KINETIC PRINCIPLES OF MUSCLE CONTRACTION.pdf

KINETIC PRINCIPLES OF MUSCLE CONTRACTION Biomechanics  REMINDER: KINETICS Is a branch of the study of mechanics that describes the effect of forces on the body. Forces or loads that move, fixate, or otherwise stabilize the body also have the potential to deform and injure...

KINETIC PRINCIPLES OF MUSCLE CONTRACTION Biomechanics  REMINDER: KINETICS Is a branch of the study of mechanics that describes the effect of forces on the body. Forces or loads that move, fixate, or otherwise stabilize the body also have the potential to deform and injure the body. 2  KINETICS Internal forces from structures External forces: produced by located within the body: forces acting from outside the Active: generated by stimulated body. These forces usually muscle, generally but not originate from either gravity pulling necessarily under volitional control on the mass of a body segment or Passive: generated by tension in an external load stretched periarticular connective tissues. 3  REMINDER: FORCES Each force is depicted by an arrow that represents a vector (a vector is a quantity that is completely specified by its magnitude and its direction): Magnitude Spatial orientation Direction Point of application 4  REMINDER: TORQUE Forces exerted on the body: Traslate a body segment (Linear) Applied at some distance perpenticular to the axis of rotation (Joints) Moment arm: distance between axis of roation and the forcé Torque: the product of a force and its moment arm (Rotatory equivalent to a force) 5  MUSCLE ACTIVATION A muscle is considered activated when it is stimulated by the nervous system: Isometric: muscle is producing a pulling force while maintaining a constant length. Muscle torque = external load. Concentric: muscle produces a pulling force as it contracts (shortens). Muscle torque > external load. Eccentric: muscle produces a pulling force as it is being elongated by another more dominant force. Muscle torque < external load 6  MUSCLE ACTIVATION Terminology Related to the Actions of Muscles: Agonist: muscle group that is most directly related to the execution of a particular movement. E.g tibialis anterior: agonist of ankle dorsiflexion Antagonist: opposite action of a particular agonist. E.g. gastrocnemius and soleus: antagonists to the tibialis anterior Synergist: cooperate during the execution of a particular movement. E.g. extensor digitorum longus during ankle dorsiflexion 7  MUSCULOSKELETAL LEVERS Muscle torques occur through a system of bony levers: First class: axis of Second class: axis of Third class: axis of rotation positioned rotation is located at rotation is located at one between the opposing one end of a bone and end of a bone and the forces the muscle possesses muscle possesses lower greater leverage than leverage than the the external force external force 8  MUSCULOSKELETAL LEVERS Muscle torques occur through a system of bony levers: First class Second class Third class: most common lever of musculoskeletal system 9  KINETICS How can you perform an eccentric contraction of: Quadriceps during a CKC movement? And OKC? Biceps during a CKC movement? And OKC? Gluteus maximus during a CKC movement? And OKC? Soleus during a CKC movement? And OKC? 10  KINETIC ANALYSIS Instrumentos mecánicos: measure an applied force by the amount of strain of a deformable material. Through purely mechanical means, the strain in the material causes the movement of a dial. Manual dinamometer Pressure dinamometer Ej: medición del momento extensor de codo máximo isométrico 11  KINETIC ANALYSIS Transductores: applied force deforms the transducer, resulting in a change in voltage in a known manner. Output from the transducer is converted to meaningful measures through a calibration process. 12  KINETIC ANALYSIS Instrumentos electromecánicos: register the generated torque. A common electromechanical device used for dynamic strength assessment is the isokinetic dynamometer Measure kinetic data produced by concentric, isometric, and eccentric activation of muscles 13  KINETIC ANALYSIS Electromiografía (EMG): Electromyography (EMG) is the science of recording and interpreting the electrical activity that emanates from activated skeletal muscle. Determine the timing and magnitude of activation of several whole muscles 14  KINETIC ANALYSIS Encoder : allows the record of force parameters based on a dynamometer, mixed with data of distance and time. 15 KINETIC ANALYSIS 16