The activity trackers made by the two companies are the latest devices available through UnitedHealthcare Motion's BYOD model, enabled by Qualcomm Life.
Up to 10,000 Fitbit Charge 2 and Fitbit Alta HR devices will be provided to a representative sample of the research program volunteers for a one-year study.
This year, the research firm predicts vendors shipping a total of 121.7M wearable devices, marking a 16.6% increase from the 104.4M units shipped in 2016.
The iPhone maker has also announced the Apple Heart Study to identify irregular heart rates, including potentially serious heart conditions such as Afib.
The companies are targeting availability as soon as possible in 2018 and will continue to explore opportunities to help people better manage their diabetes.
Device shipments grew 10.3% year over year to hit 26.3 million units during the second quarter of 2017; smartwatches grew 60.9%.
If Fitbit can do it, so can Garmin; the wearable packs contactless payments and support for third-party apps.
The new products could help the Korean company capture a portion of the premium wearables market.
The company has also announced a new smart scale (Aria 2), sweat-proof Bluetooth headphones (Flyer), and new premium guidance and coaching offering.
The powerful wearable has a color screen, waterproof body and a number of sensors to watch every move you make.