Objective: To test the hypothesis that shoes made with a sole material that retains compressed thickness between steps (low resiliency) provide balance better than and comfort equal to shoes composed of high resiliency sole material.
Setting: Older subjects were recruited from a medical clinic population, and younger subjects came from a recreational sports population.
Design: A randomized-order, cross-over, controlled comparison design.
Participants: Groups comprised random samples of 30 older (mean age 66 years, SD+/-3.0), and 30 younger (mean age 34 years, SD+/-6.0) healthy men who met age selection criteria.
Measurements: Stability was inferred by sway measures: sway velocity (cm x s(-1)), X-Y area (cm2), and radial area (cm2). Comfort was measured by direct scaling and magnitude estimation using an 11-point ratio scale.
Results: Stability inferred by sway velocity was 311% (P < .001) and 31% (P < .001) poorer for younger and older groups, respectively, for high and low resiliency interfaces. Sway velocity with low resiliency interface was lower than bare platform, the lowest ever recorded under equivalent conditions (P < .001). All interfaces were equally comfortable.
Conclusions: Stability rises with low resiliency interfaces and declines with high resiliency interfaces: sway velocity in older people wearing hard-soled footwear incorporating low resiliency technology would be 20% lower than in younger people wearing most current athletic and walking shoes. Inasmuch as existing theory can not account for improved balance with interfaces, we propose that when humans are supported by rigid support surfaces, elastic biologic tissues store energy from postural adjustments and locomotion, which is returned as a reaction force causing overshoot. This amplifies frontal plane foot movement and attenuates foot position awareness, causing less precise postural adjustments and instability. Low resiliency interfaces dissipate energy and thereby moderate overshoot. Low resiliency interface technology is capable of improving stability, which portends improved health for unstable older people in particular.