Training in Heat, Cold and at Altitude
Introduction
The same training doesn't produce the same result at 12 degrees as at 32, nor at sea level as at 2,500 metres. And yet most people head out with the plan as written and try to hit the same numbers regardless of how they feel.
Adjusting for conditions isn't lowering the standard: it's understanding what your body is measuring that day.
In heat, your usual pace is no longer your usual effort. Choosing which of the two you respect is the whole decision.
Heat
It's the condition that most affects endurance performance, by a wide margin.
What happens. Your body competes with itself: it needs to send blood to the muscle to work and to the skin to cool. The result is a higher heart rate at the same pace, greater perceived effort, and performance that falls markedly in long events.
What to do:
- Go by effort, not pace. This is the central rule. In heat, holding your usual pace means training far harder than planned.
- Drink to thirst and consider salt if you sweat heavily or the session is long.
- Choose your hour. Early or at dusk changes more than any other measure.
- Light, loose clothing, and wetting your head and neck genuinely helps.
Acclimatization is real and fast. Seven to fourteen days of progressive exposure produce concrete adaptations: plasma volume expansion, earlier and more dilute sweating, lower heart rate at the same effort. If you have an event in heat, those two weeks are worth more than any supplement.
Warning signs. This doesn't allow pushing through: dizziness, nausea, severe headache, confusion, dry skin when you should be sweating, or sweating stopping. These are signs of heatstroke, a medical emergency. Stop, get in the shade, cool the body and call for help.
Cold
Less limiting for endurance and with its own particularities.
What happens. Cold muscle produces less force and power, coordination drops, and the warm-up takes longer to take effect. On the other hand, for long efforts, moderate cold usually improves performance relative to heat.
What to do:
- Warm up more and for longer. That's the main difference, especially before intense or strength work.
- Layers. Start with one extra and remove it; starting frozen is what costs most.
- Protect extremities. Hands, ears and feet lose heat fast.
- Keep drinking. In cold you feel thirst less and still lose fluid.
One specific case: in people with asthma, cold dry air can trigger bronchoconstriction. Covering mouth and nose with a buff helps considerably, and anyone with a diagnosis should follow their treatment plan.
Altitude
What happens. Lower oxygen pressure means less oxygen available per breath. Above roughly 1,500 metres endurance performance starts to fall measurably, and the drop grows with altitude.
The first thing to accept: your usual paces won't be sustainable, and that isn't a lack of fitness.
What to do:
- Lower the intensity for the first days, especially hard work.
- Go by effort, again, not pace or power.
- Hydrate more. Dry air and faster breathing increase losses.
- Acclimatization takes weeks, not days, and it's partial: you'll never perform at altitude as you do at sea level.
Acute mountain sickness. Headache, nausea, insomnia and loss of appetite in the first 24-48 hours above 2,500 metres. It's managed by not ascending further until it eases. If breathlessness at rest, persistent cough, confusion or loss of coordination appear, descend immediately and seek care: those are signs of the severe forms.
On "live high, train low": it's a real strategy for elite athletes, requires weeks of controlled exposure, and doesn't apply to someone spending a week's holiday in the mountains.
The rule common to all three
It's the same in all three cases and it resolves nearly everything: when conditions change, respect the effort and let go of the pace.
Your plan says "30 minutes at threshold pace". In heat, at altitude or in severe cold, that's 30 minutes at threshold effort, which that day will correspond to a slower pace. Insisting on the number on paper turns a moderate session into a maximal one without your deciding it.
Common mistakes
Chasing pace in heat. The most common error and the most dangerous.
Reading the performance drop as lost fitness. It's the condition, not you.
Comparing yourself with your own records from another season. Summer and winter times aren't comparable.
Acclimatizing all at once. Neither to heat nor altitude: exposure goes up in steps.
Ignoring warning signs to finish the session. No workout is worth heatstroke or altitude oedema.
Conclusion
Heat is the condition that limits most, cold demands a longer warm-up, and altitude forces you to accept lower paces for weeks. In all three, adaptation exists and takes time.
Apply the rule in your next session in adverse conditions: leave the pace screen off and go by how much you can talk. You'll do exactly the training that was planned, even if the numbers look nothing like last week's.
References
- Racinais, S., et al. (2015). Consensus recommendations on training and competing in the heat. Sports Medicine, 45(7).
- Périard, J. D., Racinais, S., & Sawka, M. N. (2015). Adaptations and mechanisms of human heat acclimation. Scandinavian Journal of Medicine & Science in Sports, 25(S1).
- Bärtsch, P., & Saltin, B. (2008). General introduction to altitude adaptation and mountain sickness. Scandinavian Journal of Medicine & Science in Sports, 18(S1).
- Luks, A. M., et al. (2019). Wilderness Medical Society clinical practice guidelines for the prevention and treatment of acute altitude illness. Wilderness & Environmental Medicine, 30(4).
- Castellani, J. W., & Tipton, M. J. (2015). Cold stress effects on exposure tolerance and exercise performance. Comprehensive Physiology, 6(1).