There’s a persistent narrative in parts of the endurance community that CTS coaches prescribe “high volume” training. It’s an easy label to apply when an athlete’s weekly mileage exceeds what many runners – recreational and professional alike – are accustomed to seeing. But the label oversimplifies a more nuanced reality. We don’t chase high volume, we optimize volume.
Optimized volume means identifying the highest workload an athlete can absorb productively, given their training history, recovery capacity, injury profile and life demands. For some athletes, that number is modest. For others, it may appear high relative to their peers. The objective is not mileage for mileage’s sake, it’s adaptation without compromise. That principle becomes especially important when an elite athlete transitions disciplines.
When Molly Seidel stepped onto the starting line at Black Canyon, many assumed her preparation required wholesale reinvention: more vertical gain, more mileage, more long trail days – more everything. Ultrarunning culture often equates new race demands with dramatic expansion, and there is some truth in that. A 100k is not simply a longer marathon. And as her coach, we did, in fact, play with all of those variables. However, we changed far less than most would expect.
I think of the approach we used as a Minimum Effective Change model: introduce only the variables required to meet the demands of the race and nothing more. The guiding question was simple: what is the smallest set of changes required to translate existing fitness to a new demand? It shaped every decision we made.
Understanding Load Beyond Mileage
In endurance sports, we often reduce training stress to mileage and intensity, but load is multi-dimensional.
Novel terrain increases neuromuscular demand. Longer continuous runs increase glycogen depletion and mechanical strain. Carrying fluids alters biomechanics. Back-to-back workload compounds tissue stress. Higher fueling volumes create gastrointestinal strain that must be trained like any other system.
When transitioning to a new event, the temptation is to layer these variables simultaneously: more vert, longer runs, more moderate intensity, stacked weekends and fueling experiments. It becomes a stacking problem – too many new stressors introduced at once.
The Minimum Effective Change model resists that impulse. Instead, it asks a simpler question: what already works at a world-class level, and what is truly missing?
What We Did & Didn’t Change
From the outside, preparing an Olympic marathoner for a trail 100k might appear to require a dramatic increase in mileage. We did not significantly increase her weekly volume. Her total load remained largely within the bandwidth she had successfully tolerated during marathon training, and that decision was deliberate.
Volume tolerance had already been built over years of elite preparation, and she was operating close to her sustainable ceiling. Adding more total hours may have increased risk without proportionate return. Her limiter for a 100k trail race was not overall volume, it was how that volume was distributed and applied, but what did change was the architecture.
In her marathon build, long runs were typically singular efforts. For Black Canyon, we increased density. Back-to-back long runs became intentional tools, and fatigue accumulation across consecutive days was introduced carefully. Recovery runs were slightly shorter and more strategically placed, allowing us to increase long run duration and stack workload without expanding total weekly volume. This shift changed the stimulus profoundly.
When density is increased, so is stress per mile. Tissue loading accumulates, neuromuscular fatigue lingers, energy demand compounds across days and specificity itself becomes load.
A traditional 20-mile road long run stresses the body differently than a 15-mile trail effort followed by a 10-mile trail run the next day, while rehearsing 60 – 90 grams of carbohydrate per hour. The mileage looks similar, but the stress profile is not.
Instead of adding mileage, we redistributed stress, which allowed us to build durability without exceeding the total adaptive capacity she had historically tolerated.
Preserving the Engine
Molly entered this build coming off a deliberate reset. After years of competing at the highest level of global road racing – and navigating the injuries that often accompany it – she stepped back to recover and recalibrate. There was rebuilding that needed to be done, but her training history returned quickly.
When we prepared her for the New York City Marathon, she was tracking in approximately 2:29 shape. That level of aerobic capacity does not disappear. It leaves a durable physiological imprint – high mitochondrial density, efficient substrate utilization and ingrained running economy. Even after a break, those qualities resurface faster than they are built.
Molly arrived in ultrarunning with elite-level marathon fitness and an Olympic medal on her résumé. Her aerobic capacity, lactate threshold speed and efficiency were not developmental projects, they were established strengths. Our job was not to reinvent her engine; it was to preserve it – and then extend it.
