thighs drop to roughly hip-crease level, an ATG squat takes your knee flexion well past 120 degrees. The name is blunt but descriptive: you’re lowering your hips as close to the ground as possible.
How ATG Squats Differ From Standard Squats
The depth distinction matters more than it sounds. A parallel squat brings your knee joint to roughly 110 degrees of flexion, which looks like your thighs are level with the floor. A 90-degree squat actually stops slightly above parallel. An ATG squat pushes past both of these markers, taking the knee to 130 degrees or more and requiring the hips, ankles, and spine to accommodate a much larger range of motion.
That extra range changes everything about the movement. Your torso angle, weight distribution, and the demands on your joints all shift significantly once you pass parallel. The muscles working hardest change too, which is one of the main reasons people train this way.
Glute Activation Increases With Depth
The clearest benefit of going deeper is greater glute involvement. A study measuring electrical activity in the hip and thigh muscles found that the gluteus maximus contributed about 16.9% of the total muscle effort during a partial squat, 28% during a parallel squat, and 35.4% during a full-depth squat. That’s roughly double the glute contribution compared to a partial squat.
Interestingly, the same study found no significant differences in the contribution of the hamstrings or the two quadriceps muscles measured (inner and outer) across squat depths. So the extra depth doesn’t necessarily make your quads work harder. It primarily shifts more of the load onto the glutes during the upward phase of the lift. If building glute strength is your goal, depth is one of the most effective tools available.
What It Takes to Get There: Mobility Demands
Most people can’t drop into a full ATG squat on their first try, and the limiting factor is usually ankle mobility. Research reports that the average ankle dorsiflexion needed during a deep squat is around 38.5 degrees. For context, average dorsiflexion measured with a bent knee is only about 16 degrees in men and 21 degrees in women. That gap explains why so many people feel stuck before they reach full depth, and why their heels lift off the floor.
Ankle dorsiflexion range of motion is actually one of the strongest predictors of how deep someone can squat. In men, ankle and hip flexibility together accounted for about 43.5% of the variance in squat depth. In women, ankle mobility and dorsiflexor strength explained about 32.4%. Hip flexion range matters too, but the ankle is where most people hit their wall first.
This is why you’ll often see people use elevated heels (squat shoes or small plates under the heels) when training ATG squats. The raised heel compensates for limited ankle range and allows the knees to travel further forward without the torso collapsing.
The “Butt Wink” Problem
As you descend past about 120 degrees of knee flexion, your body needs to find extra range of motion somewhere. That somewhere is usually the pelvis. The pelvis tilts backward (posteriorly) to create more room for the thigh bone to keep flexing. This posterior pelvic tilt pulls the lower spine into a rounded position, and that rounding at the bottom of a squat is what lifters call “butt wink.”
Two things cause it. The first is a mobility limitation in the hips. If your hip sockets don’t allow enough flexion, the pelvis compensates by tucking under. The second is poor control of the lower back and pelvis, where the spine flexes earlier than it needs to, before you’ve even used up your available hip range. Some people also have structural differences (longer femurs, variations in hip socket angle) that make deep squatting without pelvic tilt genuinely harder.
A small amount of pelvic tilt at full depth is normal and probably unavoidable. It becomes a concern when it’s exaggerated, happens early in the descent, or occurs under heavy load, because a rounded lumbar spine under compression is more vulnerable to disc injury. Goblet squats with a kettlebell are a useful way to practice pelvic control at depth. Holding the bottom position for a few seconds builds awareness of where your pelvis is and helps you learn to brace against the tilt.
What Happens to Your Knees at Full Depth
Knee stress during squats follows a predictable pattern. Compressive forces on the kneecap increase as the knee bends further, and peak patellofemoral joint stress occurs at around 90 degrees of flexion. Adding external load (a barbell) further increases that stress at every angle from 45 degrees onward.
Beyond 90 degrees, something interesting happens. The contact area between the kneecap and the thigh bone increases, which helps distribute force over a larger surface. This is sometimes called the “wrapping effect.” So while the total force on the knee continues to rise, the pressure per unit of area doesn’t spike as dramatically as you might expect.
The posterior cruciate ligament (PCL) bears the most significant load during deep flexion. Research on deep flexion activities found that they generate net posterior forces on the knee of 58 to 68% of body weight, with peak forces occurring between 90 and 150 degrees. The PCL’s role in stabilizing the knee at these extreme angles is substantial, though not fully understood. For people with a PCL injury or reconstruction, deep squatting carries real risk and should be approached cautiously. For healthy knees, the available evidence doesn’t show that deep squatting causes damage, but the forces involved are meaningfully higher than those in a parallel squat.
Performance Benefits of Deep Squats
Training through a full range of motion has carryover to explosive movements. Research on young soccer players found significant correlations between full squat power and sprint times across multiple distances, with correlation values ranging from moderate to strong. Power generated during a full squat with about 82 to 86% of body weight on the bar showed the clearest relationships with short sprint performance.
The logic is straightforward: if you’re strong through a larger range of motion, you can produce force from more joint positions. This matters in sports that demand acceleration from deep positions, like a sprinter in the blocks, a basketball player landing and jumping, or a soccer player changing direction. Training only to parallel builds strength only to parallel. Going deeper extends your effective range.
Who Should and Shouldn’t Go ATG
ATG squats are a tool, not a requirement. They work well for people who have the ankle and hip mobility to reach full depth without excessive spinal rounding, and who want to maximize glute development or build strength through a complete range of motion. Athletes in sports requiring deep positions (Olympic weightlifting, martial arts, some field sports) benefit from training at these depths specifically.
They’re a poor fit for people loading heavy weight through a range of motion they can’t control. If your lower back rounds significantly, your heels come off the floor, or you feel pinching in the front of your hips, you haven’t yet earned the depth. Working on ankle dorsiflexion, hip mobility, and pelvic control with lighter loads (or bodyweight) is the more productive path. Squatting to a depth you own with good mechanics will always be more effective than forcing range you don’t have.