Review of the Wearables in Practice Symposium – April 6th 2018

An exciting and informative Symposium!

Friday 6th of April, finally we were heading to Soesterberg with a nice group from the University Medical Center Groningen (UMCG) to visit the “Wearables in Practice” symposium, which was organised by the Human Factors department of TNO (the Dutch Organisation for Applied Natural Scientific Research). The theme of the Symposium, Wearables in Practice, covered many of the new, smart, devices we increasingly see on the market. From smartwatch to accelerometer, and even smart alcohol meters which could help addicts, all facets of smart, wearable devices were represented here.

The day itself was organised very well, with an interesting program, and it was a lot of fun to take a look at what is happening at TNO. Also the diverse backgrounds of guests, from bussinesses to universities, and even the Royal Dutch Airforce, made it an interesting, diverse, and especially informative day. As cherry on top, I was invited to give a presentation about ACTman, a new piece of software developed by me in cooperation with scientists from the UMCG and the University of Groningen. ACTman finally allows researchers to automatically process and analyse physical activity data within mere seconds! This is especially impressive given the far longer times it took prevously to process and analyse such data, and that it cuts out a lot of the manual labour involved. As such, ACTman facillitates researchers and people interested in physical activity data in analysing large amount of activity data quickly and accurately.


Buyers Guide: Actigraphs

Points to consider

A common question faced by actigraphy researchers is: “Which Actigraph is most suitable for my study?”.

However, it is hard to give a simple and straightforward answer, as the optimal choice for your situation depends on your study design, e.g.,  study duration, sample characteristics, analysis goals, etc.

As such I have compiled some points which should be considered when choosing an actigraph for academic purposes:

1. Does the considered actigraph provide you with the raw data?

This is one of the most important points when considering actigraphs for academic purposes, and one of the most overlooked ones. 

“Why is this so important?”, you might ask. Well, when the raw data is not provided, the data can be somewhat akin to a black box. That is, you will have no idea what happened to the data beforehand. Perhaps the manufacturer uses a transformation on the data, or perhaps some smoothing functions. This will often be documented very sparsely, if at all.

As such, you will have at best only a partial idea of what your data respresents, possibly obfuscating your results, and your control over your own study.

Hence, when a device offers you access to the raw data you will have a better idea what happened to it and what it really means.

2. In what kind of unit will the actigraph measure?

This point is very much related to the first one. There are various units in which the actigraph can deliver its data. For example gravity units, activity ‘counts’, and manufacturer-specific units.

There are clear disadvantages with using aggregated count data, or manufacturer-specific units; they are not well suited for comparison among devices, argumentation and documentation regarding these units and their calculation could be withheld or stored behind paywalls,  the algorithms creating these counts could introduce unwanted alterations, tranformations, smoothing, or noise to the data. 

Hence, having a actigraph measure registered in a transparent, undisputed unit, which can be easily compared, and relates directly to a measurable force of nature – such as milligravity units – could prove benefical.

3. How valid is the data it provides?

When you are interested in sleep patterns, make sure your actigraph is validated against polysomnography, which is the go-to reference method in sleep research.

In any case it is good to make sure there are validation studies backing up manufacturer claims about validity and reliability. Also make sure  your actigraph of choice is validated in an equivalent sample population. 

4. How long will the considered actigraph last before it needs new batteries?

This is an important point as battery issues can seriously hamper the quality of your dataset. Even worse, the maximum battery duration given by the manufacturer might well be an overstatement which fails to materialise under normal conditions.

In the case of one of our own studies we were once confronted with an actigraph which boasted a battery life of 4 months. As such, we designed our whole study around this period. Hence our dismay when participants returned en masse with their empty actigraphs after a mere 2 months.

Thus, we had to make an ad hoc change to our design wherein we sent participants a new actigraph near the 2 months mark. This lead to unexpected costs for sending devices, an extra burden for participants, and worst of all missing data.

Therefore, make sure you know and test the actual battery life when considering an actigraph for your study!

5. Does it support user comfort and compliance?

Luckily, when compared to other physiological measurements – such as long-term ECG’s using skin irritation inducing electrodes – actigraphy is relatively benevolent. 

In my experience users can easily wear a well-designed wrist-worn actigraph for months on end without reporting any serious discomfort. 

This is a huge advantage as it thus allows for the collection of true large scale continuous datasets. This is especially important when planning complex and demanding analyses, as a lot of other measures, such as: questionnaires, daily diaries (ESM / EMA), or ECG’s, just can’t deliver enough data to conduct such complex analyses with a decent power-level.

While having participants wear an actigraph may be simple enough, having them consistently press an event marker to denote bed times and wake-up times can pose a much harder task. Such sleep logs are highly valuable in anyone interested in conducting sleep analyses.

Remember to regularly motivate and remind participants of using the event marker, or if a participant was not that consistent, you could try salvaging the sleep log by using the sleeplog_from_markers functionality from our ACTman R package which imputes missing marker presses by using the median times instead.

