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:
- It is known that the quadriceps exert an anterior translational pull on the tibia, which can strain the ACL
- However, a couple of studies have recently shown that the PCL is strained during a forward lunge, not the ACL (the ACL is spared)
- 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
- 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
- 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”)
- 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!
- 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)
- During the entire lunge movement, the ACL was never activated (it doesn’t get stretched)
- 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
- At the bottom of the lunge, the gluteus maximus provided 67% of the posterior pull on the tibia (1,940N or 436 lbs)
- The semitendinosus was responsible for 20% of the posterior pull on the tibia (460N or 103 lbs)
- 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.
- 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!
- 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.
- 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).
- 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).
- This has implications for ACL rehabilitation (as well as PCL rehab).
- 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.
- 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.
- 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.
- 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.
- 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).