62 | Chapter 4 quantity of gait measures in the present analyses: mean number of strides per day (206-208), mean walking duration per day (hours) (206-208), sedentary time (hours) (208) and number of locomotion bouts (208). Similarly, for quality of gait, walking speed (206, 208), walking speed variability (209) and stride regularity in the VT and ML directions as a measure of consistency of the stride-to-stride gait pattern were examined (210). Moreover, harmonic ratio was determined in the VT (211, 212) and AP directions as a measure of gait symmetry between left and right steps (211, 212). The root mean square of trunk acceleration in the ML direction was included as a measure of gait intensity, which indicates the amount of trunk movement (213). Sample entropy in the VT (209) and ML directions was determined as a measure for gait complexity, which indicates the level of automaticity of walking, where less attention reflects more unpredictable fluctuations in the gait pattern of an adaptive system (209). The maximal Lyapunov exponent was assessed as a measure for gait stability (204), and the index of harmonicity in the AP direction as a measure of smoothness of the gait pattern (204, 211). The gait quality composite score was calculated as a weighed sum of the root mean square of trunk acceleration in ML direction, the index of harmonicity in ML direction, the magnitude of the acceleration at the dominant period in the frequency domain in the AP direction and the autocorrelation of the acceleration at the dominant period in the frequency domain (177). In all measures, higher scores indicate a better gait quality, except for the walking speed variability, Root Mean Square of trunk acceleration and Lyapunov exponent. Statistical analysis Data were analysed using IBM SPSS Statistics version 28 (IBM Corp. Armonk, NY) and RStudio version 1.3.1073 (RStudio Team. Boston, MA). All available gait data was analysed when participants wore the sensor for at least 2 days for 18 hours per day and had a complete SPPB test. Analyses were performed on the complete cases, which lead to a total of 229 cases (see Figure 4.1). Descriptive statistics Information was collected about age, sex, body mass index (BMI), hand grip strength, timed up and go test, use of walking aids and frailty status. Descriptive statistics were checked for normality and if normally distributed the mean and standard deviation were calculated. If not normally distributed, the median and interquartile range were calculated. For sex, use of walking aids and frailty status, frequencies and percentages were calculated and reported.
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