In certain dark corners of changing rooms and internet message boards (and, well, screaming down from the front covers of muscle magazines) are certain fibs that the fitness industry has been selling since Mr Olympia shrugged his first kettlebell. Learn to cut through the noise to build a better body, the right way.

The Longer You’re In The Gym, The Better The Results

Your body composition can largely be explained by the laws of thermodynamics. If energy in is greater than energy expended, you get bigger. Reverse it and you shrink. Energy in is comparatively simple to control. Energy out fluctuates depending on everything from how much you exercise to your sleep patterns to, well, how much energy you put in.

Which is why 20 minutes in the gym can be more effective than two hours, if you spend every second sweating rather than ambling between machines checking Twitter. Instead, try high-intensity interval training, says Oliver Sprague from MotivatePT. Switch between 30 seconds at 100 per cent intensity – you should feel on the edge of passing out – then rest for 30 seconds. The oscillation between effort and calm produces an effect called excess post-exercise oxygen consumption (EPOC) which translates as an increased metabolism – and increased energy out – for 48 hours after you leave the gym. Train harder and smarter in less time.

(Related: 12 Ways To Look Good In The Gym)

Big Weights Build Mass; Light Weights Are For Tone

First of all, know that there is no such thing as ‘toning’. Personal trainers invented the idea so women would start lifting weights without worrying that they might end up like Arnie. ‘Tone’ is a combination of increased muscle mass and reduced fat levels, which materialises as less wobble in your arms and legs. The way to achieve it is not huge reps with light weights, much as the only way to build bulk is not few reps with weights that bend the barbell.

“Quality is quality,” says Dylan Jones, PT and founder of P4Body. “The longer your muscle fibres are under load the greater the intensity. It’s much better to drop the weight and lift with good form, than to load the bar and use every other muscle group in the body cheating it up.” If your glutes are helping your bicep curl, then all that extra weight isn’t going to make your biceps any bigger.

Sit-Ups Build Six-Packs

Blame every boxing film you’ve ever seen, but sit-ups are not the way to build a six-pack. This is misapplied logic – you curl a weight to build your biceps, so understandably you’d assume that the same movement would turn beer belly to washboard. But there’s two misconceptions at work here.

First, your six-pack is not all abs. Definition also demands strong obliques and a defined rectus femoris, muscles best activated by bicycle crunches and planks, according to a study by the American Council on Exercise. Second is the fact that boxers also run, punch and jump themselves to single-digit body fat, all while eating little more than chicken and rice. Unless you’ve got less belly fat than a greyhound, your abs are going to stay invisible. It’s time to hit the road.

(Related: How To Get A Six-Pack – Without A Single Sit-Up)

You Need Protein Shakes To Build Muscle

It’s easy to understand where this misapprehension comes from – all the biggest guys in the gym have a protein shaker glued to their right hand. But the fallacy comes in that suffix: shake. Muscle is built from proteins and as long as you’re getting a full spectrum in high enough quantity – between 1.2g and 1.7g per kg of body mass per day, depending on how hard you’re training, according to research by the American College of Sports Medicine – then it doesn’t matter where it comes from.

Fitness magazines, bankrolled as they are by protein manufacturers, will attempt to convince you that you need whey protein directly after training and casein to support overnight muscle growth. This is true if you’re an Olympic athlete putting in six hours of to-failure training every day. For the guy who only hits the gym three times a week, a few extra eggs at breakfast and double helpings of chicken at dinner is plenty.