When Fierce Leaves You Flat - Hot Weather Triathlon Racing Adjustments

When the mecury is rising, or most probably risen, how do you cope with the challenge of racing in hot conditions? In today's blog we deal with ways to deal with warm weather racing to ensure you don't wilt by the roadside.

Even the pros midjudge pacing, witness Taylor Knibb and Lucy Charles-Barclay falling by the wayside in 2025's Kona battle. No matter how much training you've done you have to understand the effects of overpacing, under / over hydrating or messing up your electroytes or cooling strategies.

Thermo regulation is key, and as someone whose thermoregulation is more messed up than most thanks to the mother of all car accidents in my 30s I understand this all too well

When dehydrated:

1. Reduced blood plasma volume

• There is less blood available for cooling.

2. Higher heart rate (cardiovascular drift)

• Your HR rises even if pace stays constant, some is expected but if your HR:Pace ratio goes above 7% you're in for a tough day

3. Reduced sweat rate

• Body cooling becomes less effective, especially in weather hotter than your core temperature

4. Increased core temperature

• Leads to overheating and slower pace, and in extreme cases you'll be on the IV drip at the end of your race.

5. Reduced muscle blood flow

• Less oxygen delivery → earlier fatigue and less perception of the situation you are in

Why Athletes Push Through

Triathlon is full of type A athletes, those used to pushing their bodies, in their particular training environment in preparation for their races. Understanding the impacts of dehydration and warm weather then failing to prepare at basic level for warm weather racing through acclimation or mitigation because "I'll be all right on the day" is poor judgement. Then there are those who just don't realise how warm weather can creep up. or how much they need to drink in competition. Combine that with a dropped bottle at the start of the bike, or an aid station out of fluids and you have a race-ending perfect storm. When was your last sweat test?

At it's simplist. Know your body weight. Naked. Before your work out. Go hard at your race effort for 60 minutes. Do this for bike and run, as weather, humidity and wind speed effects sweat loss. Weight yourself when you get back in. Take water only on the effort whenever you feel thirsty. If running maybe run around the house with access to your water bottle. The difference in your weight between pre and post effort - the water's weight is your is your sweat rate per hour. To find if your sweat is heavy in sodium there are professional tests you can use and mail back for results, or easy signs like white streaks on kit, muscle cramping, stinging eyes when sweat drops in. We'll deal with the sodium aspects in a future blog Once you know this figure then you can estimate how much body weight mass you lose from sweat loss. For endurance events, sports science generally recommends keeping dehydration below ~2–3% body weight. Then it's a matter of hydrating accordingly

Example:

• 75 kg athlete

• 2% loss = 1.5 kg (~1.5 L fluid)

Female Triathlete Face Sweating

Know Your Limits

Body Weight Loss

Effects

1%	Slight increase in heart rate, minor thermoregulation changes

2%	Noticeable endurance performance decline (~5–10%)

3%	Significant cardiovascular strain, rising core temperature

4–5%	Major performance drop, risk of heat illness

6–8%	Severe fatigue, dizziness, possible heat stroke

>10%	Medical emergency

Sweat Rates In Hot Races

Endurance athletes commonly sweat:

• 0.7–1.0 L/hour in moderate weather

• 1.0–2.0+ L/hour in hot/humid conditions

Elite triathletes in Kona often exceed 2.0 L/hr

 Ideas For Hot Weather Triathlon Racing Adjustments

Ideally acclimation, training deliberately and mindfully in excess clothing. Getting your body core temperature up (take medical advice if you're not sure) using a sauna. Workouts in the middle of the day. Many multisporters swear by turbo sessions in a hot steamy shower room.

Arriving early if you can at race destination or a hot weather training camp 2-3 weeks out from your main warm weather race. Heat acclimation for 10–14 days before race improves:

• sweat rate

• plasma volume

• cooling efficiency

During the race take advantage of ideas like:

• Ice under cap

• Cold sponges

• Pouring water over head and neck

• Ice in tri suit

• Never missing opportunity to hydrate and or picking up any bottles you drop
  

What this means for 70.3 and IM racing

Hydration needs vary by athlete, sweat rate, and temperature, but general guidelines:

Pre-race

• 2–4 hours before start:~5–7 ml of fluid per kg body weight(Example: 70 kg athlete → 350–500 ml)

• Include electrolytes (especially sodium) if the race will be hot.

• Urine should be pale yellow, not clear or dark.

During the race

Typical ranges used in Ironman/70.3 racing:

Bike (main hydration phase):

• 500–900 ml per hour fluid

• 400–1000 mg sodium per hour

• Adjust depending on sweat rate and temperature.

Run:

• 400–800 ml per hour

• Small frequent drinks at aid stations.

Key Takeaways:

👉 Match as much of your sweat loss as practical, but do not try to replace 100% (usually 60–80% replacement is ideal)

👉 Reduce target power/pace by 5–15% depending on conditions, especially on the bike where it's super easy to over do it