For some, the contemporary fitness centre is a hive of determination and achievement, a dojo for the 2010s where men let off steam via Zen-like control of their bodies. For others, it is a temple of insecurity, a battleground where terrified masses fruitlessly confront their unsightly midsections while the world looks on, pityingly.

In between the extremes, there’s mild (perhaps creatine-induced) euphoria, decided ambivalence, romance (yes, really) and, of course, guilt, among gym members. Of the 4.4 million in the UK, only one third regularly made it beyond the turnstile in 2014. Naturally, the resulting hormonal/emotional cocktail (not to mention the terrifying locker-room aromas) makes for an interesting dynamic.

It’s wrong to say that the gym is a social leveller – most major outfits charge upwards of £70 a month, roughly equivalent to the cost of buying one MacBook per year. But it seems to bring together people from all ages and many walks (or is it squats?) of life. And the following tribes are as consistent from gym to gym as the barbells and fist-pumping Muzak.

You will hear him before you see him, his bestial grunts thundering from the weights room. But see him you will, and probably much more of him than you would like to. This mountain of a man, typically found purposefully raising large masses from floor to ceiling as if the free world is dependent on his thighs, adheres to a strict dress code: the bigger his chest, the smaller his tank top. In some extreme cases, said garment amounts to little more than a loose jersey harness, angry nipples glaring out accusingly from either side. No one knows (ungh) how long he has been labouring away (grrrraaaah) at the deadlift station (meeeeeuuurgh), nor how he manages, with that prodigious girth, to navigate the narrow spaces that life might throw his way once he leaves the gym’s air-conditioned hangar. But everyone, yes, everyone, is a reluctant expert in the fine details of his overwhelming musculature. When attention levels drop, he will face the mirror and make bits of himself jiggle. When things get really desperate, he will sort of nod and pose to his reflection in an intense, but loving way. Whether you’re repulsed or intrigued by this behaviour, it’s difficult to ignore.

Hitting people in the face – or boxing, as it is more generally known – is not just a good way of solving minor disputes and lodging respectful complaints at restaurants, it also builds core strength, increases agility and burns a load of calories. What’s more, no one will laugh at you for doing it, unless they’re looking for trouble themselves. It’s no surprise, then, that the gym-bound Boxerciser imagines himself to be somewhat more credible than your regular cross-training pretty boy. But, really, come on. He arrives haughtily with several friends and various bits of punchable paraphernalia, the skimpiness of his satin shorts (cut high at the side) offset by the tribal tattoo motifs slathered on his vest or tee. He’s way too tough to wear shoes or socks – what’s athlete’s foot to a man that talks with his fists? – and conspicuously avoids all functional areas of the gym, preferring to jump around on hard concrete, ankles be damned. As he begins his terrifying-looking work-out, it’s not clear exactly which school of martial arts he currently attends, but there’s kicking, jabbing, skipping, scowling and a drunken-looking cuddle with one of his pals that spills across onto the stretching mats. Ultimately, though, his endgame is clear: destroy the punching bag. Furiously laying into it with everything he has, he keeps on his toes, ducking and dodging the frenetic blows that come his way. Except they don’t. The bag just swings a little bit. It’s like a puppy barking at its own reflection. But less cute.

In days gone by, you might have spotted this febrile gym-goer clutching a wrinkled piece of paper or two – usually torn from the pages of Men’s Health – or maybe even a card with tickboxes, listing the exercises he’s patiently worked out at his gym induction. But now you’re just as likely to see him staring blankly at his iPhone (he drops this on the floor a lot), cradling it this way and that to try to work out just how exactly he’s supposed to swing the kettlebell he has dangling limply from one arm. He has roughly 20% of the information he needs to make a proper go of it. Poor guy – it’s mid-January and he’s finally decided that enough is enough, no more lager, gym three times a week. Though he’s wearing brand-new trainers, he hasn’t quite worked up the conviction to invest in the rest of his gym look, opting for a band T-shirt and some board shorts, or perhaps a comfortable zip-up fleece that is far, far too hot. Patient observers will see him try a multitude of different exercises, all of which he confronts with utter bewilderment and gives up on almost immediately, face flushed. When he glances at the clock and realises it’s nearly time to go home, he panics and rushes over to the treadmill, jogging a few minutes before hitting the emergency stop button. He doesn’t bother to stretch. Tsk tsk. You’d love to give him some advice, but then again, you were basically him six months ago, and nobody helped you. Enjoy the feeling of superiority. You are, after all, in a gym: it won’t last long.

