Assessment of Physical Activity Intensity with Accelerometers and Oxygen Consumption.

The study compares objective methods of assessing the intensity of physical activity. The goal was to identify the differences in physical activity intensity measured through indirect calorimetry and triaxial accelerometry on the wrist and waist, using the counts cut-off points for the accelerometers and ventilatory threshold one (VT1) and two (VT2). This research is a cross-sectional analytical study of university women (n = 35, 22.4 ± 1.9 years old). Triaxial accelerometers and portable ergospirometry were used during an incremental standardized walking-jogging test in an oval track of 160 m length (speed increments every minute with an audible signal from 0.84 m/s to 2.37 m/s). Accelerometry (from wrist and waist), oxygen consumption, and ventilatory response data were collected during the test. VT1 and VT2 were estimated through VSlope (VO2/VCO2) and carbon dioxide production/minute ventilation (VCO2/VE), respectively. An open-source statistical software was used. All the participants were able to finish the test. VT1 was found in stage 2 (n = 5), stage 3 (n = 5), stage 4 (n = 3), stage 5 (n = 8), stage 6 (n = 5), stage 7 (n = 3), stage 8 (n = 1), and in stage 9 (n = 5). VT2 was found during the incremental test only in 9 volunteers, in stage 7 (n = 2), in stage 8 (n = 3), stage 9 (n = 2), and stage 10 (n = 2). Differences between wrist and waist accelerometer measurements were observed in higher intensity stages of the test. Higher PA intensity measurements were found in the wrist, mainly above VT1. Also, there were differences between physical activity intensity levels detected by accelerometers and VT1 and VT2. The commonly used methods to assess physical activity intensity show no agreement in identifying the speed at which vigorous-intensity physical activity begins during an incremental test.