You’re training for a marathon in southern Utah and it’s already 86°F before sunrise. Your heart rate spikes, you can’t cool down, and your stomach starts cramping 10 miles in. Running in extreme heat during peak marathon training feels impossible, but it doesn’t have to derail your race. These 7 strategies will help you survive long runs when it’s 90°F before dawn.
Quick Answer
The direct fix involves four shifts: adjust your pacing by effort (not pace), pre-cool before you start, hydrate with electrolytes instead of plain water, and wear cooling gear. If conditions are unsafe (heat index above 105°F or humidity above 80%), move the run to a treadmill with air conditioning. The goal is to keep your core temperature from skyrocketing and your heart rate under control.
- Pre-cool for 20–30 minutes before the run.
- Run by perceived effort, not your usual pace.
- Drink 500–700 ml of fluid per hour, half of it with electrolytes.
- Use a cooling towel, ice bandana, or light-colored moisture-wicking clothing.
Why This Happens
When the temperature is 88°F and humid, your body struggles to dump heat. Blood is shunted to the skin to cool you, reducing oxygen delivery to working muscles. Your heart compensates by beating faster – that’s why your heart rate drifts up even at an easy effort. Abdominal cramping often comes from dehydration combined with a lack of electrolytes (sodium and potassium). Early-morning runs also catch you after a night of fluid loss, so you start already slightly dehydrated.
The combination of heat, high humidity, and low overnight recovery creates a perfect storm for poor performance and gastrointestinal distress. Acclimatization takes 10–14 days of consistent hot-weather running, but you need active cooling and hydration strategies during that window.
Step-by-Step Method
Follow these steps in order on your next hot long run:
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Pre-cool your core – Take a cool shower (not cold) for 10 minutes, or apply ice packs to your neck, groin, and armpits. Drink 500 ml of cool electrolyte beverage 30 minutes before you head out. This lowers your starting core temperature.
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Check the weather – If the heat index (temp + humidity) is above 105°F, skip outdoor running. Use a treadmill with AC instead. For mild heat, proceed.
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Dress for the heat – Wear a white or light-colored singlet, shorts, hat, and sunglasses. Avoid cotton. Use a cooling neck gaiter (dip in water and freeze overnight) or a cooling towel.
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Adjust your pace – Forget your goal marathon pace. Run by effort: you should be able to speak in complete sentences. Monitor heart rate – expect it to be 10–15 bpm higher than normal. Slow down until it stabilizes. A good rule is to start 45–60 seconds per mile slower than your cool-weather easy pace.
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Hydrate on a schedule – Drink 150–200 ml of fluid every 20 minutes. Alternate between water and an electrolyte mix (sodium, potassium, magnesium). If you sweat heavily, consider a salt tab.
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Cool during the run – Pour water over your head and wrists at every aid station (or carry a handheld bottle). Swish cold water in your mouth without swallowing to trigger a cooling reflex. Re-wet your cooling towel as needed.
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Listen to stop cues – Stop immediately if you feel dizzy, confused, nauseous, or if your stomach cramps become sharp. Walk in the shade, cool down, and rehydrate. Pushing through can lead to heat exhaustion or heat stroke.
Common Mistakes
1. Drinking only plain water. Without electrolytes, you flush out sodium and risk hyponatremia (low blood sodium), which causes cramps, bloating, and confusion. Always include an electrolyte source on long runs above 75°F.
2. Running the same pace as usual. Your body works harder in heat. Insisting on your normal pace spikes your heart rate, increases fatigue, and raises injury risk. Let pace go – effort is the right metric.
3. Ignoring early warning signs. A slight headache, chills, or goosebumps in the heat are early signs of heat illness. Many runners push through, leading to collapse. If you feel any of these, stop and cool down immediately.
4. Wearing dark or tight clothing. Dark colors absorb heat. Tight clothing traps sweat and prevents evaporative cooling. Choose loose, light-colored, moisture-wicking gear.
5. Eating a heavy meal before the run. Large meals before hot runs divert blood to digestion and away from your muscles, causing cramps and sluggishness. Stick to a small snack (banana, toast) 60–90 minutes before.
