But did you think about the wardrobe?
You probably should. The right clothes and gear make the difference in performance, comfort — and the cute Facebook photo you'll want to post at the end of the day, say product developers and seasoned recreational athletes.
Eileen Berner, marketing director for insulator PrimaLoft, is a self-described "weekend warrior" who does obstacle races and climbs mountains and ice in her spare time.
"Clothing is one of the first key decisions you are making in one of these events. You've checked the weather forecast, but the race starts out and you're running up a ski mountain and sweating when it's still cool and by the afternoon, it's really hot," Berner says. "It could be an eight- or nine-hour day, and you can really have the gamut in weather."
She says she can tackle pretty much anything in her lightweight Patagonia Nano Puff jacket and water-resistant, tight-fitting socks. They are her go-to items. "The best gear is the gear that when you come back from the event, you weren't cold or hot or have blisters."
For Margaret Schlacter of Salt Lake City, a regular on the Spartan Race circuit, that means nothing cotton. "I made the awful mistake the first time and wore cute cotton yoga capri pants, cotton underwear and a cute cotton T-shirt. After the swimming portion of the race, I had to roll the yoga pants into shorts and keep peeling the shirt away from my body."
She adds: "Wearing cotton underwear is like wearing white after Labor Day — it's a cardinal sin."
Schlacter participated in her first obstacle-based, multidiscipline race in 2010. Since then, she gave up her day job in education and competes full time (and is now writing a book about it).
Synthetic fabrics not only help take care of the moisture and regulate temperature better, but they also dry quickly, resist stains and don't retain as much odour, says Greg Thomsen, managing director of Adidas Outdoor. "You're looking for anything that can help you perform at a higher level."
This new generation of fitness buffs likes outdoor workouts, so makers of athleticwear had already started making the shift to moisture-moving and water-repellant materials, says Susan Branch, global head of products for Roxy. "Her activities are from land to sea, and we are designing and developing for that."
She also wants sun protection, mesh ventilation and pockets since she might not be ending where she started, Branch adds. Those features are becoming standard, she says. "The things to look for if you're going to be in a boot camp or mud run or mini-triathlon are really things that are fairly common these days and available."
Her other recommendations are slim, body-hugging silhouettes for ease of movement that don't snag on obstacles and wider bra straps for support.
Something else athletes might want — but don't yet know they want — are flat-locked seams because they reduce chaffing, she adds.
Choosing footwear, though, is more specific, Schlacter says. There's a difference between running through a few puddles and submerging your foot. For a race that does involve more wetness, she skips the water-repellent trail shoes, because, while they keep a certain amount of water out, they'll also keep the water inside the shoe if it gets inside. She predicts that big industry players will soon develop a shoe that's tailor-made for these sort of activities.
Schlacter says she isn't all that concerned what she looks like when she is on the starting line, but there is no reason not to put fashion with function. She favours simplicity, down to her ponytail reinforced with an elastic headband and sheer lip balm. There's definitely no mascara, she says with a laugh.
Roxy's Branch, however, makes the case to have it all: "You should have the expectation that products made for this stuff will perform — and that you can look cute doing it. There are trend-right silhouettes that deliver on technical features," she says. "And you know you will put up a photo of you crossing the finish line on social media, so go for it!"