So you've been sitting with your legs crossed for years--even though Mom said it causes varicose veins. This might not actually be true, but it could cause other long-term problems.

More likely, varicose veins are hereditary or come with age, Dr. Naresh C. Rao, a clinical instructor at New York University's Langone Medical Center, told The Wall Street Journal. The bigger problem with crossing your legs is that it puts strain on your knees, pelvis, and lower back, and could cause permanent damage.

Pain points to a misalignment

The important thing to keep in mind is that the problems arise when your knees are not aligned. When your legs are crossed, the top knee strains the bottom knee, and the lower back and pelvis twist in an unnatural position. Over time, this misalignment could cause some skeletal impairment, which Rao says would require physical therapy or treatment from an osteopathic physician. (This can also reverse some of the damage already done, if you aren't yet experiencing chronic pain.)

Standing up for your health (and career)

You really should only sit with your legs crossed about as long as it would take to drink a cup of coffee, says Rao. Instead, sit with your legs and feet straight in front. Even better, get a footstool so your feet can lie flat.

But the best option, according Rao, is to just not sit for longer than an hour at a time. Aches and pains are often a symptom of using our bodies in unnatural ways--like sitting sedentary at a desk all day. That's why Rao has a standing desk. "As an osteopathic physician, I can say with authority that our bodies are meant to move." He stresses the importance of getting up to walk around for five minutes every hour.

And studies show that getting up from your chair isn't just good for your physical health--it might also make you better at your job. Having the option to stand and work for just 1.6 hours per day can boost productivity by a lot, according to a study from Texas A&M University's Health Science Center. Call center workers--observed over a six month period--proved that an investment in standing desks is a good business decision. Those with stand-capable desks were 23 percent more productive in the first month and 53 percent more productive over the next six months.

So next time you're going to cross your legs, don't. It's time to stand up instead.