Mobility, dexterity, and body structure conditions

Why it matters

Mobility and dexterity conditions span a wide range of causes and severity levels. Some people have limited fine motor control; others have no voluntary limb movement at all. The solutions range from ergonomic keyboards to eye tracking to sip-and-puff devices. Understanding the categories helps match the right AT to the right need. (BoK p. 18)

Four categories of mobility and dexterity conditions

The BoK groups mobility-related conditions into four functional categories: (BoK p. 18)

1. Fine motor and dexterity impairments

These affect the precision and control of small movements — required for standard keyboard use, mouse pointing, and touchscreen interaction. Causes include:

• Tremor (essential tremor, Parkinson’s disease).
• Spasticity (cerebral palsy, multiple sclerosis).
• Weakness from muscular dystrophy or arthritis.
• Repetitive strain injury.

2. Ambulation impairments

These affect walking and mobility through physical space. People may use canes, walkers, crutches, manual or power wheelchairs, or scooters. Physical environment barriers (steps, narrow doorways, heavy doors) are the primary concern. ICT may also be affected if ambulation impairment co-occurs with upper-limb limitations. (BoK p. 19)

3. Muscle fatigue conditions

Conditions such as multiple sclerosis, post-polio syndrome, and chronic fatigue syndrome cause muscle fatigue that fluctuates. On good days the person may interact with standard technology; on high-fatigue days they may need AT. The need for flexible AT that does not require constant reconfiguration is particularly relevant. (BoK p. 19)

4. Body structure differences

Conditions affecting limb presence, length, or structural integrity — limb absence, limb differences from birth or amputation, skeletal dysplasia. The functional impact on AT selection depends entirely on which limbs and how much motor control remains. (BoK p. 19)

ICT barriers

• Small click targets require precision pointing that many users with tremor or spasticity cannot achieve reliably.
• Keyboard shortcuts requiring simultaneous key presses (e.g., Ctrl+Alt+Delete) are difficult for one-handed users or those with limited dexterity.
• Time limits on sessions or form completion disadvantage users who interact more slowly.
• Drag-and-drop interactions without keyboard alternatives exclude users who cannot use a mouse.
• Touch-only interfaces on kiosks or tablets exclude users with severe upper-limb impairments. (BoK p. 20)

Assistive technology solutions

Input AT

• Switch access + scanning: One or two switches allow a user to select items from a grid that the screen cycles through. Used by people with very limited voluntary movement (e.g., a single finger, a toe, or a breath).
• Sip-and-puff switches: Controlled by breathing. Common for users with high-level spinal cord injuries.
• Eye tracking: Infrared cameras track gaze. The user directs their eyes to a target and dwells to activate a click. Used by people with no usable hand or head movement.
• Head mouse / head pointer: Tracks head movement via a reflective dot on the forehead or via a camera.
• Modified keyboards: Large-key keyboards, keyguards, one-handed keyboards, on-screen keyboards. (BoK p. 20)

Physical mobility AT

• Power wheelchairs and scooters.
• Ramps, lifts, and automatic doors (environmental modifications).
• Accessible parking and transport.

Real-world example

A job application portal requires clicking small checkboxes, drag-and-drop document uploads, and a 10-minute session timeout. An applicant with ataxia after a brain injury cannot accurately click the checkboxes or perform drag-and-drop. They use switch access with scanning — but the timeout expires before they complete the form. Three barriers, each independently excluding the user; each independently fixable with accessible design choices.