Wrist-based heart rate measurement is on the rise. But is it really time to ditch the good-old chest strap to determine your heart rate? Most new and high-end running GPS watches are either wrist-based and chest strap compatible or at least chest strap compatible. Which one is “better” or at least more suited for your needs?

Wrist-based heart rate measurement is light based. A small LED at the back of the watch emits green light which is reflected more from the wrist vein when there is less blood blood present in the vein. When the heart pumps, more blood arrives in the wrist vein and the green light reflection is decreased. These small “reflective cycles” are detected by the watch. The time between the cycles is used to calculate the heart rate. However, this repetitive pattern analysis is challenging and prone to measurement “noise”. This noise might be introduced by the individual wearing the watch. For example some people’s veins might reflect light better than others. Also the position of the watch matters. It should be worn relatively tight and about 1-2 cm above your wrist. Finally, the “blood signal” measured at the wrist might be weaker than when measured directly at the heart, simply because it is further away from the source. As a result, changes between maximum and minimum reflection might be small and difficult to analyze. This is especially true during situations with rapidly changing heart rates where the reflective “peaks” and “valleys” occur in difficult to analyze irregular patterns.

Chest strap based heart rate measurement on the other hand relies on the detection of an electrical signal emitted from the heart. Weak electricity propagates through the heart muscle in order for it to contract and to be able to pump blood. Measuring this signal directly at the “source” is very accurate and less “noise” is introduced by the biology of the user or other factors. Despite this, also a chest strap needs to worn correctly (tightly, right under the chest muscle).

So which technology is better for your workout? To check this I wore both a chest-strap based Garmin Foreunner 610 and a wrist-based Garmin Foreunner 735XT and went for a 11km run. This run included some sprints in the beginning (100m, 200m, 500m, 200m, 100m) and a 1km uphill tempo run towards the end. Here’s the bottom line: Both technologies are very comparable! Fig. 1 below shows the two differently measured heart rates (FR610 = chest strap, FR735 = wrist). Especially at “steady state” when the heart rate does not fluctuate much both technologies are very comparable. Before the run when I was just standing around both showed about 70 bpm (beats per minute, not plotted). Also the averages of both technologies either over the entire run of 11 kilometers or per finished kilometer are very comparable. Overall both curves look very similar, but the difference is significant when analyzed with a Student’s t-test (p = 0.027, two-tail, paired). Despite this, the difference of on average 1.4 bpm is so low that it has no practical relevance when your heart rate is around 160 bpm during a workout. Even the sprints around kilometer 3 and the long high-intensity hill sprint around kilometer 9 did not introduce a large difference on average.


Fig. 1: Comparison of the average heart rates per kilometer over the course of a 11km run obtained with a chest strap-based technology (FR610) or a wrist-based technology (FR735). Both technologies are comparable when averaged over longer time periods, although the wrist-based measurement seems to measure slightly lower values.

But how do things look like when you zoom into the data? Especially, when concentrating on situations with a lot variability? I did the pyramid sprints in the beginning to find this out. I sprinted 100m, 200m, 500m, 200m and finally again 100m with 200m breaks in between to let my heart rate go repeatedly up and down. For both watches, in Fig. 2, you can clearly see the black lines, indicating the speed, go up and down as you would expect for the five sprints and recovery phases. In both cases also the heart rate, represented by the gray lines, react as expected: Similar peaks as the speed, but with a slight delay. It is, however, surprising that the chest strap-based heart rate seems to be measured in a much smoother way. In addition the recovery phases between the sprints are picked up as expected. The wrist-based technology seems to have trouble here. Heart rate maxima are very similar, but drops during the 200m recovery phases lasting about 1 minute are less pronounced.


Fig. 2: Comparison of heart rate and speed during pyramid sprints obtained with a chest strap-based technology (FR610) or a wrist-based technology (FR735). GPS-based speeds are similar as expected, but the heart rate fluctuates much more when measured at the wrist and does not respond as accurately as chest strap-based measurements to rapid changes, for example during the recovery phases between two sprints.

During short time scales wrist-based heart rate measurements might therefore have more trouble to pick up rapid heart rate changes, especially when large differences between maxima and minima are present. Despite this, the overall performance of both technologies is very comparable and probably accurate when averaged over longer times such as minutes or an entire run, even if high-intensity phases such as sprints or hill running are present.

For you as an athlete this means the following: Wrist-based measurement is a hassle-free and accurate way of gaining insights into training status and workout intensities during longer training runs or training runs involving longer intervals such as Fartleks or hill sprints. If your training requires accurate heart rate measurements during very variable high intensity workouts, you might want to consider using the good-old chest strap. Classical track-based workouts involving 200m or 400m repeats with relatively short recovery phases in between, would fall into this category.

