Ali Wood comprehensively tests the Garmin Active 4s and tells us how to hack the open water swimming tracking.

Tracking open water swimming with a smart watch

Being a cold water swimmer with an aversion to chlorinated pools, I had to do a bit of a workaround to test Garmin’s Pool Swim app in the sea. There is no option for tracking open water swimming with the Garmin Vivoactive watch (and indeed on a lot of smart watches). This is because it uses lap data rather than the GPS signal, which gets lost each time the watch is dunked and takes time to reconnect.

The Garmin Vivoactive watch isn’t designed for cold water swimming but if you can measure some kind of lap you can still use it


So, for measuring performance and GPS distance in open water, you might be better going for a watch like the Garmin Swim 2.

My Garmin Active 4s swim fix for open water

To work out my swolf in the sea, I first used the Walk app to measure the distance between two groynes. It was 112m. I then entered this into the watch settings as a pool length, and treated it like a regular lap. 

I jumped in, pressed the Active button, and off I went. At the groyne I pressed the Active button to indicate my lap was complete, and it gave me a swim time of 2:07 minutes (127 seconds), which is a pace of 1:53 minutes per 100m. Like with the running app, I can use this feature to swim faster. 

Measuring my swolf using the pool swim app on the Garmin Vivoactive watch

What is swolf? Improving swim technique with a smart watch

Where the Garmin Vivoactive 4s comes in handy for swimmers is the ‘swolf’ measure. This records the number of strokes you do in a given length and adds this to the time to create a score. So, for example, if a length takes you 30 seconds and your watch records 15 strokes (when your wrist hits the water), you get a swolf score of 45. Like golf, a lower score is better. 

What happens to your heart rate in cold water?

On one occasion I managed to massively increase my heart-rate without doing any work… you might call that cheating!

As a keen cold water swimmer, I decided to measure my heart-rate going from a gentle walk on the beach to stripping to my swimsuit and jumping in the sea in February. 

My resting heart-rate is quite low anyway, but went from 70 to 135 in a few seconds as I shrieked and gasped, waiting for my breath to come back. 

Increased heart rate is one of the body’s typical responses to cold water shock, and is why the RNLI’s advice if you fall in cold water is simply to float until your heart-rate recovers. 

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Interestingly, I did the same thing after a run (jumping in wearing only a bikini), when my heart-rate was already 120 from the exercise.

I expected to experience a similar jump in BPM, but my heart-rate – already elevated by running – didn’t change at all… though the water, at 8 degrees, still felt freezing!

Note, however, when you’re actually swimming, with your wrist submerged (as opposed to jumping around like a lunatic) the Garmin Vivoactive 4 can’t monitor heart-rate.

Click to read Ali’s full in-depth review of the Garmin Vivoactive 4s

Garmin Vivoactive 4s