Biomechanics Year 11 Physical Education

Learning Intentions At the completion of this task you should be able to demonstrate knowledge of the following biomechanical principles:  Balance and stability  Summation of force  Leverage  Projectile Motion or Momentum At the completion of this task you should be able to demonstrate knowledge of the following biomechanical principles:  Balance and stability  Summation of force  Leverage  Projectile Motion or Momentum

An introduction to Biomechanics Biomechanics:  ‘The study of how the physical laws of mechanics apply to the human body’  It is the science concerned with the internal and external forces acting on the human body and the effects produced by these forces. Biomechanics:  ‘The study of how the physical laws of mechanics apply to the human body’  It is the science concerned with the internal and external forces acting on the human body and the effects produced by these forces. Kinesiology:  It is the organization of information dealing with motion or it is the study of movement.  Kinesis = Movement.  Ology. = Science

Purpose of studying biomechanics  To learn how to analyze the movement of the human body and to discover the underlying principles.  To improve human performance.  To prevent occurrence of injury during performance.  To evaluate posture exercises based on individual needs and the efficient methods of using the body in daily living  To learn how to analyze the movement of the human body and to discover the underlying principles.  To improve human performance.  To prevent occurrence of injury during performance.  To evaluate posture exercises based on individual needs and the efficient methods of using the body in daily living

 It allows a skill to be broken down into sub skills

 Biomechanists analyse an athletes performance. This enables them to model ideal performances and determine where possible problems in technique are occurring. This information is then used by the athlete and coach to ensure that the techniques used are the best available.

 Melinda Gainsford Taylor- Top Australian Sprinter (Gold in 200m)  Spent many hours having her sprint start analysed and compared with other top sprinters. This helped her learn to gain better extension of the lead leg during take-off and achieved significant greater speed out of the blocks

Why learn about Biomechanics

AREAS OF STUDY, RESEARCH AND PRACTICE  Sport and Exercise Science  Coaching  Ergonomics  Equipment Design  Gait & Locomotion  Orthopedics - Rehabilitation -Physiotherapy, Occupational Therapy  Prosthetics and Orthotics  Motor Control  Computer Simulation  Sport and Exercise Science  Coaching  Ergonomics  Equipment Design  Gait & Locomotion  Orthopedics - Rehabilitation -Physiotherapy, Occupational Therapy  Prosthetics and Orthotics  Motor Control  Computer Simulation

Biomechanical Principles  Coaches aim to assist their athletes to improve their sporting competency and so achieve their performance goals. As a contribution to achieving these outcomes, coaches require sport specific knowledge and an understanding of biomechanical principles relevant to sports performance.

Balance and Stability Balance: ‘Balance is a person’s ability to control their equilibrium in relation to gravity only.’ Equilibrium: ‘a state of physical balance (objects are at rest)’. – that is, all the forces acting on them are balanced Balance: ‘Balance is a person’s ability to control their equilibrium in relation to gravity only.’ Equilibrium: ‘a state of physical balance (objects are at rest)’. – that is, all the forces acting on them are balanced Stability: Stability is your ability to “return to a desired position”.

Equilibrium  Static Equilibrium When the whole body is stationary- e.g. a gymnast holding a handstand  Static Equilibrium When the whole body is stationary- e.g. a gymnast holding a handstand  Dynamic Equilibrium The body remains balanced during movement- e.g. when running your body is constantly ‘balancing’ and ‘rebalancing’.

Centre of Gravity (COG)  The centre of gravity is the point at which gravity appears to be acting upon an object, this is for the most part the same as the point around which the mass of an object or person is equally distributed in all directions.  For the average human, the centre of gravity is at the centre of the pelvis when they are standing in the anatomical position. The centre of gravity shifts slightly upwards for males due to their larger shoulder mass, but centre of gravity is always athlete specific. This means that an athlete with larger legs will have a lower centre of gravity unless their upper body is also large and balances the mass.  The centre of gravity is the point at which gravity appears to be acting upon an object, this is for the most part the same as the point around which the mass of an object or person is equally distributed in all directions.  For the average human, the centre of gravity is at the centre of the pelvis when they are standing in the anatomical position. The centre of gravity shifts slightly upwards for males due to their larger shoulder mass, but centre of gravity is always athlete specific. This means that an athlete with larger legs will have a lower centre of gravity unless their upper body is also large and balances the mass.

Comparing the COG for male, female and child.

COG The centre of gravity moves according to the athlete’s body position. For example, in the runner in the image his centre of gravity is in the lower region of the pelvis and in front of his body, because his upper body is leaning forwards. Having the centre of gravity lower and in front of his lower body is advantageous for acceleration.

Centre of mass refers to the point where the entire weight of an object is concentrated – the theoretical point through which gravity acts on the object. The centre of gravity (COG) in the anatomical position, while running upright, and while completing a kick in martial arts (left to right)

COG The COG in 2 gymnastics poses. Notice that the one on the left is outside of the body.

The COG has moved outside of the body in this gymnastics pose because the legs have been pointed forward

The Fosbury Flop, frequently used in high- jump allows the jumper to go over a higher bar, because they do not need their COG to go as high as other techniques.

