Are your swimmers paddling up to par? There’s no easy way to gauge the quality of your semen just by looking at it, so you’ll need to schedule an appointment with your doc to find out for sure.

But while you wait, here are scientific signs that suggest you have strong sperm. How many can you cross off?’

YOU SCULPT A LEAN MIDSECTION

Actually, you don’t even have to boast a six-pack—as long as you don’t have a gut, your semen is probably in tip-top shape.

Researchers from the Netherlands found that men with a waist circumference of 40 inches or greater had lower sperm concentrations and counts of normal-moving sperm than guys with a more whittled waist.

The researchers aren’t exactly sure why a spare tire is bad for your swimmers. But they believe carrying too much weight—especially around your midsection—may interfere with the release of sex hormones, as well as the production and development of sperm.

YOU DON’T LOOK LIKE DON DRAPER

Good news, average-looking guys! Having a masculine mug might actually hurt you down below the belt, according to a new study.

Spanish and Finnish researchers recently discovered that men who had faces that were rated as manly—i.e. wider and broader—tended to have poorer semen quality than more feminine-faced guys.

One possible reason: a theoretical explanation called the “tradeoff hypothesis.” Simply put, men have a fixed amount of energy available to devote to reproductive resources. And that energy must be distributed to a number of different components.

“So, if a male consumes more resources on semen production, he may have fewer resources available for developing attractive secondary sexual traits, like facial masculinity,” says study author Jukka Kekäläinen, Ph.D.

Quick, think of your favorite go-to protein: is it red, salty, and processed? If so, your semen might be paying the price.

YOU’RE A FISH MAN

Harvard University researchers found that men who ate the most processed meat had significantly lower counts of normal-shaped sperm compared to those who consumed the lowest.

Fish, on the other hand, seemed to have a protective effect. Guys who ate the most fish—especially dark-meat kinds like salmon and tuna—had a 65 percent greater sperm concentration than those who ate the least.

Credit fish’s omega-3s, since long-chain polyunsaturated fatty acids play a part in sperm production, the researchers say. So if you’re looking to strengthen your swimmers, sub out your pepperoni topping for some anchovies.

Here’s another reason briefs might feel a bit on the constricting side: they could be suffocating your sperm, too.

YOU SCORN THE TIGHTY WHITIES

A 2012 study from the U.K. found that men who wore boxer shorts instead of tight-fitting underwear were 24 percent less likely to have a low-motile sperm count. Motility, or how sperm swims, is important, because sluggish sperm can have difficulty reaching the egg to successfully fertilize it.

“Loose-fitting underwear may result in lower scrotal temperatures compared to tight-fitting underwear, hence an improvement in semen quality,” says study author Andrew Povey, Ph.D. There’s also evidence that elevated testicular temperatures may hinder sperm production, he says. So if you want to be on the safe side, let your junk breathe

YOU HIT THE GYM

Researchers from Harvard found that men who got their blood pumping in moderate to vigorous exercise 15 hours or more a week had a sperm concentration that was 73 percent higher than guys who didn’t work out at that intensity at all.

Not only does exercise help tamp down your weight—which can affect reproductive health—but it may also increase the expression of antioxidants throughout your body, the researchers believe. So regular gym sessions could actually prevent free radicals from damaging sperm cells.

And once you get back from breaking a sweat, resist the urge to flop down on the couch and go channel surfing. The researchers also found that guys who watched TV more than 20 hours a week had a sperm concentration that was 44 percent lower than those who kept the boob tube off.

YOU SPEAK IN FALSETTO

Okay, maybe not quite that shrill—just not a low, throaty growl. Men with those kinds of voices tend to have worse-off sperm, according to a University of Western Australian study.

Researchers found that while women did rate the low-pitched voices as more masculine and attractive, those husky-voiced men had lower concentrations of sperm in their ejaculate.

Testosterone levels may be one possible explanation for this, according to study author Leigh Simmons, Ph.D. Testosterone is associated with more masculine facial features and lower voices, but too much of it might actually suppress sperm production.

YOU DON’T NUKE YOUR LEFTOVERS IN PLASTIC

Zapping last night’s lasagna in a Tupperware container is easy, but it might be wreaking havoc on your sperm.

You can thank bisphenol-A (BPA), a chemical that can leach from plastics into your food when heated—and then into you.

Researchers from Denmark found than men who had the highest levels of BPA in their urine had a significantly lower percentage of motile sperm than those who had the lowest levels.

The scientists aren’t exactly sure what’s behind the semen squeeze, but they think the BPA might affect the estrogen and androgen activity in the epididymis in the testicles. And this, they believe, can hinder the normal development of sperm.

So before you nuke your lunch, take the 5 seconds to transfer it from a plastic container to a glass one.