An unbearably at-ease gym denizen – recognisable by his scrunched up knee socks and varsity colours – who, being the star member of his university rugby/football/rowing team, has a legitimate, practical reason to be doing all those bicep curls, burpees and ergo sprints. Damn him. His coach has told him he needs to bulk up, advised him to knock back at least three malt loafs a day and promised him success and glory if he sticks to a 12-hours-a-week work-out programme. Because he’s 20 and does nothing but binge-drink and attend the occasional seminar, this works for him just fine. If this wasn’t enough, he also brings with him those most elusive of gym accessories: friends. Not for him the Sisyphean struggle against one’s own laziness and faltering metabolism. He’s just having a good time, hanging out with his teamies – who are there in force, and all equally pleased with themselves. They spot each other on the bench presses, exhorting each other with phrases like “give me another 10 for that hottie on the netball team”. They talk about Homeland in between sets. They probably even get to go to the pub afterwards. Of all the people skulking round the water fountain, he most palpably has a life. Which is why, for the sake of your own morale, you should probably find a quiet exercise to do somewhere out of his vicinity.

You tend to go to the gym for fitness, not existential doubt. Yet the sight of this hamster-like creature thundering away on the treadmill for upwards of 40 minutes works just fine as a metaphor for the futility of the universe, if you happen to need one. Of all the manifold possibilities that the gym sends his way, he chooses just one square metre of grey rubber on which to focus all his hopes and dreams, monotonously repeating the same action day after day. And it doesn’t go anywhere – that’s the whole point of it, but it’s still sad. His eyes fixed on a horizon he will never reach, his hands clamped on rails like gravity has turned against him, he may be throwing off enough thrust to launch a moon mission, but he’s never going to see those hours of his life again. And neither will you. Especially in hotel gyms, where equipment is scarce, he will make you wait your turn, toying cruelly with your patience by feinting a cool-down before cranking up the ’mill for another 20-minute incline push, and for what? Sartre, eat your heart out.

“Just one more.” “I can’t!” “One little push.” “No, really, I…” “Come on!” You get the picture – sometimes the gym runs from the same script as the maternity ward. There are of course many vital differences. For instance, instead of a gurgling baby, you tend to leave with nigh-on full-body paralysis, your forearms scrunched up like a T-rex. And instead of a midwife, you have a personal trainer to mentor you through the ordeal. These characters, universally clad in breath-hamperingly tight black T-shirts (you won’t catch them doing any T press-ups or dumbbell rows) have one sole purpose in life: to devise novel ways to make you feel terrible, but look great (apparently). Armed with a seemingly limitless arcana of (wildly self-contradictory) sports science knowledge, they watch and wait until you’ve mastered an exercise, and then, if you’re looking too comfortable, make you jump on a 5ft-high box, or crawl under a weights bench, or spin round five times and then try to catch a rolling medicine ball (OK, not entirely likely). They’re also fond of texting you to remind you you’re not currently working out. Or to ask you what you’re eating. And all for the bargain price of £60 an hour. If you are lucky.

Commonly seen in groups of three and above, they emerge from the gym’s most tenebrous, candle-lit chambers, clouds of eldritch steam curling round their ankles, bodies drenched in effervescent liquid. We can only assume this soggy aura is sweat – it’s a little unclear, if so, how so much of the stuff has been produced organically in just 45 minutes. But evidently the ritual of the spinning class, especially when Ouija-d up with ecstatic arm waving and a soundtrack of transcendental chanting, does as much for the sudoriferous glands as it does for the core, thighs and calves. Beyond head-to-toe prunification, the most visible effect of this most strenuous discharge is to induce a state of euphoria in those who have just been, in essence, juiced, by their adored instructor. Terrifyingly, this positive attitude seems to accompany them beyond the walls of the gym, where they will assail friends, colleagues and passers by with motivational slogans and inescapably rude health. They’ll get you into a class with Stacy, if you want, but first you have to figure out who – or what – Stacy is, and what part of your eternal soul will be required as payment for initiation.

As with any situation where you’re stuck in a room with 40-plus angry strangers, the gym has the potential for much interpersonal tension. Here’s our guide to keeping things as un-obnoxious as possible.

01. Wipe it down

Towels were invented for a reason. Many gyms even supply them. Take the hint and clean up after yourself. Karmic payback in the form of other people’s sweat is not something you want to bring down upon yourself.

02.  Share your toys

Yes, it’s a pain lugging weights back and forth, although that’s ostensibly what they were designed for. But there’s nothing more frustrating than having to scamper between stations asking people if they’ve finished with their kettlebell, or if they know where the second 9kg weight is. Take only what you immediately need, and return to where you found it.

03.  Lunge gracefully

Working the lower body often pays dividends, because of the size of the muscles involved. This means, unfortunately, that everybody has to lunge at some point, though it’s not the most polite gesture. Be discreet by moving in parallel with your neighbour, rather than towards them. And please, please, wear suitable underwear.

04.  Dress for the job

You may have just bought the most amazing engineered-fit tech nylon water-repellent road leggings, but, let’s face it, you’re indoors. And, by the way, that bike you’re pedalling is not actually moving. Shorts and a T-shirt are fine.

05.  Keep a straight face

Gym-goers, especially those with personal trainers, have to do some occasionally embarrassing things. Like hanging upside down with their T-shirt in their face. Or trying to manoeuvre an inflatable sphere with just their knees. You can laugh, but expect no mercy the next time you fall off the chin-up bar.