Number of strides required for reliable measurements of pace, rhythm and variability parameters of gait during normal and dual task walking in older individuals.

The reliability with which spatiotemporal gait parameters are measured has neither been well-established for variability parameters nor during dual task walking. The purpose of this study was to examine test-retest reliability of three gait parameters representing pace, rhythm and variability in healthy older persons during normal and dual task walking and to determine the number of strides necessary to measure the parameters reliably. Twenty-four healthy adults aged 65 or older participated in the study. Subjects walked during normal and dual task (backward spelling) walking conditions at self-selected speeds and then repeated the tests. Velocity, cadence and variability in stride velocity were measured with GAITRite instrumentation. Intraclass correlation coefficients (ICCs) were calculated and the numbers of strides required to meet desired magnitudes of reliability were estimated with the Spearman-Brown prophecy formula. ICCs for velocity and cadence were high (>0.841) during normal and dual task walking, indicating strong test-retest reliability. Test-retest reliability for variability in stride velocity was moderate (ICC=0.656) in normal walking and poor (ICC=0.226) in dual task walking. While data collected from fewer than 10 to 20 strides may reliably measure velocity and cadence in either normal or dual task walking, measuring variability in stride velocity reliably may require that data be collected from hundreds of strides, particularly in dual task walking.