Balance and Posture Biomechanics PDF

BALANCE AND POSTURE Biomechanics  REMINDER: CENTER OF MASS/GRAVITY Location of the COG changes Standing position: constantly COG: anterior to the S2 vertebra 2 REMINDER: LINE OF GRAVITY...

BALANCE AND POSTURE Biomechanics  REMINDER: CENTER OF MASS/GRAVITY Location of the COG changes Standing position: constantly COG: anterior to the S2 vertebra 2 REMINDER: LINE OF GRAVITY 3 REMINDER: BASE OF SUPPORT 4 CENTRE OF PRESSURE 5  BALANCE Balance: ability to maintain the line of gravity within the base of support with minimal postural sway. Equilibrium: all acting forces are cancelled by each other resulting in a stable balanced system. 6  BALANCE It improves in case of: Wider base of Support Lower center of gravity Longer distance between the line of gravity and the border of the base of Support 7 POSTURE Attitude assumed by the body either with support during the course of muscular activity, or as a result of the coordinated action performed by a group of muscles working to maintain the stability Dynamic posture Static posture 8 STANDING POSTURE Small base of Support High center of mass Ideal posture? Best alignment possible? Lowest muscle activity? Minimal energy consumption? High variability based on anatomy Poor posture? Vs Postural stress 9  STANDING POSTURE External forces: gravity and ground reaction forces Internal forces: – Muscle activity – Tensión of noncontractile structures Ligaments Capsule Bones 10  STANDING POSTURE Line of gravity: On or close to joints axis: – Compressive forces are distributed – Less passive tensión or muscle activation Plumb line: external representation of the line of gravity – Mastoid process – Cerrvical vertebrae – Shoulder – Lumbar vertebrae – Greater throcanter – Anterior to the knee – Anterior to the ankle 11  STANDING POSTURE Postural control Complex sensorimotor skill, interaction of – Musculoskeletal system – Somatosensory system: Vision Vestibular Proprioception Cutaneus or tactile – Central nervous system integrarion and processing: Afferent (sensory) Efferent (motor) 12  STANDING POSTURE Postural sway: the unconscious, small movements that happen around the body's center of gravity in order to maintain balance Continous muscle activation with an stabilizer role: Ankle Knee Hip Spine 13  PRACTICAL EXAMPLES Try to bend forward with your back touching the wall – How far can you go? Why? Try to move your body forward maintaining your balance – Where do you feel the centre of pressure? Why? Stand on one foot with eyes open and closed – What muscle contractions do you feel? Why? 14  STANDING POSTURAL CONTROL Multiple muscle groups maintain an “isometric” activation (Postural muscle torques): Ankle: plantar flexion VS dorsiflex gravitational moment Knee: posterior joint capsule VS extension gravit. moment¿? Hip: ligaments and psoas VS extension gravit. moment Lumbar: ligaments VS extension gravit. moment Thoracic: ligaments + extensors VS flex. gravit. moment Cervical: ligaments VS extension gravit. Moment Muscle torque: Has continuous variations to control balance (Sway) Increases to maintain postural control in case of external perturbances 15  OTHER STATIC POSTURAL CONTROL To identify muscle groups activation: – Base of Support – Line of gravity – Gravitational moment: opposing muscle activations Imagine what movement would occur if all muscle groups around a specific joint suddenly relax 16  OTHER STATIC POSTURAL CONTROL To identify muscle groups activation: – Base of Support – Line of gravity – Gravitational moment: opposing muscle activations Imagine what movement would occur if all muscle groups around a specific joint suddenly relax 17  OTHER STATIC POSTURAL CONTROL Mucle torques to maintain the posture? Imagine what movement would occur if all muscle groups around a specific joint suddenly relax 18  POSTURAL CONTROL MECHANISMS Sensorimotor control under load perturbances: – Feedback control: stimulation of a corrective response after sensory detection – Feedforward control: CNS predicts the effect that a voluntary movement will have on the body and plans a sequence of anticipatory muscle activity in order to be prepared for this perturbation 19  POSTURAL CONTROL: ARM FLEXION WHILE STANDING What changes in mucle torque (Not including the arm) will occur in the body to maintain the spine posture??? - Center of mass and line of gravity go anterior - Gravity moments of each joint change, so there are opposing muscle torques: - E.g: plantar flexion or back extensors opposing torques These increases of mucle activation occur even before (Feedback) the arm starts moving (deltoid contraction)!!!! 20