The triple extension is a key movement, extending the hip, knee and ankle occurs as a major component of most sports. When one of those movements is severely restricted by say, putting the lower leg in a rigid plastic boot though, it alters the way force is produced and transferred throughout the entire kinetic chain. In skiing, it is the knees that bear the brunt. As a result knee injuries account for around 40% of all ski injuries, a massive amount, and it highlights the importance of strength and proprioception (positional awareness) about the knee.
Strength imbalances and movement inhibitions throughout the whole body can have a devastating effect on what occurs at the knee placing it in some very vulnerable positions, as well as having a negative effect on comfort inside a ski boot. The need for hamstring strength in prevention of knee ligament injury is well documented and activation of the hip abductors (move your knee outwards) is also an important element. Single leg lifts like split squats, single leg squats and lunges have a great impact on both of these. Introducing a lateral component using resistance bands is a great method of increasing the frontal plane (side to side) forces throughout the lifts.
With appropriate coaching, these movements can be mastered with bodyweight fairly quickly, it’s then possible to start adding extra weight to further increase your strength. As you become more competent, it is then possible start to manipulate the timings involved in each rep (e.g. slow on the way down or pauses at the bottom) to increase the crossover to your skiing.
NB. You should always seek supervision from a properly qualified strength and conditioning coach in order to safely get the most from your training.