Variability of the physiologic cost index during free and forced walking

The purpose of this study is to determine the variability of the physiologic cost index (PCI) for normal subjects performing two distinct gait tasks; free walking at their naturally adopted speed and forced walking at a fixed cadence. Knowledge of the PCI variability is important since this normalized index is often used to compare the walking efficiency of subjects exhibiting gait pathology, or to determine if a particular therapeutic intervention affects overall gait performance. PCI is defined as the ratio of net heart rate to velocity in the units of beats/meter, where net heart rate is the difference between average heart rate over a fixed distance and resting heart rate while standing. Sixteen subjects with no past of gait pathology (normal) were selected for this study. Of these, 3 were men (mean =28+or-7), and 13 were women (mean =32+or-10). Statistical techniques were applied using each pass as a separate sample. The results show that PCI is relatively invariant in successive passes for the same subject for either free or forced walking, but quite variable for different type of walking speeds. Moreover, the authors have also seen that PCI of fast walking is significantly different than PCI of slow walking throughout the subject population both for free and forced walking.