The Full Frame

Many of you reading this article probably encountered this product the same way that we initially did, in a journal article under the methods section. This article is intended to give you an idea of product from a feasibility standpoint from an experienced computer technician and researcher.

Disclosure statement: I am not affiliated with Actigraph in any way and have received no compensation for this review.

Actigraph GT3X

MSRP $335

The Actigraph GT3X is a tri-axial accelerometer whose claim to fame lies in its very accurate movement filter whose primary purpose to differentiate actual steps and movement from any other background noise movement that may occur while wearing the device. It is capable of measuring very small amounts of movement such as those generated by the elderly and other home-bound subjects. This device’s data is widely accepted in research circles throughout the scientific community.

To get up and running with a basic kit will run you  $706 ($349 software + $7 USB cable+ $335 GT3X+ $15 Elastic Band).

Closeup of the Device

The following are my impressions of the device and its ActiLife software.

Pros:

1. Incredibly accurate
2. Very long battery life
3. Lightweight
4. Noiseless
   
5. Intuitive and easy to use software
6. Lexan case (though I would like to see aluminum or magnesium)
   
7. Graphical display of steps and movement along the various axes.
8. Direct import of raw movement data into excel tables
9. Quick shipping, friendly & prompt staff

Cons:

1. Not waterproof
2. Slow download speed (3-7 minutes)
3. Poorly designed belt mounting loops
4. Expensive proprietary accessories (elastic belts, USB cables, cases)
5. Software NOT included with purchase of device
6. USB cables not included with purchase of device

The Actigraph GT3X is a transparent red block of plastic (judging by density, hardness, and malleability the material feels very similar to Lexan) and electronics roughly the size of a Zippo lighter. It has a weather seal along its main joint and a USB port with a rubber plug that in general won’t immediately fit and create a snug seal. Looking at the workmanship I was immediately struck by the manufacturer’s choice of form over function. Sleek lines, rounded edges, and a carefully recessed rubber plug for the USB port do little for me whose main concern would be device’s robustness.

In assessing the device’s physical weaknesses the first thing to come to mind was the thinness of the mounting loops. With moderate finger pressure I can squeeze the plastic of the loops together until they bow inward. This does not bring much confidence that the device will stay firmly attached to an active subject. Likewise I would be wary of using it on heavier subjects as their increased circumference would be much more likely to snag the device on environmental objects and possibly rip the device from it’s mounting belt. Secondly I am struck by the fact that this device is NOT waterproof. I can see through the transparent plastic a black rubber gasket that assures water resistance for the two halves but the integrity of the USB port seal is questionable at best. My ideal device would be made of metal and have a  screw-in bezel type weather seal for the USB port that would make it waterproof. There is really no excuse that it doesn’t already have a more positive belt attachment as standard equipment. Actigraph does sell a belt clip for $4 that appears to just stick to the back of the device via adhesive.  A standard USB Type A to Type B mini connector would have been very useful in lew of the proprietary USB connector used. The device transfers its 4MB of internal data verrrrry slowly to the computer. The Actigraph GT3X is using a Silicon Labs Serial to USB chip (CP2102) meaning the chip itself is capable of USB 2.0 speeds just like your camera or whatever but the serial backbone slows it down to roughly 13-20 kb/sec. It will take a good 3-7 Minutes to download a single device’s data unto your computer.

Actigraph firmware engineer Judge Maygarden writes:

“…download speeds are indeed limited by the low-power processor and serial connection. However, GT3X firmware version 2.2.0 and ActiLife software version 4.2.0 contained optimizations that allow increased throughput. This combination should reduce your worst-case download time from 6 minutes to 1 minute for 4 MB.”

Finally the battery is not easily user changeable but could be done by anyone with some soldering skill.

The Battery

The internal battery is model number LP603026, lithium ion 3.7 volt, 420 mAh and made by a company called EEMB (Link to EEMB product page)

This appears to be a good battery choice for a long lifespan, but as with any lithium-ion battery the end-user should be concerned about exposing it to low temperatures during usage as this can drastically affect battery life. My suggestion is if this is to be used outdoors during weather less than 50 F to be sure the device is indeed as close to the body as possible and under protective clothing.

The Software

The software is intuitive and user friendly. A user that is moderately skilled with Windows can get the device off and running without reading the manual. I was impressed by the fact that the device automatically detected that I was not running the latest firmware for my GT3X and prompted me to automatically download and install the update. The firmware install went well but I was unimpressed with the lack of warnings that accompanied the firmware update. If one was to accidentally unplug the device while the update was progressing it would “brick” the device and essentially turn it into a $300… brick. The average user who is not very familiar with computers may not know this and may inadvertently ruin their device in an attempt to speed up the process.

Firmware installs can be a time consuming and risky procedure for any electronic device from calculator to cell-phone, my previous fears of a device corrupted by an incomplete firmware update were answered by Actigraph engineer Judge Maygarden,

“Disconnecting the USB cable during a firmware update will NOT brick your GT3X. Firmware field updates can be tricky, but we have put a lot of effort into avoiding such problems. The device is only susceptible to “bricking” for a very short duration after the firmware upload completes, and such an event would require a battery interruption to occur.”

The graphs the device gives are very user friendly. You can choose to analyze the data in Microsoft Excel which you must have installed on your system already. You must also manually set your Excel security settings to allow VB and Macro scripts to run. This may not be possible on certain institutionally owned devices so check with your IT department or else you may end up having to do all your data analysis on a personally owned computer.

Screenshots of the software

Conclusion

Truth be told there is not much that physically separates this device from a $40 accelerometer chip or something like this NewLifeStyles Accelerometer or even an Ipod Touch/Iphone with its built in accelerometer capabilities. At a hefty price of $335 without its needed software and accessories this device is certainly marketed to the upper echelon.

I can not immediately find a direct competitor to this product. The included firmware data filtering equations that the device uses to actually sort your body movements and steps from “noise” movement seem to be the most accurate of any accelerometer of this class. A lot of programming effort went into making the software that interprets the electrical signals from the accelerometer itself and I believe that that commands a certain proprietary sum. Certainly the “movement monitoring” field is not a very competitive one for Actigraph but for the time being it seems like they have the research “pedometer” field cornered.

Excellent accuracy coupled with: easy-to-use software, friendly and attentive staff, and a laundry list of research protocols make this device a winner. If actigraph would take care of the cons mentioned at the beginning of the article I think they could firmly cement their monopoly on the market.

Kudos on an excellent product, Actigraph.