How to use the winter to build fitness

By Rune Bækgaard, Dealer Success Manager, FUSION Sportswear (Marathon PR: 2:13:57)

 

There are two types of winter days: those where you run, and those where you "should have run." That distinction becomes more pronounced the more seriously you take your running.

I like winter running because it is brutally honest. When the temperature drops, the excuses disappear. There is no chasing the "perfect" day. There is only the work.

I’ve run enough winter kilometers to know one thing: the hardest part of winter training is rarely the program itself. It’s getting out the door. The darkness, the cold, the wind, wet clothes, a long day at work, and a sofa that feels like a magnet.

So, let’s get practical. Here is what I use myself to ensure winter becomes a building phase rather than a hiatus.

 

1) Winter is the Season of Stability

 

Winter training is more about control than tempo. Especially around the freezing mark, the cold begins to take a toll if you let yourself get chilled to the bone. Controlled studies at 0°C show that endurance capacity decreases when cold stress becomes high enough—particularly if the core temperature is allowed to drift downward. It’s not that your legs magically become weak; it’s because the body uses more energy simply to keep the system warm (Wallace et al., 2023).

This is why many runners "die a slow death" on those wet, windy runs. It’s not necessarily poor fitness; they’ve become cold and damp, and the physiological "bill" starts ticking.

The goal is simple: Stay warm enough to run steadily, but not so warm that you get soaked from the inside out with sweat.

2) Layering: Three Layers, One Rule

 

In the summer, you can get away with almost anything. In the winter, your clothing becomes part of your physiology. Moisture, wind, and temperature interact, and if one of them wins, you lose.

That’s why I don’t think in "outfits," but in systems. An outer layer that cuts the wind without being noisy. A layer next to the skin that regulates without suffocating. Tights that maintain shape and warmth without feeling heavy. This is where technical running gear proves its worth—not as branding, but as a tool.

At FUSION Sportswear, we often talk about clothing as a system. It sounds theoretical, but in practice, it just means every layer has a specific job.

My typical winter setup:

• Outer layer: Something to block the wind (e.g., S2 Run Jacket or S2 Run Vest).

• Mid-layer: An active layer (I prefer the C3 Zip Neck).

• Base layer: Technical Merino 150 LS if it’s truly cold.

• Tights: Appropriate for the conditions. In transitional weather, classic tights are enough. When the frost bites, "warm" tights make sense because the warmth comes from within the fabric structure, not from added bulk. This is a crucial distinction if you still want to run efficiently.

The most important detail in a Scandinavian winter is rain and wind. Moderate cold combined with wet and windy conditions increases heat loss. Research shows that energy expenditure and carbohydrate oxidation can increase when the body is cooled under these conditions. In other words: wet and windy can be harder than "cold but dry" (Ito & Yamashita, 2024).

Two practical takeaways:

1. Prioritize a better outer layer on wet days rather than adding more insulation underneath.

2. Protect your "extremities": hands, feet, neck, and head. If these stay warm, the rest of the body feels better.

 

 

3) Nutrition: Winter Costs More Than You Think

 

When you run in the cold, you aren't just paying for the work in your legs; you are paying for thermoregulation. Recent physiological reviews describe how extra energy demands in cold environments are linked to heat production and the weight of winter clothing (Schafer et al., 2024).

This doesn't mean everyone needs an energy gel for a 45-minute run. But it does mean that long runs and extended tempo sessions can feel "empty" sooner in the winter, especially if you get cold and burn through glycogen faster.

My practice is simple:

• If the run is over 75–90 minutes and it’s cold or wet, I bring energy. It keeps the quality of the session higher.

• After a cold run, I eat sooner rather than later. The body is already working hard to settle the "heat bill."

 

4) The Airways: Protecting Your Hard Sessions

 

Cold, dry air combined with high intensity can irritate the airways. A classic study on elite runners showed bronchospasms during sub-zero training in a large portion of atopic runners, while non-atopic runners were far less affected (Helenius, Tikkanen & Haahtela, 1996).

Modern reviews on sub-zero training and airway health suggest that heat and moisture exchangers (HMEs) can reduce issues for some, noting that cold and dry air are the primary triggers (Hanstock et al., 2020).

How I handle it in practice:

• I save my hardest intervals for days with milder air or locations where I can better control the environment.

• In freezing temperatures, I warm up for much longer than I think I need to. Winter punishes impatience.

• I accept that a "good session" in January is often just controlled work without pushing the pedal to the floor.

 

5) Set Yourself Up to Show Up

 

It’s dark when you wake up and dark when you get home. You can do yourself a favor by preparing meticulously. I’ve built a routine that helps me get out the door every single time.

My morning routine:

• Clothes are laid out the night before. Not "mostly ready." Ready.

• Shoes are by the door. Jacket is hanging ready.

• I decide the route in advance. It sounds trivial, but it saves me from "negotiating" with myself at 05:30 AM.

The "Exit Strategy" rule for dark afternoons: I tell myself I only have to go out for a short loop. If the body feels terrible after 15 minutes, I can turn back home with no guilt. Nine times out of ten, I keep going. But giving myself that "out" makes it easier to start.

If you run after work, make your route "foolproof":

• Use a familiar loop close to home.

• Choose well-lit paths over the "optimal" scenic route.

• Make reflectors and high-visibility gear your standard, not an afterthought.

 

Bottom Line

If you want to use the winter to build fitness, make it a period of consistent work, not a battle to "defeat" the weather.

Keep yourself warm enough to maintain stability, but not so warm that you drown in sweat. Fuel so that the quality of your training stays high. Respect your airways, especially in the frost. And finally, remove the friction that stops you from getting out the door.

Winter doesn't require you to become a different person. It simply requires you to show up and do the work properly.

 

Literature:

Wallace, P. et al. (2023) 'Endurance capacity impairment in cold air ranging from skin cooling to mild hypothermia' [Online]. Link: https://journals.physiology.org/doi/full/10.1152/japplphysiol.00663.2023  

Ito, R. & Yamashita, N. (2024) 'Moderately cool environment with rain and wind increases cold strain and energy expenditure via carbohydrate oxidation during running exercise' [Online]. Link: https://pubmed.ncbi.nlm.nih.gov/39225023/.

Schafer, E. et al. (2024) 'Energy expenditure during physical work in cold environments: physiology and performance considerations for military service members' [Online]. Link: https://journals.physiology.org/doi/full/10.1152/japplphysiol.00210.2024

Helenius, I. & Tikkanen, H. & Haahtela, T. (1996) 'Exercise-induced bronchospasm at low temperature in elite runners' [Online]. Link: https://pubmed.ncbi.nlm.nih.gov/8693447/

Hanstock, H. et al. (2020) 'Exercise in Sub-zero Temperatures and Airway Health: Implications for Athletes With Special Focus on Heat-and-Moisture-Exchanging Breathing Devices' [Online]. Link: https://www.frontiersin.org/journals/sports-and-active-living/articles/10.3389/fspor.2020.00034/full