exercise for impaired balance

Overview of Biomechanical Terminology

  • Center of Mass (COM):

    • Defined as the center of all body mass.
    • Varies between individuals based on specific weight distribution (e.g., taller vs. shorter individuals, or those with more abdominal mass).

  • Center of Gravity (COG):

    • Defined as the vertical projection of the Center of Mass to the ground.
    • In adults, this point is typically located anterior to the second sacral vertebrae (S2S2).
    • For a typical male, it is often described as being near the umbilicus at the level of the second sacral vertebrae.

  • Line of Gravity:

    • The vertical line projecting from the COG. It is comparable to a plumb line passing directly through the body to determine the balance point.

  • Momentum:

    • The product of the mass of an object and its velocity.
    • Formula: Momentum=mass×velocity\text{Momentum} = \text{mass} \times \text{velocity}.

  • Base of Support (BOS):

    • The contact area on the supporting surface, such as the mat table, wall, or ground.
    • If a person is standing on their hands, the hands constitute the BOS.
    • A wider BOS increases stability.

  • Limits of Stability (LOS):

    • The "sway boundary" or the distance outside the BOS that an individual can move without losing balance or needing to take a step.
    • Visually described as a cone shape that becomes more narrow based on the BOS.
    • In older adults, the LOS typically becomes more narrow, leading to lower thresholds for losing balance during dynamic reaching or anticipatory activities.

Surface Interaction and Reaction Forces

  • Ground Reaction Force (GRF):

    • Based on the Newtonian principle that every action has an equal and opposite reaction.
    • GRF is the contact force between the body and the supporting surface (usually the ground).
    • It is always equal in magnitude and opposite in direction to the force the body exerts on the ground.

  • Center of Pressure (COP):

    • The location of the vertical projection of the GRF.
    • Pressure Distribution: High heels create more pressure (lb/in2lb/in^2 or PSIPSI) concentrated in the heel and toe compared to tennis shoes, which disperse pressure across a larger area.
    • Stance Distribution:
      • In a single-leg stance, the COP is located in the stance foot.
      • In a double-leg stance, the COP is distributed between the two feet.

  • Clinical Implications of Asymmetry:

    • Minor asymmetries (e.g., running on one side of a slanted road or sitting on a wallet while driving) can cause the GRF to drive up through the spine or joints, leading to unilateral hip, knee, or back pain.

The Trio of Balance Systems

  • 1. Visual System:

    • The optic nerve provides input regarding speed and direction of movement to maintain stability.
    • Vestibular Ocular Reflex (VOR):
      • VOR 1: The object stays still while the head moves; the eyes remain fixed on the object to stabilize the gaze.
      • VOR 2: Both the object and the head are moving, yet the eyes remain fixed on the object.

  • 2. Somatosensory System:

    • Relies on proprioceptors, which primarily reside in the joint spaces, as well as muscles and sensory inputs.
    • Provides "proprioception," or the body's awareness of its position in space.
    • A common clinical test involves moving one limb into a position and asking the patient to replicate that position with the opposite limb.

  • 3. Vestibular System:

    • Located in the inner ear.
    • Affected by conditions like vertigo or ear infections, which can result in dizziness and loss of balance.

Postural Adjustment Strategies

  • Ankle Strategy:

    • Used for small perturbations (light taps).
    • Involves ankle intrinsic muscles and the gastroc-soleus complex.
    • Does not typically involve head movement, thus the vestibular system is not activated.

  • Hip Strategy:

    • Occurs when the COG is pushed to the limits of stability, especially with a narrow BOS.
    • Muscles are activated in a proximal-to-distal sequence.
    • The hips move in the opposite direction of the perturbation.
    • Involves head movement, thus activating the vestibular system.

  • Step Strategy:

    • Triggered when the COG is displaced beyond the limits of stability.
    • Requires the individual to take a step to extend the BOS.
    • Activates the vestibular system due to head movement.

  • Suspension Strategy:

    • Lowering the center of mass to increase stability.
    • Primarily involves knee flexion, but also incorporates the hips and ankles.

Clinical Assessments for Balance and Fall Risk

  • Timed Up and Go (TUG):

    • Most common test; measures the time it takes to stand, walk, turn, and sit.
    • General threshold: 10 seconds.
    • Parkinson’s Disease threshold: 12 seconds.

  • Berg Balance Scale:

    • A two-page comprehensive checklist assessing 14 items, including sit-to-stand, static sitting, and limits of stability.

  • Functional Reach Test:

    • Specifically measures the anterior limits of stability using a ruler. Can be modified for seated patients (e.g., post-stroke).

  • Five Times Sit to Stand (FTSTS):

    • Measures functional strength and balance by timing how long it takes a patient to perform five repetitions of standing from a chair.

  • Romberg Test:

    • Technically a test of proprioceptive input rather than pure balance.
    • Patients stand with eyes closed; excessive swaying suggests a reliance on the visual system and may indicate cerebellar issues or lesions.

  • Balance Error Scoring System (BESS):

    • Tested in three positions: double leg, single leg, and tandem.
    • Clinicians count "errors" (corrections) while the patient's hands are on their hips.

  • Clinical Test of Sensory Integration and Balance (CTSIB):

    • Uses a dome/beehive apparatus to isolate the vestibular system by removing visual and proprioceptive inputs.

Therapeutic Interventions and Progressions

  • Static vs. Dynamic Training:

    • Static: Maintain a stable antigravity position while stationary within the BOS.
    • Dynamic: Stabilize the body when either the body or the support surface is moving outside the BOS.

  • Anticipatory (Proactive) vs. Reactive:

    • Anticipatory: Movements the patient can plan for (e.g., catching a ball, reaching for a cone, tapping a balloon).
    • Reactive: Adjustments to unexpected movements (e.g., manual perturbations).

  • Progressing Exercises:

    • Vision: Eyes open to eyes closed.
    • Base of Support: Wide to narrow to semi-tandem to single-leg stance.
    • Surface: Stable (ground) to unstable (foam pad, AIR-X pad, BOSU ball, Dynadiscs, trampoline, pillows).
    • Dual Tasking: Adding a cognitive task (e.g., counting, ABCs, or reciting directions) to a physical task.

Clinical Safety and Environmental Modifications

  • Safety Protocols:

    • Gait Belts: Must always be used with an underhand grip for balance-impaired patients.
    • Parallel Bars: The most restrictive assistive device; use them for new or high-risk activities.
    • Clearance: Ensure the treatment area is free of obstacles before starting exercises.

  • Factors Contributing to Falls:

    • Vision: Check if the patient wears glasses; lighting is crucial (especially night lights for nocturnal wandering).
    • Medications: Opioids, Xanax, and blood pressure meds (causing orthostatic hypotension) can induce dizziness.
    • Neurological Disorders: Parkinson’s (festinating gait), MS, and Huntington’s affect motor strategies.
    • Biomechanical: Surgery (e.g., ACL) cuts into proprioceptors, requiring retraining.
    • Environment: Remove throw rugs; watch out for small pets (dogs/cats) that act as trip hazards.

  • Functional Relevance:

    • Therapy must be meaningful to the patient's daily life. While balloon tapping is common, it should translate to functional activities like sit-to-stand transitions or navigating thresholds.