The Real Truth About Leg Extensions?

To be honest, I hate getting dragged into Facebook threads. I have no idea why I don’t resist the urge to post. I do it to try to help and always seem to end up arguing with some guy ( why is it always a guy) who is just dying to be right.

Let start with some facts. I am not a research guy. I am not an “evidence based” guy. What I am is a coach with 35 years in the field and some National and World Championship rings to my credit. I consider myself evidence-led vs evidence-based. I used to think that experience counts for something.

However, I find myself having to defend myself against every self professed, expert who has figured out how to generate blog hits, views and likes.

My self-inflicted dilemma this week revolves around my reaction to the old “there are no bad exercises” statement.

I of course replied ” there absolutely are bad exercises” and, in typical name internet fashion my Facebook “friends” automatically say “ok, name a few”.

In true internet argument tradition no one refutes the obvious ones ( behind the neck press, dips, behind the neck pulldowns) but, instead of saying “gee Mike you might be right there really are a few bad exercises” they trot out a few internet experts to defend two others that made my list, leg extensions and leg presses.

This post is just going to use the supposed “evidence” presented to defend the leg extension ( this is primarily because I don’t have 30 more minutes to cover leg press).

The best part is that I get called out.

I quote ” any evidence for any of your claims Mike, these guys quote a lot of research”.

In fact, what these guys do is quote a lot of research, ignore it and then offer their own opinion as “backed by the research”.

This is from Nick Tuminello’s interview with Brad Schoenfeld  ( presented in the thread in question as evidence that my opinion is wrong)

Nick – I’ve read articles by several individuals from both the fitness and rehab worlds claiming that using the leg extension machine could be dangerous to your knee joint? What’s your take – Is it dangerous – Any conclusive research showing its dangers?

Brad- This is partially true. There are a couple of issues with the leg extension that can be problematic. For one, loading is applied perpendicular to the long axis of the tibia—a fact that creates shear force at the knee joint (alternatively, loading during multi-joint movements such as the squat is mainly compressive, with forces applied parallel to the long axis of the tibia). Since a joint is better able to withstand tensile forces from compression as opposed to shear, it therefore follows that leg extensions place increased stresses on the knee joint compared with multi-joint lower body exercises.

What’s more, leg extensions tend to heighten stress to the anterior cruciate ligament (ACL). During performance of the leg extension, the quadriceps reacts to the movement by pulling the tibia forward (a phenomenon called tibial translation). The ACL in turn opposes the quadriceps by trying to prevent translation of the tibia. These two antithetic actions place a considerable amount of stress on the ACL, and can potentially injure the ligament. It should be noted that in closed chain movements (i.e. squat, leg press, etc) the hamstrings are activated as co-contractors and exert a counter-regulatory effect on the pull of the quadriceps. The co-contraction of the hamstrings and quads help to neutralize tibial translation, alleviating stress on the ACL.

That said, the aforementioned factors should not have a detrimental effect on someone with healthy knee joints provided the exercise is performed properly. I’ve seen no evidence of an increased injury risk to those with healthy knees from performing leg extensions. I could even make a case that it might help to maximally strengthen these structures to a greater extent than other exercises, as tissue adaptation is specific to the degree of stress.

The crazy thing about the above answer is that Brad says that leg extensions are clearly dangerous, as the research shows, that they caused increased shear forces at the knee, an increased ACL strain and, are not as safe as closed chain exercises but, if you have a healthy joint and do them properly he sees no “increased risk”.

What Brad does here is directly contradict himself. He presents the research based evidence ( the same research that I read twenty years that caused me and most every other competent physical therapist and athletic trainer to abandon leg extensions) and then simply says “don’t worry about it”.

They ( he and Nick) then present this article as evidence that leg extensions are fine, even though the article itself says they are not?

Brads core training review does the same thing. He presents a huge body of anti-flexion evidence and then concludes that flexion is OK.

I guess all I ask is that people read critically and see when the conclusion doesn’t match the evidence.

PS- thanks for calling me out on this one as I would have never taken the time to create this post otherwise.


2 Responses to “The Real Truth About Leg Extensions?”

  1. mboyle1959 Says:

    Type in Craig Leibenson

  2. great post Mike, do you have a link to that FaceBook post ?

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