I am a fitness etiquette ninja.
Let's start with the big one. In all types of fitness classes, the regular attendees have spots where they like to stand. "Like" in this case means a fanatical obsession whereby normally rational women transform into snarling dogs when someone infringes on their territory. A favourite instructor once suggested we should just whip down our yoga pants and pee on the floor to mark our spots. I saw a few people fumbling with their waistbands before we realized she was joking.
Standing in someone's spot is the most likely faux pas for a newbie and the consequences can be painful. If you're lucky, the mean girl and her friends will glare at you the entire class and whisper loudly about how you don't know the moves while the instructor is setting up the next song. If you're unlucky, the mean girl will stomp on the back of your heels, elbow you in the ribs or actually knock you on your ass to make the point that you're in her spot.
How can you avoid this fate? Shuffling around in a noncommittal way before the class starts and promptly moving out of the path of anyone storming up to a specific spot are good strategies to defuse any potential brawls. If something goes wrong and you end up in the crosshairs of a spot bully, pretend you're dealing with a rabid dog and speak slowly and clearly while steadily backing away: "I am sorry. I did not realize this was your spot. Please put down the water bottle." Or just give her an elbow right back and yell, "It's my spot now, bitches!"
When you arrive late to a class, quietly take a place at the back of the room. Sauntering straight up to the front row is a highly advanced move that should be attempted only by a visiting instructor, or by someone who so regularly attends the class that her spot is left open out of respect even when she isn't there. Flouting this rule can result in the extremely awkward situation where a person returns from refilling her water bottle or going pee mid-class to find you've stolen her spot. Not good.
Also in poor taste is eating garlic, Italian sausage or Pizza Hut shortly before a group fitness class. You may think no one will notice those little bursts of fragrance from your mouth or anus. You would be wrong. Dousing yourself in anything other than unscented deodorant is not appreciated either.
Again, personal space matters. We're all standing as far away from each other as possible for a reason, and it's not because of hygiene violations (okay, sometimes it is). It's because most cardio classes involve limbs flailing around wildly in all directions. If you crowd your classmates, you'll probably catch a fist or foot in the face. The offender may or may not apologize, depending on how many other fitness etiquette rules you've broken.
Sometimes bad things happen through no fault of your own. If static cling has its way with you and a purple thong flies out of your pant leg into the middle of a class, pretend it's not yours. Don't push it with your foot to the front of the class, before picking it up and squirrelling it away in your lululemon jacket pocket. That's weird. Are you really going to wear it again once it's travelled all over a dance studio floor?
While we're on the subject of attire, light-coloured workout pants are a bad idea if your perspiration glands are remotely functional. No one wants to see your vagina sweat. Pale blue and grey are especially prone to making you look like you're not toilet-trained. And if you must stroll around naked for an extended period of time in the women's locker room, for god's sake bend your knees if you need to pick something up off the floor. Particularly if this is before your shower and you're over the age of 60 with no familiarity with bikini waxes. This is the gym, not Grannies Gone Wild.
The most important fitness etiquette rule is an easy one. Have fun! Really. In every class, you'll find someone the instructor calls by name and everyone seems to know. He or she may do each move perfectly or be struggling to keep up, but what these people all have in common is a big smile and a warm hello for their classmates. Tell people you're new and ask for help if you need it. Most regulars are kind-hearted and love to help out a newbie, and it can be a real motivation to keep up your new routine when you know you're going to see a friendly face in a difficult class. Just make sure you stay out of her spot.