Rule #10
Hang It Up
Using your cell on the exercise floor, in locker rooms, or during a class is extremely inconsiderate (as is stepping over people and leaving the fitness studio for a chat). Excuse yourself only for important calls. "Take it to the lounge, front desk, or a conference area," says Kolar of Equinox, who has seen executives talking on their phones as they work up a sweat.

Rule #11
Polite: If you see someone struggling with a set, quietly and encouragingly ask if you can lend a hand. "It creates a sense of community, and it's easier than later having to give him CPR," says Clay gym's Mahabir.
Rude: Unless you're being paid as a personal trainer, keep tips on technique to yourself. For one thing, you don't know other members' goals and limitations. For another, you'll just look like a jerk. As Asylum Gym LA's Baptiste puts it, "Guys don't generally want advice from other guys."

Rule #12
Lose the Buds
Wearing headphones to a class is insulting and distracting, says Equinox's Hopkins, who adds that you risk missing out on necessary guidance and fitness benefits. "Routines are often choreographed to the music an instructor has chosen."

Rules #13-15
Personal Space, By the Numbers
Two arm lengths: The distance you should leave between yourself and the nearest exerciser while standing in front of the mirror.
Twenty-four inches: What you should leave between your yoga mat and the mats on each side of you.
One cardio machine: Minimum number of treadmills or ellipticals you should leave between yourself and the nearest exerciser if there are machines available.

Rule #16
Check before you channel-surf
Don't just start flipping stations on a shared screen. Get the attention of the people in front of that TV first to see whether they're watching it, says Equinox's Hopkins. Even then, you're better off asking for help at the front desk. The club may have picked certain channels (music TV, morning shows, sports networks) to set a mood.

Rule #17
Fend for yourself
In a packed class, saving a space or a bike for a friend is a serious faux pas. "That could be a source for a fistfight," Barton says. Graciously give the spot to the person who shows up before your tardy pal, who should understand.

Rule #18
"When you're changing, put a towel down on the bench," says Equinox's Hopkins. "No one wants to put their gym bag where you had your bare ass."

Rule #19
Avoid in-the-buff chitchat. And no matter how proud you are of your package, pack it away: Wrap up in a towel as you make your way to and from the shower.

Rule #20
Shaving naked at the sink is a no-no. Also, be a gentleman and refrain from blow-drying any body hair that isn't on your head.

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