Biomechanics

Study of Human Movement

The position our body is in affects balance and stability,

which result in improved performance

Centre of Gravity

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

Centre of gravity can lie inside / outside the body

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

CoG shifts higher if arms are raised

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

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

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

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

Line of gravity and base of support and physical activity

Line of gravity

Top of body moves towardsline of gravity

Direction of movement

Leg pushes againstground Base of support

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

Stability is improved through:

Widening the base of support

Stability is improved through:

Lowering the centre of gravity

Stability is improved through:

Keeping the line of gravity within the base of support

Stability and skill performance

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

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

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

Kicking Ball

1. Leg is bent allowing the leg to move faster2. Leg straightens, to allow maximum velocity and force to be applied to the ball.

Running speed and length of levers

1. Discuss the relative merits of long and short levers in a sprinter AND2. How a sprinter manipulates the length of levers to maximise force.

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

“Short people are stronger than tall people”

Identify two arguments in support of (pro) and against (con) this statement.Much of this comes down to what strength is – how short levers and long levers can be used to generate force for human movement.

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

Enjoy your Sport!