Strava performance graph with Mi Fit2 Heartbeat data

Using the Mi Fit2 bracelet with Strava

Strava performance graph with Mi Fit2 Heartbeat data

A few days back I got a Xiǎomǐ Mi Fit2 bracelet, and I recently discovered that it can be used with Strava on iOS to capture heart-rate data. Putting together the heart-rate data with the biking data is something I had to do manually with my Fitbit, with the Mi Fit2 it is reasonably easy.

Mi Fit App Experimental Menu
As far as I can tell, the moment the Mi Fit2 is paired with your phone, it is recognised by Strava as a heart-rate measurement device. Maybe it implements the relevant Bluetooth LE profile. The problem is, the Mi Fit2 only measures the heart-rate when you tell it, i.e. when the heart-rate is selected on the watch.

The way to force the device to measure the heart-rate regularly is by the way of the App. The following instruction are based on Mi Fit app version 2.4.3 (algorithm 1.0.95). Go to the play menu, scroll to the experimental section, and select behaviour tagging, and then select the relevant activity (there is biking). One thing to know is to stop you have to tap and hold the pause button and after some time, the option to end appears. As long as the activity lasts, the bracelet will measure the heart-rate regularly.

Élévation, rythme cardiaque, vitesse, puissance estimée, cadence

Senseurs & Vélo

L’année passée, j’ai remplacé ma montre fitbit charge par une Fitbit Charge HR (j’ai bêtement marché sur le précédent), qui est tombé en panne durant les fêtes, je soupçonne un bug dans le firmware, qui empêchait la synchronisation. L’objet a été gracieusement remplacé et je me suis remis à faire du vélo un peu sérieusement.

Comme j’ai un capteur bluetooth sur mon vélo, je peux à présent mesurer pas mal d’informatique : la vitesse, la cadence (le rythme auquel je tourne les pédales) et mon rythme cardiaque, plus de compteurs qu’une voiture classique.

Comme d’habitude le problème ne sont pas d’acquérir les données, mais d’y avoir accès. Si Strava permet l’exportation des informations au format TCX, impossible d’extirper les informations de rythme cardiaque de Fitbit, j’ai envoyé un message au support (#08575190) on verra ce que sera la réponse.

En attendant, les informations sont éparpillées sur deux dashboards, qu’il faut recoller à la main. À noter que le courbe du rythme cardiaque ne commence pas à zéro.

Élévation, rythme cardiaque, vitesse, puissance estimée, cadence

La première observation c’est que ces courbes ont beaucoup de bruit, pas réellement étonnant, vu que c’est un trajet à travers la ville. La seconde c’est qu’il n’est pas facile de corréler le rythme cardiaque avec d’autres informations: l’augmentation à la minute 23 correspond clairement à la montée vers Wollishofen, ce qui se passe à la minute 10 est moins clair, cela correspond à la région du Schiffbau, pas réellement une montée.

Malgré la ville, je suis plutôt régulier : j’ai tendance à aller à environ 20 Km/h avec une cadence aux alentours de 60 tours minute. L’avantage c’est que ce rythme ne me fatigue pas beaucoup – ici je rentrais après une heure et demi d’Aikidō – l’inconvénient c’est que ce rythme efficace est probablement un exercice négligeable.

View from the Wahoo Blue SC installed on my Merida bike, with replacement magnets

Any Magnet

View from the Wahoo Blue SC installed on my Merida bike, with replacement magnets

Biking apps seem to be built to appeal to competitive people: the notion of King of the Mountain (KoM), e.g. the fastest guy for a given segment is pretty prominent in Strava. I can’t say this interest me much. The current KoM of the A1 segment back from Aikidō is some guy called Matthias W., this had me quite confused. Be assured it is not me.

What I find interesting is to see data about how I ride, where I’m slow, which day I was fast, etc. Any good geek will tell you, more data is better, so I looked into adding some sensors to my bike. Surprisingly these things are not very expensive anymore, so I ended up buying a Wahoo Blue SC speed and cadence sensor.

The device is basically a bluetooth transmitter with two sensor plates that measure the frequency at which two magnets pass by: one on the pedal, one on the wheel. The installations instructions sounded pretty simple, except for one thing: one needs to unscrew the pedal to slip on the crank a rubber band with a magnet.

The thing is, even with the right key, I can’t unscrew the pedal – clearly I would need a longer key, the kind the guy in the bike shop has. There is a bike shop close to my flat, but it is typically closed in the morning, and closed when I come back in the evening. He is usually open on Saturdays, but this Saturday was the national holiday.

Yesterday it stuck me while I was swimming: this device probably just measures the frequency of the magnetic field, so the actual strength of the magnet would not matter, as long as it strong enough, so any magnet would do.

A few months back, I had, on a whim, bought some Neodymium magnets from Deal Extreme, I wanted to use them to fix things to the metallic frame of my office desk, which never really worked. The cool thing with these magnets is that they are really strong, and really hold on to any metal they are stuck to, like the screw that holds the pedal, the exact one I can’t unscrew.

So instead of the small magnet with its rubber band, I just stuck a bunch of magnets to the pedal, aligned everything and it works: I can now measure both speed and cadence of my biking. Sometimes, any magnet does the trick…

Strava iOS Screen Capture with a map of Zürich and statistics for a ride


Strava iOS Screen Capture with a map of Zürich and statistics for a ride

When I was a kid, I remember my father buying some distance measuring counters to mount on our bikes. A pin fixed to one of the spoke would increment a mechanical counter. Of course these did not survive long. Keeping track of my biking has always been a goal for me, but I was always frustrated by the complexity: I had a bike mount for my old Garmin GPS, but getting the data to the computer was horribly complex, I needed a serial port to USB adapter and the software for OS X was non-existent.

Things improved with the advent of smartphones and I started using Runkeeper. The program was always plagued by issues, power consumption and crashes. Things go worse recently, when crashed became systematic, and at the same time the level of nagging for premium access became obnoxious, it was time to look for another app.

A colleague had spoken about Strava so I gave it a go and I have used the iOS app for a few weeks now. I found the interface much more polished and intuitive for the basic stuff (starting and stopping a ride) and it crashes and nags way less than Runkeeper, so this is definitely an improvement.

Generally Strava seems to be more focused on biking and running: you can specify which bike you used, and rides are cut into segments which seem to be algorithmically constructed. You can see on the web interface how you compare with other bikers (there is another Matthias W. going twice my speed on some) and more importantly relative to past rides. I find this feature nice, but just wish there was an easy way to fix their name (one of them has a localization bug / typo).

My main issue with Strava is the Healthkit integration, while it exists, it is extremely buggy: the data for each ride keeps disappearing and only re-appears when I look at the given ride in the iPhone app. I also wish there would be an easy way to automatically match give rides (typically my commute to work and the aikidō dōjō) with certain routes and name and tag them accordingly.

I really hope that the Healthkit bug gets fixed because except for it, this is really a great app.