Surface is the composition of the ground on which the patient is balancing. Surfaces that are soft, unstable, sloped (hills), or uneven (thresholds, curbs, stairs, etc.) are harder for balancing. In contrast, surfaces that are hard, stable, and level are easier for balancing. Below is list of surfaces, in order of increasing levels of difficulty:
Foam is soft which diminishes sensory feedback and ankle strategy effectiveness. This makes balancing more difficult. Functional carryover of foam is how it simulates balancing on grass, sand, dirt, etc.
Narrow beam, such as ADL Hip Stick, with forefoot overhanging one side and rearfoot off the other side. Leverage at the foot is muted (due to forefoot and rearfoot being off the ground). As a result, hip strategies are emphasized for balance recovery.
Rocker boards target instability in either the sagittal (rock front-back) or frontal plane (rock laterally) to help improve balance. Rocker boards vary widely in difficulty depending on the slope and direction of the curved surfaces. It is easier to start with a rocker board that has a less aggressive arc and moves in only one direction.
Slope facing uphill, downhill, or at cross slope. Performing balance exercises on a slope helps build steadiness for uneven surfaces including ramps, curb cutouts, hills, etc.
Inflatables are unstable in all planes of motion and, as such, challenge balance in all directions.
Placing foot of the unaffected leg on an unstable surface puts the leg at a disadvantage for standing and balancing. In turn, the demand on the affected leg is increased, which helps improve weight acceptance, strength, and balance on the affected side - important for patients recovering from hip fractures, joint replacements, and strokes.
Surfaces vary widely in respect to levels of difficulty. Additionally, surface challenges (foam, rocker board, hip stick, etc.) create larger balance disruptions than movements (head turns, reaching up, weight shifting, etc.) or stances (feet together, split stance, heel-toe stance, etc.). As such, when introducing balance challenges, start by adding movements or changing stances. Progress to unstable surfaces as bigger balance challenges are needed.
Note: there are other surfaces not mentioned in this post including vibration, rolling, low friction, etc. These surfaces were not included as they are not common in most rehab settings.
Post is based on information and exercises in the The Haas Balance Book: 100+ Exercises for PT's and OT's.