Knees vs. Seated Leg Extensions: Friend or Foe? Part II

Posted: April 13, 2015 by TRU in Random, Rehab
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In case you found yourself on the edge of your seat since reading the cliff hanger at the end of part I, I’m going to get right to the point. While a fair amount of research has been done with leg extension machines, as always, much is left to be desired. But let’s look at a few points the research has been able to tell us.

  • Patellofemoral stress during seated leg extensions is greatest from 10-20 degrees (when the knee is almost fully straight)
    • One way to minimize this is to place the pad higher up the shin (closer to the knee than the ankle)
  • Studies have shown open chain such as leg extensions and closed chain such as lunges and squats place similar strain on the ACL
  • Knee stresses from leg extensions aren’t definitively supraphysiological, in other words, higher than demands of other common activities just as running
  • Research has yet to define an arthritic threshold. So we don’t know how much stress is too much/enough to accelerate knee arthritis

…And while the above is certainly nice to know, here’s the punchline:

Knee (1)

The premise that weight bearing exercises (squats, lunges) are safer, better, or more effective non-weight bearing (leg extensions) is not supported by research and still up for debate.

So for the time being, my recommendation is to do your leg extensions but don’t overdo them! Now I know this may not make a lot of sense since I just pointed out that we don’t yet know how much is too much, but that being said, if you’re doing set after set of heavy leg extensions several times a week you’re more likely to be putting your knees at odds. If on the other hand, you do a few sets of leg extensions at the end of a leg workout with a more moderate load to burnout/fatigue the quads, you’ll probably be fine…at least until we have more research suggesting otherwise.

In closing

In closing, think about joint stress the way you should think about eating. When it comes to diet, context is the key. By itself no one meal is going to make your break your physique. Why? Being fat and being lean is about habits. Which habits are repeated e.g. eating for leanness regularly, is what will ultimately make you lean. On that same token, an exercise such as the seated leg extension is unlikely to make or break your knees…by itself. Again it’s the habit(s), e.g. being obese, playing sports/running on hard surfaces, having poor body mechanics/malalignment of the knee, and then adding frequent leg workouts with heavy leg extensions that might put your knees over the edge.

So to answer whether or not a potentially provocative exercise like seated leg extensions are good or bad depends on the above. If you are already putting a lot of stress on your knees with day to day activities then the cost may outweigh the benefits—in the long run. That being said, the seated knee extension exercise is a potent quadriceps builder, and one that is unlikely to wreck your knees…by itself.




  1. Beynnon BD. Flemming, BC. Anterior Cruciate Ligament Strain In-vivo: A Review of Previous Work. J Biomech 1998. 31:519.
  2. Beynnon, B., et al. The Strain Behavior of the Anterior Cruciate Ligament During Squatting and Active Flexion-Extension: A Comparison of an Open and a Closed Kinetic Chain Exercise. The Am J of Sports Med, 1997. 25(6), 823-829.
  3. Boyd, M. L., et. al. A Comparison of Tibiofemoral Joint Forces and Electromyographic Activity During Open and Closed Kinetic Chain Exercises. Am J of Sports Med. 1996 24(4), 518-527.
  4. Chow JW. Knee joint forces during isokinetic knee extensions: a case study. Clin Biomech (Bristol, Avon). 1999 Jun;14(5):329-38.
  5. Cohen, ZA. Roglic, H. Grelsamer, RP. et al. Patellofemoral Stresses During Open and Closed Kinetic Chain Exercises. An Analysis Using Computer Simulation. Am J Sports Med. 29(4):480-7.
  6. Cohen ZA, Roglic H, Grelsamer RP, Henry JH, Levine WN, Mow VC, Ateshian GA. Patellofemoral Stresses During Open and Closed Kinetic Chain Exercises. An Analysis Using Computer Simulation. Am J Sports Med. 2001 Jul-Aug;29(4):480-7.
  7. Escamilla RF, Fleisig GS, Zheng N, et al. Biomechanics of the Knee During Closed Kinetic Chain and Open Kinetic Chain Exercises. Med Sci Sports Exerc. 1998 Apr;30(4):556-69.
  8. Heijne, A. Flemming, BC. Renstrom, PA. et al. Strain on The Anterior Cruciate Ligament During Closed Kinetic Chain Exercises. Med Sci Sports Exerc 36:935.
  9. Lutz, G., et. al. Comparison of Tibiofemoral Joint Forces During Open-Kinetic-Chain and Closed-Kinetic-Chain Exercises. J of Bone and Joint Surg. 1993 75(5), 732-739.
  10. Powers CM, Ward SR, Fredericson M, Guillet M, Shellock FG. Patellofemoral Kinematics During Weight-Bearing and Non-Weight-Bearing Knee Extension in Persons with Lateral Subluxation of the Patella: A Preliminary Study. J Orthop Sports Phys Ther. 2003 Nov;33(11):677-85.
  11. Steinkamp LA, Dillingham MF, Markel MD, Hill JA, Kaufman KR. Biomechanical Considerations in Patellofemoral Joint Rehabilitation. Am J Sports Med. 1993 May-Jun;21(3):438-44.
  12. Stensdotter AK, Hodges PW, Mellor R, Sundelin G, Hager-Ross C. Quadriceps Activation in Closed and in Open Kinetic Chain Exercise. Med Sci Sports Exerc. 2003 Dec;35(12):2043-7.
  13. Stuart MJ, Meglan, DA. Lutz, GE. Et al. Comparison of Intersegmental Tibiofemoral Joint Forces and Muscle Activity During Various Closed Kinetic Chain Exercises. AM J Sports Med 24:792.
  14. Wilk, KE. Escamilla RF. Fleisig, GS. Et al. A Comparison of Tibiofemoral Joint Forces and Electromyographic Activity During Open and Closed Chain Exercises. Am J Sports Med 24:518.

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