The world's oldest annual marathon gets under way this weekend. It's a big event for the runners, but it's also a huge one for the city of Boston and numerous companies. How much does the marathon really cost and, more important, how can investors get a piece of the action?

Physically (and fiscally) fit
A half-million spectators will witness more than 20,000 Boston Marathon runners strut their stuff on the famed course through Beantown on Monday.

Source: Wikimedia Commons.

Most Boston Marathoners gain eligibility to run the race by having completed a qualifying marathon in a certain amount of time. For example, a female runner between the ages of 45 and 49 would need a sub-four-hour qualifying time to run at Boston. But runners who don't qualify under the time limit can still participate through a charity, by raising about $3,000 for their cause. That just gets your tired feet in the door.

In addition to the $150 entry fee for U.S. residents ($200 for international residents), runners must spend money on travel, lodging, and dining. Of course, runners can't forget to pack essential running shoes and apparel. In all, a U.S.-based marathoner can anticipate spending $1,000 to nearly $3,000 to participate in the Boston Marathon. An internationally based runner will spend more. Assuming a $2,500 average tab per runner means $50 million will change hands as a result of this year's race!

Even though we mere mortals will instead fill this weekend with activities of the couch-potato persuasion, we can still profit by investing in products used in the marathon.

On your mark
For starters, even the best runners often need medical attention during the race. The shoes that Flash swore he broke in weeks ago may rub him the wrong way at mile 13. And as runners gloriously cross the finish line, despite the endorphin rush, they'll still feel pain.

Patching up runners' annoying blisters, sore joints, and aching muscles will probably come from Johnson & Johnson (JNJ -1.15%) and Pfizer (PFE -3.85%) products. For more than 125 years, J&J has brought relief to millions of consumers with its Band-Aids, Tylenol, and Bengay. Pfizer's Advil is the No. 1-selling branded over-the-counter pain reliever, and its ThermaCare Heatwraps make heat therapy portable and long-lasting. And these two Dow Jones Industrial Average bellwether stocks both pay greater than a 3% dividend yield.

Running-apparel and shoe makers Nike (NKE -0.74%) and Under Armour (UAA -2.34%) are also likely beneficiaries of the race. Nike not only holds an enviable spot as the global market leader, but it also boasts the right strategy and investments to sustain its top position. Meanwhile, newer kid on the block Under Armour has evolved into a major player in the global athletic footwear and apparel market.

Not to be outdone, lululemon athletica (LULU -1.26%), originally known for its pricey yoga pants, now flaunts lines of running gear targeted toward both sexes. Enjoying $1,900 in sales per square foot, its stores make Lululemon one of the United States' most successful retailers. And growth opportunities abound for the company in North America and overseas, particularly in Europe and Asia.

Foolish takeaway
While it's (small-f) foolish to buy a stock based on a single event (like a marathon), the overall trend toward healthy, active living grants companies such as these potential revenue boosts. As investors, we should always be on the lookout for trends that'll act as tailwinds. But evaluate several metrics when determining whether a company's stock is deserving of your dollars.