ULTRA SCIENCE
Race-fueling and GI rehearsal
Test whether your intended food, drinks and schedule work while running.
What it assesses
This field rehearsal assesses execution and symptoms rather than directly measuring carbohydrate absorption. A small randomized running study supports repeated carbohydrate practice; transfer to an entire ultra remains uncertain.
Choose one question before the session: can I take this product at the intended frequency, can I tolerate this drink concentration, or can I collect and carry the plan between aid stations? A rehearsal with several new products cannot identify which change caused a problem. A feeding test also differs from a laboratory measurement of absorption; comfortable intake is the practical outcome you can observe yourself.
A practical rehearsal
Author routine: start with an intake already tolerated. Use planned products, concentration, containers and a familiar route. Record what you actually consume, timing, effort, weather and symptoms with your own consistent scale. Change one variable next time. Rehearse opening, carrying and resupply as well as eating.
Prepare a short written schedule and count carbohydrate from every planned source, including drink. Mark planned and actual intake separately. Start the session fed as you normally would, rather than creating an artificial challenge. At each planned eating opportunity, note whether you consumed it, missed it, or reduced it, and why. Afterwards, record any later symptoms and whether packaging, taste fatigue or access caused problems.
Validity, repeatability and error
Symptom logs have no universal measurement error or pass mark. Heat, intensity, duration and pre-run food can change tolerance. A successful rehearsal does not prove normal absorption or eliminate late-race GI risk.
Describe symptoms instead of relying only on a total score: nausea, fullness, urgency and abdominal discomfort may require different practical changes. A missed feeding because a packet was inaccessible is an execution problem, not proof of intolerance. Compare sessions of similar difficulty before blaming a product. Record caffeine and unfamiliar food as separate variables so that the apparent effect of carbohydrate is not confused with another change.
What to change and what not to infer
Keep the version you can repeatedly execute comfortably; simplify a failed plan before increasing intake. Do not copy the research feeding dose as a starting prescription. Persistent or severe abdominal symptoms, blood or repeated vomiting need professional assessment rather than harder gut training.
Write the next decision explicitly: keep the product but change carrying position; keep the amount but divide the opportunities differently; or return to the last comfortable plan. A sensible success criterion is repeated comfortable execution under relevant conditions, not the largest intake achieved once. Never use a successful trial to justify introducing several untested products or a much more aggressive plan on race day.
Who, cost and repeat timing
High value for every ultra distance, especially new products, heat and multi-day logistics. Usually unnecessary for a short easy session. Cost is normal training food and time. Repeat selected rehearsals within existing long runs, not by adding exhausting race simulations; no universal number guarantees readiness.
For multi-day events, record what remains palatable later and how you resume ordinary meals afterwards. For night racing, rehearse handling food and drink in low light without deliberately depriving yourself of sleep. If ordinary nutrition repeatedly causes symptoms, seek a sports dietitian or medical assessment; avoid progressively excluding entire food groups based on a single bad run. Rehearsal should fit the training plan rather than compete with recovery.
Use this with
Evidence and limits
Evidence: Moderate. Direct running evidence; indirect for full ultra-race execution. Small trial; does not validate every food, intake target or ultra duration.
Version and review
AI-assisted evidence appraisal is not credentialed clinical review. Publication authorization and application release dates are separate from scientific review.
Evidence markers identify statements and their limits; practical examples are not validated individual prescriptions.
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