66 | Chapter 4 DISCUSSION We performed a cross-sectional study in 229 adults of 65 years and older to examine the correlations between SPPB scores and daily life gait quality and quantity as measures of functional status. In contrast to our hypothesis, we found weak correlations. As opposed to our results, Brodie and colleagues found that laboratory-assessed gait performance was positively correlated with quality of gait during daily life activities and correlations were mostly moderate to strong in 51 community-dwelling older adults (215). They also found that walking in daily life had significantly lower median cadences and larger step time variability compared to laboratory-assessed cadence (215). Based on these results, the authors concluded that laboratory-based gait measurements are more indicative of capacity than performance (215). A possible explanation of finding different results compared to the present study, is that they measured their participants during prescribed daily life activities for 25 minutes, and our participants wore the sensor for seven consecutive days without prescription of activities. Moreover, a study of Rojer and colleagues found that better gait quantity, such as lower mean sedentary behaviour and higher physical activity in 145 inpatients, was associated with better functional performance (216). They reported a median SPPB score of 1 (range 0-4) for their control group consisting of geriatric rehabilitation inpatients. In contrast, a study of Urbanek et al. (217) showed that walking acceleration and cadence estimated in a lab-based setting were significantly associated with these measures obtained from daily life acceleration data. However, their findings were based on a relative smaller sample of 51 community-dwelling older adults, with a mean SPPB score of 10 (range 10-12), indicating a higher performing population than ours. In fact, walking acceleration and cadence in the lab-based setting were both substantially higher than assessed in a daily life setting, which may indicate that participants overperform in a lab-based setting (217). Our study aligns more closely with the findings of Urbanek et al, in that we found an SPPB range of 5-12. Comparable to the findings of our study, Nicolai and colleagues found a limited correlation between the SPPB and quantity of physical activity in terms of walking time and time on feet measured by inertial sensors in 44 community-dwelling older adults (218). These limited correlations may be explained by a high intraindividual day-to-day variability of walking time and time on feet and shows that physical performance cannot be used as a surrogate marker for physical activity (218). We included more daily life gait quality and quantity measures than only walking time and time on feet, but also found only weak correlations. Furthermore, Zalewski and coworkers found that functional status was not associated with the quantity of physical activity in 59 older adults living in independent or assisted living apartments. Measures of functional status often used in clinical settings did not correlate well with the actual functioning of older adults, as assessed by gait speed and the six-minute walk test (219). A study of Van Ancum et al. showed that the clinically assessed four meter gait speed as a gait
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