6. Is the actigraph robust enough?

Robustness of the actigraph simply denotes its resistance to everyday use with the associated wear and tear. A good actigraph should be able to resist damage and continue working. The best actigraphs degrade gracefully, meaning that its core function (providing actigraphy data) is maintained while non-essential functions stop working.

Some actigraphs (when used under certain study designs) might degrade ungracefully. For example, in a study wherein participants had to measure themselves for extended periods, we assessed remaining battery life by having participants press a marker button, which caused a small LED to light up. However, only later we found out that under low battery charge, its  core function; measuring actigraphy, stopped first; while the  marker button LED was the last function to fail.

Moreover, don’t only check on the robustness of the accelerometer itself, but also the robustness of the various appendages, such as wrist-bands, chargers, and cables.

For example, rubber based wristbands can tear easily after long use or by excessive force. The main breaking point is often the place where the rubber parts are vulcanised together.  When heavy use is expected, using a wristband made from plasticised textile  can offer improved robustness.

Also, make sure you have enough spare parts and tool handy when you start your study. These can often be acquired via the actigraph importer and/or manufacturer. 

My Garage: Peugeot 205 GTi

Garage: Peugeot 205 GTi

Can’t forget my old love,

a raw, free-revving 1.6, in a light and nimble chassis,
really rewarding to drive hard. Pushed my limits time and time again in this baby.

Hope to drive one of these angels again..
My old Peugeot 205 1.6 GTi:

Identifying the Parts of an Alfa Romeo GTV

Parts Katalog: Alfa Romeo GTV (916; Spider)

Knowing exactly which part of your Alfa you might be working on, can save you a great deal of work . 

When working on my GTV, I frequently consult this Parts Katalog [1]. It offers plentiful visual aids in identifying the individual parts, and gives rough price estimates.

This Parts Katalog can be found on, which offers a wide range of downloadable workshop and car documentation.

[1] GTV-Spider_(916) Katalog. (n.d.). Retrieved from

Choosing the most suitable Heart Rate Monitor

Heart Rate Monitor Comparison table

Heart Rate Monitors (HRMs) can be used to monitor the condition and performance of the heart. Therefore, they are regularly considered for health-, sport-, and research purposes.

During my study into identifying transitions in depressive symptoms using Heart Rate- and Activity data, we gained some experience in the selection and operation of HRMs.

As such information might be useful for clinicians, researchers, and other people alike, I would like to share our findings with you in this HRM Comparison Table.

If you would like to discuss the selection and operation of HRMs with me, or if you would like to share your experiences with HRMs, feel free to contact me.

Welcome to my Website and my First Post here

This month I  gave a interview to the Dutch Arts and Auto magazine. This magazine provides information that could interest healthcare professionals around their work and spare time. They also have a website with additional news. Thanks to Monique Bowman and Kees van de Veen for the interview and photo’s!

English after Dutch

De ultieme droomauto van psycholoog/aio Yoram Kunkels (31) is een Maserati Quattroporte. Maar aangezien z’n budget twee jaar terug helaas geen dikke ton maar een krappe vierduizend euro bedroeg, rijdt hij in plaats daarvan voorlopig een Alfa Romeo GTV turbo V6 uit 1996. “Dat was de auto met het meeste vermogen voor dit budget. En hij wordt alleen maar meer waard verwacht ik, want het is een echte liefhebbersauto.”

Dat Alfa’s geplaagd worden door pech, heeft hij zelf gelukkig nog niet ervaren, vertelt Yoram, die gediplomeerd automonteur is maar zich tegenwoordig (“de autotechniek vond ik niet uitdagend genoeg”) aan het UMC Groningen verdiept in onder meer transities in hartritmes bij depressies. Wat zijn eigen hartslag betreft: die schiet omhoog zodra hij zijn 2.0 V6 turbo met 270 Nm koppel de vrije teugel geeft op de Duitse Autobahn. “Dat is natuurlijk het voordeel van in Groningen wonen. Ik zit met m’n GTV zo in Duitsland.”

The ultimate dreamcar of psychologist/PhD-student Yoram Kunkels (31) is a Maserati Quattroport. But since his budget two years ago unfortunately was not a good 100.000,- but only a tight 4.000,-, he is currently driving an Alfa Romeo GTV turbo V6 from 1996. “That was the car with the most power for this budget. And it will only increase in how much it’s worth, because this is a real collector’s car.”

That Alfa’s tend to be plagued by problems, is something he luckely cannot confirm himself, tells Yoram, who is a qualified car mechanic but who nowadays (“being a car mechanic was not challenging enough”) is investigating transitions in heart rhythms during depression. As far as his own heartbeat is concerned: it shoots up as soon as he releases his 2.0 V6 turbo with 270 Nm of torque on the German Autobahn. “That is of course the advantage of living in Groningen. I’m quickly in Germany with my GTV. “