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

Area of Science:

• Gerontology
• Exercise Physiology
• Biomedical Engineering

Background:

• Accelerometry is crucial for measuring physical activity in older adults.
• Existing accelerometer cut points for moderate-to-vigorous physical activity (MVPA) are based on young adults and may be inaccurate for older populations due to lower resting metabolic rates (RMR).
• Previous studies determining MVPA cut points for older adults had methodological limitations, including not measuring RMR and relying on treadmill-based protocols.

Purpose of the Study:

• To determine accurate MVPA hip-worn accelerometer cut points for older adults.
• To establish cut points using measured RMR and overground walking, reflecting real-world activity.
• To compare these new cut points with those derived from younger adults.

Main Methods:

• Recruited 45 older adults (mean age 70.2 years).
• Measured individual resting metabolic rates (RMR).
• Collected accelerometer data and energy expenditure during an overground walking protocol at various speeds.

Main Results:

• Mean RMR was 2.8 mL·kg⁻¹·min⁻¹.
• Determined MVPA cut points: vertical axis 1013 counts·min⁻¹, vector magnitude 1924 counts·min⁻¹, and walking speed 2.5 km·hr⁻¹.
• Observed significant inter-individual variability in cut points.

Conclusions:

• The established MVPA accelerometer and speed cut points for walking in older adults are lower than those for younger adults.
• Using cut points derived from younger adults likely underestimates MVPA in older populations.
• The new cut points will improve the accuracy of physical activity assessment and exercise prescription for older adults.