Accelerometer Metrics: Healthy Adult Reference Values, Associations with Cardiorespiratory Fitness, and Clinical Implications

Abstract

Purpose Accelerometer-assessed physical activity (PA) can be summarised using cut-point-free or population-specific cut-point-based outcomes. We aimed to: 1) examine the interrelationship between cut-point-free (intensity gradient [IG] and average acceleration [AvAcc]) and cut-point-based accelerometer metrics, 2) compare the association between cardiorespiratory fitness (CRF) and cut-point-free metrics to that with cut-point-based metrics in healthy adults aged 20 to 89 years and patients with heart failure, and 3) provide age-, sex-, and CRF-related reference values for healthy adults. Methods In the COmPLETE study, 463 healthy adults and 67 patients with heart failure wore GENEActiv accelerometers on their non-dominant wrist and underwent cardiopulmonary exercise testing. Cut-point-free (IG: distribution of intensity of activity across the day; AvAcc: proxy of volume of activity) and traditional (moderate-to-vigorous and vigorous activity) metrics were generated. The ‘interpretablePA’ R-package was developed to translate findings into clinical practice. Results IG and AvAcc yield complementary information on PA with both IG (p = 0.009) and AvAcc (p < 0.001) independently associated with CRF in healthy individuals (adjusted R2 = 73.9%). Only IG was independently associated with CRF in patients with heart failure (p = 0.043, adjusted R2 = 38.4%). The best cut-point-free and cut-point-based model had similar predictive value for CRF in both cohorts. We produced age- and sex-specific reference values and percentile curves for IG, AvAcc, moderate-to-vigorous PA, and vigorous PA for healthy adults. Conclusions IG and AvAcc are strongly associated with CRF and, thus, indirectly with the risk of non-communicable diseases and mortality, in healthy adults and patients with heart failure. However, unlike cut-point-based metrics, IG and AvAcc are comparable across populations. Our reference values provide a healthy age- and sex-specific comparison that may enhance the translation and utility of cut-point-free metrics in clinical practice.

Relative and absolute intensity accelerometer metrics decipher the effects of age, sex, and occupation on physical activity

“…light, moderate, and vigorous PA in minutes), alternative cut-point-free metrics are increasingly being used in research. 2,3,[5][6][7] Cut-point-free metrics have the advantage of enhancing comparability across studies, populations, and the most commonly used raw acceleration devices. 8 The average level of acceleration observed over each 24-hour period assesses the average daily intensity and is commonly used as a proxy for volume of PA (AvAcc_ ABS ).…”

“…8 The average level of acceleration observed over each 24-hour period assesses the average daily intensity and is commonly used as a proxy for volume of PA (AvAcc_ ABS ). 6,7 The distribution of the acceleration across the day (e.g. the relative proportions of time in higher and lower intensities of PA) provides a complementary measure of the PA pro le, the intensity gradient, that gives independent information to total volume (IG_ ABS ).…”

“…the relative proportions of time in higher and lower intensities of PA) provides a complementary measure of the PA pro le, the intensity gradient, that gives independent information to total volume (IG_ ABS ). 6,7 This is important as the combination of volume and intensity may explain more variance in health than either alone. 6,7 Looking beyond the absolute intensity of accelerometer-based PA, Orme et al (9) recently proposed expressing absolute metrics of PA relative to the measured or predicted acceleration corresponding to an individual's physical capacity/cardiorespiratory tness (CRF).…”

“…6,7 This is important as the combination of volume and intensity may explain more variance in health than either alone. 6,7 Looking beyond the absolute intensity of accelerometer-based PA, Orme et al (9) recently proposed expressing absolute metrics of PA relative to the measured or predicted acceleration corresponding to an individual's physical capacity/cardiorespiratory tness (CRF). 10 This approach was recently used by Rowlands et al (10) to develop the relative intensity gradient (IG_ REL ), which re ects the intensity distribution of a 24-h day relative to an individual's maximum (aerobic) acceleration.…”

“…Both the volume and intensity of accelerometer-assessed PA have been shown to decrease with age 7,11 and differ between sexes. 12 However, what is often not considered is the well-documented impact of age and sex on CRF.…”