Measuring moderate-intensity walking in older adults using the ActiGraph accelerometer.

Anthony Barnett,David Barnett,Ester Cerin,Daniel Van Den Hoek

doi:10.1186/s12877-016-0380-5

Abstract

BackgroundAccelerometry is the method of choice for objectively assessing physical activity in older adults. Many studies have used an accelerometer count cut point corresponding to 3 metabolic equivalents (METs) derived in young adults during treadmill walking and running with a resting metabolic rate (RMR) assumed at 3.5 mL · kg−1 · min−1 (corresponding to 1 MET). RMR is lower in older adults; therefore, their 3 MET level occurs at a lower absolute energy expenditure making the cut point derived from young adults inappropriate for this population. The few studies determining older adult specific moderate-to-vigorous intensity physical activity (MVPA) cut points had methodological limitations, such as not measuring RMR and using treadmill walking.MethodsThis study determined a MVPA hip-worn accelerometer cut point for older adults using measured RMR and overground walking. Following determination of RMR, 45 older adults (mean age 70.2 ± 7 years, range 60–87.6 years) undertook an outdoor, overground walking protocol with accelerometer count and energy expenditure determined at five walking speeds.ResultsMean RMR was 2.8 ± 0.6 mL · kg−1 · min−1. The MVPA cut points (95% CI) determined using linear mixed models were: vertical axis 1013 (734, 1292) counts · min−1; vector magnitude 1924 (1657, 2192) counts · min−1; and walking speed 2.5 (2.2, 2.8) km · hr−1. High levels of inter-individual variability in cut points were found.ConclusionsThese MVPA accelerometer and speed cut points for walking, the most popular physical activity in older adults, were lower than those for younger adults. Using cut points determined in younger adults for older adult population studies is likely to underestimate time spent engaged in MVPA. In addition, prescription of walking speed based on the adult cut point is likely to result in older adults working at a higher intensity than intended.

Highlights

Accelerometry is the method of choice for objectively assessing physical activity in older adults
With Metabolic equivalent (MET)-based physical activity (PA) intensity values computed using the conventional resting metabolic rate (RMR) of 3.5 mL · kg−1 · min−1, older adults would be working at higher relative intensities than assumed and their time spent in PA above activity intensity thresholds would be underestimated [12]
Models with random intercept and slope including a linear and a quadratic term of METs provided the best fit for vertical axis (VA), vector magnitude (VM) and walking speed (Fig. 2)

Summary

Introduction

Accelerometry is the method of choice for objectively assessing physical activity in older adults. Many studies have used an accelerometer count cut point corresponding to 3 metabolic equivalents (METs) derived in young adults during treadmill walking and running with a resting metabolic rate (RMR) assumed at 3.5 mL · kg−1 · min−1 (corresponding to 1 MET). The few studies determining older adult specific moderate-to-vigorous intensity physical activity (MVPA) cut points had methodological limitations, such as not measuring RMR and using treadmill walking. With a lower RMR, the energy expenditure in absolute terms associated with a given MET activity intensity threshold will be lower in older compared to younger adults. With MET-based PA intensity values computed using the conventional RMR of 3.5 mL · kg−1 · min−1, older adults would be working at higher relative intensities than assumed and their time spent in PA above activity intensity thresholds would be underestimated [12]

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Discussion

Conclusion