If your usual easy pace suddenly feels like work once winter hits, you’re not losing fitness. Cold weather changes how your body responds to running, and understanding those changes makes it easier to stop grinding through every run and adjust in ways that actually help.
American exercise physiologist and endurance coach Dr. Alyssa Olenick explains: “Cold weather affects multiple body systems, not just your comfort level.” The mismatch between pace and effort in winter has real physiological roots, and the cold doesn’t need to be extreme to have an impact.
Your heart works harder at the same pace
“Your cardiovascular system is working harder before you even start,” Olenick says. “Blood vessels constrict to protect your core, blood pressure rises, heart rate increases at the same pace you’d normally cruise through.” Cold temperatures trigger blood vessels to constrict as your body works to preserve core heat. That response increases blood pressure and raises cardiovascular demand earlier in a run.
The result is familiar to anyone who runs through winter—a pace that once felt relaxed now requires noticeably more effort, especially before you’ve fully warmed up.
Performance drops down the priority list
In cold conditions, energy is redirected toward temperature regulation. That shift can leave less available for speed and efficiency, even on runs that would normally feel routine. “Your body is prioritizing keeping you warm over peak performance,” Olenick explains. “And that’s not a fitness problem. That’s your body doing its job.” Forcing pace in these conditions often leads to faster fatigue without much training payoff.
Cold air affects your breathing, too
Winter doesn’t just change how your heart and muscles respond. Breathing cold, dry air can irritate the airways, particularly during harder efforts.
“Up to 50 per cent of winter athletes experience some degree of bronchoconstriction from cold dry air,” Olenick says. “It’s real, it’s common, and it gets worse the harder you’re breathing.” That tight, burning sensation in the chest has a physiological explanation, and it’s one reason high-intensity workouts feel especially rough in the cold.
A runner’s guide to extreme winter weather
How to train without fighting your body
Despite the added strain, winter can be a productive time for training. Lower-intensity running supports aerobic development, and winter conditions naturally encourage that shift. “It’s one of the best times to build aerobic base because you’re naturally running easier,” Olenick writes. “Which is what most of us need more of anyway. Run by effort, not pace, when it’s cold. Let your watch say what it says.”
That approach may also include more treadmill runs, shorter long runs or skipping speedwork when conditions are extreme. “Sustainable winter running is far better than forcing yourself through misery,” she adds. Cold affects runners differently depending on climate, body composition, airway sensitivity and layering. Adjusting effort rather than chasing numbers helps maintain consistent training throughout the season.