Ho Chi Minh City averages around 27–29 °C all year with high humidity, and northern summers are just as tough. Heat is the number one factor runners in Vietnam need to manage. Here's how.

Why heat slows you down

When it's hot and humid your body sends more blood to the skin to cool you down, and sweat evaporates poorly in humid air. Your heart rate rises at the same pace, so the same run feels much harder. Expect to run 20–60 seconds per kilometre slower on a hot, humid day. That isn't lost fitness; it's physiology.

Acclimatise

Your body adapts to heat in about 10–14 days of regular running. You'll sweat earlier and more, and your heart rate will settle. If you've just moved to Vietnam or come back from a cooler country, keep runs easy and short for the first two weeks.

Timing is everything

  • In the south, run before 6:30 am or after 6:30 pm
  • In Hanoi, winter (Nov–Mar) is great at any time; in summer go very early
  • Avoid hard efforts between 10 am and 4 pm in hot months

Hydration

  • Drink 400–600 ml of water in the 2 hours before a run
  • For runs over 60 minutes, carry water or plan a route past a shop and take electrolytes (sodium!), not just plain water
  • Weigh yourself before and after a long run: every kilo lost is roughly a litre of fluid to replace
  • Pale yellow urine = well hydrated

Dress for it

Light-coloured, loose, technical fabrics (not cotton), a cap or visor, sunglasses and sunscreen. Some runners pour water over their head and neck or carry a cold towel.

Know the warning signs of heat illness

Stop, find shade and cool down immediately if you notice:

  • Dizziness, confusion or stumbling
  • Nausea, headache or chills ("goosebumps in the heat")
  • You stop sweating or your skin feels hot and dry

Heat stroke is a medical emergency. Call 115 (ambulance in Vietnam), move the person to shade and cool them aggressively with water and ice while you wait.

Adjust your goals

Run by effort or heart rate, not pace. Save fast sessions for the cooler months or early mornings, and pick races in the October–March season if you're chasing a personal best.