The shoes you wear can make you feel slim, sexy, and stylish-or they can leave you wincing in pain. 

Ever wonder how much damage you are doing when you walk to work in sky-high heels or scuff through errands in flip-flops? We wanted to find out for sure, so we took three 40-something women to a high-tech motion-analysis laboratory to test out four different types of shoes: flip-flops, high heels, dress flats and toning sneakers. (Results were compared with our gold standard of comfort-a simple pair of running shoes). 

At the lab, the women were outfitted with sensors to measure muscle and joint activity so we could see precisely what types of stress their bodies were subjected to. Read on to learn the findings and (since we know shoe choice is not always based purely on practicalities) get expert advice on how to make even those stilettos as foot-healthy and pain free as possible.

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How Flip-Flops Wreck Your Body

They may be your favorite things to slip on as soon as the weather gets warm, but flip-flops aren't as foot-friendly as you might think. Here's why:

Scrunch time.
Only a thin strap and your bunched toes keep flip-flops from coming off. That constant grip makes it impossible for your arch to flex normally, which in turn compromises the way your forefoot pushes off when you step forward. Deprived of a powerful push-off, our testers compensated by using their hips, forcing their knees and hips to absorb more impact. In addition, your butt and the backs of your legs are less engaged in your stride, weakening those muscles over time, says Katy Bowman, a biomechanical scientist and the author of Every Woman's Guide to Foot Pain Relief.

Short steppin'.
Wearing flip-flops shortens your gait, so you can't expect to get very far very fast in them. Eventually your shortened stride may lead to lower-body fatigue, which in turn may make you more inclined to hop in a cab or get in your car rather than walking, says Philip J. Vasyli, a podiatrist and the founder of the orthotic company Vasyli International.

Flip-Flops Lab Result: Our testers were up to 2.5 times less stable in flip-flops than sneakers.

Flip-Flop Fixes

Stretch it out.
To help your toes recover from the stress of being clenched, stretch the muscles along the top of the foot, says Bowman. Stand with your feet hip-width apart, then place one foot behind you, turning the tops of your toes to the floor. Try to keep both knees straight, stand tall, and don't let your ankle roll out to the side as you stretch. Start by holding the stretch for a few seconds on each side (your foot might cramp initially because it's not used to stretching this way), and work up to 60 seconds on each side.

Shop smarter
If you can't fathom going through a flip-flop-less summer, opt for a more structured pair. Look for a contoured arch that fits to the shape of your foot (look for brands that have the American Podiatric Medical Association's seal of acceptance) rather than the flimsy corner-drugstore ones that look like they're stamped out of a piece of rubber.

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How High Heels Cause You Pain

There's a reason most women willingly forgo comfort to squeeze their feet into stilettos: Adding inches makes you look slimmer, accentuates calf muscles, and even lifts your backside.

But you may be doing lasting damage if you live your life in heels. A 2011 Danish study found that walking in heels can increase the risk of osteoarthritis sixfold. Here's what else we found in testing:

Tighter quads.
Imagine standing on the edge of a ski slope with your toes pointing downhill. To compensate for this tipped-forward position, it's natural to bend your knees slightly and arch your back. As a result, your quads are forced to work overtime, which makes them tight and prone to injury. Walking with your knees slightly bent also puts 200 percent more stress on your kneecaps, which can wear away at the cartilage and increase your risk of developing arthritis, says Howard Dananberg, DPM, a podiatrist in Bedford, New Hampshire.

Screaming shins.
The added height of heels puts extra strain on the shin muscles, which control the forefoot. This repetitive strain can eventually lead to painful shin splints.

Knotty calves.
Heels put your calf muscles in a shortened position. Over time, this can become permanent: One study in the Journal of Experimental Biology found regular heel wearers had calf muscles that were an average of 13 percent shorter than those of nonheel wearers, making it uncomfortable for them to walk without heels because their natural stride was thrown off.

High Heels Lab Result: Our testers walked slowly in heels than sneakers. Wear them daily and the decrease in calorie burn could add up to a 5-pound gain in a year!

High Heels Help

Stretch it out.
Give your calves a good daily stretch like this one from Bowman: Stand with your feet hip-width apart and place a rolled-up towel under the ball of your right foot. Lower your right heel to the floor. Once you're comfortable here, take a small step forward with your left foot, keeping your hips square. Hold for 20 to 30 seconds and work up to 60 seconds.

Massage your shins.
Relieve shin pain with a gentle self-rubdown, applying long vertical finger strokes down the front of your lower leg. Then focus on kneading the muscles horizontally, says Bowman.

Embrace the commuter shoe.
Switch to low-heeled options for getting places, and save those skyscrapers for when you're mostly sitting pretty.

Shop smarter
Feet swell over the day, so if a shoe feels slightly tight at 7 a.m., it'll be a vise by nightfall. Only buy shoes that are roomy enough, and consider going lower. Research shows that 2-inch heels create impact forces 4 percent greater than flats, while 3-inch heels boost stress by 33 percent.

