1. Kinetics:
def. describes the effect of forces on the body (applies to musculoskeletal system)
-force: consider as a push or pull that produce: arrest, or modify movement.
Newton’s second law: F = ma
Force is directly proportional to the acceleration of the mass
(SIU) of force is (Newton)
(N): 1 N = 1 kg × 1 m/sec2

2. Musculoskeletal Forces:
Forces (loads) that:
move,
fixate, or
stabilize the body also have the potential to deform & injure the body.
Healthy tissues resist changes structure & shape
-Tissue weakened by:
Disease,
Trauma, or
Prolonged disuse

3. The manner forces (loads) applied on musculoskeletal

4. The ability of periarticular connective tissues to accept and disperse loads is an important topic of research within:
Physical rehabilitation,
Manual therapy, and
Orthopedic medicine.
Clinicians & scientists are very interested in how variables such as aging, trauma, altered activity or weight bearing levels, or prolonged immobilization affect: the load-accepting functions of periarticular connective tissues.

5. The stress-strain curve

6. The stress-strain curve:
-Vertical (Y) stress : the internal resistance generated as the ligament resists deformation, divided by its cross sectional area. (The units of stress are similar to pressure: N/mm2.)
-Horizontal(X) strain : percentage change in a tissue’s length relative to original (preexperimental length).
-Stiffness (Young’s modulus): The ratio of the stress (Y) caused by an applied strain (X) in All connective tissues measure (stress/strain)

7. The stress-strain curve:
Tightness: abnormal pathologic condition of high stiffness.
Elastic region :The initial nonlinear region that followed by subsequent linear region.
Strained tissue within Elastic zone returns to original length (shape) once the deforming force is removed.
Elastic deformation energy :The area under the curve. Most of the energy used to deform the tissue is released when force is removed

8. Yield point : elongated the tissue beyond its physiologic range
Yield point : elongated the tissue beyond its physiologic range. At this point, increased strain results in only marginal increased stress (tension).
Plasticity :physical behavior of overstretched (over compressed) tissue.
Plastic deformation :overstrained tissue; at this point microscopic failure has occurred & the tissue remains permanently deformed.
Plastic deformation energy : (Unlike elastic energy) not recoverable in its entirety even when the deforming force is removed.

9. The stress-strain curve:
ultimate failure point when the tissue:
1-partially or completely separates &
2-loses its ability to hold any level of tension.
Viscoelastic :the physical properties of tissues associated with the stress-strain curve change as a function of time are considered.
Creeping :progressive strain of a material when exposed to a constant load over time.
force is removed

10. Time dependent property of creep

11. The stress-strain curve in summary:
-Similar building materials as steel, concrete, & fiberglass, periarticular connective tissues within human body possess unique physical (material) properties when loaded or strained.
-Although data from research provide insight into many aspects of patient care, including: 1- Understanding mechanisms of injury,
2-Improving design of orthopedic surgery,
3-Judging effectiveness of certain physical therapy forms, as prolonged stretching or use of heat to induce greater tissue extensibility.

12. Internal & External Forces:
-Internal forces :structures within body. These forces may be (active) or (passive).
-(Active force) generate by stimulate muscle but not necessarily under volitional control. Muscles typically largest of all internal forces.
-(Passive forces) in contrast, generated by tension in stretched tissues including: intramuscular connective tissues, ligaments, & joint capsules.

13. Internal & External Forces:
-External forces : forces from outside body. -These forces usually originate from either:
1-Gravity
2-External load,
3-Physical contact, as applied by a therapist against the limb of a patient.
-Vector :physical quantity that is completely specified by its magnitude and its direction.
-mass & speed are scalars not vectors.
-Scalar quantity that is completely specified by its magnitude & No direction.

14. opposing pair of internal and external forces: Internal force (muscle) pulling the forearm & External (gravitational) force pulling on the center of mass of the forearm.

15. Internal & External Forces:
-In order to: completely describe vector in biomechanical analysis it must be known
Magnitude
Spatial orientation(Angle of pull)
Direction
Point of application
1-The Magnitude
force vectors indicated by length of the arrow.

16. 2. The Spatial orientation :
-indicated by length the position of the shaft of arrows.
Force oriented: vertically often referred as the Y axis.
The orientation also described by the angle between the shaft of the arrow & a reference coordinate system.

17. 3- The Direction : -indicated by the arrow head.
-Internal force acts upward, typically described in a positive Y
-External force acts downward in a negative Y.
-Direction & Spatial orientation of a muscle force & gravity are referred to line of force & line of gravity.

18. 4-The point of application :
base of vector arrow contacts part of body.
The point of application of the muscle force is where the muscle inserts into the bone.
Angle-of-insertion :between tendon of muscle & long axis of the bone on insertion. changes as the joint move.
The point of application of the external force depends on whether the force is result of:
1-gravity resistance (physical contact). Gravity acts on center of mass of body segment. Resistance occur anywhere on body