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You made the fitness resolution while raising your glass of bubbly on New Year’s Eve, and you’ve worked out three times a week for more than a month. But the scale. Is. Not. Budging.

Isn’t it possible that you’re actually fitter — that you have more lean body mass and less fat — even though the scale hasn’t changed?

Indeed, it is.

This is why trainers such as D.C. strength and conditioning coach Gabe Free are more interested in measuring your body composition, which looks at lean body mass compared with body fat, than just your body weight, which gives your overall weight and doesn’t discriminate between fat and muscle even though, as we know, one generally is less desirable than the other.

“People get caught up with a number on the scale. But that kind of misses the point,” Free says. “What we want to do is improve strength and increase lean body mass.”

Technically, you could improve strength and increase lean body mass while gaining — rather than losing — weight, depending on your starting point. Because, as we know, muscle weighs more than fat.

Meir Magal, professor of exercise science at North Carolina Wesleyan College in Rocky Mount, agrees that the body-composition measurement is more discerning as a way to measure fitness.

It is also often a better tool than BMI (body mass index, in which body mass is divided by the square of the body height), he says.

“If you have someone who is very muscular, they might show up as obese when you use BMI,” Magal says. “Body composition is a far superior measurement.”

Body-composition tests

So why don’t we hear more about body-composition tests if they’re so much better than BMI and mere weight tracking?

Well, they require skill and, in some cases, can be costly. The cheapest and most common way is to use calipers, which measure skin folds by pinching your skin in at least three relatively fat-heavy areas: in men, the chest, abdomen and thigh; and in women, the triceps, abdomen and thigh.

This is the method Free uses regularly with his clients.

“We might do it once a month or at the completion of a specific training program goal,” he says.

A slightly more involved but usually pretty affordable method is the bioelectrical impedance analysis (BIA), in which a machine sends electrical currents through the body to determine fat-free body mass.

Lara Atella, co-owner of Hot Yoga Capitol Hill, uses this method. One of the things it looks at is water content in the body, so it is important that the test taker isn’t overhydrated or underhydrated and hasn’t worked out before the test.

More expensive but more accurate body-composition tests include underwater weighing and DEXA scans (a type of X-ray). These are often used by professional and collegiate athletes.

Some numbers to keep in mind in terms of body composition:

People might say things such as “He has zero percent body fat,” but that is a fallacy.

The body needs some fat, and those levels are different for men and women: Essential fat for men is 2 to 5 percent, and for women, it’s 10 to 13 percent. But that is not the number to aim for, Atella says.

Instead, for fit women, the target is 21 to 24 percent, and for fit men, it’s about 14 to 17 percent. For athletes, the corresponding numbers are 14 to 20 percent for women and 6 to 13 percent for men.

“It’s important for women to have that essential body fat, or it can mess with your hormone levels, which can lead to hair loss, fatigue and you can lose your period,” Atella says.

‘Skinny fat’: Low weight, high fat

It is possible to be what Atella calls “skinny fat.” In other words, your body weight and BMI can be low while your body fat is high, which is not considered fit.

On the other hand, that’s not necessarily connected to health risks. A high waist circumference, though, is associated with increased disease risks.

Sigh. It’s not just overall fat but also where it’s located that matters. This is why Atella also measures waist circumference and blood pressure.

“You could have high body fat, but that’s not necessarily dangerous unless that fat is all around the waist,” Atella says.

A waist greater than 351/2 inches for women and 39½ for men is associated with hypertension and heart disease, Magal says.

There are, of course, genetic variations. Some people can have a rotund body shape and be healthy.

Fitness: Marathon, not sprint

Let’s say you are still upset about your lack of progress on the scale and decide to go on a juice cleanse diet to “lose 10 pounds in 10 days.”

“It’s not a good idea to lose that much weight that fast,” Free says. “You didn’t put the weight on overnight, and it’s not going to come off overnight.”

In fact, he says, the “crazy cleanse diets” work in the sense that you drop weight rapidly, but in the process you lose three times more lean body mass than fat. And it’s never a good idea to lose muscle mass.

Muscles not only make you stronger, but more lean body mass is also associated with better metabolism.

A diet that supports muscle growth needs protein and some fat — which many cleanse diets virtually ban.

Magal suggests that anyone interested in fat loss and increased fitness needs to consult a nutritionist to set up a sensible plan.

Free eats 1½ to 2 grams of protein per day per kilogram of body weight (example: 220 pounds = 100 kg; 1.5 grams of protein x 100 kg = 150 grams of protein per day).

Free acknowledges that it isn’t always easy to persuade clients to step off the scale, but there are success stories. He has a client whose goal was to drop a significant amount of weight but in the end didn’t budge the scale as much as he lost fat and became strong.

“He trusted the process. His clothes fit better, he feels better, and he’s much stronger.”

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Boston is a fitness trainer and freelance writer. She can be found at gabriellaboston.com.