Regular movers get fewer respiratory infections — one of exercise science's most consistent findings — yet marathon fortnights show infection spikes. Both facts fit one curve, and knowing it lets you train confidently through winter.

Exercise is immune circulation; overreach is immune taxation.

Key Takeaways

  • Each moderate session surges immune patrols for hours.
  • The J-curve: moderate training protects; exhaustive extremes tax.
  • Sleep and fuelling are winter training variables, not extras.
  • Neck-check: above = easy allowed; below = rest, fully.

What a Single Session Does

During moderate exercise, surveillance pumps up: natural killer cells and other responders surge into circulation several-fold, patrolling tissues at elevated rates for hours after. Regular repetition of this 'patrol surge' is a leading explanation for exercisers' infection advantage — alongside anti-inflammatory adaptations and better sleep. Each workout is, immunologically, a neighbourhood watch shift.

The J-Curve

Plotted against training load, infection risk draws a J: sedentary baseline, LOWER risk through moderate regular activity, rising again at prolonged-exhaustive extremes without recovery (the classic post-marathon window and overtrained-athlete sniffles). Modern nuance debates how much is true suppression versus exposure and symptom-reporting — but the practical shape survives: the middle of the curve is a gift; the far right requires professional-grade recovery management.

Winter Training Rules

Keep the habit through the season — moderate movers are precisely the protected group. Adjust the margins: respect sleep as a training variable, fuel sessions (carbohydrate availability moderates stress-hormone response), manage cold-air comfort per our cold-weather guide, and let genuinely heavy blocks come with deliberate recovery weeks.

Training While Sniffly

The neck-check heuristic clinicians share: above-the-neck symptoms (mild congestion, scratchy throat) permit easy sessions if energy agrees; below-the-neck signs (fever, chest symptoms, body aches) mean full rest — exercising through systemic illness courts complications, myocarditis the serious one. Return gradually after fever: easy days, patience, no heroics.

Season verdict: the exercise habit is immune infrastructure — protect it from both abandonment and overreach.

Frequently Asked Questions

How much exercise optimises immunity?

The protected middle is broad: roughly 150+ minutes of moderate movement weekly, regularly spread. More is fine with proportionate recovery.

Why do marathoners get sick after races?

Prolonged exhaustive efforts transiently stress immune regulation — combined with exposure-heavy events and depleted sleep, infection windows open. Recovery protocols close them.

Should I work out with a cold?

Mild above-the-neck symptoms permit gentle sessions by feel; fever or chest involvement means rest until recovered, then graded return.

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Sources & Further Reading

Educational content only — not medical advice. Sources are general references on the topic, not studies of the BreathiZen formula.