Happy training with all this technology around your wrist and chest!

If you are into biking, running or any other outdoor activity in can be quite entertaining/helpful to record your activities with a GPS. The resulting tracks (in .gpx format) are easily obtainable from for example Garmin devices or the Strava app. Routinely these tracks are overlayed with maps such as Google Maps or Open Streetmap, but it is also possible to take the latitude, longitude and altitude information out of these GPX tracks and plot them in 3D.

Here’s an example how to do this in MATLAB (you need the Mapping Toolbox).

First, add the .gpx file into the MATLAB path folder, here I call it “Bergankunft.gpx”.

Now tell MATLAB to read the .gpx file, extract latitude, longitude, and elevation and plot the obtained information:

route = gpxread(‘Bergankunft_with_Niklas.gpx’);
x = route.Latitude;
y = route.Longitude;
h = route.Elevation;
plot3(x, y, h, ‘b’, ‘LineWidth’, 8)
grid on

Now you have your track as 3D figure and you can manually turn it and study your efforts in 3D 😉

In order to make a video of the whole thing download a MATLAB function created by Alan Jennings which allows you to create a video of any rotating 3D ‘lot (https://ch.mathworks.com/matlabcentral/fileexchange/41093-create-video-of-rotating-3d-plot?s_cid=ME_prod_FX).

I used the following settings:


CaptureFigVid([-180,10;-360,20;], ‘Bergankunft3D’,OptionZ)

Please also check out Alan’s instructions in order to understand what the variables mean. Most important are frame rate, the total duration, and the angles at which the plot is turning and captured.

The resulting small video (MP4) will be saved in your MATLAB path folder and you can watch it with any media player.

In my case (a trailrun from Lauterbrunnen to the Gspaltenhornhütte in Switzerland) the result looks like this:

Yes we can image mRNA

October 18, 2013


Hello Basel!

August 30, 2013

BaselStay tuned for my next exciting project!

Designing a poster

August 1, 2013

Presentation time. In order to attract a few people to my talk I designed this poster with the freely available GIMP software. It takes a while, but the possibilities that GIMP has to offer are astonishing. The software is great for creative outbursts. And wouldn’t it be nice if scientific posters could become more appealing to the eye in the future? The Biology Department of the University of North Carolina at Chapel Hill is already quite good at it: http://www.flickr.com/photos/biologyposters/.


Crossing 45° North

April 13, 2013


Partly painted walls – Boston


Enjoying some liquid sugar – Boston


Winter swimming (no pictures) – Somewhere in the woods


The Atlantic – Rockport


Freeclimbing or something like that – Rockport


Gone fishing – The Atlantic


Mont Royal РMontr̩al




A house in Montréal


A factory in Montréal


More houses in Montréal (it’s a beautiful city though, photos are selective)




Montréal at night (on top of Mont Royal)


Parking lot






Québec and its frozen river/part of the sea


See above


White Mountains hiking


Random impressions

February 7, 2013

No biology today, just photos from Boston. Click here for a little soundtrack and click the individual photos for higher resolution.

28 12 13 14 15 16 17 18 19_b 20 22 23 24 25 26 27

Getting visual

December 9, 2012

My current project explained in a short video. For biological science beginners and only in German. My apologies for these restrictions!

Check the video HERE.

Building a Single Speed

September 5, 2012

Mine is done. Now construct your own Single Speed bike. Here’s what you’ll need:

