Exciting New Glute Research Pertaining to Knee Biomechanics in the Lunge

By November 8, 2012 Glute Training

I want to be the first to report some very cool research that has emerged pertaining to the role of the gluteus maximus during the lunge exercise.

A study was just recently published titled: Computational modeling of a forward lunge: towards a better understanding of the function of the cruciate ligaments.

Before I delve into things, just so we’re all on the same page, here is a video of Eric Cressey performing the forward lunge exercise:

* I bet Eric wishes that the glutes could also protect against hair-thinning…ba da ching! Folks I’ll be here all night!

Okay, back to the study. I’ll try to sum things up as simply as possible. Here are the cliff-notes:

  1. It is known that the quadriceps exert an anterior translational pull on the tibia, which can strain the ACL
  2. However, a couple of studies have recently shown that the PCL is strained during a forward lunge, not the ACL (the ACL is spared)
  3. The researchers who published these papers have speculated that this phenomena is due to hamstrings co-contraction, but until now no models have examined the contributors to the posterior pull on the tibia during the lunge
  4. Much of the gluteus maximus fibers insert into the iliotibial tract (70-85%) *see pic below…not the best pic but it’s slim pickens on Google images
  5. When the glute max contracts, it pulls on the iliotibial tract, and in the lunge movement this tension exerts a posterior translational pull on the tibia (in other biomechanical terminology that I’m trying to teach my readership – you could say that it creates a “knee flexion moment”)
  6. Surprisingly, at the bottom of a lunge, the quads do not exert an anterior pull on the tibia (they actually produce a posterior drag of 98N or 22 lbs) *you’re welcome for converting Newtons to pounds!
  7. The quads only exert an anterior pull at the top of the lunge, and this force is modest at best (max of 430N or 97 lbs)
  8. During the entire lunge movement, the ACL was never activated (it doesn’t get stretched)
  9. Rather, the PCL is activated (stretched) during the entire movement, and the peak loading on the PCL reaches 2,880N or 647 lbs at the bottom of the lunge
  10. At the bottom of the lunge, the gluteus maximus provided 67% of the posterior pull on the tibia (1,940N or 436 lbs)
  11. The semitendinosus was responsible for 20% of the posterior pull on the tibia (460N or 103 lbs)
  12. The other hamstrings (semimembranosus and biceps femoris) didn’t contribute any posterior pull on the tibia

* If you can gain access to the full paper, please do so and check out Figure 4. The graph sums up the entire story in terms of contributors to translational forces on the tibia at various depths.

