Inclusion Criteria:  able to communicate in English, alert, cooperative, and competent to provide informed consent, willing to participate (as evidenced by attending the single data-collection session), and have no physical impairments that would prevent their being able to push and pull a wheelchair over a soft surface  Exclusion Criteria:  have unstable medical conditions that might make the handling of a manual wheelchair dangerous, or emotional problems that might make participation unsafe or unpleasant.