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

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

The manner forces (loads) applied on musculoskeletal

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.

The stress-strain curve

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)

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

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.

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

Time dependent property of creep

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.

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.

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.

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.

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.

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.

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.

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 2-resistance (physical contact). Gravity acts on center of mass of body segment. Resistance occur anywhere on body