⏵ Course guide · North Texas lakeside singletrack
The Isle du Bois Trail Run runs well-groomed singletrack along Ray Roberts Lake, a North Texas tradition with a 4M, 10M, 20M, and 50K all built from the same repeating loop. I will walk you through the loop structure and cutoffs first, then give you a pacing and fueling plan built for this approachable, technical North Texas course, plus free tools to dial in your own numbers.
These facts come from the official Blaze Trails Running race page. Check the current year details, cutoffs, and aid stations before you commit. Race logistics change year to year.
The core loop runs roughly 11 miles: the 10M covers it once, the 20M twice, and the 50K three times. The 4M runs a separate, shorter loop of its own. All distances start and finish at the same aid station on the east side of Lake Ray Roberts.
Official race copy describes the trail as a mix of well-groomed singletrack with some technical sections of roots and rocks. Less than 1,000 feet of gain per loop keeps the elevation modest, but the technical stretches deserve real attention, especially on your second or third pass for the 50K.
If significant rain hits before race day, the course moves to the Greenbelt trail within the same state park, and the race communicates the change through email and social media. Check your inbox and the race's channels in the days before if the forecast looks wet.
Aid stations sit between 1.5 and 4 miles apart, water and endurance drink at every stop plus standard ultra fare like bananas, oranges, PB&Js, chips, Oreos, fig cookies, soda, and Salt Stick. Drop bags for the 50K and 20M can be left at the Start/Finish aid station only.
With all runners required to start their final loop by 1:45 PM and a hard 5:00 PM course cutoff, your pacing plan needs to hit that mid-race gate, not just arrive at the finish on time.
On the 3-loop 50K, calculate what pace gets you back to the start/finish by 1:45 PM to begin your final loop. A race-time calculator projection helps you set an average pace target, but check it specifically against that mid-race deadline rather than only the 5:00 PM overall cutoff.
A grade-adjusted pace target for the rooty, rocky stretches gives you an honest number for what you can sustain on your third pass, when fatigue makes technical footing more dangerous, not less. Runners who push the easy, well-groomed sections early tend to pay for it with slower, more careful footing on later loops.
⏵ Free tools to pace this course
Early December in North Texas usually runs cool, but a 7:30 AM start still means several hours of daylight running for 50K and 20M finishers.
Aim for roughly 60 to 90 grams of carbohydrate per hour on the 50K and 20M. With aid stations spaced 1.5 to 4 miles apart carrying bananas, oranges, PB&Js, chips, Oreos, fig cookies, and soda, you have frequent, predictable access, so plan to top off regularly rather than carrying a full race's worth of calories.
Sodium in the 300 to 500 mg per liter range covers most runners in typical early-December North Texas weather. Salt Stick is available at aid stations as a backup if you need more than your own plan provides.
⏵ Build your fueling plan
Get a carb, sodium, fluid, and caffeine plan per hour built for your weight, your goal time, and a cool December North Texas day with the free ultra fueling calculator. 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, this exact repeated-loop course profile, and your projected splits. Summit Line reads your real training, builds a plan for technical North Texas singletrack, and rehearses your fueling so race day is something you execute, not guess at.
The official race page describes the trails as a mix of well-groomed singletrack with some technical sections of roots and rocks, and less than 1,000 feet of gain per full loop. This is an approachable North Texas course by elevation, and the main challenge on the 50K comes from covering three loops with real technical footing sections rather than sustained climbing.
Blaze Trails states less than 1,000 feet of gain for each full loop, but does not publish a total figure per distance. The 50K covers three of the roughly 11-mile loops, the 20M covers two, the 10M one, and the 4M runs the shorter loop once, so use the per-loop figure as your planning building block rather than an invented total.
This is a cupless race, so bring your own hydration device (you can also buy a $5 reusable collapsible cup at packet pickup). Aid stations carry water and endurance drink along with bananas, oranges, peanut butter and jelly sandwiches, potato chips, Oreos, fig cookies, soda, and Salt Stick. Aim for roughly 60 to 90 grams of carbohydrate per hour on the 50K and 20M, and sodium in the 300 to 700 mg per liter range. Build your own numbers with the free ultra fueling calculator before race day.
All runners must be on their final loop by 1:45 PM, and the hard course cutoff is 5:00 PM, when all runners must be off course. On the 3-loop 50K, that gives you until 1:45 PM to start your last lap, so pace your first two loops with that deadline in mind rather than the 5:00 PM finish alone.
No. Pacers are not allowed for any event at this race. Any participant found running with someone who has not registered and paid for the event will be disqualified, so plan to run the full distance solo.
The repeated ~11 mile loop structure (three laps for the 50K) means frequent access to the start/finish aid station, which is friendlier for a first ultra than a remote point-to-point course. With less than 1,000 feet of gain per loop and well-groomed singletrack, this is one of the more approachable Texas 50Ks, as long as you respect the 1:45 PM final-loop deadline.
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<a href="https://runsummitline.com/guides/isle-du-bois-trail-run">The Isle du Bois Trail Run course guide</a><iframe src="https://runsummitline.com/embed/race/isle-du-bois-trail-run" style="width:100%;max-width:420px;height:180px;border:0;" loading="lazy" title="Isle du Bois Trail Run course guide by Summit Line"></iframe>This guide is independent and for planning only. The course details, dates, cutoffs, and aid stations come from public sources and can change year to year, so confirm the current specifics with the official race before you register or run. The fueling and pacing advice is general and not medical advice.
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