My Thoughts

  1. Assuming the model is legit, this new research is a big deal as it changes our understanding of knee biomechanics during the forward lunge and possibly other knee dominant movements such as the squat (I call them axial extension movements). In my glute presentations I have a slide that says, “Good Things Happen When You Have Strong Glutes” along with a cool pic that shows the glute’s influence on the rest of the body. It’s the truth!
  2. The form described in the study seemed legit (upright torso, push through heel, etc.). The descent went to a 90 degree knee angle but since the knee was allowed to migrate forward past the toes, the tibia wasn’t necessarily vertical and therefore the lifter could have “stopped short” and had more ROM available. This probably wouldn’t affect the results much though.
  3. The gluteus max and semitendonosus indeed counteract the quadricep forces on the tibia, but one could say that they “over-conteract” and actually load up the PCL (also, it doesn’t take much to counteract the quad’s pull, especially as the lunge descends).
  4. The glute max is a much bigger player than the hammies in pulling rearward on the tibia due to the iliotibial tract insertion, and this is especially true considering the hammies are shortened and not activated much in a lunge (or a squat for that matter).
  5. This has implications for ACL rehabilitation (as well as PCL rehab).
  6. Though the PCL is highly loaded during the lunge, anecdotally this does not present a problem for the vast majority of lifters. So it appears that the PCL possesses considerable tensile strength.
  7. The lunge doesn’t appear to load the ACL, but this doesn’t mean that it’s “knee-friendly” or that it’s ideal for every lifter. There are many more structures in the knee than just the ACL that can experience damage and irritation. The reverse lunge with a slight forward lean and a decent stride length will take some load off the knee and place more load at the hip.
  8. Though studies like this make me jump for joy (new stuff is cool, especially pertaining to lunges and glutes), we should always exercise prudence and be somewhat skeptical. It does indeed make biomechanical sense and is logical to envision the glute max tensioning the iliotibial tract and pulling back on the tibia, but 436 lbs worth of rearward pull? That sounds a bit KARAZY! I’m not saying it’s too good to be true, I’m just saying that it pays to be patient with the literature. For example, I’ve seen varying reports on the biomechanics of the thoracolumbar fascia, depending on the researchers/labs/models.
  9. I’d like to see the study duplicated with other models. I’d also like to see a study utilizing heavy loading (this model just examined a bodyweight lunge) and subjects with varying anthropometry. I’m familiar with the model they used but all models contain assumptions and have limitations. For example, they made assumptions with the level of glute activation that I’m not quite comfortable with. It’s also unclear at this time as to which hamstring muscles are most active in varying hip extension exercises. Right now I’m aware of three studies pertaining to this topic: In a recent study, my friend Jurdan and I found that the long head of the biceps femoris experienced the most damage in a lunge; another recent study showed that the kettlebell swing, RDL, and single leg glute bridge were semitendinosus dominant while the back extension was biceps femoris dominant; and yet another recent study showed that the biceps femoris and semimembranosus was more activated than the semintendinosus in the straight-leg deadlift. So we’re just starting to learn more about specific hamstring mechanics during hip extension exercise. The model these researchers used had findings that didn’t jive with what Jurdan and I found in our study.
  10. Based on this information, it appears that this video I made a couple years back is outdated (but still looks really cool with the diagrams haha).

35 Comments

  • What are your thoughts on the concepts that anterior glide of the femur in relation to the tibia causing a stretch response to the patellar tendon and sub-patellar connective tissues being one of the most common causes of anterior knee pain in a forward lunge, which explains why anterior knee pain isn’t present in the same amount during a backwards lunge? Wouldn’t the glutes and semimenbranosus posterior force cause some additional shear force between the tib and femur, which would have to be buffered by an active quad? Great points on the stress effect to the ACL and PCL.

    • Bret says:

      Hi Dean! Good question – my take is that you simply get a greater knee moment during the forward lunge (and you have to be explosive to spring back into place, creating horizontal ground reaction forces which will manifest in greater stress on the knee). I should send you this study – much of the forces were joint reaction forces at the knee (anterior)and ankle (posterior). So the knee structure is indeed taking a beating, but many folks can deal with it while others cannot (which you know as a trainer). Look for an email from me.

  • Why do you think that your findings and these findings differed so much in terms of bicep femoris activation? Load, tibia angle, method of measuring activation, foot positioning, subject training level?
    Also it is interesting that the ACL didn’t register any loading despite the subjects being allowed to tract their knee over their toes. Like you mentioned it would be interesting to see how other knee structures were effected

    • Bret says:

      Another good question…I wonder what Jurdan would say (he’s the hamstring expert). We used an MRI technique that shows muscle damage…other studies referenced used EMG. This study involved a computerized model (Anybody Tech, which is actually a complicated system – I’ve seen an overview of it and it’s pretty crazy…detailed biomechanical modeling…they can be found here: http://www.anybodytech.com/), but they made assumptions in regards to muscle activation, that muscles activate in a way to minimize fatigue. I happen to know the activation patterns in the lunge, so I’m curious if their model is similar. You’re asking great questions!!!

  • Jensen says:

    Great write up! Thanks for sharing this. In terms of training implications, what is your opinion on how the glute and /or ham activation during this exercise would transfer to a more “ACL injury specific” ROM (near terminal knee ext with valgus)? Do you think the ROM to far away for much carryover?

    • Bret says:

      Jensen, I’ve seen some papers showing that it’s hard to tear the ACL with just sagittal plane activity (but genetics and tibial plateau shape play a big factor), so a good program teaching proper jumping and landing mechanics (absorb with the hips and prevent valgus), in addition to a good RT program that strengthens all the hip and thigh musculature (including the muscles that prevent valgus collapse) would be ideal. Just my two cents!

