Causes and Solutions for Anterior Knee Pain with Squatting

It’s leg day and you’ve completed your pre-workout routine— pre-workout drink with way too much caffeine, cardiovascular warm-up, band work, foam rolling and maybe some stretching. It’s time to start the first few warm-up sets but there is a problem—your darn knee hurts when you try to squat, lunge or do step-ups. Maybe you have been pushing though it for a while or maybe it’s a new onset of pain that feels like it should just go away on its own.

Patellofemoral pain syndrome (PFPS) is a relatively common cause for knee pain in the gym.  This condition affects up to an estimated 40%1 of adolescents and active young adults. The diagnosis of PFPS is typically based on the presence of pain in the front or underneath the patella (knee cap) and is commonly irritated by prolonged sitting, squatting, kneeling, running, and stairs. PFPS is often a diagnosis of exclusion17—a diagnosis made by a process of elimination. What’s the problem with this? If you see a provider because the front of your knee hurts and all you leave with is a diagnosis that means, “The front of your knee hurts,” it can be a disappointing experience.

There are many tools to manage pain (creams, gels, medication, ice, etc) but these options only address pain and not the underlying causes. This article will cover the four most common impairments associated with PFPS, how to identify these impairments and how to train them! Before you skim the rest of this article and skip to the training, please take the time to understand some anatomy and biomechanics of the knee joint and I promise, you will leave with a greater understanding of this problem.

A little biomechanics and anatomy- short and sweet

The patellofemoral joint is a unique and complex structure between the patella (knee cap) and the end of the femur (thigh) bone. The patella acts as a dynamic lever3 for the quadriceps(quads) and experiences some of the highest loads of any structure in the human body—up to 7 times body weight during a squat.2 Without the patella, the quads would have a much harder time extending the knee. When the quads contract, they produce a compressive force against the patella. Think of a strong rubber band on the top of your thigh and running over the top of the knee cap, attaching to the tibia (shin) bone. If you pulled that band, it would press down against the knee cap- this is how the quads compress this bone.

(Huberti, Hayes, 1984)19

Compression is an important concept you need to understand when thinking about PFPS. The other is contact area underneath the knee cap. To illustrate contact area, think about standing on a surface. You have all your body weight against the ground and the force is distributed throughout your whole foot. Now imagine standing on a golf ball in the middle of your foot. Your body weight hasn’t changed but the contact area has. When you reduce the contact area, you reduce the area of force distribution. Ouch! This is an important concept because the combination of reduced contact area under the patella and elevated joint reaction forces is detrimental with respect to patellofemoral joint loading.2 The contact area between the undersurface of the knee cap and the femur(thigh) bone will help determine how well loads are distributed during exercise. At 30 degrees of knee flexion (bend), the area of contact between the knee cap and the end of the thigh bone is around 2.0cm19. This area of contact increases as the knee is flexed further. At 90 degrees of knee flexion (a right angle at the knee), the contact area triples up to 6.0cm19. See the above graph for illustration.

Training- open vs closed kinetic chain

When people have PFPS they don’t need to stop training! Understanding basic biomechanics will go a long way when training with knee pain. Now that we have reviewed joint compression and contact area, let’s briefly review open and closed kinetic chain exercise as well as how this relates to PFPS. During an open kinetic chain (OKC) exercise (seated knee extension machine), the quads will increase their force as the knee straightens. While this is occurring, the contact area under the patella also reduces. This is why people with PFPS often have pain during this exercise, specifically at the top of the movement when the knee is straight.[36].png

During a closed kinetic chain exercise (squat), the further you squat down, the larger the contact area under the patella; however, as the knee moves into further degrees of flexion, the resulting force from the quad on the knee cap also increases (see above image).

(Powers et al, 2014)20

Dr. Chris Powers, physical therapist and expert in biomechanical aspects of human movement, produced a great study where he looked at OKC and CKC exercises and resulting patellofemoral (PF) joint forces. He further divided the OKC exercises into constant (hanging weight) and variable (machine) resistance exercises for the knee. The take-away message- to minimize PF joint stress and still work the knee through a full range, the squat exercise should be performed from 45° to 0° of knee flexion and the knee-extension-with-variable-resistance exercise should be performed from 90° to 45° of knee flexion20. This study provides a great starting point for people training with PFPS.

