More than anything, worn-out running shoes can destroy your workout, and even your health. Shin splints, knee pain, ankle pain, and even back pain can all result from working out in old shoes.

When to toss them: A good rule of thumb: if you're using your shoes 5 to 6 times a week you'll need new ones every 3 to 6 months. If you use them less often than that, then every 8 to 12 months should be good. If at any time you feel pain in your knees, ankles, or shins that wasn't there before, it's likely a sign it's time to replace your shoes. Of course, it's better to do this before you're in pain, so toss your running shoes if:

• You can hold your shoe at both ends and twist it easily (the sole should feel firm)
• You find yourself tying the laces really tight to feel supported
• Your midsole looks worn down or you can feel it when you're running

Help them last longer: Only wear your shoes when working out, since any running or walking wears them down. If you run often, get two pairs of shoes and rotate them, so each pair has time to decompress. After every workout, loosen the laces and open your shoes to air them out, and store them in a cool, dry place (not your gym bag or trunk). Never put your running shoes in the washing machine. If you do need to clean them, use a scrub brush, mild soap, cold water, and let them air dry.

*Sources: Andrew Schrage, co-owner of Money Crashers Personal Finance. Ilyse Baker, top 10 FitOrbit.com trainer. Janette Janero, group fitness director at Florida International University. Michele Bohbot, Electric Yoga designer and Master Yogi.

It's usually pretty obvious when you need to replace those old (holey) socks. Sure, nobody will see the holes, but your feet will suffer -- and you'll end up with painful and unsightly blisters.

When to toss them: Obviously if there are any holes or thinning in the material, it's time to splurge on some new socks. Another early warning sign: If you feel them moving separately from your foot when exercising; socks should grip your feet like a second skin.

What to replace them with: The right socks will not only last longer, but also keep your feet feeling good during and after your workout. So look for ones with cushioning on the sole and made from a micro-fiber fabric (as opposed to cotton, which retains the sweat from your feet and creates a wet environment for bacteria and fungus).

*Sources: Andrew Schrage, co-owner of Money Crashers Personal Finance. John Paul Ouvrier, director of Fitness4Charity.org.

No offense to all the gym teachers out there, but our experts say you're better off with fitted, moisture-wicking material than the classic gym class sweats and tees. But no matter what material you choose, your workout bottoms won't last forever.

When to toss them: When you see pilling, when fitted pants feel loose, when the moisture-wicking material just isn't working like it used to, and when the fabric thins too much (this typically happens in the butt or knee area, depending on your go-to workout).

Why you shouldn't hang on to them: Worn out pants can cause chafing, distract you from your workout (if you're constantly readjusting your clothes), and can be pretty embarrassing if they're so thin they become see-through when you sweat.

*Sources: Phylise Sands, founder of Red Daisy sports bra line. Kira Karmazin, founder of KiraGrace yoga apparel.

Anyone larger than an A cup can attest to the importance of a well-fitted sports bra, but it's not always easy to trash these often-expensive pieces.

When to toss them: After six months to a year, or whenever the straps feel loose. Also, if you gain or lose weight you'll want to rethink your size and buy a new bra.

Help them last longer: Don't put your sports bras in the dryer, since that can make the elastic wear out faster. It's also smart to rotate which ones you wear every day, so the same one or two don't get overused.

What'll happen if you hang on to them: If your sports bra isn't properly supporting your chest, you can get pain and discomfort, damage the elasticity of your breast tissue, and put strain on your back.

*Sources: Heather Montgomery, blogger for runningwithsass.com. John Paul Ouvrier, director of Fitness4Charity.org.

Want to walk into the gym feeling confident and ready to kick butt? Our experts say a new workout top (preferably in a fun color) can get you in the perfect frame of mind. Consider it an excuse to go shopping.

When to toss them: Generally after two years, or when you notice pilling, seams unraveling, or fitted tops losing their shape.

How to help them last: A seamless top in a polyester/lycra blend draws sweat away from your body and limits chafing (a nice bonus while you're working out), and will also generally last longer than a cotton shirt.

*Sources: Janette Janero, group fitness director at Florida International University. Michele Bohbot, Electric Yoga designer and Master Yogi. Phylise Sands, founder of Red Daisy sports bra line.