By this point in your quest for total “jackitude”, I’m sure you’ve heard the saying, “Never let your knees go past your toes.”
I’m not sure how this saying started, but I assume it started during a game of Dungeons and Dragons, perpetuated by a long standing myth that some guy blew out his o-ring sitting on a toilet, which resembled a squat. Then, as time progressed, the o-ring became the knees (You know how the telephone game works, right?) and there you have it. Now, you can’t start squatting in any gym without some trainer, who has a certification bought off a seal at Sea World, running up yelling at you through a pre-pubescent, squeaky voice that you’re going to destroy your ACL.
And that, my fellow iron friends, is how the myth of “Never let the knees go over the toes,” started.
Often times in daily moving, your knees travel past your toes, such as when climbing stairs (according to a study by the American Sports Medicine Institute, 0-66 degrees of flexion is normal in this instance), or squatting down to grab that pesky piece of food that fell on the floor. Yet, even though this occurs daily, people inherently still think it’s bad for you and you’ll inevitably catch the Bubonic plague.
The argument largely begins when sheer forces to the knees are examined under load while squatting. According to the American Sports Medicine Institute, maximal compressive forces were found at exactly 91 degrees of flexion, compared to 90 degrees during a leg extension exercise. The article goes on to say how electromyographic data illustrated greater hamstring and quadriceps contraction during the squat than the other tested exercises.
The thing you should focus on is the hamstring and quadriceps recruitment/contraction, as those are the muscles that support the knee in positioning. Without the contraction between the two, the probability of getting injured is greater than if only focused on one muscle contraction.
In application to sport, where your knees will travel ultimately depends on a few factors, such as what squat you’re performing (low bar, high bar, front), and body proportions (long femur, short femur, etc.). In effort to properly utilize your hamstrings, it’s necessary for your knees to travel slightly in front of your toes in order to get that “bounce” out of the hole, and also for your quads to assist in muscling up the weight. If you want to be an efficient squatter, it makes sense to utilize every muscle you have.
The fact of the matter is, squatting increases the strength of the musculoskeletal system, including the quadriceps and hamstrings, which in turn strengthen (presuming you’re performing the squat properly) the joints. Stay balanced in your mid-foot, keep the bar over the middle of said mid-foot, stay tight, and allow your body to do what it naturally wants. The more you try to keep your shin vertical, the less balanced you’ll likely be (unless you’re a wide squatter, which is a different story for a different day).
Fry, A.C., J.C. Smith, and B.K. Schilling. Effect of hip position on hip and knee torques during the barbell squat. J. Strength Cond. Res. 17(4): 629-633. 2003.
Wilk, Kevin, Rafael Escamilla, Glenn Fleisig, Steve Barrentine, James Andrews, and Melissa Boyd. "A Comparison of Tibiofemoral Joint Forces and Electromyographic Activit During Open and Closed Kinetic Chain Exercises." A Comparison of Tibiofemoral Joint Forces and Electromyographic Activit During Open and Closed Kinetic Chain Exercises. N.p., July 1996. Web. 19 Sept. 2012. <http://ajs.sagepub.com/content/24/4/518.short>.
Maitland, Murray, Stanley Ajemian, and Esther Suter. "Quadriceps Femoris and Hamstring Muscle Function in a Person With an Unstable Knee." Quadriceps Femoris and Hamstring Muscle Function in a Person With an Unstable Knee. N.p., Jan. 1999. Web. 19 Sept. 2012. <http://ptjournal.apta.org/content/79/1/66.full>.