11PDHPE Preliminary Course

Core 2: Focus Question 3How do biomechanical principles

influence movement?

THE BIOMECHANICS OF MOVEMENT

Biomechanics is the science concerned with forces and the effect of these forces on and within the human body.

A knowledge of biomechanics helps us to:• choose the best technique to achieve our best performance with considerationto our body shape. For instance, an understanding of the biomechanical principles that affect athletic movements, such as the high jump, discus throw, golf swing and netball shot, improve the efficiency with which these movements are made. This improves how well we perform the skill.• reduce the risk of injury by improving the way we move• design and use equipment that contributes to improved performance.

MOTIONMotion is the movement of the body from one position to another

Some bodies are inanimate (non-living) such as basketballs, shot puts; whilst other bodies are animate (living) such as golfers, footballers.

Motion itself can be divided into 3 categories:•Linear•Angular•General

LINEAR MOTIONLinear motion takes place when a body and all parts connected to it travel the same distance in the same direction and at the same speed.

The easiest way to determine if a body is experiencing linear motion is to draw a line connecting two parts of the body; for example, the neck and hips. If the line remains in the same position when the body moves from one position to another, the motion is linear.

ANGULAR MOTIONAngular motion the motion of a body about a fixed point or fixed axis. Angular movement plays the dominant role because most of an athlete’s movements result from the swinging, turning action of the athlete’s limbs as they rotate around the joints.

Many terms are used to refer to angular motion. Movements include rotating, spinning, swinging, circling, turning, rolling, pirouetting, somersaulting and twisting. All of these terms indicate that an object or an athlete is turning through an angle, or number of degrees. In sports such as gymnastics, skateboarding, basketball, diving, figure skating, and ballet, the movements used by athletes include quarter turns (90 degrees); half turns (180 degrees); and full turns, or “revs” (revolutions), which are multiples of 360 degrees

GENERAL MOTIONGeneral motion a mix of linear and angular, which we simply call general motion. In sport, a mix of linear and angular movement is most common.

Even those sport skills that require an athlete to hold a set position involve various amounts of linear and angular motion. For example, a gymnast balancing on a beam. In maintaining balance on the beam, the gymnast still moves, however slightly. This movement may contain some linear motion but will be made up primarily of angular motion occurring around the axes of the gymnast’s joints and where the gymnast’s feet contact the beam. Perhaps the most visible combination of angular and linear motion occurs in a wheelchair race. The swinging, repetitive angular motion of the athlete’s arms rotates the wheels. The motion of the wheels carries both the athlete and the chair along the track. Down the straightaway, the athlete and chair can be moving in a linear fashion. At the same time the wheels and the athlete’s arms exhibit angular motion

;

Improving performance in activities that encompass linear motion usually focuses on modifying or eliminating technique faults that contribute to any non-linear movements.

Excessive up and down, rotational and lateral movements are examples of faults that erode performance directed towards achieving the shortest, most efficient pathway. Swimmers who use an irregular arm pull that results in a zigzag movement pattern

along the pool surface are examples of poor application of linear motion.

For swimmers, excessive movement increases drag which slows down a swimmer.But what is drag and how does a swimmer eliminate it to enhance their swimming?

MOTION

ENHANCING MOTIONHow motion is classified depends on the path followed by the moving object.We will focus on linear motion in a range of sporting activities and apply the

principle to enhancing performance.

VELOCITYVelocity is equal to displacement divided by time.

Displacement is the movement of a body from one location to another in a particulardirection, or an ‘as the crow flies’ measurement.

Velocity is used for calculations where the object or person does not move ina straight line. An example is a runner in a cross-country race. Activities toimprove speed may also relate to velocity. Improving the velocity of implementssuch as javelins or arrows requires specialised training, as does improving theperformance of athletes in non-linear events such as marathons.

SPEEDSpeed is equal to the distance covered divided by the time taken to cover distance

So, if a runner runs 100m in 12 secs

Speed is important in most sports and team games. The player who canmove quickly has a distinct advantage in games such as touch football, rugbyand soccer because not only is that player difficult to catch, but he/she can usetheir speed to gather opponents quickly in defence.

Much of our potential for speed is genetic and relates to the type of musclefibre in our bodies. However, individuals can develop their speed as a result oftraining and technique improvements, the basis of which is the developmentof power and efficiency of movement.

MOMENTUMMomentum the quantity of motion the body possesses

Mass refers to the amount of matter in a body

The application of the principle of momentum is most significant in impactor collision situations. The principle can be applied to certain sporting games such as rugby league and rugby union, where collisions in the form of tackles are part of the game. However, collisions between players in sporting events tend to exhibit different characteristics to that of objects due to a range of factors, including:•the mass differences of the players — in most sports, we do not see the huge variations in mass that we find between cars, bicycles and similar objects• elasticity — the soft tissue of the body, which includes muscle, tendons andligaments, absorbs much of the impact. It acts as a cushion.• evasive skills of players which often result in the collision not being ‘head-on’.In some cases there may be some entanglement just prior to collision, suchas a palm-off or fend. This lessens the force of impact.

The momentum described in the previous situation is called linear momentum because the object or person is moving in a straight line.

MOMENTUMThere are numerous instances in sport where bodies generate momentum butthey do not travel in a straight line; for example, a diver performing a somersaultwith a full twist, football kick, discus throw and golfswing. In each of these cases, the body, part of it, or an attachment to it such asa golf club or tennis racquet, is rotating. We call this angular momentum.

Angular momentum is the quantity of angular motion in a body or part of a body

Angular momentum is affected by:• angular velocity For example, the distance we can hit a golf ball is determinedby the speed at which we can move the club head.• the mass of the object. The greater the mass of the object, the more effort weneed to make to increase the angular velocity. It is relatively easy to swinga small object such as a whistle on the end of a cord. Imagine the effort thatwould be needed to swing a shot-put on a cord.• the location of the mass in respect to the axis of rotation. With most sport equipment, the centre of mass is located at a point where the player is able to havecontrol and impart considerable speed. Take baseball bats and golf clubs forexample. Here, the centre of mass is well down the shaft on both pieces ofequipment. This location enables the player to deliver force by combiningthe mass of the implement at speed in a controlled manner, thereby maximising distance.

REVISION