⏵ Course guide · Winter ultra, Mat-Su Valley
The Susitna 100 sends runners, bikers, and skiers across frozen swamps, lakes, and rivers on marked trails through Alaska's Mat-Su Valley every February, human-powered and self-sufficient. I will walk you through what makes a winter 100 different from a summer one, then give you cold-weather pacing and fueling strategy, plus free tools to dial in your own numbers.
These facts come from the official susitna100.com race site. Detailed vert, aid, and cutoff numbers are not published there, so confirm current logistics and mandatory gear requirements with Alaska Winter Wilderness Races before you commit.
The Susitna 100 crosses frozen swamps, lakes, and rivers on marked snowmachine and dogsled trails through the Mat-Su Valley near Big Lake, a very different terrain problem than most summer trail ultras.
This is not a running race with a fat-bike side event bolted on. Run, bike, and ski divisions all cover the same marked winter course, so the terrain and conditions test are shared across every discipline. Choose the division that matches your winter training, not just your usual race distance.
Trails are marked, but conditions in the Mat-Su Valley in February are genuinely winter: frozen surfaces, potential wind exposure on open lakes and swamps, and cold that does not let up overnight. Winter expedition races in this category have historically required mandatory survival gear, so treat gear preparation as seriously as fitness preparation, and confirm the current year's requirements directly with the race.
Cold, snow, and darkness all slow you down in ways a summer pace chart will not predict, so build your time budget around winter reality, not warm-weather splits.
Snow-covered and frozen trail rarely runs at your flat, dry-ground pace, and February daylight in Alaska is short, meaning a large share of the race happens in the dark. A grade-adjusted pace target still helps, but pad your estimate for winter footing and reduced visibility rather than assuming your summer 100 mile splits will hold.
⏵ Free tools to pace this course
Staying warm burns extra energy, and cold slows your thirst signal even as layers and effort dehydrate you, so winter fueling needs a different plan than a hot-weather ultra.
Cold weather dulls thirst even when you are losing real fluid through breathing hard air and sweating under layers. Aim for roughly 60 to 90 grams of carbohydrate per hour, and drink on a set schedule rather than waiting to feel thirsty. Keep fluids and gels somewhere they will not freeze solid, inside a jacket layer or an insulated bottle, since frozen fuel does you no good on course.
⏵ Build your fueling plan
Get a carb, sodium, fluid, and caffeine plan per hour built for your weight and your goal time with the free ultra fueling calculator, then adjust for keeping everything from freezing on a winter course. Browse the rest of the free running tools at the tools hub.
⏵ Train for it with Summit Line
Get a race-day plan built around YOUR fitness and a winter 100 mile course. Summit Line reads your real training, builds a plan for cold-weather endurance, and rehearses your fueling so race day is something you execute, not guess at.
It is a winter, human-powered 100 mile race across frozen swamps, lakes, and rivers on marked snowmachine and dogsled trails in Alaska's Mat-Su Valley, run in February. The difficulty is not just distance, it is cold. Alaska Winter Wilderness Races builds the event around self-sufficiency in true winter conditions, and events in this category have historically required mandatory cold-weather survival gear. If you have not raced or trained overnight in sub-freezing conditions before, this is not the race to learn on.
Winter expedition races like the Susitna 100 have historically required runners to carry mandatory cold-weather and survival gear, since much of the course crosses remote, frozen terrain with limited support. The official race site is the authoritative source for the current year's specific gear list, so confirm it directly with Alaska Winter Wilderness Races before you build your kit rather than assuming a previous year's requirements still apply.
Cold weather changes fueling in two ways: your body burns more energy just staying warm, and cold temperatures can blunt your thirst signal even as you dehydrate through breathing and sweat under layers. Aim for roughly 60 to 90 grams of carbohydrate per hour, and keep fluids warm when you can, since cold drinks are harder to get down consistently over many hours. Build your baseline numbers with the free ultra fueling calculator, then plan for how you will keep food and fluids from freezing on course.
The race does not publish cutoff times on its public homepage. Given the winter, self-supported nature of the event and the real risk of frozen or difficult trail conditions, confirm the current year's cutoffs and safety requirements directly with Alaska Winter Wilderness Races at info@susitna100.com before you commit to a start.
All three. The Susitna 100 is a human-powered event with separate run, bike, and ski divisions covering the same marked winter trail through the Mat-Su Valley. The shorter Little Su 50K runs the day after the 100 miler, on February 14, 2027 for the next edition, and gives runners a lower-commitment way to experience the same winter terrain.
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<a href="https://runsummitline.com/guides/susitna-100">The Susitna 100 course guide</a><iframe src="https://runsummitline.com/embed/race/susitna-100" style="width:100%;max-width:420px;height:180px;border:0;" loading="lazy" title="Susitna 100 course guide by Summit Line"></iframe>This guide is independent and for planning only. The course details, dates, and gear requirements come from public sources and can change year to year, so confirm the current specifics with Alaska Winter Wilderness Races before you register or run. The fueling and pacing advice is general and not medical advice.