Warm-weather season is officially upon us. And with the feel-good sunshine and lush outdoor scenery, there’s no time like the present to breathe new life into your workout regimen. But before so much as picking up a jump rope or dusting off your running sneakers, it’s important—make that essential—that you’re armed with the right sports bra.

“Sports bras are often an afterthought, and most women are wearing ill-fitting ones without knowing it,” says Laura Tempesta, a sports bra expert and founder of Bravolution. “During exercise, force on the breasts is intensified and wearing the wrong size will cause pain and discomfort.” And it’s not just about short-term benefits—the effects of wearing the wrong sports bra, especially on the neck and back, are cumulative over time.

“Not enough support, and the continuous compression of muscles in the neck like the upper traps, levator scapulae, and pectoral muscles can cause chronic postural overload,” explains Emily Kiberd, a chiropractor and founder of the Urban Wellness Clinic. “This will place excess strain on the structures of the neck leading to tension headaches; muscle tightness; short, shallow breathing; anxiety; and nerve pain.”

From finding just the right amount of stretch to the nuances of strap and underband size, here is a guide to picking the best sports bra for optimal comfort and health.

Be Wary of Too Much Stretch
There’s a simple rule of thumb for overall fit: “The more a sports bra stretches, the more your breasts will move,” explains Tempesta. “Sports?bras?need to fit tighter than everyday?bras, but not so tight that you feel restricted or like you can’t breathe.” While a style may seem more comfortable because it’s stretchy, the likelihood of breast pain goes up with the amount of breast displacement. How much “give” you can withstand is dependent on how high-impact your activity is. “For yoga, you can get away with more stretch,” Tempesta says. “But with running, any stretch in the straps, cups, or even underband will result in excessive breast movement. I cringe every time I see a woman running in a?bra?that was clearly made for yoga.” When weighing the options, it’s all about finding the right combination of encapsulation and compression—especially for larger busts, where the breasts must be contained as well as compressed to reduce movement. That being said, you have to be careful a style doesn’t fit too small. “It will compress the muscles in the upper back, which are usually tight if you sit hunched over a computer all day,” says Kiberd, who adds that it will also prevent proper lymph drainage, which is the body’s natural system for ridding the body of toxins and inflammation.

Find the Right Cup Size
“Women often assume their bra size is set in stone,” says Tempesta.?“But it’s a mistake to simply buy your usual bra size.?Bras are like any other type of garment: You aren’t always going to be the same size in every manufacturer and every style.” For robust support, avoiding exposed breast tissue is ideal. “If you can see cleavage, the?bra?is either the wrong size or not a good fit for your shape,” she says. If you’re going to be using the bra in a high-intensity capacity, you should be testing it out accordingly in the dressing room by running in place, as well as jumping up and down. Better yet, use the slow-motion video feature on your smartphone to film yourself as you move and observe how your breasts are moving in the bra. “You’ll be surprised how much breast tissue will spill out of an ill-fitting?bra?when viewed in slow motion,” says Tempesta.

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Make Sure the Underband Is Taut
“Most of the?bra’s support should come from the underband,” insists Tempesta.?“If it’s too loose or not supportive enough, the burden of support will move to the shoulder straps and that will cause shoulder and back pain.” To ensure an underband is tight enough, Tempesta recommends reaching around and pulling the underband away from the back to gauge how much room there is. “It shouldn’t pull out more than an inch for high-impact exercise,” she says. “You need enough room to expand your lungs, but you don’t want the band to shift, which will cause chafing. You want the underband to lock down and support you.”

Pay Close Attention to the Straps
One of the most common mistakes Tempesta encounters are straps that aren’t the right length, or veer toward too thin. “Generally, wider shoulder straps help distribute the pressure and weight better,” she explains. “Thin shoulder straps dig in and can cause pain.” When the latter happens, the compression from the tight straps causes constriction on the brachial plexus, “an important nerve bundle that goes from your neck down into your arm,” warns Kiberd. In terms of strap span, it’s important that a design doesn’t go too high up on the neck, which can cause shoulder and neck pain. In terms of design, as long as the straps aren’t too skinny, crossed-back styles tend to provide more stability and postural support as they “maintain a better position of the shoulders,” says Kiberd.

Look for a Breathable Fabric
When it comes to performance fabrics, it’s a myth that cotton is better than synthetics for athletic use. “Cotton absorbs moisture, but doesn’t allow it to dry quickly,” says Tempesta. Another detail to consider is how much padding there is in the cups, as foam absorbs sweat and doesn’t dry quickly. “Excessive moisture in the breast area can lead to chafing and discomfort,” says Tempesta. Always opt for breathable materials like microfiber nylon or polyester to “let your skin and muscles breathe as you work up a sweat,” says Kiberd.