Body Balance and Stability Control Balance is a very important factor in athletic performance Generally depends upon the location of the centre of mass and how stable that centre of mass is

Equilibrium Static equilibrium System is at rest The state of a system that is not experiencing any change in its direction or speed Dynamic equilibrium n System is moving with constant velocity

Balance Process whereby the body’s state of equilibrium is controlled for a given purpose The base of support and location of the centre of mass is manipulated If the line of gravity passes through some part of the body’s base of support, the body will be balanced

Stability A measure of the difficulty with which equilibrium can be disturbed A net external force is required to overcome the static equilibrium of a sprint start There is a trade-off between maximizing stability and acquiring speed off a mark

To increase stability in static equilibrium Increase the base of support Increase the inertia of the body Decrease the vertical distance between the centre of mass and the base of support

To increase stability in dynamic equilibrium Enlarge the body’s base of support in the direction of the external horizontal forces Adopt a starting position in which the centre of pressure is close to the edge of the base of support whenever a quick acceleration is important When slowing down or reversing directions in running, lean backwards but keep normal frictional forces high to prevent slipping When tripping or falling, reflex movements may help to regain the loss of balance or to create a new base of support

Somersaulting – Angular Kinetics Angular kinetics is concerned with the generation of rotations and the control of these rotations All objects posses inertia and do not wish to begin rotating If an external moment of force is applied to the object, it will experience an angular acceleration

Off-centre External Forces Any external force that acts away from the body’s centre of mass will create a moment of force acting on the total body Usually, the off-centre force is a reaction force from the ground or equipment, resulting from the internal muscle forces generated by the athlete If an athlete has forward momentum and a pivot point is created, then some or all of the linear motion can be transferred into angular motion

Transfer of Momentum Within the Body Sometimes athletes accelerate specific body parts while in contact with the ground Upon leaving the ground, athletes lock these segments to the rest of their bodies The joint angles these segments make with the trunk become fixed The momentum created by these segments becomes part of the momentum of the total body

Rotations While Airborne Rotations cannot be generated when airborne Once the body is airborne, only gravity acts on the body The angular momentum (the amount of angular motion) is conserved Changes in body shape will decrease/increase the moment of inertia about the somersaulting axis If the moment of inertia increases, the athlete will have more reluctance to rotating and will have slower angular velocity

I ω I ωI ω A A B C BC The inverse relationship between moment of inertia (I) and angular velocity (ω)