When a Step Is Not a Step! Specificity Analysis of Five Physical Activity Monitors

Area of Science:

• Wearable technology and biomechanics
• Health monitoring and physical activity assessment

Background:

• Physical activity is crucial for overall health.
• Accurate step counting by activity monitors is essential for reliable physical activity measurement.
• Non-stepping movements can lead to inaccurate step counts.

Purpose of the Study:

• To evaluate the specificity of five different activity monitors.
• To assess the accuracy of step detection during various non-stepping daily activities.

Main Methods:

• Five activity monitors (ActivPAL micro™, NL-2000™, Withings Pulse O2™, Fitbit One™, Jawbone UP™) were simultaneously worn by participants.
• Participants performed prescribed non-stepping activities (e.g., deskwork, cycling, driving, household chores).
• Video recording and direct observation were used to compare false positive step counts from monitors against actual movements.

Main Results:

• All tested activity monitors registered false positive steps during at least one non-stepping activity.
• The Withings™ monitor exhibited the highest specificity, with false steps only during outdoor cycling.
• Jawbone™ and ActivPAL™ monitors showed significant false step counts during various activities, including reaching and cycling.

Conclusions:

• Non-stepping physical activities can lead to inaccurate step detection by activity monitors.
• This inaccuracy can negatively impact the quantification of physical activity based on step count.
• The Withings™ activity monitor demonstrated superior specificity in distinguishing steps from non-stepping movements.