Spin classes usually aren’t just spin classes (especially with new, super-intense versions popping up like SoulActivate). Most of the classes also incorporate a section that blasts your arms, too. But there’s one reason you might want to ignore the instructor the next time they say to pick up that set of light free weights.

It’s tempting to make sure you feel the burn every day when you’re working toward strong, toned arms. The only issue? Back-to-back arm-targeted workouts are a big no-no, according to Kayla Kleinman, the New York City–based personal trainer behind Kayla in the City. She says if you did a hefty arm routine the day before, you might want to fight the urge to work them again during your spin class.

“If you don’t allow yourself proper recovery and a day off from working those muscles, you don’t give the muscles time to rebuild.” —Kayla Kleinman, personal trainer

“When you do, let’s say, bicep curls, you’re creating teeny-tiny tears in the muscle fiber of your biceps. Your body then knows to rebuild these fibers, which in turn strengthens the muscle,” Kleinman tells me. “Part of this rebuilding process is recovery; after the tears occur, your cells are working to rebuild. If you don’t allow yourself proper recovery and a day off from working those muscles, you don’t give the muscles time to rebuild.”

To successfully (and safely) grow your muscle mass, slow and steady definitely wins the race—and overdoing it might set you back. “While you might think more is more when it comes to arm workouts—or any workout for that matter—your body needs down time to also recover so it can come back stronger,” Kleinman says.

So, what should your ideal routine look like? It depends on the person, but there is a rule of thumb: “Obviously the key is to not go crazy five to six days a week doing all arms, all the time. Instead, focus on two to three arm-heavy days,” Kleinman said. For the other days of the week, simply focus on lighter weights, body-weight movements like yoga, or cardio like spin cycling. “It’ll give your arms time to recover and target the muscles in a slightly different way.”

When you follow these rules—even if that means skipping the arms portion of your spin class—your arms could be Popeye-strong in no time, especially if you load up on spinach-heavy green juices in the process.

Here’s why doing sled workouts like Lucy Hale is so good for toning your arms and back. Also, try the barre-inspired workout that tones your arms and abs at the same time.