Rather than immediately pivoting to ultra-specific fatigue blocks, we began by reinforcing structured threshold work. Threshold remains one of the strongest determinants of long-duration performance. The ability to sustain a high percentage of VO2max efficiently underpins success whether the race lasts 2 hours or eight.
As we transitioned toward race-specific preparation, intensity distribution shifted and high-intensity sessions became sparse. The majority of her work occurred in Zone 2, with controlled exposure to Zone 3. The objective was not to increase peak speed. It was to increase the durability of that speed.
Her limitation was not how fast she could run, it was how long she could carry that pace across uneven terrain without mechanical or metabolic breakdown.
There was also a broader lens guiding these decisions. Molly has paid the physical cost of chasing global podiums. Stress fractures and setbacks shape how you approach the next chapter of a career, and her move toward ultrarunning includes sustainability and enjoyment as much as competition.
We weren’t preparing for a single race in isolation. We were protecting the arc of her next several years. Preserving the engine meant respecting what was already built – and resisting the urge to tinker with it unnecessarily.
Fueling as the Largest Untapped Variable
If training architecture was the structural adjustment, fueling was the largest performance opportunity.
In marathon racing, fueling is simplified. Aid stations are frequent, carbohydrate intake is moderate and fluid is handed to you on the run. In a 100k, the athlete must carry fluids, self-regulate intake, manage electrolytes and consume carbohydrates at levels that can exceed 80–100 grams per hour. This was entirely new for Molly.
Long runs became fueling rehearsals and carbohydrate targets were practiced repeatedly until gastrointestinal tolerance improved. In training, she worked up to approximately 80 grams of carbohydrate per hour – not because that was the race target, but to expand her tolerance ceiling. On race day, she averaged closer to 60 grams per hour, which was a more sustainable intake that she could execute consistently under competition stress.
Hydration plans were stress-tested and crew exchanges were simplified. Even the cognitive load of eating and drinking while descending technical terrain required repetition.
To accelerate this learning curve, we brought in Stephanie Howe, PhD. Philosophically aligned, she translated fueling science into simple, actionable behaviors. Simplicity improved compliance and compliance improved consistency. Consistency improved performance.
In ultrarunning, performance rarely collapses because of inadequate aerobic capacity. More often, it unravels because fueling or hydration fails under cumulative stress.
By prioritizing metabolic durability rather than chasing additional volume, we targeted the variable most likely to determine race outcome.
Race Day Translation
On race day at Black Canyon, nothing about Molly’s physiology had been reinvented. There was no hidden mileage spike and no radical overhaul of her aerobic system. What changed was her ability to manage the variables that determine whether elite fitness survives an ultramarathon.
The early miles unfolded slightly faster than planned. The pace felt controlled to her, but she found herself at the front earlier than intended. Marathon-level speed is a powerful asset and even when it feels comfortable, it can quietly raise the physiological cost in a longer event.
By mile 32, the consequences surfaced. She had fallen slightly behind on fluids and found herself in a hole – not catastrophic, but unmistakable. The kind of moment that, if mishandled, could compound over hours.
At the aid station, we reset with extra fluids, no urgency and no theatrics, restoring her stability before returning to a rhythm.
Back on the trail, she adapted. Fluid intake increased slightly per hour and her carbohydrates remained steady. Her effort stayed controlled and the previous training rehearsals were no longer theoretical – they were applied problem-solving under fatigue.
By mile 50, cumulative stress was evident, but she was running strong. I handed her an extra bottle and insisted she take it. The look she gave me suggested she disagreed with the decision because in the moment, it felt unnecessary to her. Later, she admitted it was pivotal.
The additional fluid stabilized output and allowed her to maintain pace rather than defend against decline. In ultrarunning, performance is often less about pushing harder and more about protecting the systems that allow you to keep pushing.
From that point forward, there was no unraveling. The rhythm returned and held. The engine she built on the track and roads continued to operate, now supported by durability and fueling discipline. She ran strong all the way to the finish and secured a Golden Ticket to Western States in June.