To eliminate experimentation, we asked four ultra-endurance athletes to single out the supplement that works best for them. Think of it this way: If a natural pill can help power Dean Karnazes for 350 miles (563 kilometers) nonstop, there's a good chance it will get you through your weekend pursuit.
The athlete: Monique Merrill
Merrill's four-person Nike PowerBlast team won this year's Primal Quest, which requires skills in paddling, biking, canyoneering and night navigation. Merrill, 37, traversed 433 miles through Utah's desert mountains in 143 hours, with only 13 hours of sleep.
The Product: PowerBlast ($40 for 24 tubes; www.powerblastenergy.com/)
The Plug: "In an event like Primal, you can lose the race on the last day because you're so tired you forget you're racing. In the past we drank something like three Cokes to stay alert. But this year with PowerBlast I was totally amped and only drank one Coke -- out of habit."
The Download: PowerBlast -- a powder you can mix with water on the fly -- contains caffeine, taurine, guarana seed and yerba mat?, along with a host of vitamins. Users should stay well hydrated, as some of those ingredients act as diuretics.
The athlete: Dean Karnazes
On September 17, Karnazes, 43, set out to complete 50 marathons, one in each state of the U.S., in 50 consecutive days. Whether running the nation one state at a time or cruising nonstop for 81 hours (as he did in 2005), soreness and swelling are his nemeses.
The Product: Boiron Arnica montana 30C ($12 for 3 tubes of 80 pellets; www.drugstore.com/)
The Plug: "I use Arnica montana, a homeopathic anti-inflammatory, for aches and pains. I used to pop ibuprofen, and it really messed up my stomach. Arnica has a more subtle response, but it works equally well."
The Download: Arnica montana, an herbal extract, comes in a pellet form (see above) that dissolves under the tongue for overall soreness. Herbalists also recommend applying it in gel form to bruises and sore muscles to reduce swelling and pain.
The athlete: Seamus McGrath
McGrath, 30, and his teammate Andreas Hestler, 36, are favored to win the 2006 TransRockies Challenge, a seven-day mountain biking race that gains 37,070 feet and travels across 373 miles of the Canadian Rockies. His chief concern: muscle recovery.
The Product: GNC L-Glutamine ($18 for 100 tablets; www.gnc.com/)
The Plug: "Without a protein supplement I'd go all out one day and my legs would be thrashed the next. When you're working hard, your body uses (its own) muscle as fuel. So to repair those muscles, I use L-glutamine, one of the body's building blocks."
The Download: L-glutamine is a link in the chain of amino acids that make up the body's proteins. Surgeons often give it to their patients to speed recovery. For optimal effect, take it within an hour of your workout or just before bedtime.
The athlete: Greg Hill
In February, Hill, 31, won 24 Hours of Sunlight, an endurance ski competition in which he skinned up and skied down Colorado's Sunlight Mountain 32.5 times. As Hill knows best, freezing temperatures and extreme exertion wear heavily on the immune system.
The Product: Cold-fX ($27 for 60 capsules; www.cold-fx.com)
The Plug: "I used to tire myself out so badly that I'd end up getting bronchitis. It would keep me from training for weeks. Now I take a complex vitamin to keep my immune system strong, and if I feel something serious coming on, I take a Canadian supplement called Cold-fX."
The Download: Cold-fX is derived entirely from North American ginseng (most ginseng supplements contain little if any real ginseng.) Though it remains medically unproven, ginseng has long been revered for its purported ability to boost the immune system.