IDC said Wednesday that smartwatch shipments will more than double by 2021, led by increased shipments of the Apple Watch.

IDC said it expects 71.5 million smartwatch units to ship by 2021, up from 31.6 million that it said shipped in 2017.

Smartwatches have gained traction with a new focus on fitness tracking. The Apple Watch is now capable of more accurately tracking heart rate data, for example. Connected watches, including the new Apple Watch, also allow users to leave their smartphones behind while still having the option to place phone calls or receive text messages.

IDC said it expects similar growth across all smart wearables — including smart watches, clothing and so-called "earwear" — by 2021. IDC said 113.2 million such devices shipped this year but that the market will balloon to 222.3 million wearables shipped in 2021.

Correction: this article originally said Apple Watch shipments will double by 2021. IDC said smartwatch shipments will double by 2021, led by the Apple Watch.