  • Nicholas St John Rheault says:

    Great way to explain the balance (and importance of the P-Chain) to help keep the balance more equal so there’s less anteriro glide of the femur. Because of women having more of an anterior pelvic tilt by nature, is there a way to off-set valgus for females????

    • Bret says:

      Nicholas, this article suggests that women do not have more APT than men: http://www.ncbi.nlm.nih.gov/pubmed/21658988

      They do have a greater Q-angle, tend to exhibit more knee valgus when landing/jumping, have less hip ext/abd strength, and exhibit quad-dominant patterns.

      So they need to strengthen the glute med, glute max, and hammies and learn proper movement patterns.

  • Chris Tangredi says:

    Going into the future a little bit there Bret. I didn’t know you could post tomorrows article today…Great article none the less.

    • Naomi Most says:

      Interesting. I first thought maybe it was his WordPress clock setting, but the latest it could be in another part of the world is still earlier than the timestamp on your comment.

      So I’m guessing the internal date/time clock on his server is incorrect.

  • Awesome write up Bret! I was waiting to find the time to read this all day when I saw it in the AM and I’m glad I found it thanks to some nasty weather again here in the Northeast. What this means to me, from a performance perspective, is that someone who can develop strong and functionally sound glutes and their surrounding helpers and stabilizers(piraformis, TFL, adductors, ect…)can really maximize the use of the forward lunge while minimizing unnecessary stress applied to the ACL. Awesome choice for an athlete who is recovering from an ACL injury but is still limiting applied stress to the ligament. I’ve been a big fan of what you’ve been preaching about the importance of glute strength and everyday I see it’s a little more true. Get your glute strong and firing and almost any strength work is safer, sounder, and stronger!

    The study confirms what is seen in this video of the anatomy of knee flexion (assuming this is biomechanically correct),the ACL does not get stretched at all. The PCL does change length and seems to be elongated at 90 deg of flexion as compared to its starting length. The ACL just changes direction and comes along for the ride. In fact, it looks like the ACL is even shorter and slacked at full flexion as compared to full extension.

    Thanks for writing this up and sharing!

  • Whoops! Forgot the link to the video:

    Knee Flexion

    http://www.youtube.com/watch?v=203K_qQ2ZDk

  • Rob Panariello says:

    Bret,

    Though this may be a new study (I have not read it at this time) the findings of the posterior shear forces that occur during an exercise performance with a deep knee bend position isn’t really something we haven’t known for 20+ or so years. In the squat exercise we have known that during (deep knee) exercise performance the tibio-femoral shear forces that occur are in the posterior direction. The deeper the knee flexion angle the greater the associated posterior shear forces.

    The reason why anterior knee pain may occur in these deep knee bend position weighted exercises is not likely due to shear stress, but likely due to the greater patello-femoral compression forces that occur at the patello-femoral joint with the associated deep knee bend position. Now with that said, the deeper the knee bend the greater the patello-femoral contact area to distribute these compressive forces.

    One will also have greater stress upon the patella tendon as the moment arm from the line of the resistance with the body in an upright position will be greater at the knee than the hip (as in the front squat when compared to the back squat). Thus the quads will have a greater contribution to exercise performance.

    One will also have posterior shear forces with open chain knee extension exercises as well. Even though this is an “isolated” quad exercise if you review the 2 vector forces at the quads and patella tendon during the knee extension exercise performance, a resultant tibio-femoral posterior shear force will occur from 90 to approximately 60 degrees (as the knee extends) of knee flexion. At 60 degrees to full knee extension those shear forces become anterior in direction peaking at about 30 to 15 degrees of knee extension depending upon whom you reference.

    Since the front leg of a performed lunge exercise is similar to a (single leg) squat position one would not be surprised that similar findings at the knee occurred. Now with all of this stated, it is interesting to hear the comments of the gluts and their effect on the posterior shear forces at the knee during a deep knee bend type exercise.

