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These 6 factors determine how fast you build muscle. Here's what you can—and can't—control.

You just started a workout routine with a friend, and they’re seemingly packing on muscle overnight while you’re waiting for results. If this has ever happened to you, you’re not imagining ...
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These 6 Factors Determine How Fast You Build Muscle. Here's What You Can—And Can't—Control.

"Hearst Magazines and AOL may earn commission or revenue on some items through these links." You just started a workout routine with a friend, and they’re seemingly packing on muscle overnight while ...