Congratulations for getting through that review! Now let’s chat about four common issues contributing to PFPS:

  1. Quad tightness
  2. Poor patellofemoral (PF) mobility
  3. Hip weakness
  4. Quad weakness

Decreased quadriceps flexibility can result in increased PF compression. When the quads tighten, the muscles and tendon compress the patella into the end of the femur.11 Remember the large rubber band analogy we used at the beginning of this article. This can be one of the reasons people with PFPS display the movie theater sign– pain in the front of the knee when sitting with the knees bent for a prolonged period of time. Stretching the quads can reduce knee pain with PFPS4,10. The mechanism for pain reduction is unclear but may be a result of reducing resting muscle tension, small changes in muscle length or improving a person’s tolerance to stretch (the great debate over stretching)! Adding foam rolling to stretching may allow further changes in resting muscle tension13, although it’s unknown if this combination has short or long-term effects. If you want more information on stretching check out my article, “Stretching- Will We Ever Get it Right.”-

Poor Patellofemoral (PF) mobility has been shown to contribute to PFPS.12,21,22 When the knee bends, the knee cap should glide downward and when the knee straightens, upward. Any restriction in this movement may lead to a change in the contact area underneath it. Recall, this contact area is important and if it’s reduced, can contribute to abnormal forces and resulting pain. Here are a few videos to help you learn how to perform patellar mobility exercises:

Although we are talking about knee pain, it may surprise you to learn this can be a hip problem. Decreased hip strength or muscle control can be a problem with PFPS.13-16 There is even evidence that hip strengthening may be better than quad strengthening when dealing with this condition9. Recall our discussion about contact area and how this can influence force distribution in the knee. The hip muscles control the femur bone and will affect the contact between this bone and the patella. With a normal knee position, the line of force of the quadriceps should have a slight angulation (shown above). When the hip muscles are weak it will allow the femur to drop inward. This is a knee valgus position (above right). When this occurs, you can see from the image how this affects the line of pull and resulting force to the patella. Altering the patella’s position can reduce the contact area underneath it. As we discussed earlier, this can lead to higher joint compressive forces.

How do you improve hip strength and stability- train your butt! Gluteal training is so important and underappreciated I wrote an another article about it. In the article I give beginner and advanced gluteal exercises that can improve strength and muscle control. Check it out if you want a guide for gluteal training:

You can also follow these links for a few video demonstrations of good gluteal exercises:

Quad weakness is associated with PFPS.1,2,4,5,9,13 However, we need to make sure we start this discussion with a few bits of constructive criticism. Training the vastus medialis obliquus (VMO) was once considered a gold standard treatment for people with PFPS.

I still see a lot of people trying to target the vastus medialis obliquus (VMO) when training the quads. There are a few theories behind VMO training you should understand before we dissect this widely misunderstood topic. One theory is the VMO will atrophy faster than other muscles in the quadriceps group. A recent study23 refutes this idea. Their study included 35 participants with PFPS. The results showed selective atrophy of the VMO relative to other portions of the quadriceps was not identified in people with PFPS.23

You should also know the ability to selectively strengthen the VMO, another theory, has also been questioned.6-8,24,26 The most common way people think they are isolating the VMO is during the last few degrees of knee extension or by combining a squat with hip adduction (squatting while squeezing a ball between the knees). There have been a few small studies that show higher levels of VMO activity during these positions but we need to take a step back before misinterpreting these results. These smaller studies have been criticized for their methods. One study found the measurement of VMO activity while squatting with hip adduction was influenced by the type of electrode.6 The most recent systematic review (a large review of available studies on this topic) suggests the VMO cannot be preferentially activated by changing leg position or by recruiting other muscles simultaneously. So, when training quads, stop trying to isolate VMO, placing your body is strange activation patterns and just get the quads stronger!

The origins of PFPS can become less mystifying by removing the diagnostic label and understanding the anatomy and biomechanics of the knee. Consider the following two questions—why does my knee hurt? What do I know about the knee? The first question will send you down the typical pathway of hunting online for a diagnosis. You can end up on 20 different websites and discover 20 different possible diagnoses! You end up with a label and a few options to cover up your reason for being there in the first place—pain! The second question can send you a different direction—understanding optimal knee mechanics. What’s the difference? The second question leads to active recovery! If your answers are things like tightness, weakness, poor mobility and poor stability, you will start to see solutions to your problem—the reasons behind the pain! If you want to maximize training and minimize adverse effects, this is the right approach!

All the research used for this commentary is cited below. All my curious readers are encouraged to check out these resources. Please, subscribe to this blog if you like reading about evidence-based strength training and rehabilitation for common musculoskeletal conditions.