    As far as the loads that the PCL can handle, during my time working with my friend Hall of Fame S&C Coach Johnny Parker during his time with the NFL NY Giants, we published a study in The American Journal of Sports Medicine back in 1994 looking at the effect of the Squat Exercise on the ACL and PCL ligaments of the knee. At the time of the study the Giant’s off-season program was approximately 16 weeks in length. During the training period the players lifted literally tons of squat weight and performed literally thousands of squat reps. In review of the approximately 2,500 knee test measurements taken with a knee ligament arthrometer (for ACL/PCL ligament integrity) only 8 tests were found to be “abnormal”

    We also had 3 players who were 1 year, 5 years, and 10 years, post-op ACL reconstruction respectively, but couldn’t be included in the study because of their knee surgery. They were also too small a subject group for us to write an additional study on this subject matter. However, these 3 athletes had no adverse effects on either the ACL or PCL knee ligaments as all of their test scores were also normal as was the integrity of their knee ligaments after participating in an NFL off-season training program.

    I hope all is well,

    Rob

    • Rob Panariello says:

      Bret,

      Just happened to speak with Coach Parker to “catch up”. He reminded me that the NY Giant off-season program for this study was 21 weeks, not the 16 that I had stated. That’s (a) 5 more weeks of tons lifted and reps performed and (b) proof my memory isn’t what it used to be :).

      • Bret says:

        Great stuff as always Rob! I actually remember reading this about the squat in a post you made on SC.com (when we both used to post there), and then I read about it again in a review paper that my buddy Brad Schoenfeld wrote. I haven’t delved very much into knee biomechanics over the past few years but I come across various papers in my research review service and stay current with the literature.

        So what was exciting to me was that the glutes played such a big role in knee stability (I assumed it was the hammies).

        Agree about the compressive forces on the patella in deeper knee flexion in the squat. It’s hard for me to visualize how the quads could induce a posterior pull on the tibia…for example in this video it looks as if you’d always get an anterior pull: http://www.youtube.com/watch?v=wyiJw034ssA

        I always love hearing about your anecdotes and studies!

  • Dan says:

    Bret, great summation of the research. My thoughts lie with varying exercise selection for similar movement patterns. What are your thoughts on the sheer forces and how they may change in lunge activity when using a reverse lunge (whereby the dominant working/front leg remains in contact with the floor at all times) compared to the forward line (whereby the dominant legs is required to decelerate during ground contact to stabilise)?? In addition to those thoughts, when would you look to select one exercise type over another?

    • Bret says:

      Hi Dan, depends on the goal. With my female clients I never give the forward lunge…I give the reverse lunge as it works a little more glute IMO (though research shows they’re fairly similar in activation). For athletes, I think you should rotate different types. Sometimes forward, sometimes reverse, sometimes deficit, etc. When I wasn’t programming the forward lunge, I’d want to be doing reverse sled dragging or linear COD tasks.

  • stephane says:

    I didn’t read all the comments but I would be more interested if researches would apply to sport because the purpose is not knowledge for knowledge but how it is effective on performance and prevention and rehabilitation.
    For exemple, you work the lunges and you apply it, under a protocole, to spinters or weighligters or skiiers because for the ACL do we have to stress it to make it stronger or not. So what appears as not stressing the ACL could be good or bad according to the situation. So I need a SITUATION to apply fondamental research.

    • Bret says:

      Good question. I’d say that to make the ACL stronger then you would indeed need to stress it. But this wouldn’t be the optimal manner of preventing ACL injuries. If that’s the goal, then you want to ensure proper movement patterns (absorb the load with the hips, also prevent knee valgus which is a combination of hip flexion, hip adduction, hip internal rotation, and sometimes pelvic drop on the opposite side – so you need strong and coordinated glute med and glute max to stabilize the hips). Doing this wouldn’t strengthen the ACL, but it would prevent it from being overly-stressed.

