The BreastStroke app records on the watch how the swimmer swims. It exploits duration, acceleration and angles of the watch on the wrist.

Swimming is good for fitness and health, but first of all it is a recreational activity. Users who swim for health reasons find other apps for their purpose, as do swimmers who care for lap or meters counting or for detecting which style they are swimming. Although BreastStroke makes a limited use of HealthKit it works without any personal health features like sex, age, body weight, and so on.

BreastStroke follows a process model of breaststroke swimming. As breaststroke swimming is symmetrical and coordinates arm and leg moves, the watch sensors track the rowing and gliding of the arms, the duration of strokes, glides and rows, the turns of the palms, the pull of the rowing arms and the push of the kicking legs.

With the data observed during a swimming sample, BreastStroke aggregates key features - averages or min/max values - of the swimming performance, such as the turn of the hands while rowing or the strength of the leg kick while gliding. The values of the current sample can be glimpsed on the watch.

BreastStroke uses HealthKit workouts for tracking swims with their long observation time. Every time a user starts a swim, a HealthKit workout session begins. During the workout session a sample of swimming data is recorded until the user stops the run. All data is handled, stored and sent to the phone without any HealthKit functionality.

Up to six samples at a time can be downloaded and saved to the user’s phone. There they are displayed for a closer check. On the phone they are called HealthKit samples as they come from HealthKit workout sessions.

Just in case swimmers are not happy with their performance, they find some links to good breaststroke advice on the web, often with video demonstrations.

The BreastStroke version app 1 was tested on a watch series 2, 38 mm with an iPhone 6 in pools of 25 m / 50 m size, version 2 on iPhone XS and watch series 3, 38 mm.