It's the brainchild of two Harvard students who took some concepts from behavioural economics – mainly the idea that people are motivated more by not losing money than just by earning it – and applied it to fitness.
With Gympact you make a pact every week that involves committing to exercise on one or more days per week and agree to be fined between $5 and $50 if you don't reach your goal. At the end of the week, if you've completed your agreed number of workouts you're rewarded from the pot of money collected from those who didn’t make their goal. The rewards, however, are only between $0.50 and $0.75 per workout.
You log your visits to the gym by checking in using GPS, much like Foursquare, or alternatively by sharing data from the free Runkeeper app. If you're checking in at a gym you can only check in for one work out per day and each workout session must last for a minimum of 30 minutes. If you chose running instead, runs have to be over half a mille in length and last for over 30 minutes at a pace of over two miles per hour.
Whether the app really helps motivate you will depend a lot on your own personality. For some it'll work well, but we didn’t find it all that motivating. Perhaps because we exercise regularly anyway and therefore the rewards are quite small and hardly worth the hassle of using the app.
Also the difference between the heavy fines for not reaching your goals versus the light rewards when you do made the whole system feel like it wanted you to fail to make the owners richer!
Although we didn't have any problems with it recognising our workouts from Runkeeper, there are a lot of negative reviews on the Play store for the Android version with people experiencing problems and complaining of poor customer service.
GymPact may provide some with the motivation they need to stick with their fitness regime, but the high penalties for skipping session versus the meagre rewards for achieving your goals make it feel like a bit of a swizz.