Last Updated24 May 2023

This chapter provides background information on the biomechanics most relevant to skiing. It outlines how the muscles and skeleton function as a system to create the movements of skiing by: describing the planes of movement and how these apply to skiing; describing the key bones, joints and muscles used in skiing; and describing how the body moves as this applies to skiing.

Joints

Joints are the place where two bones meet. All bones, except for the hyoid bone in the neck, form a joint with another bone. Joints hold the bones together and allow the rigid skeleton to move.

Types of Joints Relevant to Skiing

As stated above, some joints can move in one plane of movement while others can move in all three. The range of movement of a joint is the distance it is capable of moving along the direction of its plane(s) of movement.

Ball-and-socket joints – These joints have a wider range of movement than other joints, permitting movements in all planes, as well as rotational movement around a central axis. Ball and socket joints consist of a bone with a slightly egg-shaped head that articulates within the cup-shaped cavity of another bone. The hip and shoulder are ball-and-socket joints.

Gliding joints – These joints allow sliding or back-and-forth motion and twisting movements. The articulating surfaces are nearly flat or slightly curved. Most of the joints within the wrist and ankle, as well as those between adjacent vertebrae, are gliding joints.

Hinge joints – These joints flex and extend in a single plane. The convex surface of one bone fits into the concave surface of another. Such a joint resembles the hinge of a door in that it permits movement in one plane only. The elbow is a hinge joint, while the knee is a modified hinge joint as it glides and also allows a minimal amount of rotation.

Types of Joint Movement

The joints move in specific ways within their planes of movement

Flexion – bending body parts at a joint so that the angle between them decreases and the parts come closer together (bending the leg at the knee). Increasing angle with the frontal plane.

Extension – straightening body parts at a joint so that the angle between them increases and the parts move farther apart (straightening the leg at the knee). Decreasing angle with the frontal plane.

Abduction – moving a body part away from the midline (lifting the leg away from the body to form an angle with the side of the body). Moving away from the sagittal plane.

Adduction – moving a body part toward the midline (returning the leg from being away from the body to align with the body). Moving toward the sagittal plane.

Rotation – moving a body part around an axis of a bone, this movement occurs in the axial or rotational plane such as twisting the head from side to side, turning the femur in the hip socket. Medial or internal rotation involves movement toward the midline (inward), whereas lateral or external rotation involves movement in the opposite direction, away from the midline (outward).

Circumduction – moving a limb in a circular manner, this requires a combination of flexion, extension, abduction and adduction. The ball-and-socket joints of the hip and the shoulder are two of only a few joints that are capable of circumduction.

The Ankle Joint & The Foot

The ankle joint (in conjunction with the subtalar joint) joins the two bones of the lower leg (tibia and fibula) to the talus bone of the foot. These are the most used joints for balance in the body.

The ankle is a hinge joint which, in conjunction with the muscles and tendons, moves the foot down away from the shin (plantar flexion), and up toward the shin (dorsiflexion). When the lower leg is moved onto the boot tongue while skiing the ankle movement is dorsiflexion.

Ankle tension is important for maintaining the flexed position that allows a skier to make subtle, efficient, fore/aft, vertical and lateral movement adjustments.

The rest of the movements of the ankle and foot – twisting, tipping and side-to-side motion – occur in the complex system of bones in the foot and mostly at the subtalar joint.

The subtalar joint in the foot is a gliding joint below the ankle joint, between the talus and the calcaneus bones. The subtalar joint allows for both lateral and rotational motion in the foot. This motion is also coupled. This means that when rotation of the foot occurs, lateral movement will also occur and when lateral movement occurs, rotation will also occur. Utilising this joint is essential for rotational and lateral balance. Without using this joint in skiing, holding an edge on hard snow becomes impossible.

The midtarsal joint in the foot is a gliding joint crossing the foot between the talus and calcaneus bones and the bones of the midfoot. It allows minimal amounts of adduction (movement toward the midline of the body) and abduction (movement away from the midline of the body) of the foot.

Pronation and supination are terms commonly used in reference to the position of the foot. Both occur when the foot is weighted.

These are both natural movements of the foot that occur during foot landing while running or walking. Pronation is a movement that consists of ankle dorsiflexion combined with subtalar eversion (lateral movement) and forefoot abduction (rotation inwards) of the foot (big toe side rotates down).

Supination is a movement that consists of ankle plantar flexion combined with inversion (lateral movement) and adduction (rotation inwards) of the foot (little toe side rotates down).

Eversion – involves movement of the sole of the foot away from the median plane. The foot rolls inward. For example, the lateral movements to tip the outside ski in a turn onto its inside edge.

Inversion – involves movement of the sole of the foot toward the median plane. The foot rolls outward. For example, the lateral movements to tip the inside ski in a turn onto its outside edge.

These foot and ankle movements are at the beginning of the kinetic chain in accurate edging movements and are therefore critical to accurate skiing but they are restricted by the ski boot, and can be affected by a footbed. Fine edge control movements begin in the ankles and ankle tension is essential to make the skis hold. Active engagement of the ankle muscles is important for changing edges, increasing and decreasing edge angle and therefore managing ski performance during the phases of any turn.

pronation-and-supination-inversion-and-eversion

The Knee Joint

The knee joint is a modified hinge joint and as the largest joint of the body it supports nearly all of the body’s weight. It connects the femur to the tibia and the patella (knee cap) and as a hinge joint the knee joint allows the leg to flex and extend.

Although the knee is primarily a hinge joint, rotation can occur when the knee starts to flex. The range of rotation increases as the knee flexes toward 90 degrees, with a maximum 10–15 degrees internal and 30–40 degrees external rotation. Knee flexion combines with rotation of the femur to incline the lower leg and aid angulation.

The Hip Joint

The hip joint is a ball-and-socket joint made up of the side (socket) of the pelvis and the head (ball) of the femur. The femur moves at the hip joint in all three planes. Technically the femur rotates, abducts, adducts, flexes and extends at the hip joint.

The hip joint’s range of movement plays a vital role in skiing. It allows the legs to rotate and turn the skis (rotational movement). It allows the legs to flex and extend (fore/aft movement and pressure management). It also allows the legs to move sideways, relative to the pelvis, whether by moving the leg(s) out to the side or by moving the pelvis sideways, relative to the feet (lateral movement – edging).

The Spinal Column

The vertebral column regions have varying ranges of movement of flexion, extension, lateral flexion and rotation as described in The Spine.