We love tech that is smart and functional so figuring out how the Apple Watch can nut out your swim stroke automatically is worthy of a deep dive. Calling it a multi-function watch doesn't seem right once you start pulling it apart.  Here at FINIS Australia we think saying it's a seriously smart swim tracker is just the start of it. 

FINIS design technical swim equipment that help every swimmer see results

The Apple Watch became water resistant in 2016 and OS upgrades delivered some next level metrics like set detection. This watch knows when you rest at the pool's edge and then uses that pause to divide the workout into sets of laps, showing you how far and long you swam in each, what stroke and your rest time.  All this from a watch!

Apple certainly dig data.  In order to develop the algorithms to process the stroke of swimmers of all skill levels, they gathered data from more than 700 swimmers across more than 1,500 swim sessions. But wait, then they did more!  Apple also gathered data from people swimming in one spot while wearing a mask connected to monitoring equipment through the ceiling to capture everything at play in the session. That's a ship load of data and we at FINIS salute those who turns stats into better swimming.  There is a very good reason it took so much data to fine tune the Apple algorithm.  

Swimmers will be well aware skill level affects form but getting software to understand that is a tricky business. “If you are Michael Phelps, you’re distinctively making very good differences between the four strokes— backstroke, freestyle, breaststroke, and butterfly,” says Jay Blahnik, one of Apple's tech fitness and health gurus. “If you are me, it turns out that once you look at the signals from the gyroscope and accelerometer, they’re not as strong and as clear.”

So for the tech stuff... a gyroscope and accelerometer track the motion of your strokes.  However, when you swim in open water, the algorithm supersizes it's combo by adding another sensor to the mix: the GPS chip.  When you take a dip in the ocean, river or lake, your watch uses GPS to determine how fast and how far you travel.

The development team did hit a small snag - GPS signals don’t travel through H2O. The good news is swimmers are likely to do freestyle in open water which means your arms regularly break the surface. The watch will set the GPS chip in acquisition mode for the whole swim. It goes hunting for a signal every time your hand comes up out of the water. “We’re trying to catch it every single time,” says Ron Huang, Apple’s director of engineering for location and motion services.

To recap, the accelerometer measures motion, and the gyroscope spots how many degrees the watch rotates per second. That magic data helps Apple nail stroke type.

Skilled swimmers do flip turns at the end of the pool but no matter how you turn, the watch needs to be able to spot it.  This is where the gyro earns it's keep. It measures rotation in three separate planes in space: around the x, y, and, z axis. The x-axis goes horizontally across; the y-axis is vertical and the z is straight out from the screen. Apple's software interprets the data from the gyro to nut out when you’ve reached the end of the pool and turned 180-degrees and started moving in a different direction.

Before you start your swim, the watch will ask for a few hints - namely what the pool length is. This is super handy because the watch learns how many strokes it typically takes you to complete a lap and will anticipate when you are about to turn.  If you normally need about 25 strokes, but later in the workout you take just ten, the watch will figure out you've probably stopped to take a breather on the ropes. Every swimmer knows a strategic break works wonders, full credit to any watch that gets this too!

FINIS Amnis Stream bluetooth headphones


The new FINIS Amnis Stream bluetooth headphones pair with the Apple Watch for stunning underwater sound.

FINIS pioneered bone conduction underwater sound with the Duo MP3 player and now this latest offering lets swimmers access more of their favourite music to help the laps fly by.


Learn how to pair your Amins Stream bluetooth headphones with your smart watch


September 01, 2020 — Information Finis Australia