Skiing is a strange sport; one can imagine that when attaching two pieces of wood to your feet and pushing yourself down a mountain, people get hurt. Despite an enormous amount of changes to ski equipment over the past two decades, the rate of injury among skiers remains extremely high. The Oslo Trauma Research Center reports that a competitive freestyle skier is likely to experience anywhere from 19- 24 injuries per 1000 ski runs. The knee in particular is subject to trauma, and is the most frequently injured part of the body.
The issue with skiing is that many of us are unknowingly exposing our bodies to large amounts of external forces. Even by just turning, the outside leg of a skier can be exposed to forces 2.5 times their own body weight, and a skier can experience forces up to 4 times their own body weight after a ski jump. Gravity, the same force that pulls objects down the mountain or out of the air after a jump, can also lead to a season ending injury. In addition, a skier’s knees are further exposed to injury because of the stiff or rigid ski boots being attached to skis, which in some instances work as a lever to bend and twist the knee. Consequently, there is an alarmingly high rate of knee injury associated with skiing; in particular, tearing of the anterior cruciate ligament is shown to account for up to one-fourth of competitive freestyle skiing injuries.
When you looks at research examining the situations and precursors that lead to skiing injuries, knee injuries typically occur when a skier loses balance while turning, when they catch an edge or when a skier lands with their weight backwards after a bump or jump. These situations will often occur because of a skier’s knee collapsing inwards (valgus), a skier landing with a stiff or unbent knee (hyperextension), a skier landing with their hips displaced below their knees (deep knee flexion), or an unexpected internal rotation of the knee. These movements place a considerable amount of force on the knee joint, and can cause the ACL to rupture. It is worth noting that to my knowledge there is no research that has currently examined the mechanisms or frequent causes of ACL injury in park, pipe or freeskiing.
We all participate in the same sport. Why is it that some people sustain injuries while others do not? Certainly there is an element of bad luck, and knee injuries can be caused by a seemingly ‘freak’ accident or by factors outside of the body that cannot be controlled, such as heavy snow or an icy landing. As well, unfortunately, certain people are more prone to sustaining a major knee injury due to their anatomical build or a physiological predisposition to the injury.
There are, however, several factors both inside and outside of the body that can be modified to reduce the likelihood of knee injuries. Modifications that can be made outside the body to potentially reduce knee injuries include adjustment of terrain parks, ensuring that a skier has the appropriate length of ski, proper adjustment of bindings or correct fitting of boots.
Individual factors existing inside the body may also contribute to ski injuries. Skiers with weak hamstrings, excessively powerful quadriceps, poor hip control or poor core muscle activation may be at increased risk factors for sustaining an injury because they cannot counter the forces imposed on their knee, or they cannot maintain safe skiing mechanics. In addition, a skier who shows general muscle asymmetry with movements or a strong preference to use one leg over the other also has an increased risk for injury. We can reduce injuries by (a) improving a skiers physical fitness, (b) re-training the skier’s mechanics to promote the optimal muscle firing patterns to better protect the knee and (c) provide movement strategies to prevent a skier from being exposed to a potentially dangerous situation.
A successful injury prevention program identifies individuals who are at risk and attempts to reduce the likelihood of injury from occurring by adjusting the modifiable factors that can lead to injury. Our goal is to implement a testing battery that could help identify those who display individual risk factors based on their movement patterns or level of physical fitness. There is a fair amount of information available on this topic from other sports, but to my knowledge, there is very little published work that specifically targets skiing.
Sport injuries are typically divided into two categories: (1) chronic injuries that are the result of a repetitive movement or overuse of certain muscles, (2) acute injuries that are the result of a traumatic crash or clash. Grey Cook’s Fundamental Movement Screen (FMS) is a good tool for detecting an athletes’ basic movement mechanics that may lead to injury and provides a very systematic approach to movement error detection of the most frequently used movements in sport (squatting, lunging, stepping). These movement errors may be caused by an athlete’s muscle asymmetry, a lack of specific muscular strength or a lack of mobility.
Because of the high physical demands of skiing, sport- specific or athletic testing is conducted to more closely simulate the demands a skier will experience on the mountain. The sport- specific tests were selected based on the most common risk factors associated with ACL injuries; specifically, examining an athlete’s muscular endurance, prolonged core muscle activation, dynamic stability, hamstring strength, analysis of stance/ balance and analysis of jumping/ landing mechanics.
If the testing identifies any particular deficit or limitation for a specific skier, then such limitation can be addressed with technique and mechanical training, which will prescribe corrective exercises. There is no set path for ACL injury prevention, particularly for skiing where there is a large combination of external loading forces. Many different factors must be examined and different intervention strategies used in order to minimize the risk of injuries. Addressing a skier’s individual muscle asymmetry or weaknesses is just one piece of a large puzzle. Ultimately the prevention of knee injuries will require the collaboration of movement specialists, physiotherapist, doctors, ski coaches, trainers and ski technicians.