Checklist / Decision Table
Heat-Long-Run Decision Table
| Strategy | When to Use | Key Tip |
|---|---|---|
| Pre-cooling | Before any run in temps above 80°F | Cool shower or ice packs for 20 min |
| Pacing by effort | Every hot run | Cap heart rate at 10–15 bpm above resting |
| Treadmill | Heat index >105°F or humidity >80% | Set incline 1–2% to simulate outdoor |
| Hydration schedule | All runs above 75°F | 500–700 ml/hour, half with electrolytes |
| Cooling gear | Runs above 85°F | Freeze a neck gaiter or carry a cooling towel |
| Acclimatization | First 2 weeks of hot weather | Reduce long-run volume by 20–30% |
Pre-Run Checklist
- Check heat index and humidity forecast
- Pre-cool (shower or ice packs)
- Drink 500 ml electrolyte drink 30 min before
- Wear light-colored, moisture-wicking clothing
- Pack handheld bottle with electrolyte mix
- Bring cooling towel or frozen neck gaiter
- Adjust goal pace to “easy effort” (45–60 sec/mi slower)
- Apply sunscreen (SPF 30+)
When This Advice Does Not Apply
These strategies are for healthy runners in peak training who are not experiencing illness or injury. If you have a known cardiovascular condition, asthma, or are on medications that impair heat regulation (e.g., diuretics, beta-blockers), consult your doctor before attempting hot runs. Also, if the temperature is above 100°F or humidity above 85% (dewpoint > 70°F), postpone outdoor running entirely. For races – do not try new strategies on race day. The advice here is for training adaptation, not for PR attempts in the heat.
Realistic Example
A runner in St. George, Utah, is preparing for the St. George Marathon. Week 12 calls for an 18-mile long run, but the forecast shows 88°F at 5:30 AM with 60% humidity. They wake up at 4:15 AM, take a 10-minute cool shower, drink 500 ml of an electrolyte mix, and wear a white singlet, shorts, hat, and a frozen neck gaiter. They start at 9:30 min/mile instead of their usual 8:30 pace. Every 20 minutes they drink 200 ml alternating water and electrolyte drink. At mile 8 they pour water over their head. At mile 14 they feel a mild headache and slight cramping; they slow to a walk, rehydrate, and decide to finish 16 miles instead of 18. They later adjust their training plan to move the next 20-miler to a treadmill with AC during a forecasted heat wave. The runner completes the marathon successfully 3 weeks later in cooler conditions.
Final Takeaway
When training for a marathon in extreme heat, your priority is managing core temperature and effort – not hitting a specific pace. Pre-cool before you start, hydrate with electrolytes, wear cooling gear, and be willing to cut the run short or move it indoors if conditions become unsafe. Your body will adapt over 10–14 days, but only if you respect the heat and back off when warning signs appear.
FAQs
Should I run outside in 90 degree heat before sunrise?
It depends on humidity. If the heat index (combined temp and humidity) is below 105°F, you can run outside using the strategies in this guide. However, if humidity is above 80% or the dewpoint is above 70°F, the air is too saturated for sweat to evaporate effectively, making heat stroke more likely. In those cases, run on a treadmill with air conditioning or postpone until a cooler day.
How do I prevent abdominal cramping on hot long runs?
Abdominal cramps during hot runs often stem from dehydration and electrolyte imbalance. To prevent them, start your run well-hydrated (urine should be pale yellow). Drink 500–700 ml of fluid per hour, with half of it containing electrolytes (sodium, potassium). Also avoid eating a large meal within 2 hours of the run. If cramps start, slow to a walk, drink electrolyte solution, and apply gentle pressure to the area.
What should I drink during a long run in extreme heat?
Alternate between plain water and a sports drink or electrolyte mix. For runs over 90 minutes in heat, plain water alone can dilute your blood sodium, causing hyponatremia. Aim for 250–350 mg of sodium per 500 ml of fluid. You can also use salt tablets or chews every 30 minutes. Avoid caffeinated or sugary drinks, which can dehydrate you further.
Can I use a treadmill for marathon training in heat?
Yes, absolutely. A treadmill with air conditioning is a safe alternative when outdoor heat index exceeds 105°F or humidity is dangerous. Set the incline to 1–2% to better simulate outdoor effort. You can adjust the pace to match the effort you’d run outside on a cool day. Treadmills also allow you to control temperature, so you can still hit your mileage without heat risk.
How much slower should I run when it’s 90°F?
Start with a pace that is 45–60 seconds per mile slower than your easy pace on a 60°F day. Monitor your heart rate – if it drifts more than 10–15 bpm above normal within the first 2 miles, slow down further. The exact slowdown depends on humidity, direct sun, and your personal acclimatization. The key is to run by effort (RPE of 5–6 out of 10), not by your watch.
How long does it take to acclimate to running in heat?
Most runners experience significant heat acclimatization after 10–14 days of consistent hot-weather training. During this period, your blood plasma volume increases, you start sweating earlier, your sweat becomes less salty, and your heart rate stabilizes. However, full adaptation can take up to 3 weeks. During the acclimatization window, reduce your long-run volume by 20–30% and avoid overdressing.