How to Pick the Right Size Dumbbells for Your Workouts

A fitness expert reveals the magic number of pounds you should be lifting for a more effective strength training routine

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You absolutely love your cardio sculpt fitness class-you know the instructor, you have your spot on the floor, and you know to expect a mix of cardio and strength moves. Plus, you know the set-up and what weights to use. But that's where routine might be holding you back. Think about it: You're loyal to this class, and you've stayed loyal to the same size dumbbells every week. It might be time to step up your weight game-how did you decide five pounds was the correct weight for your fitness level in the first place?

"Adding extra resistance in the form of weights, whether it's dumbbells, barbells, or kettlebells, is the most efficient way to challenge your muscles," says Liz Barnet, head instructor at Uplift Studios in New York City. "Only through strength and resistance training can you increase muscle density, which is essential for achieving a 'toned' appearance, and keeping your body working effectively."

Read: toned, not muscular, ladies. Just because you decide to add on more weight doesn't mean your going to instantly bulk up (not that there's anything wrong with bulking up, if that's what you're working toward!). If that were the case, body builders wouldn't need to spend half as much time working on their size and fitness. "There's a misconception that lifting weights will make you look huge and muscular, when in fact having more muscle density will raise your metabolism higher and therefore burn more calories and torch fat," says Barnet.

So how should you choose which size dumbbells to grab in class, or even when you're training on your own? Most instructors recommend between five and 10 pounds because that's a reasonable amount of weight for individuals to work with. But don't let that suggestion cloud your judgment. "Keep in mind what other things you do in life outside of the gym that require you to manage an external load," says Barnet, "like the stuffed-to-the-brim tote you carry to work, which can be an upward of eight pounds."

Barnet suggests giving yourself an assessment: Choose an exercise and weight you feel comfortable with. You should be able to perform 10 to 15 repetitions with good form. If you feel like you could do more than that, it's time to up the weight. (Learn When to Use Heavy Weights vs. Light Weights.)

"If you're an experienced exerciser, you should increase weight when moves you are familiar with feel easy after 15 to 20 reps," she advises. "Increase by no more than five to 10 percent every few weeks."

One size doesn't fit all in the gym either. So it's OK-and encouraged-to grab more than one size weight too, and adjust as necessary. Bicep curls might be perfect with 15 pounds, but you may need to scale back to 10s for tricep extensions. And that's what you should do-don't sacrifice strength and progress because you're nervous to grab more than one set of weights.

"If you accidentally select weights that are too heavy for you, you can always scale down to a more manageable weight," says Barnet. "It happens all the time at the gym. You want to push yourself but also be sure you're able to complete the entire workout as prescribed with good form."

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