Every running season brings the same debate: does cold air make your body work harder to stay warm, or does summer heat force it to spend extra energy cooling down?
To sort out the confusion, Videnskab.dk asked Michael Voigt, a professor of sports science at Aalborg University, to explain what actually happens inside the body.
Michael Voigt explained that the amount of energy you use during a run is determined primarily by the workload, not by the weather.
In his view, a steady run at a given pace requires roughly the same amount of oxygen, and therefore the same amount of energy, whether the air temperature hovers just below freezing or sits in comfortable summer warmth.
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Why the heat feels harder
Many runners notice that warm-weather workouts feel heavier. Michael Voigt notes that this sensation is real but misleading.
When the temperature climbs, your body diverts blood toward the skin to release heat.
That shift can make a run feel more demanding, even though your actual energy expenditure is unchanged.
There is one meaningful exception: very long sessions in high heat.
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In those conditions, dehydration can set in, reducing blood volume and making oxygen transport less efficient.
Michael Voigt explained that runners often slow down as a result, which can actually lower total energy use.
Effort matters more than the season
The takeaway, according to Micheal Voigt’s explanation to Videnskab.dk, is straightforward: weather doesn’t grant a shortcut to weight loss.
Cold days don’t increase calorie burn, and warm days don’t automatically boost fat loss.
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What counts is the intensity and duration of the effort, not the number on the thermometer.
For runners debating whether to head out on winter routes or wait for summer sunshine, the science offers little reason to postpone.
Dress for the conditions, pace yourself sensibly, and let consistency, not temperature, drive the results.
Sources: Videnskab.dk.
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