Heat and performance: what really happens in the body

Before adapting your training, you must understand what heat does physiologically.

As soon as the outside temperature exceeds 25°C, the body activates its thermoregulation mechanisms: it sends more blood to the skin to dissipate heat, to the detriment of the muscles. The direct consequence: for an identical effort, the heart rate increases by 10 to 20 bpm.

What you were doing in Zone 2 at 15°C mechanically becomes Zone 3 at 30°C — without you having changed anything in your pace.

Acclimatization: the 14 days that change everything

The human body is remarkably adaptable — but this adaptation takes time. It takes an average of 10 to 14 days of progressive exposure to heat for physiological adaptations to truly take hold.

• Plasma volume increases by 3 to 5%, which improves oxygen transport and facilitates thermoregulation.
• The body begins to sweat sooner and more efficiently, anticipating the rise in temperature.
• The heart rate for a given effort gradually drops back toward its usual values.

What this implies in practice: the first two weeks of heat are not meant for performance. They are for acclimatization. Reducing intensity by 15 to 20% during this period is not a concession — it is an investment.

Guiding your effort by heart rate, not by sensations

In summer, subjective sensations are deceptive. Heat creates a diffuse fatigue that distorts the perception of effort. The best tool then becomes heart rate — or better yet, heart rate reserve.

The practical rule: in high heat, lower your target zones by 5 to 10 bpm. If your usual Zone 2 is between 140 and 155 bpm, aim for 130 to 145 bpm during heat waves. The cardiovascular adaptation will still occur — without the risk of overtaxing the system.

Shifting sessions to before 9 am or after 7 pm is not just a question of comfort. It is a performance decision: the temperature can vary by 8 to 12°C between the middle of the day and early morning, which radically changes the actual load imposed on the body.

Hydration: beyond "drinking enough"

Summer hydration is misunderstood. Drinking large quantities of water is not enough — and can even become counterproductive.

The weigh-in test is the most reliable tool to calibrate your actual needs: weigh yourself before and after the session. Each kilogram lost corresponds to about 1 liter of fluid to be replenished.

A loss of more than 2% of body weight leads to a measurable drop in cognitive and physical performance. Beyond 3%, the risk of heatstroke becomes serious.

The hyponatremia trap

Drinking too much water without sodium dilutes the salt concentration in the blood. This phenomenon, hyponatremia, causes nausea, cramps, and headaches — and is often confused with dehydration, leading one to drink even more.

For sessions exceeding 60 to 75 minutes, reintegrating electrolytes — sodium primarily, followed by magnesium and potassium — is not an option; it is a physiological necessity.

Concrete benchmarks:

• 500 ml of water in the 2 hours preceding the effort.
• 150 to 200 ml every 15 to 20 minutes during the effort.
• For long sessions: 400 to 800 mg of sodium per liter of fluid.
• After the effort: 1.5 liters of fluid per kilogram lost, spread over 2 to 3 hours.

Summer recovery: the window most miss

Heat slows down muscle repair processes — the body mobilizes part of its resources to thermoregulate, to the detriment of tissue reconstruction. Recovering in summer therefore requires more attention, not less.

The 30-minute metabolic window

In the 30 minutes following an effort, muscles are in a state of maximum nutrient uptake. This is the moment when protein and carbohydrate intake is most effectively used for recovery.

Aiming for 20 to 30g of protein combined with moderate glycemic index carbohydrates in this window significantly accelerates glycogen resynthesis and muscle reconstruction.

The choice of protein is not trivial: whey proteins are ideal in this post-effort window thanks to their rapid absorption. Casein, which is slow-digesting, is more relevant before bed to support nocturnal reconstruction.

Contrast bathing rather than just a cold shower

A cold shower after effort is common — but contrast bathing, alternating hot and cold, is documented as being significantly more effective at reducing inflammatory markers and delayed-onset muscle soreness.

The recommended protocol: 1 to 2 minutes in hot water (38 to 40°C), then 1 minute in cold water (10 to 15°C), repeated for 3 to 4 cycles. The alternation creates a vascular pump effect that accelerates the elimination of metabolic waste.

Sleep: the most underestimated variable

It is at night that the body produces most of its growth hormone — and therefore when muscle reconstruction actually happens. Heat often degrades the quality of deep sleep.

A few concrete adjustments: bedroom temperature between 17 and 19°C, exposure to natural light in the morning to regulate the circadian cycle, and avoiding intense effort in the 3 hours before bed. High post-exercise body temperature delays sleep onset.

AERTH pieces designed for summer: when the material becomes performance

Equipment is not neutral. In hot weather, what you wear directly determines the quality of your effort — and your ability to prolong it.

At AERTH, every piece is designed around one principle: that the garment should never be what you are thinking about during the effort. The selected materials offer maximum breathability, wick away moisture without weighing you down, and maintain their shape after every session.

The technical t-shirt relies on a dual-material construction designed for summer conditions: a light front that does not restrict movement, and a micro-perforated back that dissipates heat — so that nothing you wear gets between you and your effort.

Manufactured in Portugal and Oeko-Tex certified, AERTH creations are designed to last — in their construction as well as their aesthetic. No intrusive logos, no passing trends. Simple, subtle, silent pieces. The ones you come back to season after season because they do what they promise, without doing anything more.

Mindset: the quiet discipline of summer

There is something special about someone who trains in July, without an audience, without a near competition, without visible outside pressure. This is where the true nature of a practice is revealed.

Summer training is not measured by records. It is measured by the quiet constancy of the person who returns, again and again, because they have understood that the elegance of a practice is built in these moments — when no one is looking.