Principles of Biomechanics

Motion We define motion as the action or process of change in position. Movement is a change in position from one point to another. Two things are necessary for motion to occur Space (space to move in) Time (time during which to move)

Motion Two Types of Motion Linear: motion in a straight line. Force generated by athletes muscles. Ex. Sprinter running down track. Rotational: movement about an axis Force is off centre resulting in rotation Body or body part spins around an axis. Ex. Ice skater in spin.

Principles of Biomechanics Seven principles are grouped into four categories: Stability Maximum Effort Linear Motion Angular Motion

Principles of Biomechanics Stability The ability to maintain one’s balance is crucial in sport. Principle #1 The lower the centre of mass, the larger the base of support, the closer the centre of mass to the base of support, the greater the mass, the more stability increases.

Principles of Biomechanics Centre of mass point at which a person or object’s mass is concentrated. Line of gravity vertical line passing down through centre of mass to ground Base of support area between the supporting limbs.

Principles of Biomechanics Maximum Effort Principle #2 The production of maximum force requires the use of all the joints that can be used. Athletes should perform slower, controlled movements and high intensity. Body segments usually move at the same time.

Principles of Biomechanics The more joints used in a movement the more muscles contracting = more force exerted. Football kickers (soccer style) use one more joint movement (hip rotation) to provide greater force.

Principles of Biomechanics Slapshot in hockey – involves the legs, shoulders, arms and stick. Leaving out one joint would reduce the shot’s force.

Principles of Biomechanics The production of maximum velocity requires the use of joints in order – from largest to smallest. Larger, slower joints start the movement and faster joints contribute once the preceding joint reaches peak speed. The aim is to reach maximum velocity of movement at impact or release.

Principles of Biomechanics Maximum velocity can be achieved by combining the speed of previous movements and transferring this speed to the final segment or implement – hand, foot, stick etc. used to propel another object.

Principles of Biomechanics Examples Basketball jump shot large leg muscles begin motion then other joints in sequence pelvis, trunk, shoulder, elbow, wrist and fingers on follow through. The speed at the end of a body segment or implement is directly proportional to the implements length. Golfer use longer club to hit ball farther

Principles of Biomechanics Momentum is amount of motion an athlete or object has developed. Linear momentum is amount of momentum developed in a straight line. Impulse: the application of force over a period of time that results in a change in the amount of momentum an athlete or object has.

Principles of Biomechanics Joint range of motion is amount of movement at a joint. Streamlining: is minimizing the surface area of an object in the direction of motion and making this surface as smooth as possible so that the flow of water or air past the object is smooth

Principles of Biomechanics The greater the applied impulse, the greater the increase in velocity. If a skill requires maximal application of force, the joint should be moved through a larger range of motion. Force is applied for longer and impulse is greater. Ex. Player jumping the highest is one who bends their knees the deepest. leg strength

Principles of Biomechanics Often occurs in reverse – absorption in catching or controlling a puck or ball. Momentum is dissipated over time or distance through absorption Prevents injuries as well Landing. Ex. Catching a ball, move hands inwards to increase time force is applied.

Principles of Biomechanics Movement usually occurs in the direction opposite that of the applied force. Newton’s 3rd Law every action has an equal and opposite reaction. When an athlete pushes against any playing surface or piece of equipment. When the athlete exerts a force the surface (water, ground ice) pushes back with the same force and in the opposite direction. Spearing Injuries

Principles of Biomechanics Some forces operate in directions opposite that of movement. Air and water resistance are important factors in many sports. Skiing, speed skating, swimming, cycling

Principles of Biomechanics Counter by streamlining. Change body position to decrease air resistance speed skater Swimmers full body swimsuit streamline body position for skiers cyclist helmet position

Principles of Biomechanics Angular Motion Angular motion plays a key part in all sport. Circular motion that occurs around an imaginary line called the axis or rotation. Moment of force or torque.

Principles of Biomechanics Angular motion is produced by the application of a force acting at some distance from an axis, that is, a torque. Athletes are concerned about Three kinds of torque rotations of entire body off centre force rotation of individual body segments muscles produce torque rotation of projectiles impart spin.

Principles of Biomechanics Injuries from torque - pitcher shoulder Opponent imparts torque off centre force to knock athlete off balance. E.g. tackle, check Sumo vs Rampage

Principles of Biomechanics Angular momentum is constant when an athlete or object is free in the air. Once airborne an athlete will travel with a constant angular momentum Ex. Diver rotates in air, momentum constant while in air. Can change rate of rotation by repositioning limbs or trunk. Hangtime