BiomechanicsBiomechanics

Study of Human MovementStudy of Human Movement

The position our body is in The position our body is in affects affects balancebalance and stability, and stability,

which result in improved which result in improved performanceperformance

Centre of GravityCentre of Gravity

Centre of gravityCentre of gravity can be defined as “the can be defined as “the point at which all parts point at which all parts of the body are of the body are equally balanced”.equally balanced”.Because the Because the centre centre of massof mass is the point is the point of an object where all of an object where all parts are evenly parts are evenly balanced, it changes balanced, it changes depending upon what depending upon what position the body is in.position the body is in.

Centre of gravity can lie inside / Centre of gravity can lie inside / outside the bodyoutside the body

CoG lies around the navel in neutral CoG lies around the navel in neutral upright position with arms at sideupright position with arms at side

CoG shifts higher if arms are raisedCoG shifts higher if arms are raised

CoG can lie outside the body: E.g. in CoG can lie outside the body: E.g. in dive roll / tuck, pike, fosbury flopdive roll / tuck, pike, fosbury flop

Line of GravityLine of Gravity Line of gravityLine of gravity is the vertical line that is the vertical line that passes through the centre of gravity to the passes through the centre of gravity to the ground.ground.The line of gravity is important when The line of gravity is important when determining stability:determining stability:If the line of gravity falls If the line of gravity falls withinwithin the the object/person’s object/person’s base of supportbase of support the the object is relatively stable.object is relatively stable.If the line of gravity falls If the line of gravity falls outsideoutside the the object/person’s base of support….object/person’s base of support….

Base of SupportBase of SupportBase of supportBase of support is the is the area within an object or area within an object or person’s point of contact person’s point of contact with the ground.with the ground.

The larger / wider the base The larger / wider the base of support = more stableof support = more stableNarrow base of support = Narrow base of support = less stableless stable

Line of gravity and base of Line of gravity and base of support and physical activitysupport and physical activity

Line of gravity

Top of body moves towardsline of gravity

Direction of movement

Leg pushes againstground Base of support

StabilityStabilityStabilityStability is vital for all movements. is vital for all movements. Improved stability often allows skills Improved stability often allows skills to be executed more effectively.to be executed more effectively.Stability can be improved through Stability can be improved through increasing abdominal strength. This increasing abdominal strength. This improves body control and speed as improves body control and speed as a person is able to move their centre a person is able to move their centre of gravity in a direction more of gravity in a direction more effectively.effectively.

Stability is improved through:Stability is improved through:

Widening the Widening the base of supportbase of support

Stability is Stability is improved through:improved through:

Lowering the Lowering the centre of centre of gravitygravity

Stability is improved through:Stability is improved through:

Keeping the line of gravity Keeping the line of gravity within the base of supportwithin the base of support

Stability and skill performanceStability and skill performance

Players that can make Players that can make themselves more themselves more stable or control their stable or control their instability are able to instability are able to apply more force and apply more force and can complete skills can complete skills more successfully.more successfully.

LeversLevers The amount of leverage a person possesses is The amount of leverage a person possesses is dependent on the length of their body, in dependent on the length of their body, in particular the length of their arms and legs.particular the length of their arms and legs.Longer leversLonger levers result in greater speed at the end result in greater speed at the end of the lever arms – this is beneficial for throwing of the lever arms – this is beneficial for throwing and striking objects.and striking objects.Short leversShort levers can be moved with less force and can be moved with less force and at greater speeds – this is beneficial for moving at greater speeds – this is beneficial for moving body parts quickly and applying strength for body parts quickly and applying strength for pushing, pulling and lifting objects.pushing, pulling and lifting objects.

Levers in the human body can be Levers in the human body can be manipulated to improve speed and manipulated to improve speed and apply large forces at the same timeapply large forces at the same time

Kicking BallKicking Ball

1. Leg is bent allowing the leg to 1. Leg is bent allowing the leg to move fastermove faster

2. Leg straightens, to allow 2. Leg straightens, to allow maximum velocity and force to be maximum velocity and force to be applied to the ball.applied to the ball.

Running speed and length of leversRunning speed and length of levers

1. Discuss the relative merits of long 1. Discuss the relative merits of long and short levers in a sprinter ANDand short levers in a sprinter AND

2. How a sprinter manipulates the 2. How a sprinter manipulates the length of levers to maximise force.length of levers to maximise force.

When raising the leg off the ground, a sprinter When raising the leg off the ground, a sprinter bends the leg by flexing the knee, creating a bends the leg by flexing the knee, creating a short lever which allows them to quickly move the short lever which allows them to quickly move the leg into a tuck position underneath the hips. The leg into a tuck position underneath the hips. The knee is then extended outwards, so a large stride knee is then extended outwards, so a large stride can be taken, allowing the sprinter to cover a can be taken, allowing the sprinter to cover a large amount of horizontal distance before the leg large amount of horizontal distance before the leg presses against the ground carrying them presses against the ground carrying them forward. A long lever – when their leg pushes off forward. A long lever – when their leg pushes off the ground – allows a large amount of force to be the ground – allows a large amount of force to be imparted into the ground, allowing the sprinter to imparted into the ground, allowing the sprinter to move forward with greater speed.move forward with greater speed.

““Short people are stronger than Short people are stronger than tall people”tall people”

Identify two arguments in support of Identify two arguments in support of (pro) and against (con) this (pro) and against (con) this statement.statement.

Much of this comes down to what Much of this comes down to what strength is – how short levers and strength is – how short levers and long levers can be used to generate long levers can be used to generate force for human movement.force for human movement.

Short people have shorter levers because their Short people have shorter levers because their body segments (e.g. upper arms) are a shorter body segments (e.g. upper arms) are a shorter length, therefore they can apply more force with length, therefore they can apply more force with those levers – wrestlers and power lifters are those levers – wrestlers and power lifters are typically short and have well-built physiques. Tall typically short and have well-built physiques. Tall people could be stronger than short people when people could be stronger than short people when applying force at high speeds (such as swinging a applying force at high speeds (such as swinging a tennis racquet at a ball) – the end of their levers tennis racquet at a ball) – the end of their levers (such as their arms) is travelling at a greater (such as their arms) is travelling at a greater momentum and can therefore impart more speed momentum and can therefore impart more speed into the object being propelled.into the object being propelled.

Enjoy your Sport!Enjoy your Sport!