Some things are better after they're broken in (jeans, shoes, husbands). But once a sports bra has broken down, it should be tossed out. If it's consistently air-dried (hot tumble drying ruins Lycra), a sports bra should last about 100 wearings. Not keeping tally? Here's how to know when it's time to send your old jog bra the way of those '80s leotards and headbands.
Perform a stretch test. Gently tug the elastic straps and band. If you don't feel any resistance, buy a new bra.
Compare the old and the new. Stack a new sports bra on top of a similarly styled old one. If the old bra has a wider band and longer straps, throw it out.
Go with your gut. "When a sports bra loses its oomph, you risk developing motion-related sagging," says LaJean Lawson, an exercise-science researcher at Oregon State University, in Corvallis. A sports bra provides almost twice the support of a regular bra. For a quick test, jog in place wearing a normal bra, then a sports bra. If your breasts don't feel significantly more secure, get a new one.