Over 75 million Americans will be using dedicated activity trackers by 2021, over double the current user base, according to a new study by Juniper Research. The same study suggests that this will be a $20 billion hardware market annually within 5 years.

The findings also suggest that consumers’ perception of wearable trackers will slightly shift to make them seem more necessary. Vendors like Fitbit, Withings and Misfit are leading this change, making integration with medical databases a priority and focusing on encouraging users to lead healthier lives, rather than getting fitter.

This will move the wearables battleground from consumer hardware to institutional partnerships and software integration, with companies that are being able to make their devices and systems part of healthcare practices reaping the largest rewards.

The research also revealed that the range of metrics wearables measure has increased in recent years, with heart rate and related metrics becoming more common. This will accelerate the merging of the fitness and health wearables categories, which already have a degree of overlap.

Interestingly, Juniper forecasts that nearly 25% of fitness trackers will be something other than a wristband by 2021. Nevertheless, core functions will remain unchanged — to record activity and provide advice.

“The promise of a healthier life remains the biggest reason for wearables use,” research author James Moar said in a statement. “The ability to collect more and better data on consumers, coupled with advances in artificial intelligence, will allow these devices to provide tailored advice, and have a much clearer impact on consumers’ lives in future.”

The whitepaper, “Fitness Wearables ~ Going the Extra Metric” is available to download from the Juniper website together with further details of the full research.