The Activbody Activ5 is a portable fitness device that helps track your progress with isometric workouts. With HealthKit integration and a companion Watch app in mind, Apple is now selling the accessory at its US retail and online stores.

Unlike a typical workout like running or weightlifting, isometric sets are static — you don’t move. They involve applying pressure against your own body, holding the position and maintaining the intensity of your strength pushing against yourself.

Whereas with weightlifting you can chart your progress based on your ability to lift increasingly heavier weights, it’s much harder to know if you are improving at isometric workouts. Health tracking devices like Apple Watch also struggle to collect any useful data at all, because you aren’t moving so the accelerometer cannot detect activity.

The Activ5 is a small handheld spongey pad that contains pressure sensors. The accessory is accompanied by an Activ5 Training app that includes suggested workouts and tutorials. These workouts are designed to be completed on-the-go; the app features more than 100 5-minute strength-training exercises.

Pressure data from your workouts is tracked as stats and charts in the Activbody app, and can be shared to the Apple HealthKit database.

The coaching app is available for iPhone, iPad and even a stripped-down variant for the Apple Watch. The Bluetooth-enabled unit is powered by a single AAA battery that should last between six to twelve months between charges.

Activ5 fitness tracker is now being stocked in Apple Stores across the United States and is also available to order online.

Apple retail customers will be able to demo the Activ5 directly in the store. Today, representatives from Activ5 will be running workshops at Apple Michigan Avenue, Chicago, and Apple UTC, San Diego.