Saturday, March 2, 2013

Strengthening Your Quads: Another Reason It’s a Failed Approach

A number of times, I’ve expressed my frustration with physical therapy’s obsession with quad strengthening to treat weak, painful knees.

On this blog, I once compared strengthening your quads before strengthening your joints as being similar to putting your shoes on before your socks.

And in Saving My Knees, I related how following this advice almost ruined my knees.

To me, this approach just doesn’t make much sense.

Now here’s some clinical evidence:

In September 2010, the Journal of Pain reported the results of an interesting study. The question that researchers set out to investigate: Does knee pain reduce muscle strength?

A test was performed on 18 healthy subjects. To create knee pain, “hypertonic saline” was injected into the fat pad near their patellas. After that, subjects had their maximum muscle strength measured while flexing and extending their legs. On a separate day, a placebo that caused no pain was injected into the fat pad, then the strength measurements were made again.

The findings: muscle strength was 5 to 15 percent lower under conditions of induced knee pain. The amount of reduction was proportionate to the severity of the pain. The conclusion (my bold):
This study showed that knee joint pain has a significant impact on muscle function. The findings provide evidence of a direct inhibition of muscle function by joint pain, implying that rehabilitative strengthening exercises may be antagonized by joint pain.
In other words, your joint pain is working at cross purposes with your attempts to strengthen muscles in your leg. You’re trying to make muscle fibers stronger when they’re able to effectively function at only 85 to 95 percent (or maybe even less, if your knee pain is quite severe) of capacity.

Now be careful to grasp the full import here -- the 85 to 95 percent doesn't refer to the percentage of your maximum strength if you were fit and toned. It’s 85 to 95 percent of your existing strength.

You may be thinking: Well, 85 to 95 percent doesn’t sound too bad. But remember the optimal way to strengthen muscles. You push them to their limit, then they respond by going through a repair/rebuild cycle.

But if you can recruit only 85 percent of their strength, how can you push them hard enough? (Note that I’m not even addressing the elephant in the room -- should you try to push this hard anyway and risk further damage to your joints?)

By the way, an interesting corollary to these findings should be that the worse your knee pain is, the less successful the strengthening approach should be. And, at least based on anecdotes I’ve heard, that sounds just about right.


  1. Knee pain - Go for an accurate diagnosis and home prescription need to do critical analysis of knee problems

  2. Hi, I've read your book on Kindle, and I very much appreciate you sharing your experiences with knee pain.

    There is a lot of evidence that weak quadriceps lead to increased knee pain. Ditto for *tight* quadriceps, which are often caused by over-exertion of weak quadriceps. Below are some sources from scientific journals.

    There are a lot of causes for knee pain. For chrondomalacia patella, the root cause is often a misaligned patella, improperly tracking over its surrounding cartilage. I argue, based off of my own experience and research, that a first step towards addressing this misalignment should be achieving an optimal balance of strength between the hamstrings and quadriceps.

    "In women but not in men, quadriceps weakness was associated with increased risk for tibiofemoral and whole knee JSN.":

    "Relatively weak quadriceps are associated with increased knee pain":

    1. Hi Derrick. Thanks for the comments.

      You have to be careful sending me studies, because there's always the chance I might read them. ;)

      Did you read the conclusion of the second one? ("Ratio of Hamstring to Quadriceps Femoris Muscles' Strength in the Anterior Cruciate Ligament Insufficient Knee.") You might want to take another look. It supports more what I'm saying than what you believe.

      The other study, I've got lots to say, but I'm not going to squeeze my remarks into a short comment section. I plan to do a blog post later on both of these studies, so thanks for sharing.

      Look, one big point of mine: Strong quadriceps are great. There's no disputing that. The problem is this: Once you have a bad knee joint, how do you get those strong quadriceps? My experience: Strengthen your knee joint first, then focus on your quadriceps. To me, this is just a logical sequence.

    2. I did read the second study's conclusion. It had five parts. #1 and #5 support my stance, and #2,3,4 are vacuous.

      They're vacuous because to say that there isn't an optimal absolute HQ ratio is as inert and obvious as saying there isn't an optimal body weight for every human being.

      But from the study: "5) a suitable HQ ratio may be the HQ ratio of the patient's uninvolved knee."
      This kills two birds with one stone. First, it suggests that proper muscle training may be conducive towards knee health. Second, it correlates high HQ ratio with poor knee health. This arguably suggests that a structural anomaly is a cause of the knee injury (or, at least a contributing factor/hindrance to rehabilitation).

      I totally agree that it's madness to strengthen the quadriceps if the knee joint can't handle the exercise. But the quads don't need the knee in order to get stronger. The converse is false!

    3. Hmmm. Of course you realize that #2,3 and 4 -- the "vacuous" parts of the conclusion -- are what the study set out to prove in the first place? "The main hypothesis was that the patients with an optimal absolute HQ ratio (50%-80%) have better outcomes than the other patients." So the author conducted this study to prove a hypothesis, which in the end he admits he couldn't prove.

      But I'm glad you think it makes sense that there's a great deal of variability among people with regard to HQ ratio, and that this variability doesn't matter much. If you believe that, it's logical to believe there's a great deal of normal variability for other things too -- such as say tracking and mistracking of the patella during knee flexion -- and that this variability probably doesn't matter all that much either. If so, our beliefs are probably closer than I thought. ;)