A kinematic analysis of the rapid step test in balance-impaired and unimpaired older women

Little is known about the kinematic and kinetic determinants that might explain age and balance-impairment alterations in the results of volitional stepping performance tests. Maximal unipedal stance time (UST) was used to distinguish “balance-impaired” old (BI, UST < 10 s, N = 15, mean age = 76 years) from unimpaired old (O, UST > 30 s, N = 12, mean age = 71 years) before they and healthy young females (Y, UST > 30 s, N = 13, mean age = 23 years) performed the rapid step test (RST). The RST evaluates the time required to take volitional front, side, and back steps of at least 80% maximum step length in response to verbal commands. Kinematic and kinetic data were recorded during the RST. The results indicate that the initiation phase of the step was the major source of age- and balance impairment-related delays. The delays in BI were primarily caused by increased postural adjustments prior to step initiation, as measured by center-of-pressure (COP) path length (p < 0.003). The Step landing phase showed similar, but non-significant, temporal trends. Step length and peak center-of-mass (COM) deceleration during the Step-Out landing decreased in O by 18% (p = 0.0002) and 24% (p = 0.001), respectively, and a further 12% (p = 0.04) and 18% (p = 0.08) in BI. We conclude that the delay in BI step initiation was due to the increase in their postural adjustments prior to step initiation.