Unit 3 Notes Flashcards
Three principal types of internal force
Tensile
Compressive
Shear
Tensile Force
Pulling
Compressive
Squeezing
Shear
Sideways (pushing)
Direction of normal or axial stress
perpendicular to analysis plance
Direction of Shear Stress
parallel to analysis plane
Types of complex load
Bending and Torsion
Describe bending
one side experiences compression
one side experiences tension
Common bending injury
femoral neck fracture in elderly
Describe torsion
one end rotates clockwise
one end rotates counterclockwise
Symbol for Stress
𝞼
Unit of stress
N/m2 (pascal)
What does stress cause
deformation
what is deformation
change in shape
What is strain
a measure of deformation
a change in length
what is the symbol for strain
𝜺
Extensibility
ability to stretch without being damaged
Elasticity
ability to return to original shape after being stretched
Elastic Region
Further stress results in permanent deformation
Plastic region
yield point to failure point, permanent deformation returns to new length
Cortical bone
compact bone, outside
Cancellous bone
trabeular or spongy
inside
Factors that influence force production
Temperature
Structural Factors
Neural Factors
Mechanical Factors
Structural Factors
Fiber type
Muscle Architecture
PCSA (physiological cross sectional area)
Describe strap and fusiform musculotendinous unit
fibers run parallel to tendon, aligned with force
Describe unipennate musculotendinous unit
indirect force acting on tendon, not parallel
Neural Factors
Number of motor units
rate of action potentials
Motor Unit
Single motor neuron and all of the muscle fibers it innervates
Neural factors for increasing force output
- recruit more motor units
- increase rate of action potentials
Common method for measuring neural input
EMG (electromyography)
What can you see in EMG data?
Onset
Offset
Magnitude
Duration
EMG uses
Address Coordination
Asssess nerve conduction
Biofeedback
Predict Isometic muscle force
Mechanical Factors
Length
Activation History
Velocity
Stretch Shortening Cycle
Stretch immediately prior to a concentric muscle action
Eccentric-Concentric Coordination
What happens to muscle force at fast speeds
Fast shortening decreases force
Fast lengthening increases force
For a given muscle length which type of muscle action produces the highest force?
Eccentric
Where does peak power occur?
1/3rd 1RM
If muscle force is constant when is muscle torque maximized?
WHen the moment arm is maximized (longest distance)
