Medical-Grade Physical Activity Monitoring for Measuring Step Count and Moderate-to-Vigorous Physical Activity: Validity and Reliability Study.
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BACKGROUND The use of physical activity PA monitors is commonly associated with an increase in habitual PA level in healthy and clinical populations The PiezoRx is a medical grade PA monitor that uses adjustable step rate thresholds to estimate moderate to vigorous physical activity MVPA and is a valid indicator of free living PA in adults Laboratory validation of step count derived MVPA in adults is needed to justify the use of these monitors in clinical practice to track individuals progress toward meeting PA guidelines that are based on MVPA not steps OBJECTIVE The objective of our study was to assess the validity and interinstrument reliability of the PiezoRx to derive step count and MVPA in a laboratory setting compared with criterion measures and other frequently used PA monitors in a diverse sample of adults METHODS The adult participants n 43 39 4 years SD 15 2 wore an Omron HJ 320 pedometer an ActiGraph GT3X accelerometer and four PiezoRx monitors during a progressive treadmill protocol conducted for 6 minutes at speeds of 2 4 3 2 4 0 5 6 6 4 and 7 2 km hour respectively The four PiezoRx monitors were set at different MVPA step rate thresholds MPA in steps minute VPA in steps minute 100 120 110 130 height adjusted and height fitness adjusted RESULTS The PiezoRx was more correlated intraclass correlation ICC 97 PUnder 001 to manual step counting than the ActiGraph ICC 72 PUnder 001 and Omron ICC 62 PUnder 001 The PiezoRxs absolute percent error in measuring steps was 2 2 ActiGraph 15 9 Omron 15 0 Compared with indirect calorimetry the height adjusted PiezoRx and ActiGraph were accurate measures of the time spent in MVPA both ICC 76 PUnder 001 CONCLUSIONS The PiezoRx PA monitor appears to be a valid and reliable measure of step count and MVPA in this diverse sample of adults The device s ability to measure MVPA may be improved when anthropometric differences are considered performing at par or better than a research grade accelerometer