It may boast a sturdier chassis, but inside, the GS5 Active has (almost) all the Android 4.4 KitKat goodness as the S5, and all of Samsung's own additions as well, like a heart-rate monitor -- though it lacks the fingerprint scanner.
See that blue button? That's for you. A short press opens up a dashboard for sports-related apps and a long press launches the camera. Don't worry, you can swap functions all you'd like in the Settings.