August brings long days, holidays, new surroundings… and training conditions that are nothing like what you’re used to. Are you working out in the mountains? Under the blazing sun? After hours of travel or a late night? Then it’s time to ask an important question: Are your training zones still accurate? Let’s look at how heat, altitude, and accumulated fatigue can impact your training zones — and how to adapt without throwing away your progress.
🔥 Heat: A Heart Working to Cool You Down, Not Push Performance
What Actually Happens
In hot conditions, your body prioritizes thermoregulation. Heart rate rises not because you’re working harder, but because blood is diverted to the skin to release heat.
Result: Higher HR, less oxygen for working muscles. You feel more fatigued, and performance suffers.
Most affected zones: Heart rate-based zones, especially Zone 2 (which can easily feel like Zone 3 or 4).
Real-world effect: Misjudged effort → unintentional overload → risk of burnout.
Actionable Strategy
- Lower your training load on hot days — no guilt.
- Swap cardio-focused sessions (like long Zone 2 efforts) for technique or strength work when possible.
- Train early in the morning and stay on top of your hydration — before, during, and after sessions.
Heat and performance loss: how much do cyclists and triathletes lose?
🏔️ Altitude: Less Oxygen, More Lactate, Less Control
What Actually Happens
Above 1,500–2,000 meters, oxygen availability drops and your energy system balance changes.
Result:
- Lactate threshold occurs earlier
- Aerobic efficiency decreases
- Harder to maintain mid-to-high intensity zones for long durations
Most affected zones: Power- or pace-based zones (Zones 3–4–5): performance numbers simply drop at altitude.
Real-world effect: You feel flat, even when pushing — it’s not about fitness, it’s physiology.
Actionable Strategy
- Accept lower numbers — don’t compare to sea-level benchmarks.
- Focus on different goals: optimize movement economy at lower intensities rather than chasing VO2max work.
- If staying at altitude for 7–10+ days, you can plan a structured aerobic block — but only after some adaptation.
Best tips for altitude training
🥵 Accumulated Fatigue: When the Nervous System Takes Over
What Actually Happens
This isn’t about weather or elevation — it’s about your internal balance. Heavy loads, poor sleep, mental stress… all affect the autonomic nervous system.
Result:
- Higher resting heart rate
- Difficulty reaching high-intensity zones
- Slower recovery between intervals
Most affected zones: All of them — especially Zones 4–5, as the body limits top-end output to protect itself.
Real-world effect: You feel like your fitness has dropped, even if the data doesn’t show it long-term.
Actionable Strategy
- Watch for abnormal shifts in your usual metrics (resting HR, HRV, recovery time).
- Add active recovery days — even if they weren’t planned.
- Don’t rely on data alone: irritability, poor sleep, and lack of motivation are real signs too.
When Should You Recalculate Your Zones?
You don’t need to re-test every time the temperature changes. But it can make sense in certain cases:
- After a prolonged stay at altitude (physiological adaptation)
- After extended periods of extreme heat
- After a break, injury, or significant training load change
2PEAK Performance Test for Cycling, Running and Swimming
✅ Good to know: 2PEAK automatically adjusts your zones over time based on your training data. But you can also manually enter a new test whenever you feel something has shifted.
Conclusion
Training zones are a powerful tool — but only when viewed in their real-world context. Heat changes your cardiovascular response, altitude changes your muscle chemistry, and fatigue alters everything.
In summer, the real strength lies in adapting your training to the conditions. You don’t lose fitness by slowing down when needed. You lose it by ignoring the warning signs.