How do we get the most effective workout and the best results? To understand our bodies. Here's nine ways that being a woman can affect your workout, courtesy of Charlotte Andersen for Shape.com, and why you should care. We're feeling more motivated already!

Junk in the trunk
Sofia Vergara is an excellent example: Women store fat differently than men. And these "fatty bits" have implications far beyond splurging on high-impact sports bras and workout pants that make our butts look amazing. While women's lower centers of gravity and smaller muscle-to-mass ratio makes it harder to bang out pull-ups like the boys, our tendency to store "gluteofemoral fat" (fat in our hips, butts, and thighs) gives us a huge leg up on the men: A 2010 study from Oxford University found that body fat in the thighs and backside, as opposed to storing excess fat around the midsection, helps protect against heart disease and diabetes.

"Don't be concerned about a little (or more than a little) subcutaneous body fat, especially on your lower body," says Mark Sisson, author of The Primal Blueprint and a paleo fitness expert. "If you've been trying in vain to lose that stubborn jiggle on your thigh, consider that maybe, just maybe, it's there for a reason. Even if you're not interested in having a child, it's likely that the presence of lower-body fat indicates good health (and the ability to get pregnant)," he says. "The research outlined above suggests that classically feminine patterns of fat deposition are healthier than classically male patterns. And even if you don't like your gluteofemoral fat, rest assured that the males in your life likely do!"

Knee pain? Blame your Q-angle
According to the American Academy of Orthopaedic Surgeons, women are two to 10 times more likely to suffer a knee injury than men, thanks to a biomechanical difference in the angle of our hips to our knees called our "Q-angle."

"Because of wider hips, women's knees are more vulnerable to high-impact activities like plyometrics, sprinting, or sports like soccer that require quick changes of direction," says Steve Toms, head of personal training for Lifetime Fitness and corrective exercise specialist.

Since you can't change your bone structure, Toms suggests strengthening the muscles that surround your pelvis to boost core stability. It sounds counterintuitive, but for many women, the key to ameliorating knee pain is building strength in the glutes and hips. Try adding frontal-plane lunges to your routine and working your way up to single-leg exercises to build stability in the hips, Toms advises.

Risky time of the month
You might want to be extra careful when Aunt Flo makes her monthly visit. Australian researchers found that female athletes are more likely to get injured during their periods than any other time of their cycle. Why? Low estrogen at the beginning of the menstrual cycle (when you're actually bleeding) causes reduced muscle tone and impairs coordination, making you more susceptible to injury, especially in the knees, feet, and ankles.

It's not just our physiology that suffers. Rachel Cosgrove, in her book 'The Female Body Breakthrough,' adds that "more than one study has shown that exercise feels harder the week before and the week of women's periods because of increased levels of progesterone and decreased levels of serotonin." You may find that your workouts feel harder than usual and that you're more tired, but don't beat yourself up if you don't set a personal best this week. Just get in and get it done," Cosgrove says.

If you want to make the most of menstruation, power through those weight routines. According to Cosgrove, your body's fat-burning potential peaks during this time. And there's more good news: Taking birth control can help counter the negative effects. The Aussie scientists say, "there's now quite a global body of research saying that the pill actually is protective of injuries. It protects you from injuries, it improves performance, and improves muscle function." Birth control as a performance enhancer? Double win!

Increased pelvic mobility
Thanks to the flexibility of our "birthing hips," we can pop a baby out without splitting in half. But those same pliable ligaments can cause pain and injury, especially in the joints connecting our hips to our spine (the sacroiliac joints), says Diane Lee of Diane Lee & Associates (http://dianelee.ca/), a physiotherapy clinic that specializes in helping women heal pelvic pain. Unlike most joints, the SI joints are fused together with a very small range of motion. Increasing that range of motion-as often happens during pregnancy-can destabilize the entire pelvic girdle.

"Sacroiliac joint dysfunction occurs in both genders, but it's far more common in women," Lee says. Your pelvic girdle is the primary stabilizer of all movements, so when your pelvis is out of alignment, everything else follows. "It's like having your pantyhose twisted; everything needs to be aligned to work properly."

SI pain can have many different causes, so Lee cautions that "there is not one prescription for healing." Each case is individual. Her expert recommendation: Find a physiotherapist who has experience working with women and get an evaluation.

And then there's pregnancy...
If you think wearing a weight vest amps up your workout, try strapping 30+ pounds to your abdomen for nine straight months. Okay, so you don't start out 30 pounds heavier, but you get my point: Pregnancy is the ultimate form of weight lifting. It's also the primary way in which men and women differ. What does that mean for your workout? Aside from the obvious added resistance, experts recommend that pregnant women take the following precautions during exercise: stay hydrated, don't allow yourself to overheat, avoid any activity that could cause you to fall on your stomach, and tone down your weight lifting in the third trimester to avoid straining already loosened ligaments.

These restrictions will certainly impact your workout, but they don't mean you need to skip exercise altogether. Research on the topic concludes: "In the absence of any obstetric or medical complications, most women can maintain a regular exercise regimen during pregnancy. Some studies have found a greater sense of well-being, shorter labor, and fewer obstetric interventions in physically well-conditioned women as compared with other women."

Shin splints love the ladies
Shin splints are every runner's nemesis, but women are three times more likely to be afflicted than men, according to Australian researchers. Plus, a study of female athletes published in the Journal of the American Medical Association found that women's shin splints are up to three-and-a-half times more likely to progress to stress fractures than men's.

Additional risk factors for shin splints include flat feet and overpronating (excessive inward roll of the foot after landing)-both conditions that also affect more women than men. Researchers speculate that this may be due to increased prevalence of osteoporosis in women, the effects of the pregnancy hormones in relaxing ligaments in the feet and legs, and/or the prolonged wearing of high heels. So if you're feeling pain during your Saturday morning runs, you may want to ditch your date-night stilettos on Friday.

Your metabolism is more efficient
Anyone who's gone on a diet with their husband or boyfriend knows the frustration of watching him shed pounds simply by ditching soda and beer while we count every calorie and still don't see results. But our metabolisms are more efficient for a good reason. In times of scarcity, women maintain their body mass and are better at utilizing fat stores than men, allowing us to keep the species going. This has benefits in a non-neanderthal setting too. A 2000 study published in the Canadian Journal of Applied Physiology found that women are better at burning fat (as opposed to carbs) to fuel their cardio sessions than men.