Correlation of ISO 16840-2:2007 impact damping and hysteresis measures for a sample of wheelchair seating cushions.

Hysteresis and impact damping measures were made on 37 wheelchair seating cushions according to ISO 16840-2:2007 Wheelchair seating-Part 2: Determination of physical and mechanical characteristics of devices intended to manage tissue integrity-seat cushions. These measures were then correlated using Spearman and Pearson correlations to investigate the relationship between them. Correlations were also conducted on the subset of cushions comprising only those with planar foam construction. Correlation between the hysteresis measures (h250 and h500) and the mean number of rebounds greater in amplitude than 10% of the peak acceleration amplitude (R10%) were weak, as were the correlations between the hysteresis measures and the mean peak first rebound acceleration (aa). Correlations between hysteresis and the mean peak second rebound acceleration (a2), and also hysteresis and the ratio of first and second peak (a2:aa) however were moderate. Results demonstrate that the relationship between these two measures is complex. The assertion implicit in ISO 16840-2:2007 is that the two measures are related, but this study shows that these should not be assumed to be equivalent or used interchangeably.