Body Balance and Stability Control Balance is a very important factor in athletic performance...
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Transcript of Body Balance and Stability Control Balance is a very important factor in athletic performance...
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
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 ω I ω
A
A
B C
B C
The inverse relationship between moment of inertia (I) and angular velocity (ω)