Western States® 100-Mile Endurance Run

Erin approached the Western States 100 with a structured fueling plan to support her body’s energy demands. Over the near ~19-hour race, she averaged just over 80g/h of carbs, hitting the widely accepted benchmark for ultra-endurance performance, and bang on her pre-planned intake. Her strategy centered around gels, taken ~every 30 minutes, alongside some energy drink mixes. Across the full distance, she consumed over 1.5 kilograms of carbohydrate, showing both commitment and discipline in executing her plan, despite some GI issues.

The first half of the race unfolded mostly according to plan. Erin reported feeling strong and moving well through the high country and canyons, likely supported by her consistent energy supply. However, post-Michigan Bluff (roughly the 90km mark), things went downhill. GI issues became apparent, with vomiting episodes every 5-10 miles from this point to the finish. Despite her best efforts to continue eating and drinking, much of what she consumed was likely not being absorbed effectively before it was lost through sickness, leading to a clear energy dip late in the race. This far into the race, Erin’s stores of glycogen (carbohydrate) in the muscles would have been low, even with a suitable carb-load the day before, and so without being able to effectively absorb the ingested carbohydrate (gels or drink mixes), Erin’s energy availability would’ve ultimately been insufficient to support her performance.

The sudden loss of fuel efficiency in the final third of the race could be attributed to several factors. While 80g/h is considered optimal under most conditions, heat stress can reduce gastric emptying and increase gut permeability, making it harder to absorb large amounts of carbohydrate. Studies have shown that gastrointestinal tolerance can diminish significantly in hot weather, particularly when high sodium and carbohydrate loads are consumed simultaneously (i.e., not ‘decoupled’). Despite gut training ahead of the race, it’s likely that some additional practice of this strategy during similar environmental and intensity conditions will be helpful in future to prevent such debilitating sickness. Additionally, if experienced again, easing off her carb intake and drinking some fluids with electrolytes could help Erin get back on track. Despite the challenges, Erin managed to push through with remarkable grit, continuing to fuel even as her body intermittently rejected it and got herself to the famous Placer High School Track finish line.

When it comes to hydration, Erin sits in a unique category of athletes, those with exceptionally high sweat sodium losses (>1500mg/L). In a race like Western States, with a wide range of conditions and temperatures peaking above 30°C (86°F), managing fluid and sodium intake becomes imperative to maintaining performance. Erin’s strategy incorporated a variety of electrolyte products through drinks to match her losses.

Over the full race, she consumed ~14.6 litres of fluid and over 14,000mg of sodium. This resulted in an average sodium concentration of about 970mg/L, a lot lower than her known sweat sodium losses. Despite this, she reported no cramping across the race and subjectively stayed on top of hydration. However, looking at the early stages more closely, it appears she may have spaced her intake out inconsistently. Between the start and Dusty Corners (roughly the first 6.5 hours), her sodium concentration ranged from 1300 to 1760mg/L (closer to her known losses). From Robinson Flat (~48km) onwards, the relative sodium concentration of Erin’s bottles until the finish remained under 1000mg/L. It’s likely that alongside a high sweat rate due to the heat and her high exercise intensity, Erin would have accumulated a significant deficit during the race.

Though she reported peeing a couple of times across the ~18 hour racing duration, it’s likely she experienced some dehydration late on from the reduction in sodium and expected difference between intake of fluid and actual sweat loss, but the fact that she avoided cramping and felt her fluid intake was generally “about right” shows her strategy was fundamentally appropriate. Erin’s race illustrates how important it is to plan and focus on both timing and total sodium intake so that losses are managed and as a result of better absorption, gut comfort is maintained.

Caffeine has been shown to reduce perceived exertion, enhance mental focus, and improve performance in prolonged efforts. Erin kept her caffeine intake conservative and controlled at ~4mg/kg total; well within the optimal performance range. She started her race day with a cup of black coffee, and then layered in three caffeinated gels spaced strategically throughout the race: one between Robinson Flat to Dusty Corners (50-61km), another between Dusty Corners and Michigan Bluff (61-90km), and the final one around Foresthill (~100km).

This approach worked well at the start, providing some stimulation without excessive spikes in circulating caffeine levels. Erin didn’t experience any jitteriness or caffeine-related crashes, and her use was timed to support alertness through the key middle miles of the race. Interestingly, she didn’t load up on caffeine late in the event, despite struggling with energy levels in the closing hours. Given her prevalent stomach issues and sickness this was likely a sensible strategy. For future races, small amounts of caffeine in the final 4-5 hours (assuming well-tolerated) might provide an additional boost to counteract the deep fatigue of the final miles.