Why won't Health app sync any activity?

So I would really like to sync all my fitness and workout data with the Health app but it doesn't seem to communicate with my fitness trackers. I've owned a Nike GPS watch for years and was never able to get it to sync data with the Health app. I figured it was just an issue with the Nike software or something but I just purchased a Garmin watch and it's not syncing any data either. I have selected all the required permissions and authorizations etc. The only activity that will show in the Health app is my steps that my iPhone tracks. Isn't a huge deal because the Garmin software is pretty comprehensive but it is really annoying just because I'm an Apple fan and would like to use the app. It will sync data with the SleepCycle app and MyFitnessPal however.