Need to revise classification of physical activity intensity in older adults? The use of estimated METs, measured METs and V̇O2Reserve

Background Multiples of resting metabolic rate (RMR) are often used to classify physical activity intensity, a concept known as the Metabolic Equivalent of Task (MET). However, the METs metrics may misclassify physical activity intensity in older adults because of age related changes in RMR and maximal aerobic capacity (V̇O2max). This study aimed to 1) compare classifications of activity intensity by estimated (METsestimated) and measured (METsmeasured) METs and 2) compare physical activity classified by absolute (METsmeasured) versus relative intensity (%V̇O2Reserve) in older adults. Methods Ninety-eight adults aged 75-90 years participated in the study. RMR and V̇O2 during sitting, standing, daily activities and 6-minute-walking-test were measured. V̇O2Reserve was defined as the difference between V̇O2max and RMR. Moderate and vigorous intensity was classified as 3 and 6 METs and 40% and 60% of V̇O2Reserve, respectively. Paired t-tests and a confusion matrix were used to investigate aim 1 and 2, respectively. Results METsmeasured was 24% lower than the standard 1 MET of 3.5 ml O2·min-1·kg-1. METsestimated underestimated the intensity during daily and walking activities when compared to METsmeasured. Nevertheless, when comparing METsmeasured to percentages of V̇O2Reserve, a mismatch was shown for moderate intensity in 47-67% of the participants during daily activities, and 21% of the participants during self-selected gait speed. Conclusion Applying METsestimated for older adults leads to potential underestimation of physical activity intensity, suggesting that current classification metrics should be revised for older adults. V̇O2Reserve is a candidate metric for establishing precise physical activity intensity cut-points for older adults.