The number of athletes that I have worked with who would feel safer licking the bottom of their shoe after a night on Bourbon Street than locking their knees out while training is incredible. Lets get to the bottom of this exercise conundrum. 


Evidence-based ACL prevention strategies are especially critical for youth athletes and should be included in any comprehensive strength and conditioning program. Athletes should be taught to avoid a stiff-leg landing.  However, some athletes reinterpret this recommendation to mean: ALL knee extensions make you susceptible to catastrophic knee injury ALL of the time. It is very important that athletes understand the difference between landing and pushing off. 

The landing should be soft and "athletic" while the push-off should be stiff and powerful. 

In order to run faster or jump higher, you must be able to produce maximal horizontal (sprinting) or vertical force (vertical jumping) into the ground. Avoiding terminal knee extension during training will sabotage your ability to produce maximal force into the ground and power either forward (sprint speed) or up (vertical jump height). Here is an excellent breakdown of the debate between horizontal and vertical ground reaction forces related to training for sprint speed. 


As the legend stands around the water cooler at your local gym - anytime you hit full knee extension while exercising, you grind up your joints a little more. It's simple: joint surface health is partially dependent on movement through available and normal ranges of joint motion. In other words, the surfaces of your joints prefer to be moved through full ranges of joint motion regularly. Your joint surfaces will struggle to stay smooth, lubricated and healthy if you ignore a certain section of available joint range of motion. 

See THIS exercise error in action

How to master the art of necessary knee extension

  • Avoid pelvic tilt. Anterior or posterior pelvic tilt will make it very hard for the joints/structures below to function properly. 

RELATED: How to Fix Major Exercise Errors - Core Positioning

  • Practice terminal knee extension. The "TKE" is an exercise that is typically reserved for rehab or for addressing patella tracking issues. In a seated position with leg extended, place a rolled towel under/behind your knee and press firmly down into the towel. This can also be done in standing by looping an anchored band around the back of one knee and firmly extending your knee back into the resistance of the band. 

RELATED: 3 Pro Training Tips From the L.A. Lakers’ Strength Coach 

  • Get help from a partner. I've written before about the importance of training with a partner. If you notice that during your squats or dead lifts you are failing to reach full knee extension, have a training partner gently press against the back of your knee at the top of the lift. Challenge yourself to meet your partner's pressure to achieve a tall knee position. If you happen to be alone, you can use a band anchored in front of you and looped around the back of your knees while you perform a body weight squat or dead lift. At the top of the movement meet the resistance of the band to reach full knee extension. This will help you to groove the correct pattern. 


  • During jump landings.
  • If you have pain during knee extension. 
  • If you have an acute knee joint injury such as a meniscus tear. 
  • If you have a history of degenerative joint disease and knee extension causes pain. 
  • Immediately following knee surgery without being cleared by a MD and/or PT. 
  • The structure of your knees is such that you go into significant, visible or painful hyper-extension in a tall-knee position. 
  • During a recumbent leg press exercise with extreme weight (if you insist on doing this exercise.) 
  • If you have trouble avoiding rocking into low back extension when you reach full knee extension be sure to go back and practice the simple fixes above. 

Bottom line

There is no need to be scared of locking out your knees as long as you understand when and how to do it correctly. Grasping this concept will help you train more efficiently and effectively on your quest to run faster, jump higher and be a better athlete. 


@tdathletesedge #TDAE #fitness#exercise

Tim DiFrancesco, PT, DPT, ATC, CSCS is the Head Strength & Conditioning Coach for the Los Angeles Lakers and Founder of TD Athletes Edge, where he provides fitness, recovery and nutrition guidance to aspiring and professional athletes. For training advice, visit and follow him on Twitter/Instagram through @tdathletesedge.


Beardsley, C. (2013, March 4). Why do sprint coaches need to know about horizontal forces? Retrieved April 25, 2015.