  1. Everything starts out with a nice frame. I would suggest a 1970s/80s steel frame, but that’s basically a matter of taste. Buy a new one (expensive!), buy a used one, or use that old dusty frame from your garage. Some things you should care about when deciding for a frame: (A) Think about the size you need. This table gives you an overview. Mentioned is the height in centimeters of the seat tube. (B) Check whether a headset and a bottom bracket is still part of the frame, since both are quite expensive parts and relatively difficult to mount. If you can check/ask for the quality (smooth movements, no slackness). (C) Next thing on the list is to check what kind of back dropouts the frame has. For a single speed bicycle horizontal dropouts are best because they allow you to adjust chain tension. I have a frame with vertical dropouts you’ll need an extra chain tensioner later (which kind of destroys the great look of your new bike). (D) The last thing is to check is in what state the frame finishing/paint is. Make sure there is no rust in the headset and bottom bracket area.
  2. If your frame has a bottom bracket already just buy a fitting crankset. If a chainring is attached already make sure that it’s not too large. A 53-tooth chainring is definitely too large for a single speed bike and pedalling will be quite heavy. For me a 46-tooth chainring is perfect. In case your frame doesn’t have a bottom bracket, you should first find out which standard-type you need.This mainly depends on the diameter and the width. Here’s an overview. For the headset there’s basically only one standard. Mounting both parts into your frame is quite complex and if you are not an experienced bike mechanic you should seek the assistance of your favourite bicycle shop.
  3. Now the hardest part is over and you can start searching for the essential parts of your bike that actually make the frame look like a bike: The wheels. Since a single speed bike is not a fixed-gear bike you can use a freehub. I think it’s a bit more comfortable and safer for a beginner. Best thing is to use 28” (inch) diameter rims. For the back wheel just remove the cassette from the freehub and replace it with a single speed conversion kit. Once you have it it’s about 15 minutes work to set it up. I am using a 18-tooth sprocket in combination with the already mentioned 46-tooth chainring in front which is perfect for flat cities and longer journeys. So choose your sprocket size wisely.
  4. For the likely case that you have horizontal dropouts: Be aware that back wheels with quick release skewer might slip if you are a strong guy. I recommend to replace the quick release axle with a standard axle with nuts. If you can find a solid axle with the same diameter and thread pitch and a couple of nuts it will work. Remember that your  new axle should also be at least 4 cm longer than the old (quick release) hollow axle. You need some special tools for it, but you local bike shop can probably assist you.
  5. Now buy some tires. This might seem a bit early, but it’s good to buy them now because you need to check whether they fit your brakes and frame. I’m using 28 mm wide Continental Grand Prix Four Season tires because I think they are fast and comfortable at the same time. Get some high quality inner tubes as well.
  6. It’s time for brakes now. Mounting them is not difficult, just have a look at an existing bike. However, sometimes some fiddling is necessary to get them parallelly aligned.
  7. Next, organize yourself a seat post and a saddle. It’s very important that the diameter of the seat tube exactly matches the diameter of the seat post. Otherwise, you’ll always have fun with a slightly down-sliding seat post. Also find a handlebar now that fits your needs and you think is comfortable.
  8. A bike is nothing without the chain. I would buy a new chain to prevent slipping issues. A special single speed chain is not necessary. To shorten the chain you need a special tool that you can again find in your favourite bike shop (or borrow one from a friend). Concerning the chain: Shimano offers a system called “Quick Link” which makes closing the chain, after having adjusted the length, very easy.
  9. Last, but not least get some pedals. If you cannot decide whether you want to use bike shoes with cleats or not, just buy pedals with a regular and a cleat side.

Parts you should consider to buy new include bottom bracket and headset, as well as front chain ring, sprocket and a chain. New rims and tires are nice, but not necessary. As I wrote, sometimes you will probably need the assistance of an experienced bike mechanic. Probably you will also have to pay him or her, but I definitely think you can have a very beautiful and good working single speed bicycle for around 200€. Well, I think that’s it. Have fun. For more info there is also the famous single speed/fixed-gear bible by the late Sheldon Brown. His “Bicycle Technical Info” page supplies with everything you need to know. If you are from Groningen, you should also pay a visit to Fietsje, a great bike shop with many useful single speed accessories.

Something about my current OOLP! – an out-of-lab-project:

This is an absolutely not biology or biophysics related blog entry. And that is because once in a while its nice to do something completely different, but in contrast to the Python’s I’d like it to be visible. I like sports, but since Groningen is not the best place in the world to go running, it is pretty awesome to go biking. Also the city itself offers some nice possibilities. So it was only a question of time to start an out-of-the-lab-project including the construction of a bike. I chose a total bottom-up approach. Buying, finding or asking for every part. Some progress so far, can be seen below:


First I wanted to construct a real fixie, meaning a bike with no brakes and one single and even fixed gear. That means you have to pedal constantly. It’s as simple as you can get it. It gives you the perfect feel for the road. It’s Gods first bike. However I decided not to construct a real fixie. I wanted brakes. Somehow it felt safer that way. However, this bike will still be a pretty basic bike. The brakes are the highest level of technology you will find on this bike. It’s based on a 1980 Ludo frame from Belgium. In 1964 Eddy Merkx became world champion on such a frame. Of course we’re talkin’ steel frame here. Durable, plain simple. And a bit heavy. But when you’re building a bike with no gears you shouldn’t complain about cycling becoming a bit difficult once in a while.


After having to cut new screw threads at the headset and the bottom bracket (the bike dealer did that), finally a 46er chain ring and some cranks could be mounted. Also a handlebar is part of the ensemble now. Oh yeah and my dad luckily assisted on adding some brakes. Nice old Shimano’s which had to be modified quite a bit in order to fit the world champion frame. I hope during the next weeks I’ll find a nice back wheel (and front wheel). The rest are only details. And then the cruising begins. Until I stop.