Easy Foot Pain Cures
 

How Flats Cause Foot Pain

Flats sound like the healthier alternative to heels, but the truth is that even a basic ballet flat or canvas casual can be just as problematic, says Megan Leahy, DPM, a podiatrist with the Illinois Bone & Joint Institute in Chicago.

Arch enemy.
Many flats lack internal support (like the kind you find in a sneaker). Without it, the ligaments and tendons along the bottom of your foot can overstretch and the arch can collapse, says Marlene Reid, DPM, a podiatric surgeon in Naperville, Ill. This in turn can lead to the painful foot condition plantar fasciitis-a notoriously hard-to-treat burning or aching along the bottom of the foot. Poor internal support is especially problematic if you're naturally flat-footed.

Strained soles.
Many casual flats have even less interior cushioning than heels or sandals. This lack of padding can trigger pain in the heel or ball of your foot when you're walking, especially if you have high arches, says Leahy.

Flats Lab Result: In our tests, women put about 25 percent more impact on the heel with each step when wearing flats, compared with pumps.

Fixes for Flat Shoes

Give your feet a workout.
To wear shoes with no built-in support, you need to strengthen the tiny foot muscles that support your arches, says Bowman. Try doing toe lifts: Raise your big toe without moving the rest of the gang. It may seem impossible at first, but it's like riding a bike, says Bowman, you just have to master the coordination. Until you get the knack, wiggle your toes and rub your feet vigorously, which will stimulate your nerve endings and help wake up your feet. Do 20 toe lifts per foot.

Stretch it out.
Just as the abductor/adductor machine at the gym strengthens your outer and inner thighs, you can work your toe abductors and adductors to make the muscles of your foot stronger and more supportive. Start by interlacing your fingers with your toes to help press them apart, then spread and relax them without assistance from your hands. Hold the stretch long enough to sing the alphabet. Do this once a day (or up to three times if you have bunions).

Bump it up.
Help strengthen the small muscles in your feet and lower legs by striding barefoot across an uneven surface such as cobblestones. This also helps stimulate the nerves in your feet. Buy a pre-made cobblestone mat with smooth stones already glued to it, or find (or make) a bumpy space to walk back and forth on in your backyard.

Add OTC insoles.
If you have flat feet (your wet footprint shows the entire foot), foam or rubber insoles can help prevent your arches from collapsing. If you have high arches (you see only the heel and ball of your foot in your footprint), look for an insole with more rigid arch support.

Shop smarter
Look for flats with an insole that curves along the same lines as your foot and arch. Then try to fold the shoe in half-it should bend only at the ball (the same place your foot naturally bends as you walk). Also avoid pairs that fold right in the middle or roll up easily.

New Treadmill Workouts

How Toning Shoes Cause Foot Pain

Shoes with rounded or "rocker" soles that purportedly increase muscle activity and boost calorie burn are big business-after all, who doesn't want to get a workout without really working out? But despite their medical provenance (rocker-bottom shoes were originally engineered to help patients with pain in the balls of the feet, says Leahy), consider the following before you get a pair as a fitness tool.

Stress case.
The rigid soles prevent arches from naturally flexing. Eventually, this can cause your arches to flatten and lead to overpronation (when the feet excessively roll in while walking). The result: Your feet absorb less shock, causing your knees and back to take on extra stress.

Teeter trouble.
Testers were slightly less stable in the rocker-bottom shoes. The Consumer Product Safety Commission's Web site is loaded with complaints about injuries from toning shoes (including tendinitis; foot, leg, and hip pain; and even broken bones resulting from falls). 

Rockers Lab Result: Surprise! Our testers worked their butt and thigh muscles less when wearing tone-up shoes, compared with simple sneakers.

Relief from Rocker Shoes

Be inspired (but don't skip your strength workout).
If these shoes help you feel more conscious of the benefits of every step you take and make you want to walk more, go for it! But don't skip proven strengtheners. The best way to tone your lower body is with strength moves such as squats and lunges, not just walking around in toning shoes.

Work your wobble muscles.
Because these shoes make you unstable, they can lead to ankle injury. To strengthen the muscles around the ankle, practice standing barefoot with one leg lifted, keeping your standing knee straight, and try to minimize wobbling. Start with 30 seconds and work up to 60 seconds at a time.

Take it slow.
The convex soles force you to change your natural gait, so it can take your muscles a while to get used to the movement. "At first you should not wear these shoes all day, every day," says Leahy. Start with about an hour a day and build up gradually. And listen to your body: "If you start to develop pain in your back, hips, knees, feet, or ankles, switch shoes," she adds.

Shop smarter
If you're determined to try the rocker technology, look for a pair that actually bends at the ball of the foot. This will allow your foot to flex more naturally despite the extra thickness of the sole.