The humble squat might just be the most effective exercise you can do: It engages the entire lower half of the body, including the hips, glutes, quads, hamstrings, and calves, while also hitting the core, shoulders, and back. A perfect squat is a symphony of muscular coordination throughout the entire body, achieving the rare feat of simultaneously building muscle and burning fat thanks to its high metabolic demand (read: it burns a lotta calories because it works a lotta muscles). But how low should you go?

Let’s end the suspense: The perfect squat is a deep squat, with the hip crease going all the way past the knees (or “ass to grass,” as some eloquently put it). Deep squats recruit more muscles, burn more calories, and are particularly good for building a nice, strong butt. (And who doesn’t want that?) But there’s a lot more to this exercise than one might think. It’s not just important to stretch—without a strong core, loose shoulders, an engaged back, and high mobility, the risk of injury multiplies.

But Aren’t Deep Squats Bad For You?

No! Contrary to popular belief, squatting deep is not bad for the knees—studies have found there is no difference between partial, parallel, and deep squats in terms of the impact on the front knee joint Patellofemoral joint kinetics during squatting in collegiate women athletes. Salem GJ, Powers CM. Department of Biokinesiology and Physical Therapy, University of Southern California, Los Angeles, CA, USA. Clinical Biomechanics (Bristol, Avon), 2001 Jun;16(5):424-30.

In fact, deep squats might actually increase knee stability The effect of exercise on anterior-posterior knee laxity. Steiner ME, Grana WA. American Journal of Sports Medicine, 1986 Jan-Feb;14(1):24-9. Most of the connective tissue in the knee is made up of two ligaments: The anterior and posterior cruciate ligament, also known as the ACL and the PCL. Studies show the forces inside the ACL and PCL decrease the more the knee is bent, meaning the deeper you squat, the less pressure there is inside the knees The forces in the anterior cruciate ligament and knee kinematics during a simulated pivot shift test. Kanamori A, Woo SL, et al. Musculoskeletal Research Center, Department of Orthopaedic Surgery, University of Pittsburgh Medical Center, Pittsburgh, PA, USA. Arthroscopy, 2000 Sep;16(6):633-9. The importance of quadriceps and hamstring muscle loading `on knee kinematics and in-situ forces in the ACL. Li G, Rudy TW, et al. Musculoskeletal Research Center, Department of Orthopaedic Surgery, University of Pittsburgh, PA, USA. Journal of Biomechanics, 1999 Apr;32(4):395-400. In situ forces in the anterior cruciate ligament and its bundles in response to anterior tibial loads. Sakane M, Fox RJ, et al. Department of Orthopaedic Surgery, University of Pittsburgh, PA, USA. Journal of Orthopedic Research, 1997 Mar;15(2):285-93. . It’s also a better way to get stronger. In fact, research has shown that parallel squats with heavy weights are less effective at increasing strength than deep squats with a lighter weight Knee Joint Kinetics in Relation to Commonly Prescribed Squat Loads and Depths. Cotter JA, Chaudhari AM, et al. Department of Orthopedics, University of California, Irvine, CA, USA. Journal of Strength and Conditioning Research, 2013 Jul;27(7):1765-74. .

Not only is squatting deep safe and effective, but it’s a one-way ticket to a nice, strong booty: Studies show the gluteus maximus is over 25 percent more engaged during deep squats than when squatting parallel The effect of back squat depth on the EMG activity of 4 superficial hip and thigh muscles. Caterisano A, Moss RF, et al. The Department of Health and Exercise Science, Furman University, Greenville, SC, USA. Journal of Strength and Conditioning Research, 2002 Aug;16(3):428-32. .

So long as there’s no history of injuries, “ass to grass” is the way to go. However, if you do have knee issues (and sitting at a desk all day is no good for the knees), there’s nothing inherently wrong with sticking to parallel squats.

So How Do I Squat Deep?

With care. A deep squat is a more complicated and, if performed incorrectly, riskier than the standard variation. The exercise needs to be treated with respect—this ain’t no bicep curl. There is an enormous number of joints and muscles that work together in a very broad range of motion to perform this movement, so extra special attention needs to be paid to mobility, flexibility, stability, and coordination. Yes, sometimes that stuff isn’t very fun, but (and we can’t stress this enough) injuries are a lot less fun.

If you never squat deep, it’s likely you don’t have enough control, flexibility, or strength to do so with heavy weights—yet. Take a step back (literally), remove the weight, and study the basics first.

1. Concentrate on mobility.

Mobility” is a word that gets thrown around a lot, but what does it mean in the context of lifting weights? Physical therapist and Greatist expert Dr. Mike Reinold defines it as the body’s ability to perform a task without compensation. Ever tried a bicep curl with a weight that’s a little too heavy and found your hips and back bending and swinging? That’s the body compensating for a lack of strength, bless its heart. But when form goes down the drain in an attempt to lift a lot of weight, the body is at greater risk for injury. That’s especially true when it comes to squats.

There’s a huge range of issues that might contribute to poor mobility, but Reinold emphasizes the importance of flexible ankles, hip flexors, and knees. If any part of the squatting motion feels tight, but doesn’t cause any pain, there’s nothing wrong with trying to improve mobility on your own:

“Try lying on your back, bending your legs, and going through a squatting motion. If there’s tightness in a muscle group that keeps the movement from being executed perfectly, that can often be fixed with the right stretches, massage, or a self-myofascial release technique like foam rolling or using a trigger point ball.”

Reinold emphasizes the importance of regularly employing these techniques: A few minutes per day is better than an hour once a week.

2. Engage your muscles.

After a full body warm-up that includes dynamic stretches, it’s important to remember to engage your muscles as the squat is performed. The heavier the weight, the more important it is that the abs, shoulders, and upper back stay engaged, creating a stable base for the weight. Flex the thighs, squeeze the butt, tense the stomach, and, in the case of back squats, activate the upper back by pulling down on the bar. This helps stabilize the body and keep the body from compensating by making sure that all the right muscles are doing their part.

3. Go back to basics.

There are, sadly, a lot of ways to squat badly. Even if your parallel squats can lift a lot of weight, Reinold recommends beginning your deep squatting routine using only your bodyweight, then gradually increasing the load. Starting from the beginning again, while pretty frustrating for advanced lifters, is the best way to fill any lingering gaps in your strength, stability, and form. He also recommends checking in with a physical therapist when embarking on a new weight training regimen.

“You don’t need to have an injury to see a PT,” he says. “If you’re interested in really increasing your strength in a safe way, and especially if you’re having difficulty making progress, find a physical therapist with a good background in movement quality. They’ll look at your body through a different lens and properly assess the best way to move forward.”

The Takeaway

Some people will naturally have better mobility and stability than others. That’s why there’s no one size fits all approach to strength training, and why for some of us, deep squats aren’t on the table. Nonetheless, they’re worth aiming for: Deep squats are an incredibly valuable tool to build strength and lose body fat, and the steps we’ve outlined are holistic—better mobility, posture, strength and flexibility will benefit every aspect of your fitness.

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