Wearing a sports bra is essential for every woman who is active. Because breasts can move as much as 4 inches up and down as you run, depending on your size, you need all the support you can get to stay comfortable, and prevent wear and tear to the delicate skin near your chest.
Even if your muscles near your chest are well defined, your breasts have no muscles, so one the skin is damaged, there is no return!
Even if you have little to support, too much stretching on a regular basis, caused by bouncing or movement can result in sagging and shape loss. Sports bras are essentials for all sports, from low impact yoga, to high impact running.
Fitting a sports bra is a lot simpler than choosing a daily bra, because sports bras lack the under wiring you find in most bras and are based around your usual cup size.
It is always a good idea to try on a bra, and even to jump around in it if you get the chance.
The design of a sports bra is based around stretch fabrics that sit on the chest, restricting movement like a bandage or taping via compression.
For yoga and similar low impact sports you can choose a bra that offers more of a compressive design, like a cropped top with added stretch, and for running you could choose a more supportive bra that uses both cups for separation, as well as the stretch, cropped compression design for hold and comfort.
Dependent on your personal preferences, you may need more than one sports bra.