The benefits of exercising seem to be popping up everywhere lately: It helps relieve stress. It helps you focus more at work. It leads you to be more confident, outgoing, and just generally awesome. It can even bring about world peace. OK, just kidding, I made that last one up.

But here's one I'm not making up: It could bring huge gains to your portfolio, via the companies who profit from our increasingly health-conscious ways. I'm talking about companies like Nike (NYSE: NKE), lululemon athletica (Nasdaq: LULU), Town Sports International Holdings (Nasdaq: CLUB), and Life Time Fitness.

Are all fitness stocks created equal?
Of the companies listed above, the last two are probably the riskier investments. These companies own and operate fitness centers in the U.S. -- something we all love in theory, but definitely not necessary for a healthy lifestyle. They are, in fact, somewhat of a luxury, and as such they are usually one of the easiest and earliest things to get cut when money gets tight -- especially if it's between that or better workout gear and higher-quality foods.

Fellow Fool Sean Williams really doesn't like the fitness center stocks, noting their cyclicality and lack of pricing power. I'd say he's right on the money. Their one saving grace may be the growing trend of group workouts, like Zumba, fitness boot camps, and cycling classes. But you don't necessarily need a gym for those things. They can all be hosted independently, and much like Jane Fonda's VHS tapes, could end up being a passing fad.

Just do it
While there is room for the fitness center companies to turn the game around as more and more Americans choose to follow a healthier lifestyle, things look a lot more promising (and stable) for companies that offer the workout gear, like Nike, Under Armour (NYSE: UA), or Lululemon. Even companies like Gap (NYSE: GPS) stand to see increased revenue from the athletic lines their brands offer.

Nike has a seriously strong brand abroad, and is making a big push into China to capitalize on it. While Gap's athletic offerings are still a small part of revenue, Gap's "other" segment, which includes Athleta and Piperlime, recently saw 34% sales growth. Under Armour continues to impress the Street with a 37% gain year to date and now realizes more than twice the earnings per share it did at the end of 2009.

Lululemon in particular has been an amazing multibagger for many of its investors. It succeeded by creating a unique brand that resonates with a growing audience worldwide. Some of our top analysts have discovered the next rule-breaking multibagger and put together a special free report with all the details you need to know. Click here to read it now.