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Ultra-Endurance Power: Rebecca Rusch and the Dirty Kanza

The Dirty Kanza represents the pinnacle of ultra- endurance gravel racing. Over 200 miles, through trying conditions, the Dirty Kanza is a test of endurance that only the toughest survive. Once past the 10-hour mark, a race really falls into the ultra-endurance category. Rebecca Rusch, who has won the Leadville 100 mountain bike race four times and the 24-hour solo mountain bike world championships three times, knows this zone well. She has won the Dirty Kanza on three occasions with her last win occurring in 2014. Her power files from the event show just what it takes to not only finish this event, but also what it takes to win the elite women’s category.

I have analyzed hundreds of ultra-endurance power files over the years, and they all follow a similar pattern— The first four to five hours are ridden at a strong tempo pace, usually around 80 percent of functional threshold power (FTP), and from there the remaining ride is done at solid endurance pace around 65 to 70 percent of FTP.  The winners generally create a gap over the rest of the competition in the first four to five hours. Unless there is a mechanical or serious nutritional problem, the winner maintains this gap and/or steadily grows it all the way to the finish. After about six hours, most riders fatigue at relatively the same rate, so if there is a gap it generally holds or slightly grows.

In 2013, Rusch, had an incredible race. She rode with the top men, and used the momentum of that group to establish a solid lead ahead of the second and third place women. It was risky since the intensity was a high percentage of her FTP, much higher than she would have chosen to expend on her own. is creates a potential issue—by riding at a high intensity early on in the race, she would not be able to maintain a strong pace in the closing hours. Even worse, she risked bonking, cramping or just completely fatiguing. In the first five hours of the race, she maintained an intensity factor of .86, which essentially means she rode at 86 percent of her FTP, or the upper end of level three tempo zone. Contrast this to the men and women who are professional triathletes that ride at an IF of .75 for the bike leg of the Ironman. Even then, they occasionally have trouble finishing the run strong. Additionally, look at an intense Tour De France mountain stage that is five hours long—the average IF for these falls between .75 and .78. This really puts into perspective the intensity of effort that Rusch put out, and she still had over seven hours to ride. 

Like I stated before, most normal pacing strategies in ultra- endurance events include a more intense  effort in the first four to six hours as the winner establishes his or her lead. However, this effort is generally not at 86 percent of FTP. Instead, the effort is closer to 80 percent. is might seem like a small difference on paper, but the 18-watt difference between 233 watts and 215 watts can be a large margin in a short race, let alone a 12-hour event.

The ability to maintain her pace throughout the remainder of the race is also remarkable. Breaking the race down into segments from aid station to aid station exemplifies this steady effort. Her wattage only decreased 15 percent from the last two hours to the last two, from a normalized power of 236 watts to 200watts. Most impressively, in the last five hours her average normalized power only decreased by two watts from 202 to 200! After an incredible first five hours, she not only had enough energy to continue for the win, but she barely fatigued in the later portion of the race. 

Rusch continued her winning ways a year later, though her path to victory differed. In 2014, a massive mud bog at about an hour into the race completely blew apart the groups of riders.  is prevented her from staying with the front group of guys, but she did exit this wheel stopping, fork clogging section as the first woman. At this point, she said, “I was psyched that I came out as the  first woman, but the front guys were completely blown apart, and there was no peloton or big group at all to stick with.  The race became a bunch of smaller groups and one or two riders working together. At that point, I realized I just needed to put it into a steady pace and stick to that all the way to the  finish. I caught some groups, but it the conditions were tough, and that made it hard for any groups to work together.”

The mud bog proved a trying section and Rusch rode at 295 watts, or 96 percent of her FTP, for that hour.  This was an important strategy, as the best racers will ride most intensely during the hardest part of an ultra- endurance race. This establishes the biggest gap on the competition and makes the most sense from an energy expenditure perspective. In this case, it was mud that created the obstacle, but in other situations a long or steep climb, a head wind or a difficult trail can be the decisive section. The best riders will generally win or lose the battle for the top step in these demanding scenarios.

Rusch continued her performance in the rest of the race and didn’t fatigue. Her average normalized power was lower than the previous year, but from hour three, with an average wattage of 164, until the  final hour, she actually increased her wattage and  finished that last hour with a normalized power of 171. Increasing the pace over the course of nine hours is one impressive demonstration of pacing.

Clearly understanding the demands of the event are key preparation for any ride or race. For the Dirty Kanza, the main demands are clear: complete a 200- mile race on gravel roads through possible mud or dusty conditions and do it in less than 15 hours.  e minor demands include: the ability to ride in a paceline for long hours, proper fueling by eating and drinking, pacing for 12 hours so you don’t fatigue before the finish. Pacing is critical to success in any bike race, but the longer the event the greater the importance. Successful ultra-endurance riders can ride at a higher pace for four to six hours to establish the gap between them and other competitors. To train for this kind of event, one needs training rides of around 14 hours to increase their endurance. Additionally, FTP intervals will improve peak sustainable power and also train the muscles to ride a tempo pace for at least four hours. Here’s a workout to help conquer an ultra-endurance road event. When you are able to complete this workout without being totally crushed, then you’ll be ready for your event.

| Hunter Allen |  ROAD |

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