What does skiing and squatting have to do with knees? Well, if either one are not performed properly they both can be pretty damaging on the knees…duhhhh, we already know this. But what exactly is it that is hurting our knees and how do we fix it? Tune into this weeks midweek mobility, brought to you from the ski slopes of Vail Colorado and Off Peace ski shop, as Dr. Megan talks about a common mechanism of injury for ACL tears among alpine skiers.
Although roughly 80% of ACL injuries among skiers are due to equipment related issues, there are still some precautions we can take to reduce to reduce our risk of tear or injury. Contrary to dry land squatting technique of loading the weight through the heals, in alpine skiing you want more of a forward displacement weight through the balls of the feet while driving the hips and the torso forward. In skier jargon, we want to stay out of the “back seat” The reason for this is anatomically a posterior weight displacement will cause a posterior to anterior force of the tibia on the femur. With the addition of rotary forces throughout a skiers turn, this causes a repetitive shear force on the ACL. This cumulative trauma to the ligament is what causes the ligament to break down overtime and possibly even completely rupture.
Beings that skiing is an open environment with constantly changing terrain and conditions, staying forward and maintaining form is not always possible. This is where strength and motor control training play an important role ACL injury prevention. Activation of the posterior chain, specifically the biceps femoris(hamstring), can aid and reduce stress on the ACL by providing rotary stability and preventing forward translation of the tibia on the femur during knee flexion.
If done properly, squatting can actually have the reverse affect on the knees from its rumored “being bad for the knees”. Practicing proper slow and controlled squats can help train and strengthen the muscles used during the squatting nature of skiing. EMG studies show the majority of the prime mover muscles used in skiing actions contract eccentrically, just as they do in the lowering of a squat. Also, since the hip angle generally does not have significant change during a turn in skiing, the rate or speed of contraction during skiing is relatively slow.
This being said, the type of training that you should do to get ready to hit the slopes should involve predominately lower body exercises with a large eccentric bias and a relatively slow rate of contraction. This means that you should do the exercises slowly in a controlled fashion concentrating on technique to maximize the benefits of the exercise and transfer to skiing performance.
Dr. Megan uses special guest Ken Reynolds, a long time skier and coach, to give examples on how proper warm up and strength training can help keep those knees in shape and stable throughout the season.
Kroell J, Wakeling JM, Birklbauer J, Seifert J, Mueller E. The influence of sustained sub-maximal skiing on the Frequency and intensity content of the EMG signal. In: Cabri J, Alves F, Araújo D, Barreiros J, Diniz J, Veloso A editors. 13th Annual Congress of the European College of Sport Science.Estoril; 2008.
Rossi M, Lubowitz J, Guttmann, D. The skier’s knee. Arthroscopy: The Journal of Arthroscopic and Related Surgery, Vol 19, No 1 (January), 2003: pp 75-84