Young Adults Largely Depend on Vision for Postural Control When Standing on a BOSU Ball but Not on Foam

What happens at the sensory level when a person is balancing on compliant surfaces? Compliant surfaces such as both-sides-up (BOSU) balls are often used as a form of "proprioceptive exercises." Clinical theories in neurorehabilitation suggest that compliant surfaces disrupt the somatosensory contribution to balance and increase reliance on vision and vestibular input. Understanding the sensory aspects of compliant surfaces' exercises would have important implications for balance training of athletes and of people with somatosensory deficits such as people with recurrent ankle sprains. We tested this clinical theory in a sample of 30 healthy young adults and 10 adults with a history of repeated ankle sprains while they were standing on a BOSU ball, memory foam, or floor. We measured participants' center of pressure response to dots projected on a screen, moving mediolaterally at one of the 3 frequencies (0.4, 0.48, and 0.56 Hz). We calculated magnitude of the postural response (gains) and participants' primary frequency (PF) of sway and compared it between surfaces per frequency. In both groups, gains were significantly higher on the BOSU compared with floor or foam (p < 0.001) with no significant difference between floor and foam. The PF difference was significant (p < 0.001) with a clear peak matching of the visual stimulation frequency only on the BOSU. During a single session of stance on compliant surfaces, visual dependence was a dominant factor on a challenging condition. When prescribing BOSU exercises to young adults as specific balance training, trainers should consider its effect on increased visual dependence with respect to that session's goals.