It turns out that with a few tweaks, getting frisky between the sheets can give you a cardio workout, train your core and tone your legs, bum and tum - and it's much more enjoyable than being barked at by a militant gym instructor.
But before you get down and dirty, Rebecca Dakin, AKA The Great British Sexpert, says: "It does require high-energy love-making sessions to lose weight.
"So my first bit of advice would be to build stamina."
Step up: Edging, an orgasm control technique where a person gets right up to the point of orgasm before stopping and starting again.
The author, hypnotherapist and coach explains: "Work on edging with your partner so that you can both last longer pre-orgasm.
"Usually penetrative sex pre-ejaculation is only a six-to-eight minute job maximum, so you want to be building to at least 30-40 minute sessions to have an impact.
"And the sweatier, the better!"
While you're working towards this, there are also certain positions to practise that will maximise the results from your marathon sex workouts.
If you thought the top sexercise moves would involve complicated Karma Sutra contortions, think again.
Provided you're both equally committed, this 'boring' position can give your core a real workout.
"Missionary is very underrated', says Rebecca. "But it's quite energetic and the butt clenching makes it a good one for glutes.
"For the partner on the bottom, there's an opportunity to push yourself upwards - engaging your core and using your glutes - so that you're moving together rather than just lying there."
"You can really work on engaging your core with this one," says Rebecca.
"Make sure to also move your butt upwards rather than let them do all the work."
You'll also be using your quadriceps and glutes to help brace yourself against the impact.
"The key with this position is to squat with your feet flat," says Rebecca.
That way you'll be toning your legs, bum and tum all at once.
But if squats are too intense to start, build up from the more common cowgirl position with your knees down.
You will still be working your lower abs and pelvic muscles, and if you hug your legs into your partner's side, you'll engage your quads and calves, too.
With the bridge, the receiving partner is facing upward, using all four limbs to hold their body weight off the bed.
This one works all the major muscle groups you want to hit: biceps, triceps, abs, glutes, quads and calves.
But, be warned! It's not easy.
You might want to try it first with pillows under your back to help support your weight - you will still be engaging your buttocks and inner-thigh muscles.
It's worth the extra effort though: "This one's really good for clitoral stimulation," says Rebecca.
If you're familiar with the lotus yoga pose, you'll have an idea of what this position entails.
Rebecca explains: "If he sits down cross-legged and the female sits on top and straddles, you can get a good intimate connection with this one but it can also be quite energetic.
"You've just got to co-ordinate and get the bounce right."
The core is engaged to stabilise the body and the thrusting gives the glutes a good workout.
And the award for the sex position with the least sexy name goes to...
Nevertheless, the wheelbarrow is a great move to work up a sweat.
The receiving partner starts on the floor and uses their hands to balance in a plank-like position.
Then the giving partner lifts the receiving partner's legs off the ground and holds them at waist level.
"For him, this position is great for legs and core, and for her, the arms," says Rebecca.
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