  • Rob Panariello says:

    Bret,

    We don’t strengthen the ACL we find way’s to protect it, i.e. lower extremity mobility, strength, proprioception, proper take off, deceleration, landing mechanics, etc… As you have stated we also know that mobility and strength at the hip may prevent as well as resolve certain knee pathologies. Some friends of mine are team physicians of various NFL teams. One specific NFL team of physicians that I know and have spoken to, looked at something very interesting during last year’s NFL combine. While evaluating the college football players participating in the combine for the upcoming NFL draft, the relationship between a player’s history of knee surgery/pathology and lack of hip internal rotation (IR) was reviewed. Of all the players tested, those with a history of knee pathology and/or surgery i.e. ACL reconstruction, MCL injury, meniscal injury, etc., ALL had limitations in hip IR. The most consistent relationship re: limitations in hip IR and resulting knee injury appears to occur in those football players with a measured limitation in hip IR of 10 degrees or less.

    Now one could logically state was the lack of hip IR the cause of the knee pathology or did the limitations in hip IR occur as a result (after) the knee pathology. We may not know this answer at this time, and certainly more research is needed in this area, but many medical professionals appear to have the opinion that a lack of hip IR will result in greater knee stresses due to the necessary (abnormal mobility) compensation at the knee that occurs for the limitations of IR at the hip. This limitation in hip IR may set the table, so to speak, for possible increased risk of a knee injury.

    More work is needed in this area at this time but it certainly makes sense as this observation also occurs at the shoulder. We know that a lack of shoulder (also a ball and socket joint) IR (GIRD) may put a throwing athlete at risk of shoulder and/or elbow pathology.

    Best,

    Rob

  • Eugene says:

    Your diagram and explanation was of greater value to all of us then all the in-talking in Greek and Latin. What % of all your readers do you think can understand those 3000 words of physiology? Good job interpreting that for non PhDs and making the info understood and making it useful info we can translate into exercises in the gym. Thank you, Bret. The diagrams were a Big help.

  • Michael M says:

    Really great update. Love a good biomechanics update.

    A couple questions.

    1) I’m curious if this has any implications for knee extensions. To me the problem with them has been the anterior tibial pull on the acl due to lack of co contraction. After reading this article what strikes me is this can be fixed with 1) cueing to fully contract the glutes and hamstrings, making it almost a slow moving isometric exercise rather than purely concentric and 2) lying down instead of seated at 90 degrees will put the glutes in a better position to help pull the knee posteriorly.

    2) I’m especially curious about what this means for patellar pain. I did some squats after reading this using the image of trying to pull my tibia backwards with my glutes/hams and it really helped. I’m curious if this posterior pull on the tibia has some structural effect that makes the patella track better, like sharper angle of the patella tendon (from its distal attachment being pulled back) holding the bottom face of the patella flatter against the patellar track for larger contact area.

    • Rob Panariello says:

      Mike,

      Here are my thoughts. With regard to your knee extension exercise question. If your sitting at a 90 degree angle at the knee you will have 2 vector forces produced at the knee at the initiation of exercise performance. The 1st vector force goes straight up vertically from the patella tendon. The 2nd vector is from the quad going back directly toward you. When you add these 2 vector forces together the resultant force is upward and backward, this is why the tibia translates posteriorly (a tibio-femoral (TF) shear force) with an isolated quad contraction perform at 90 degrees of knee flexion.

      This posterior shear force remains (no stress upon the ACL) but decreases as you kick forward lifting the weight until you reach a knee angle of approximately 60 degrees of knee flexion. This is the “neutral point” where there is neither posterior nor anterior shear force at the TF joint. As you continue to extend the knee the shear forces become anterior in nature, thus stressing the ACL and depending upon whom you reference, max forces occur at anywhere from 30 to 15 deg of knee extension.

      As far as the squat exercise is concerned, in the deep knee bend position all shear forces occur in the posterior direction. If you would like to reduce patella femoral compression forces during squat exercise performance then you would squat using a vertical tibia technique. By maintaining a vertical tibia you need to have more trunk and hip flexion during exercise performance. This “flexion” will bring the bar forward so that the line of the resistance is closer to the knee than the hips. This will create a greater moment at the hips resulting in a greater hip extensor muscle contribution and less quad contribution for a successful lift to occur. Posterior TF shear forces will increase due to a greater contribution of the extensor muscles but patella-femoral compressive forces (though they do remain) will decrease due to a decreased exercise contribution of the quads.

