MILLER, NORA E., STRATH, SCOTT J., ALEXANDER, NEIL B., TWARDZIK, ERICA, SWARTZ, ANN M., WELCH, WHITNEY A.
Purpose: Compare physical activity intensity in older adults with type 2 diabetes mellitus (T2DM) using individualized, relative cutpoints with standard, absolute cutpoints.
Methods: One hundred older adults with T2DM (68.9 ± 5.1 yr, 65% male, 32.7 ± 6.3 kg·m−2, 7.2% ± 1.1% glycosylated hemoglobin) completed a two-speed walking protocol (varying, walking between 1 and 2.5 mph), followed by a modified Bruce peak exercise test. Participants wore an accelerometer-based physical activity monitor at their waist, and oxygen consumption was measured. Afterward, participants wore the activity monitor for seven consecutive days. Linear equations for each individual were derived from the activity counts and energy expenditure measured during the walking protocol. Relative intensity cutpoints were calculated by using standard classifications of 44% oxygen consumption (V˙O2)peak to determine moderate and 59% V˙O2peak to determine vigorous intensity. Average time spent in intensity categories per day were calculated using relative and absolute (moderate, 2020 counts per minute; vigorous, 5999 counts per minute) cutpoints. t-Tests were run to compare estimated time spent in intensity category by cutpoint.
Results: Mean V˙O2peak was 17.9 ± 4.5 mL·kg−1·min−1 and relative cutpoints were, on average, 1033.5 counts per minute (SD, 741.2 counts per minute) for moderate and 2211.7 counts per minute (SD, 1512.4) for vigorous activity. Using the relative cutpoints, participants accumulated an average of 157.2 min (SD, 73.7 min) of light, 33.3 min (SD, 35.6 min) of moderate, and 15.6 min (SD, 26.7 min) of vigorous activity per day. Use of the absolute cutpoint resulted in significantly different estimations based on intensity category: light, 200.7 min (SD, 74.7 min; P < 0.05); moderate, 7.1 min (SD, 9.2 min; P < 0.05); and vigorous, 0.006 min (SD, 0.04 min; P < 0.05) of activity per day.
Conclusions: These results suggest utilization of absolute cutpoints may underestimate daily relative intensity levels of physical activity in older adults with T2DM. This misclassification may improperly inform dose–response relationships and population-based prevalence of physical activity in these and may extend to other clinically important populations.