June 13, 2026 · 5 min read

Spring Fatigue and Cycling Training — Why Power Dips Despite a Good Plan

Spring fatigue is a real physiological effect — a circadian rhythm shift, post-winter vitamin D deficit, and barometric pressure swings all lower energy levels independent of how good your training plan is. The problem is the symptoms (lower motivation, harder-feeling intervals) are easy to mistake for overtraining, and the two need very different responses.

What's physiologically happening in spring

• Circadian rhythm shift — lengthening daylight shifts melatonin release, which temporarily hurts sleep quality for some people.
• Vitamin D deficit — after winter, vitamin D levels are typically at their annual low, and vitamin D has a documented effect on muscle function and immunity.
• Barometric pressure swings — more frequent weather front changes in spring load the autonomic nervous system, which some people experience as an energy dip.

How do you tell spring fatigue apart from overtraining?

The key difference is the trend in PMC and HRV. With spring fatigue, TSB and CTL look normal, and the energy drop is general — it affects work and concentration too, not just training. With overtraining, you see a clearly negative TSB persisting for weeks, reduced HRV, and a specific power drop at the same RPE during training — that's a signal to cut load, not just wait it out.

How to adjust your training plan during this period

• Don't drop base volume — easy Zone 1–2 sessions usually don't worsen the problem, and consistency helps stabilize your circadian rhythm.
• Stay flexible on high-intensity intervals — if RPE is noticeably higher than usual at the same power, push the key session back 1–2 days instead of forcing it.
• Manage daylight exposure — training outdoors around midday supports vitamin D synthesis and circadian rhythm stabilization at the same time.

Does vitamin D supplementation help with spring fatigue?

In people with a confirmed deficiency (25(OH)D blood test), supplementation improves wellbeing and muscle function within a few weeks. Without a confirmed deficiency, the effect is less predictable — start with testing, not with high-dose supplementation "just in case."

When to check the data instead of guessing

If the energy dip persists longer than 2–3 weeks and shows up in your training data too (rising heart rate at the same power, falling power at the same RPE), check your fatigue chart (PMC) over a longer window — that will separate a temporary seasonal dip from a real recovery debt that needs a deload week.

Bottom line: spring fatigue is real and passes on its own within a few weeks, provided you don't try to "train through it" with extra intensity. The key is distinguishing it from overtraining using data, not how you feel in the moment.

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