The world of activity trackers has been rapidly expanding beyond just wrist and armbands that monitor a few key vital signs and movements. We're now seeing the energence of very specific tools like ResisTrack, which claims to "monitor and track the exact force" that muscles generate.

Unlike most other muscle trackers like Gymwatch, Mbody or the Squid shirt, that cover some part of your body to directly measure your output, ResisTrack attaches to fitness equipment like resistance bands, cable machines and suspension trainers. At the same time it connects to a smartphone app via Bluetooth to provide instant feedback on the amount of force generated by each muscle movement.

One of the selling points of this sort of system is its ability to accurately show the difference in strength between your left and right muscles in real time, to help ensure symmetrical muscle development. Resistrack also keeps count of your reps, sets and breaks, and like many other fitness trackers, its software includes training programs and social elements to provide a little motivation boost.

Because ResisTrack is limited in the type of equipment it works with (there's no way to use it with freeweights, or any non-cable or band-based apparatus, for example), it may be better thought of as a complete exercise program, providing over 120 exercises that it's capable of tracking to work most muscle groups.

ResisTrack's greatest utility could be its ability to measure your muscle output when you're away from the gym or doing some impromptu exercises with resistance bands, that would make it more difficult to quantify your workout and ensure that both sides are being exercised equally.

The device has gone through three generations of prototypes and its inventor, Marco Zoltan Daroczi, is looking to launch the product through Kickstarter. His crowdfunding campaign has so far gotten off to a slow start, inching towards just US$5,000 of its $78,213 goal with 23 days to go as of this writing.

Kickstarter backers who pledge at least £66 (US$103) will receive a ResisTrack scheduled for delivery in December. For £82 ($128), you can upgrade to a package including a ResisTrack and a set of resistance bands.

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