Lowering your COG Lowering your centre of gravity also helps to increase stability because it needs to be lifted higher before it moves outside of the base of support. This becomes very useful in combat sports such a jujitsu or sumo wrestling. It is also used by blockers in the NFL or to create a more effective rugby league tackle. The NFL blocker lowers his COG in order to increase his stability and remain upright while blocking the sacker

 Lowering the centre of gravity increases balance and stability in sport. This is why you can change direction faster by bending your legs and getting lower to the ground. It increases your stability, allowing you to adjust to greater force production by the legs.

Line of Gravity (LOG) The line of gravity is an imaginary vertical line from the centre of gravity to the ground or surface the object or person is on. It is the direction that gravity is acting upon the person or object. In the image you can see the line of gravity in red going down to the ground from the centre of gravity, indicating the force of gravity upon the sprinter.

Line of Gravity (LOG)  The location of this line in relation to the base of support has a huge influence on balance and stability. In the anatomical position (right) the line of gravity is between the legs and feet right under the person. The line of gravity (LOG) is a vertical line from the centre of gravity to the ground/surface the athlete is on.

 The closer the line of gravity is to the centre of the base of support the better balanced a person is in this position. If the line of gravity fall outside of the base of support the person must provide corrective muscle action, usually movement otherwise they will fall.  This is why the sprinter’s line of gravity is in front of his base of support (back foot on the ground) because it must be there in order for him to be stable and move forwards. If the line is in his base of support and he starts running, he will fall backward, unless he moves the line to in front of him.  The closer the line of gravity is to the centre of the base of support the better balanced a person is in this position. If the line of gravity fall outside of the base of support the person must provide corrective muscle action, usually movement otherwise they will fall.  This is why the sprinter’s line of gravity is in front of his base of support (back foot on the ground) because it must be there in order for him to be stable and move forwards. If the line is in his base of support and he starts running, he will fall backward, unless he moves the line to in front of him.

LOG  Since a lower centre of gravity means better balance and stability, a shorter line of gravity between the centre of gravity and the ground also means better balance and stability. So rugby player dodging through the defence will shift her line of gravity outside of her base of support in various directions as she changes direction and will also lower her centre of gravity. The LOG falls outside the base of support and will be to the side and in front of the player in order to allow her to continue to accelerate forward and to her left (our right).

Base of Support (BOS)  The base of support is the area around the outside edge of the sections of your body in contact with the ground/surface. Below you can see these areas shaded in various body positions.

Standing with feet close together provides a smaller base of support (BOS)

BOS whilst walking. This is a larger BOS than standing with feet together.

BOS increases as the distance between the feet increases.

 The larger the base of support the more stable the person/athlete is able to be. When an athlete is anticipating contact from an external player, they will naturually widen their base of support IN THE DIRECTION OF FORCE (or impeding force). What that means is that if you are about to have a forward run into you, you don’t abduct at the hips and widen your support, as this will not help you. Instead, you stagger your feet front to back in order to increase your stability. That is you would place your feet like the middle image above.

 However, widening your base of support also makes you less mobile. In order to increase mobility and improve acceleration you need to reduce your base of support. For example, the rugby player who is weaving through her opponents has a small base of support, to make her more agile, but she is also less stable. Smaller BOS allows the athlete to accelerate faster and be more mobile.

The hand making contact with the ground increases the BOS When there are big changes in direction, stability is often increased by adding contact points. Whether this be having 2 feet on the ground to step an opponent or ………

…..putting a hand on the surface of a wave when turning. Often the hand in surfing provides limited support, as the water does not provide the same stability as the ground, but it does increase your stability.

The BOS is only at the rear foot as the front foot is off the ground. This requires faster acceleration in order to avoid falling over. When is comes to movement the athlete seeks to keep their line of gravity outside of their base of support in order to create acceleration and continued movement. As with our sprinter who puts his line of gravity in front of his base of support in order to allow stability in movement. However, the further the distance from the base of support, the greater acceleration is required to maintain stability. Once a set velocity is reached, often the line of gravity is brought back closer to the base of support, as the body becomes more upright in order to maintain the velocity with both balance and stability.

Therefore equilibrium (balance control relies on:  The location of the centre of gravity – the lower of centre of gravity, the more stable the object is.  The size of the base of support – Wider = more stable  The location of the centre of gravity in relation to the base of support – an object is more stable when its COG is located above its base of support In other words, stability is related to a body’s centre of mass, line or centre of gravity and its base of support.  The location of the centre of gravity – the lower of centre of gravity, the more stable the object is.  The size of the base of support – Wider = more stable  The location of the centre of gravity in relation to the base of support – an object is more stable when its COG is located above its base of support In other words, stability is related to a body’s centre of mass, line or centre of gravity and its base of support.

Factors that affect the degree of stability of an object The location of the centre of gravity in relation to its base of support The area of the base of support The body’s mass or weight The height of the centre of gravity Factors that affect the degree of stability of an object

Applying this to sport Using the concept pf stability/equilibrium, has he made an effective tackle? Could he be even more effective? Conversely what has the ball carrier done wrong?