Staying fit requirea effort, but apps on your devices can able to help you with this journey. Installed on your smartphone or wearable device, apps can deliver different benefits. When combined with gadgets for the gym, you're already on your way to an environment that's focused on improving your health and fitness. We've identified nine essential fitness app types you should install. For each type of fitness app, we've provided some examples that you can download on Apple's App Store or the Google Play Store.