Torque is a vector quantity that measures the capacity of an applied force to produce rotation in a rigid body around a specific point or axis. In other words, it is the force applied to a lever to generate rotation.
While turning the skis, Torque is “felt” at the hips because the femurs connect these two points. It can be envisioned as follows:
- The hips are the motors that turn a key.
- The femurs are the body of the key (the lever).
- The feet/skis are the tip of the key that fits into the lock (the snow).
It is essential to include the skier’s anthropometry here, as the length of the femurs define each individual’s natural mechanical advantage. In biomechanics, the femurs act as a third-class lever. Force is applied near the joints (hip muscles) to move a long arm (the bones) that terminates at the skis.
Torque in Skidding vs. Carving
Torque is applied in both scenarios, but its biomechanical function changes radically depending on the type of turn. For the purpose of this article, it is crucial to distinguish between Rotational Torque (skidding) and Maintenance Torque (carving).
- In Skidded Turns (Active Steering Action): in this case, the torque is dynamic and rotational.
- Function: hip rotator muscles generate torque to rotate the femur about its longitudinal axis.
- Result: the ski “pivots” to change direction.
- Physic context: this is an application of torque to overcome the static friction of the snow and force lateral displacement (sliding).
- In Carved Turns (Supporting Action): here, the torque is static or resistive (defined as Critical Maintenance Torque or CMT).
- Function: although the ski does not “pivot” (as it follows its natural sidecut radius), there is a massive lateral torque attempting to “open” the legs or “flatten” the ski against the snow.
- Edging Torque: to maintain the ski on its edge at angles of 30° or 45°, the adductors and abductors muscles must generate torque that counteracts centrifugal force.
- Physic context: in carving, torque is not used to “turn” the ski, but rather to sustain the inclination angle against snow pressure. If this hip torque is released, the ski loses its edge grip and begins to skid.
Comparative Summary:
- Skidding: torque to change the ski’s orientation (rotational force).
- Carving: torque to maintain the integrity of the ski’s angle (edging/stabilization force).
Without hip torque, a carved turn would “collapse” under our weight due to the immense pressure returned by the snow during the steering phase. “Collapse”, in biomechanics, refers to the structural failure of the kinetic chain (ankle-knee-hip). If the muscles fail to generate enough torque, the joints buckle—typically the knee moving into a functional valgus position or the hip dropping—causing the ski to flatten and lose its edge grip.
We should take into account that our weight encompasses more than just static body mass; it includes the effective weight generated by velocity and inclination (G-forces) during the arc.This statement justifies the necessity of hip-centric strength training (adductors and glutes). Without internal torque, the “wall” of snow is strong enough to physically straighten our legs or force the system into a fall.
Torques vs Forces
Why talk about “Torques” and not just “Forces”? This is a fundamental technical distinction: forces displace us, but torques (or moments) make us rotate or lean. In skiing, the balance point is our edges on the snow. Imagine our body is a lever anchored at that point:
- Force is the push or pull (e.g., gravity pulling our center of mass downward).
- Torque is the turning effect produced by that force because it is applied at a distance from the ground (our height).
If we only talked about forces, we would be analyzing whether we “fly away” or sink. By talking about torques, we are analyzing why we can maintain a specific lean angle without collapsing.
An explanation from a physics perspective:
- Rotation vs. Translation: ‘Forces’ explain why we move in a straight line. ‘Torque’ (or moment of force) explains why we rotate or tilt relative to a point (in this case, our center of mass).
- Balance in the turn: when skiing, we don’t just move forward; our body leans to compensate for different forces. “Torque” measures the tendency of those forces (gravity, centrifugal force, snow reaction) to make us “fall” toward the inside or outside of the turn.
- Multiple torques, one axis: if we used “forces,” we would only be talking about pushes and pulls, but by using “torque,” we are referring to the lever effect that each of those forces exerts on our body.
While Torques and Forces are related, they explain different aspects of our skiing stability:
- Forces explain “Where the we go” (Translation), determining our path and acceleration. If we only analyze forces, we are looking at ourselves as a single point moving through space.
- Torque explains “If we tip over” (Rotation), as it is the “turning effect” of those forces around a specific point (like the skis on the snow).
- Gravity Torque wants to pull us “down” toward the inside of the turn.
- Centrifugal Torque wants to pull us “up” toward the outside of the turn.
Why the distinction matters?
- We can have balanced forces (moving in a steady arc) but unbalanced torques (leaning too far in and falling).
- To “carve” successfully, we must use our muscles to create an internal torque that counters the external torques from gravity and the snow.
Conclusion: using just “forces” would ignore the rotational balance and the lever arms required to stay upright while leaning.
