4 The Short Physical Performance Battery does not correlate with daily life gait quality and quantity | 59 BACKGROUND The Short Physical Performance Battery (SPPB) consists of performance measures of lower extremity function and is frequently used to determine and monitor functional status in older adults by healthcare professionals in clinical practice (183). Functional status is a broad term referring to one’s ability or capacity to execute tasks and activities of daily living (184, 185). A decrease in functional status is associated with an increased risk of falling, loss of independence in activities of daily living and decreased mobility (186, 187). The SPPB consists of a combination of three functional tests: 1) the Three Stage Balance test, 2) the Four Meter Walk test, and 3) the Five Times Sit to Stand test (183). The SPPB takes a few minutes to complete and requires little equipment and training to administer (188). Additionally, the result of the SPPB can be easily converted to overall scores, and the SPPB is reproducible and sensitive to changes in functional status over time (189). On the other hand, the SPPB has the disadvantage that it is usually done in a clinical setting, in which people tend to show their best performance and not what they usually do in daily life, which hampers the ecological validity (190). Daily life performance can be measured by wearable inertial sensors. Inertial sensors are low-cost, unobtrusive, reliable and valid, and can be used in one’s own environment without additional burden (191-193). Sensor based daily life gait quality and quantity measures, such as number of steps and walking speed, have been shown to be related to consequences of functional decline in community-dwelling older adults (194). For example, these measures are associated with increased fall risk and physical inactivity (194-196). A disadvantage of these gait measures is that one’s daily performance may be contaminated with challenges that one may encounter in daily life, for example walking the stairs when living on the second floor. Both the Short Physical Performance Battery (SPPB) and daily life gait quality and quantity measures obtained from wearable sensors are used to measure functional status, and for both measures it has been demonstrated that a deterioration is associated with poorer outcomes such as an increased risk of falls (194, 197). The SPPB includes sub-scores for gait, balance, and sit-to-stand (i.e., muscle strength) performance, which are all important requirements for gait function (191-193). Studies have shown that gait performance, as assessed in both standardized tests and real-world settings, reflects a fundamental aspect of functional status in older adults (191-193). It is therefore generally assumed that the SPPB and daily-life gait quality and quantity are interrelated and interchangeable, but it has not yet been established to what extent they are correlated with each other. Therefore, the aim of this study was to assess the correlations between the SPPB and daily life gait quality and quantity in community-dwelling older adults. If the SPPB and gait quality and quantity appear
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