      • Bret says:

        Great response Rob – much appreciated!

        Mike, I think that just getting the hip extensors strong and learning to sit back and use them during squat/lunge movements is sufficient…you don’t have to think of it as keeping isometric tension (though it’s interesting to note that the hammies don’t change length much in a squat). I don’t believe that lying down puts the glutes in better position to pull on the tibia; they’re going to be stretched a bit in a flexed position which I’d imagine adds to the tension they can produce. Like Rob said, you could feel better simply because you’re sitting back more with a better lean, and this reduces quad contraction and subsequent compressive forces on the patella-femoral region. Finally, I don’t think you “rest” the hip extensors at the bottom of a squat; I think the hammies are shortened and can’t do much, the adductors are in a good position to provide extension torque, and the glutes are stretched to provide some passive force. Sure they’re not activated maximally, but they still provide considerable force.

  • Michael M says:

    A few more questions.

    Do these findings carry over to a squat, or is huge posterior pull something unique to lunges?

    If similar, I’d be extremely curious to see these measurements taken on a below parallel squat. A hypothesis that came into my head after reading this is that perhaps the loss of this backwards pull on the tibia in a very deep squat is what makes it dangerous. As you get deep there is a tendency to relax the glutes/hams and kind of just ‘rest’ on the knee and the compressed flesh of the calf/thigh touching each other. Pinching the posterior horn seems to be the main worry with very deep squats. It seems like a posterior pull on the tibia would help to pull the tibia backwards and get the posterior horn ‘out of the way’ as the femur rolls back, but when that is lost due to relaxation the posterior horn/tibia is no longer pulled posteriorly and is in a position to get pinched. My biomechanics understanding is meager compared to yours, but I’m wondering if this line of thought makes sense or is supported by any evidence.

    Finally, how the heck do the quadriceps create a posterior pull in the flexed position? Do you think this might be a measurement error?

  • Shimin says:

    Rob Panariello, every time I read one of your comments your knowledge of exercise sicence amazes me, keep up the good work.

  • Rob Panariello says:

    Shimin,

    Thank you for your kind words.

  • Sven says:

    Rob, thanks a lot from me too.

  • Daniel says:

    Hi Bret,
    Your studies on glute training are bar none, light years ahead of others! Good stuff. Quick question: I strained my hamstrings recently (most likely b/c of weak glutes). How long should I wait to start doing some gluteal training/activation. I know that if I keep trying to move around the extension work is going to keep going to the hams rather than the glutes. On the flip side though I don’t want to re-injure my hams while trying to do some glute stuff. Any tips? Thanks a lot!

    Dan

    • Bret says:

      Dan, do open chain glute work right away, assuming it doesn’t hurt. Lots of clams, side lying abductions, quadruped work, etc. This could be a blessing in disguise as it will allow you to increase gluteal recruitment while the hamstring heels.

  • Joe Miller says:

    While I can’t say that I understand all of the technical language, it does sound like the GM is really controlling the motion of the femur within the knee joint. A couple of papers come to mind:

    Powers, C.M. 2003. Influence of Altered Lower-Extremity Kinematics on Patellofemoral Joint Dysfunction: A Theoretical Perspective. J Ortho Sports Phys Ther vol 33 No 11 pp 639 – 648

    Souza and Powers. 2009. Predictors of Hip Internal Rotation During Running.Am. J Sports Med. Vol 37 No. 3 pp 579 -587

    And given the results of changes in knee biomehanics after hip abductor strengthening protocol documented by Ferber et al.

    Ferber, Kendall, Farr. 2011. Changes in knee biomechanics after a hipt-abductor strengthening protocol for runners with patellofemoral pain syndrome. J. Athletic Training 46(2):142-149

    I have opted to treat my own PFPS with a combination of barbell weighted glute bridges (thanks Glute Guy!), weighted side leg lifts, and band resisted clam shells. My hope is that with increased strength and activation I will gain better control over the rotation of the femur within the knee joint when that joint is under load.

    –Joe

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