Both triathlons and adventure racing are tough events and often push participants beyond their mental and physical limits, but "what sport is tougher?" Having competed and coached triathletes for 8 years and participated in adventure racing for over 5 years, I am often asked this question.
It all has to do with your definition of toughness. For adventure racing and triathlons, toughness is a combination of factors that include training requirements, physical and mental endurance, risk, and skills set.
Some of these components are shared by both sports while others are unique to each. To make the comparison equitable, I will compare an Ironman-distance race to a 12-hour adventure race.
The training miles and hours involved in Ironman training are staggering. Sixty- to seventy-mile bike rides are often followed by eight- to ten-mile runs. This mileage often adds up to six hours, or more of training a day, and this does not include pool time. In the months leading up to a race, athletes often train 6 days out of the week.
Adventure race training also includes an endurance component, but the miles and hours do not add up the same way. For the mountain bike leg, for example, 50 percent of the ride will be uphill and the other 50 percent will be downhill and rarely will you pedal on the downhill.
In essence, a four-hour mountain bike ride is really two, or so hours of pedaling. Trail running for an adventure race and asphalt running during a triathlon can be identical in terms of miles and hours, but street running certainly puts more stress on the body. Lastly, kayaking and swimming are remarkably similar, even using the same muscle groups.
The Ironman, or any length triathlon for that matter, is about efficiency, sustained effort, and quick transitions. Once you get out of the water, your equipment and training are helping you maintain the fastest possible speed on the bike and run with minimal interruptions. Even food and water are taken without pause.
Adventure racing teams have to frequently stop and look at the map throughout the race, and on average have 25 to 30 checkpoints(CPs). Not only do you have to find CPs using a map, but you also have to stop and get your passport punched. The stops and transitions can add up to one to two hours of rest time.