You hear it from fitness instructors. You read it in ads for yoga, Pilates, or barre studios. You see it in #fitstagrams, magazines, and your newsfeed. I just got an email today about a new workout that promises that "long, lean body that everyone wants.”

Sure, not everyone actually wants that lithe look. But for those who do, promises of longer, leaner muscles can be just the motivation you need, especially when you hear it from trainers and professionals you trust. But is it realistic—or even honest?

Muscles 101

Long Lean Muscles: Arms

Muscles contract and stretch to move bones, kind of like stretchy rubber bands, but they technically have fixed lengths. "You can't change where muscles begin and end; it's your anatomical predisposition," says Michael George, a certified functional fitness trainer and Ph.D. candidate.

Which is to say: Baby, you were born this way. If you happen to have a “short” calf muscle (compared to other people), you could spend all day downward-dogging, but that won’t magically transform the length of your legs. Similarly, all the barre in the world won't make you taller, but it will improve your posture, strength, and flexibility. It doesn't mean it's not worth doing; it just means it won't perform a miracle.

So what's the difference between a ballerina and a power lifter? The answer is a combination of two things: how they train and what they eat.

Get Strong, Not Long

While you can’t control the actual length of muscles, you can control the way you develop muscles.

Isometric contractions (think: tensing a muscle but not actually moving, like holding a plank) utilized in workouts such as barre or yoga develop muscles differently than dynamic or isotonic movements, where the muscle stretches and contracts through a range of motion, like push-ups. Plus, perfoming a high number of reps of tiny, controlled movements engages and strengthens a different set of muscle fibers (slow-twitch) than big, explosive movements, which work fast-twitch fibers.

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There are pros and cons to each method, but on a structural level, both isometric and dynamic exercises lead to greater strength, firmness, and tone in the muscle, says Tanya Becker, certified trainer and co-founder of Physique 57. In fact, doing a combo of both is ideal for getting quick results.

It's also possible to train muscles at different lengths by performing exercises that first stretch the muscle and then engage it, says Bret Contreras, a certified strength and conditioning specialist. For example, a sprinter might train their hamstrings to be stronger when stretched by doing Romanian deadlifts. But this doesn’t mean you’ll actually see a big difference, Contreras says.

We know this probably isn't what you want to hear, but if you really want to appear "longer and leaner," it’s going to happen in the kitchen, not in the gym.

The Skinny on Body Fat

Long Lean Muscles: Eating

To really see the changes from all your hard work, you need a reduction of body fat, George says. “It’s 80 percent diet and 20 percent cardio and strength work.”

And yes, women can and should strength train without worrying that they will turn into The Incredible Hulk. “It’s a common misconception that if women use heavy weights, they’re going to get big and bulky,” George says. That’s not going to happen, because women have less muscle tissue and less testosterone than men, he adds. Resistance exercise increases leg muscle protein synthesis and mTOR signalling independent of sex. Dreyer HC, Fujita S, Glynn EL. Acta physiologica (Oxford, England), 2010, Jan.;199(1):1748-1716.

The false promise here is merely a matter of semantics. Saying you can build “long, lean muscles” is a flawed generalization that capitalizes on the fear of getting "big." We need to get more specific about what we want. What most people are looking for is not “length,” it’s definition and reduced body fat.

The Bottom Line

To answer the question: No, you can't alter the actual length of muscles, but you can train and—more importantly—eat in a way that results in having leaner, more defined muscle tissue on your body.

Saying you can build "long and lean muscles" to market a workout or a method of training is just that—marketing. Find what works for you, fuel your body properly, and it won't matter how you label your muscles—you'll feel like an all-around badass from the inside out.

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