Lab Guide 14

Center of Mass vs. Center of Gravity

• Center of Mass (COM) is the point in the body where mass is equally distributed in all directions.
• Center of Gravity (COG) is the vertical projection of COM to the ground.
• The COG shifts as the body moves, but COM remains constant unless mass is gained or lost.

Sensory Systems for Balance Control

• Visual system: determines body position relative to surroundings.
• Vestibular system: detects head movement and orientation to help maintain balance.
• Somatosensory system: uses muscle and joint sensors to provide feedback on body position

Balance Strategies from Minimal to Large Perturbations

• Ankle Strategy: Small sway, minimal perturbation (e.g., standing still)
• Weight-Shift Strategy: Moderate adjustments, reaching sideways (e.g., picking up an object)
• Hip Strategy: Large perturbations, sudden corrections (e.g., stopping suddenly on public transportation)
• Suspension Strategy: Lowering COM to maintain stability (e.g., crouching on uneven terrain)
• Stepping Strategy: Significant perturbations, restoring base of support (e.g., catching balance after being bumped)

Types of Balance Training

• Sensory organization (proprioceptive) balance training: Challenges balance by removing visual input and adding an unstable surface (e.g., standing on foam with eyes closed).
• Anticipatory balance training: Requires planning and control for expected movements (e.g., playing catch with a medicine ball).

Center of Mass and Center of Gravity

• Center of Mass (COM) is the point where a body’s mass is equally distributed.
• Center of Gravity (COG) is the vertical projection of the COM to the ground.
• The COG shifts as the body moves, while the COM remains constant unless mass is gained or lost.

Balance Control Sensory Systems

• Visual: Provides information about body position relative to surroundings.
• Vestibular: Detects head movement and orientation to help maintain equilibrium.
• Somatosensory: Provides feedback on body position via sensors in muscles and joints.

Balance Strategies

• Ankle Strategy: Relies on ankle muscles for minimal perturbations, like standing still or slight swaying.
• Weight-Shift Strategy: Shifts weight side to side for moderate adjustments, like reaching sideways.
• Hip Strategy: Corrects balance with larger perturbations, similar to sudden stopping on a bus.
• Suspension Strategy: Lowers the COM by bending knees and hips to stay stable, useful on uneven terrain.
• Stepping Strategy: Takes a step to regain balance with significant perturbations, like being bumped.

Balance Training Types

• Sensory Organization (Proprioceptive) Balance Training: Challenges balance by removing visual input with difficult terrain, enhancing somatosensory and vestibular systems.
  • Example: Standing on foam with eyes closed.
• Anticipatory Balance Training: Requires planning and control for expected movements, like catching and throwing. Challenges balance through weight shifting and dynamic stability.
  • Example: Standing on ground, playing catch with a medicine ball.

Balance Training

• Balance training is a must for non-complex patients.
• Understanding different motor strategies for balance control is key.
• Ankle strategy for minor perturbations.
• Weight-shift strategy (lateral) for lateral perturbations.
• Suspension strategy for regaining balance after a stumble.
• Hip strategy for larger perturbations.
• Stepping strategy for larger perturbations when unable to maintain balance.
• Combined strategies can be used depending on the situation and patient's capabilities.

Safety Considerations

• Always use a gait belt during balance training.
• Stand where the patient is likely to fall to ensure their safety.
• Ensure a safe environment free of obstacles and with a stable surface to hold onto.
• Guard the patient at all times during balance exercises.
• Prepare carefully by considering the exercise goal and type of training.
• Decide if the exercise is for in-clinic or home program (HEP).

Position and Perform

• Prioritize patient safety when positioning.
• Determine the necessary equipment for the exercise.
• Observe posture and alignment while performing, looking for substitutions.
• Always guard! Teach the patient the exercise with clear instructions.

Steady State Balance Exercises

• Steady state static balance exercises involve maintaining balance while standing still.
• Steady state dynamic balance exercises involve maintaining balance while moving.
• Anticipatory postural control focuses on maintaining balance during planned movements.
• Reactive postural control emphasizes reacting to unexpected perturbations.

Sensory Organization for Balance

• Sensory organization includes vision, vestibular and proprioceptive systems.
• Base of support and surface can vary to challenge balance (static and dynamic).
• Normal stance is a basic starting point.
• Romberg's stance incorporates single point focus and foam block.
• Off-set tandem involves single finger support and dynadisc.
• Tandem stance requires no hand support and uses a rocker board.
• Single leg stance requires no hand support and uses multi-directional wobble board, arms at sides.

Patient Case Examples

• Case #1: Mrs. Doubtfire
  • 68 year old patient, sustained a fall while exiting the shower.
  • Likely needs balance training to prevent future falls.
• Case #2: Elroy Jetson
  • Sustained a head injury after a fall.
  • In a medically induced coma, regained consciousness, weak, struggles to sit up.
  • Goal: To independently sit up at the edge of the bed for 10 minutes within a week for a meal.
• Case #3: Jane Jetson
  • Recently had a Left Total Hip Arthroplasty (THA).
  • WBAT (Weight-bearing as tolerated).
  • Difficulty walking with a walker – feels unsteady and wobbly.
  • Difficulty standing and moving the walker without losing balance.
  • Needs to be able to transfer to bed independently.