FITNESS fans are wearing gadgets during sex that monitor how many calories they are burning, a survey has found.

A third of owners of Fitbit-style fitness wristbands admit to treating lovemaking as a workout by keeping them switched on in bed.

And just 10 per cent own up to their lover that they are doing it.

The bands track movement and use the results to help calculate the number of calories burned, usually from gym workouts or jogging.

But many said they had carefully analysed aerobic performance before and after having sex. And nine per cent confessed to trying to make romps last longer for a better workout.

Lovers sneakily monitoring their performance include women but there were more men admitting to it.

The survey of 1000 wristband owners by supplier LaptopsDirect.co.uk also revealed 79 per cent consider sex to be a genuine form of exercise.

Marketing manager Mark Kelly said: “People are using wearable technology to monitor activity from steps walked to calories burned during workouts.

“So it isn’t too much of a stretch for people to start getting curious about their performance between the sheets. Calories burned during sex are just as valid as those torched in the gym.”

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