June 13, 2026 · 4 min read

Spring Fatigue and Training — Why Power Drops in Spring Despite a Good Plan

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

What's happening physiologically in spring

• Circadian shift — the lengthening day shifts melatonin release, which temporarily disrupts sleep quality for some people.
• Vitamin D deficiency — after winter, vitamin D levels are usually at their yearly low, and it has a documented effect on muscle function and immunity.
• Atmospheric pressure swings — more frequent weather front changes in spring stress the autonomic nervous system, which some people experience as an energy dip.

How do I tell spring fatigue from overtraining?

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

How to adjust your training plan during this period

• Don't cut 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 clearly higher than usual at the same power, push the key session back 1–2 days instead of forcing it.
• Get daylight exposure — outdoor training around midday supports both vitamin D synthesis and circadian stabilization at once.

Does vitamin D supplementation help with spring fatigue?

In people with a confirmed deficiency (a 25(OH)D blood test), supplementation improves well-being and muscle function within a few weeks. Without a confirmed deficiency, the effect is less predictable — start with a test rather than "just in case" high-dose supplementation.

When to check the data instead of guessing

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

Bottom line: spring fatigue is real and typically resolves on its own within a few weeks, as long as you don't try to "train through" it with extra intensity. The key is telling it apart from overtraining using data, not just how you feel.

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