Tackling 21.1 kilometres through the streets of Singapore is as much a test of environmental resilience as it is of cardiovascular fitness. With tropical humidity regularly hovering above 80% and pre-dawn temperatures rarely dipping below 26°C, managing sweat loss and electrolyte balance can make or break your finish-line goals.
Ahead of the BYD Singapore International Marathon (SGIM) presented by adidas, we sat down with Singapore national triathlete and 100PLUS ambassador Herlene Natasha Yu to unpack how an elite endurance specialist plans, practices, and executes her hydration blueprint. From pre-loading fluids 48 hours prior to taking advantage of on-course 100PLUS hydration stations every 3 kilometres, Herlene breaks down how every runner can stay strong, stave off cramping, and cross the line re-energised.
Pre-Run Preparation: Hydration Starts Days in Advance
For many first-timers, pre-race hydration often feels like an afterthought—a quick gulp from a water bottle in the holding pen at the start line. According to Herlene, that approach leaves you playing catch-up before the race has even begun.
When preparing for a demanding 21K effort, Herlene’s hydration window opens well before race morning:
"Hydration starts for me at least 2 days before the main race," Herlene explains. "Before heading out for my run, I make sure to top up on hydration, especially with 100PLUS electrolytes. It has a bit of carbs in the drink too, so that helps with carb loading."
Entering a half marathon in a well-hydrated state prevents premature cardiac drift (where your heart rate climbs higher at the same running pace due to reduced blood volume) and primes your glycogen stores with readily usable carbohydrates.
Photo: SportPlus.sg / Isis Ang
On-Course Execution: The 3km Checkpoint Strategy
Once out on the road, waiting until you feel parched is a recipe for mid-race bonking. Thirst is a lagging indicator of dehydration; by the time your brain signals thirst, your body may already be operating at a 1% to 2% fluid deficit, degrading endurance performance and thermoregulation.
Herlene’s approach during a 21K revolves around clockwork consistency and alternating fluid types:
"At every 3km point, I’ll alternate sipping on 100PLUS isotonic and water," she notes. "This helps me replenish fluids and electrolytes throughout the run, especially in Singapore’s hot and humid weather. I don’t wait until I feel thirsty before drinking. Staying ahead of my hydration is important to help maintain my performance."
Herlene points to the on-course amenities at the BYD Singapore International Marathon as a major logistical advantage for participants:
"I usually plan my hydration around every 3km, taking advantage of the water stations along the route. For the SGIM, runners can look forward to having 100PLUS available at the hydration stations, making it easier to stay hydrated and keep going throughout the race!"
Fuelling and Electrolytes: Why Water Alone Isn’t Enough
One of the most persistent myths in long-distance running is that drinking pure water is sufficient to get you through 21 kilometres in the tropics. While plain water replaces lost volume, sweat contains critical electrolytes—principally sodium, potassium, and magnesium. Flushing your system with plain water without replenishing salts can dilute blood sodium levels, leading to hyponatremia, muscle cramps, and extreme fatigue.
"What's one hydration myth I wish runners would stop believing? Drinking only water for hydration," Herlene highlights. "With the amount of sweat loss in Singapore’s hot and humid environment, electrolyte imbalance has to be taken into consideration as well."
To replenish what sweat strips away, Herlene turns to 100PLUS ACTIVE as an essential staple in her training arsenal:
"100PLUS ACTIVE is one of my go-to drinks during training because it’s non-carbonated and contains added vitamins, carbohydrates, and electrolytes to support my performance. It helps me replenish what I lose through sweat while providing carbohydrates to fuel my runs and keep me going, especially during longer sessions."
Formulated specifically for high-exertion training, 100PLUS ACTIVE is non-carbonated, smooth on the stomach during heavy breathing, and enriched with B vitamins (B3, B6, B12) alongside an optimal blend of electrolytes and carbohydrates to blunt fatigue.
For athletes juggling domestic preparation with overseas camps or destination races, portable hydration is equally critical. Herlene relies on the 100PLUS Effervescent Tablet:
"Additionally, the 100PLUS Effervescent Tablet is very convenient to have, especially with all my overseas races this year."
Offering on-the-go electrolyte replenishment in a compact tube, the effervescent tablets allow runners to drop essential hydration directly into their portable bottles anywhere in the world.
Photo: SportPlus.sg / Isis Ang
Surviving the Tropics: Lessons Learned the Hard Way
Training for multi-discipline endurance events under Singapore's midday sun has given Herlene firsthand insight into what happens when fluid loss goes unmanaged.
"Running in Singapore’s heat and humidity means I have to be much more intentional about hydration because of the amount of sweat and fluid that I lose throughout the run," she reflects. "I think many runners underestimate how much fluid they can lose through sweat, especially when running in Singapore’s humidity. You might not always realise how much you’re sweating, so don’t wait until you feel thirsty or exhausted before thinking about hydration. Plan ahead and stay consistent!"
Even national-level competitors have had to adapt through trial and error:
"When I first started, I didn’t pay as much attention to hydration and focused more on just getting through the training," Herlene admits. "Over the years, I’ve learnt that hydration is an optimal factor to pay attention to. Most of the time, I’m training under the hot sun and heat, and occasionally, due to dehydration, I experience a headache which affects my training. That’s why it’s important to stay on top of my hydration."
After tough training blocks, Herlene prioritises immediate post-workout recovery:
"The sessions that require the most hydration after are definitely those with a higher intensity as well as those with a longer duration."
Photo: SportPlus.sg / Isis Ang
Herlene’s Advice: Train Your Gut and Practise Before SGIM Race Day
Just as you wouldn't lace up an untested pair of racing flats on race morning, you should never debut a new hydration plan on the SGIM start line. Gut tolerance—how effectively your stomach empties fluids and absorbs carbohydrates while running at tempo—is a trainable system.
"It’s really important! Just like you practise your pacing and nutrition, you should practise your hydration during training too. This helps you figure out what works for your body, how much you need to drink, and how your stomach responds," Herlene advises. "Sometimes if I drink excessively, I start to get a stitch. Therefore experimenting with different amounts of fluid prior to race day will prevent any stomach issues on race day!"
Her parting advice for beginners tackling the 21K distance boils down to balance, discipline, and awareness:
"Don’t underestimate the importance of hydration! Don’t wait until you feel thirsty to start drinking. Make sure you’re getting a good balance of water and isotonic drinks, as isotonic drinks help replenish the electrolytes and carbohydrates you lose and use during exercise."
Herlene Yu’s Half Marathon Hydration Cheat Sheet
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48 Hours Out: Begin hydrating proactively. Top up with 100PLUS electrolytes and light carbohydrates to pre-load glycogen and fluids.
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Race Strategy: Plan fluid intake around every 3km checkpoint. Alternate between water and isotonic drink to balance sodium and fluid levels.
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Do Not Wait for Thirst: Sip small volumes consistently before dehydration triggers fatigue or a drop in pace.
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Choose the Right Formula: Utilise non-carbonated 100PLUS ACTIVE for easily digestible in-session fuelling with vitamins and electrolytes. Keep 100PLUS Effervescent Tablets handy when travelling or on long self-supported routes.
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Practise in Training: Test your exact hydration volumes and intervals on your weekend long runs to eliminate stitches or gastrointestinal distress on race day.