Actiwatch Spectrum System


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Facility Summary

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Brief Summary

The Actiwatch Spectrum is a waterproof, nonintrusive, sleep-wake monitor worn on the wrist of a crewmember. The device contains an accelerometer for measuring motion and color sensitive photodiodes (a photodetector capable of converting light into voltage) for monitoring ambient lighting. Together, these capabilities enable the Actiwatch Spectrum to be used to analyze circadian rhythms, sleep-wake patterns, and activity.

Facility Manager(s)

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Facility Representative(s)

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Johnson Space Center, Human Research Program, Houston, TX, United States
Respironics Inc., Murrysville, PA, United States

Sponsoring Space Agency

National Aeronautics and Space Administration (NASA)

Sponsoring Organization

Human Exploration and Operations Mission Directorate (HEOMD)

ISS Expedition Duration

September 2010 - September 2012

Expeditions Assigned


Previous ISS Missions

Information Pending


  • Onboard
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    Facility Overview

    • The Actiwatch Spectrum captures data on subject activity and motion and the amount of ambient light to which the subject is exposed.

    • The Actiwatch Spectrum is a replacement for an older Actiwatch system and comes with the added capability to differentiate between multiple wavelengths or colors of ambient light across a broad spectrum (400-700 nm). The Actiwatch Spectrum also has the added capability to display time and function as a watch.

    • The Actiwatch Spectrum can be used to investigate a number of activities such as sleep quality, sleep onset, hyperactivity and other daily routines.
    The Actiwatch Spectrum System is a modified commercial-off-the-shelf (COTS) system consisting of the Actiwatch Spectrum Kit, Actiwatch Spectrum, Actiwatch Spectrum Dock, Actiwatch Spectrum Universal Serial Bus (USB) Cable, and Actiware Software (version 5.52 or later). The Actiwatch Spectrum is a small, battery-powered, limb-worn device that simultaneously detects body movement and light intensity. The unit can be used to investigate a number of activities such as sleep quality, sleep onset, hyperactivity and other daily routines. The Actiwatch Spectrum System will be used by experiment teams for baseline data collection on the ground as well as onboard the International Space Station (ISS). The Actiwatch Spectrum is designed for intravehicular activity (IVA) only and, although waterproof to a limited extent, should be removed prior to performing any activity that would put the hardware at risk of immersion in water. The Actiwatch Spectrum can be programmed to collect data in a variety of modes including activity, photopic light, red-green-blue (RGB) light or several combinations thereof. Data is sampled by the Actiwatch sensors at a frequency of 32 Hz and may be recorded at a variety of epochs: 15 and 30 seconds and 1, 2 and 5 minutes. Total recording time is limited by the data collection mode and epoch setting. For example, an Actiwatch configured for activity, RGB light and photopic light at a 15-second epoch is able to collect data for 9 days while an Actiwatch configured for activity only at a 1-minute epoch can collect data for 182 days. When initialized, the Actiwatch Spectrum may be configured to begin recording data immediately or delay data acquisition to a specific time and date. In addition, the Actiwatch can be configured to either collect data until the memory is full or halt data acquisition and go to sleep mode (a low-power, battery saving setting) after a user-specified length of time. When collecting data until the memory is full, the Actiwatch will go to sleep mode once it can no longer continue recording data. The Actiwatch Spectrum is also capable of detecting when the watch is worn against skin or a conductive surface (< 2mm separation) and recording event markers.

    The Actiware Software is used for data analysis, file management, configuring an Actiwatch Spectrum for data collection and retrieving data from an Actiwatch. Data downloaded from an Actiwatch is stored in a user-specified database file and organized by the subject ID used to configure the Actiwatch. The Actiware Software may be used to access subject information and view or analyze data for sleep parameters and rhythmicity. Raw data or statistics may also be exported for external analysis or archival. Battery life may be checked using the Actiware Software while communicating with an Actiwatch. While the Actiware Software supports older versions of the Actiwatch hardware, the Actiwatch Spectrum and Actiwatch Spectrum Dock cannot be used with older versions of Actiware, Actiwatch Readers or Actiwatches.

    The Actiwatch Spectrum System was first launched on STS-133/Flight ULF-5 in February 2011. Replacement of internal batteries will not be performed on-orbit, therefore, periodic resupply of fresh Actiwatches is planned. The Actiwatch Spectrum is currently used in the ambulatory monitoring portion of the Integrated Cardiovascular experiment aboard the ISS. Activity data collected by the Actiwatch is analyzed in conjunction with cardiovascular data from other devices to estimate the amount of work the crewmember?s heart performs on a daily basis.


    Facility Operations

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    Results/More Information

    Results Publications

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    Ground Based Results Publications

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    ISS Patents

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    Related Publications

      Mallis MM, DeRoshia CW.  Circadian Rhythms, Sleep, and Performance in Space. Aviation, Space, and Environmental Medicine. 2005; 76(6 Suppl): B94-107.

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