Las Vegas isn’t the healthiest place to be in early January if you’re a tech blogger, but this year one of the most interesting trends at the CES trade show is fitness gadgets.

Specifically: fitness gadgets that work with companion apps on iOS and Android. Announcements this week from Fitbit, 4iiii, BodyMedia, Basis and Withings, among others, show the frenetic activity going on in the iFitness space.

Fitbit, along with Nike’s FuelBand, is probably the most high-profile brand in this sector, thanks to its existing mix of wearable gadgets and apps.

Yesterday it unveiled the Flex Wristband, a $100 device designed to be worn on the arm, tracking steps, distance and calories burned, transmitting the data to an iOS or Android app.

The company is facing competition from Withings though, which unveiled its Smart Activity Tracker yesterday too. It’s a memory stick-sized device worn in pockets, on belts or in arm bands, which measures activity and sleep, then syncs with its own companion apps.

Startup 4iiii showed off its Viiiiva connected heart-rate monitor at CES (yep, it’s running with that whole ‘four i’s’ thing); BodyMedia debuted its BodyMedia Core 2 tracker; and Basis showed off an Android app for its existing fitness-tracking band, which went on sale at the end of 2012.

How many winners can there be in this fitness gadgets field? Nike is unlikely to duck out, leaving all the other gadget+app startups to battle for consumer awareness. In the short-term this should make for rapid innovation in hardware and apps, although in the longer term, a handful of these companies are likely to make a lasting impact.