  1. Hensley CP. Management of patients with patellofemoral pain syndrome using a multimodal approach: a case series. J Orthop Sports Phys Ther. 2009;39(3):234-6.
  2. Powers CM, Bolgla LA, Callaghan MJ, Collins N, Sheehan FT. Patellofemoral pain: proximal, distal, and local factors, 2nd International Research Retreat. J Orthop Sports Phys Ther. 2012;42(6):A1-54.
  3. Yamaguchi GT, Zajac FE. A planar model of the knee joint to characterize the knee extensor mechanism. J Biomech. 1989;22:1-10.
  4. Mason M, Keays SL, Newcombe PA. The effect of taping, quadriceps strengthening and stretching prescribed separately or combined on patellofemoral pain. Physiother Res Int. 2011;16(2):109-19.
  5. Kooiker L, Van de port IG, Weir A, Moen MH. Effects of physical therapist-guided quadriceps-strengthening exercises for the treatment of patellofemoral pain syndrome: a systematic review. J Orthop Sports Phys Ther. 2014;44(6):391-B1.
  6. Wong YM, Straub RK, Powers CM. The VMO: VL activation ratio while squatting with hip adduction is influenced by the choice of recording electrode. J Electromyogr Kinesiol 2013;23:443-7.
  7. Spairani L, Barbero M, Cescon C, et al. An electromyographic study of the vastii muscles during open and closed kinetic chain submaximal isometric exercises. Int J Sports Phys Ther 2012;7:617-26.
  8. Wong YM, Straub RK, Powers CM. The VMO: VL activation ratio while squatting with hip adduction is influenced by the choice of recording electrode. J Electromyogr Kinesiol 2013;23:443-7.
  9. Khayambashi K, Fallah A, Movahedi A, Bagwell J, Powers C. Posterolateral hip muscle strengthening versus quadriceps strengthening for patellofemoral pain: a comparative control trial. Arch Phys Med Rehabil. 2014;95(5):900-7.
  10. Mullaney MJ, Fukunaga T. CURRENT CONCEPTS AND TREATMENT OF PATELLOFEMORAL COMPRESSIVE ISSUES. Int J Sports Phys Ther. 2016;11(6):891-902.
  11. Amis AA. Current concepts on anatomy and biomechanics of patellar stability. Sports Med Arthrosc Rev. 2007;15(2):48-56.
  12. Puniello MS. Iliotibial band tightness and medial patellar glide in patients with patellofemoral dysfunction. J Orthop Sports Phys Ther.1993;17(3):144-148.
  13. Nicholas JA Strizak AM Veras G. A study of thigh muscle weakness in different pathological states of the lower extremity. Am J Sports Med.1976;4(6):241-248.
  14. Khayambashi K Mohammadkhani Z Ghaznavi K Lyle MA Powers CM. The effects of isolated hip abductor and external rotator muscle strengthening on pain, health status, and hip strength in females with patellofemoral pain: a randomized controlled trial. J Orthop Sports Phys Ther.2012;42(1):22-29
  15. Dolak KL Silkman C Medina McKeon J Hosey RG Lattermann C Uhl TL. Hip strengthening prior to functional exercises reduces pain sooner than quadriceps strengthening in females with patellofemoral pain syndrome: a randomized clinical trial. J Orthop Sports Phys Ther. 2011;41(8):560-570.
  16. Fukuda TY Melo WP Zaffalon BM, et al. Hip posterolateral musculature strengthening in sedentary women with patellofemoral pain syndrome: a randomized controlled clinical trial with 1-year follow-up. J Orthop Sports Phys Ther. 2012;42(10):823-830.
  17. Cook C, Hegedus E, Hawkins R, Scovell F, Wyland D. Diagnostic accuracy and association to disability of clinical test findings associated with patellofemoral pain syndrome. Physiother Can. 2010;62(1):17-24.
  18. Kapandi IA. The Physiology of the joints, vol. 2, Lower limb. 5th ed. Edinburgh: Churchhill Livingstone, 1985.
  19. Huberti HH, Hayes WC. Patellofemoral contact pressures. The influence of q-angle and tendofemoral contact. The Journal of bone and joint surgery. American volume. 1984; 66(5):715-24.
  20. Powers CM, Ho K, Chen Y, Souza RB, Farrokhi S. Patellofemoral Joint Stress During Weight-Bearing and Non—Weight-Bearing Quadriceps Exercises J Orthop Sports Phys Ther. 2014; 44(5):320-327.
  21. Getka A. Patellar hypomobility and the flexibility of the iliotibial band and the femoral quadriceps. Ortopedia, traumatologia, rehabilitacja. 2005; 7(6):656-9.
  22. SelfeJ, Janssen J, Callaghan M, et al. Are there three mai. subgroups within the patellofemoral pain population? A detailed characterisation study of 127 patients to help develop targeted intervention (TIPPs) Br J Sports Med 2016;50:873-880
  23. Giles LS, Webster KE, McClelland JA, Cook J. Atrophy of the Quadriceps Is Not Isolated to the Vastus Medialis Oblique in Individuals With Patellofemoral Pain. The Journal of orthopaedic and sports physical therapy. 2015; 45(8):613-9.
  24. Cerny K. Vastus medialis oblique/vastus lateralis muscle activity ratios for selected exercises in persons with and without patellofemoral pain syndrome. Physical therapy. 1995; 75(8):672-83
  25. Chester R, Smith TO, Sweeting D, Dixon J, Wood S, Song F. The relative timing of VMO and VL in the aetiology of anterior knee pain: a systematic review and meta-analysis. BMC musculoskeletal disorders. 2008; 9:64.
  26. Smith TO, Bowyer D, Dixon J, Stephenson R, Chester R, Donell ST. Can vastus medialis oblique be preferentially activated? A systematic review of electromyographic studies. Physiotherapy theory and practice. 2009; 25(2):69-98.

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