Squats – are they safe for your knees?

You’ve heard it before, squatting past 90° is bad for your knees. So what’s with all of those trainers promoting deep ‘ass to grass’ squats? While evidence suggests that deep squats promote greater strength development due to greater glute activation, controversy exists over the safety of deep squatting, especially for those with pre-existing knee conditions. So what is right for you? Read on to find out more!

Knee anatomy

In order to explain exactly what happens when you squat, lets first brush up on our knee anatomy. Your knee is a complex structure consisting of bones, joints, ligaments and soft tissue and is controlled by several key muscles. All play a key role in the optimal function of your knee.

Bones: Femur (thigh bone), Tibia (shin bone), Patella (knee cap)

Joints: Patello-Femoral Joint between your Patella and Femur (PFJ) and Tibio-Femoral Joint between your Tibia and Femur (TFJ)

Ligaments: Collateral ligaments (medial and lateral) which control sideways movement and cruciate ligaments (anterior and posterior) which control the forward/back movement between your tibia and femur

Other soft tissue: Cartilage which covers the bone inside the joint (ie. over the ends of the tibia and femur as well as the back of the patella), and Meniscus which is extra padding found in your knee joint to absorb force and protect your cartilage from damage

Key muscles: Quadriceps (thigh muscle) which straighten the knee and Hamstrings (behind the thigh) which bend the knee. Please note that there are several other muscles that are involved in knee control and movement however they are too complex to go into for the purposes of this article!


Squatting and the force

Now that we understand our knee anatomy a little better, let’s look at the forces occurring in the knee when we squat.

There are two types of forces at play when you squat:

  1. Shear force – Involves the forward/backward movement between your tibia and femur and is controlled by your anterior and posterior cruciate ligaments (ACL and PCL). Shear force reduces as you squat past 90° and is minimised when your feet are in a neutral position or slightly turned out.
  2. Compressive force – is due to the weight load placed on your knees (both body weight and external weights such as dumbbells, kettlebells and barbells) and is absorbed by your cartilage and meniscus. In your PFJ, compressive force is greatest at 70°-100° of knee flexion and decreases thereafter At your TFJ, force increase as you pass 90° flexion


So what does this all mean?

Deep squats enable greater activation of lower-body musculature (particularly your glutes) when compared to shallow squats. If you have healthy knees, given that most of the forces described above decrease after 90°, ‘ass to grass’ (deep) squats should be ok, as long as you use correct form (described below).


What if I have ‘bad’ knees

So that’s great for those with healthy knees, but what if you have bad knees?

If you have TFJ arthritis or meniscus damage, the compressive force will be your issue.  You’ll probably find that squatting to 90° is fine but don’t go deeper. You may also need to reduce your weight to allow you to perform squats comfortably.

If you have PFJ arthritis (or your knees make all sorts of grinding and clicking noises when under stress and sometimes swell after exercise), you will need to consider reducing your squat range to 60°degrees (because the deeper you go, the greater the contact between the patella cartilage and femoral cartilage and in damaged knees, this can rub and cause more damage – which is the grinding sound). You could also try a front squat (or goblet squat) instead of a conventional squat which places less compressive and shear force through your knee.

In summary, if you don’t have 100% healthy knees:

  1. Only squat to 60-90°
  2. Try the front squat instead
  3. Reduce your weight as required
  4. Choose some of the many other exercises that can be used to develop your glutes, hamstrings and quads
  5. Consult your trusted Physiotherapist


So what is correct squatting form?

Whichever type of squat you do, the five key things you need to focus on are:

  1. Place your feet where they naturally want to go. You might be told that your feet should be shoulder width apart and facing straight ahead. However, as every single one of us is different, your body will tell you where your feet are most comfortable. They can be wider than shoulder width, one foot slightly in front of the other (for example if you have a slight leg length difference) or with your toes slightly turned out. Experiment to find the position that is most comfortable for you
  2. Always maintain the natural curves of your spine to not only protect your back, but also allow the muscles at your hips (and therefore knees) to work optimally (otherwise the stress through your knees may increase)
  3. Make sure your knees track in the same direction as your toes – if your knees fall inwards or outwards, you place too much stress on the inside or outside aspects of your knees which can cause damage
  4. Keep your weight through your heels – this will reduce the compressive force through your PFJ by enhancing activation of your glutes and hamstrings
  5. Use an appropriate weight – don’t go too heavy too early. Make sure your technique is correct even as you fatigue before increasing your load


Other important information

Please also note that to perform a full squat, you need adequate ankle range of motion. Without this, your knees will tend to fall inwards, placing them under great stress and at risk of injury. How do you know if your ankle range is insufficient? Usually your heels will lift off the floor when you squat and your knees may fall in. Calf stretching and ankle range of motion drills will assist this. In the meantime, you can also practice squatting with your heels elevated (on small weights plates) until you have adequate range of motion.

Top squat tips:

  1. Warm up properly
  2. Choose the squat that’s right for you – full squat for healthy knees, reduced range and/or front squat for compromised knees
  3. Don’t go too heavy too quick – it’s much better to start with a lighter weight, get your technique right and ensure your knees can handle the activity before slowly loading up. Trust me, your body will thank you for it
  4. If it hurts – stop, modify you activity and see your local physiotherapist for guidance

Remember, as always, everybody is different so you need to find what works for you. If you have any concerns, please consult your trusted Physiotherapist. With their extensive knowledge of human movement, correct technique and how to train around injuries, they and can provide you with individual guidance.


We hope you enjoyed learning all about knee anatomy, the ins and outs of squatting and how to squat safely. If you have any questions, please feel free to contact us at [email protected]