Long runs carry incredible reward: that euphoric rhythm, the mental clarity, the achievement when you finish.

But they also come with hidden risks. Knowing them, and how to handle them, gives you an edge — not just for running longer, but for running smarter.

1. Immune suppression: Why you’re more vulnerable after big K’s

Q: Can a long run make me more prone to getting sick?

A: Yes — when the session goes past about 2 hours or pushes you into unusual stress zones, your immune system can dip.

One study found that ultra‐endurance efforts triggered changes in white blood cell profiles (e.g., reduced regulatory T cells) which may reflect suppressed immune defence. PubMed Central+2PubMed+2

Tip: Ensure you’re well‐rested before your long run, stay consistent with recovery, and prioritise nutrition and sleep post‐run to avoid that “open window”.

2. Dehydration & electrolyte loss: The silent throttler

On hot or humid days, your body battles two fronts — the distance and the environment. Even mild dehydration can reduce performance, increase fatigue and leave you inviting injury.

Tip: Rehydrate strategically: pre-load fluids and electrolytes, sip during the run, and refuel immediately afterwards. This is a NON-NEGOTIABLE..

3. Load spikes = injury invites

Q: Why do I feel sore or injured even though I’ve been consistent?
A: Sometimes it’s not about consistency — it’s about jumping volume or intensity too fast.

A large study found runners who increased their weekly distance by more than ~30% had a markedly higher injury risk. PubMed

Tip: Increase your long-run distance gradually. Avoid “coming back in one go” after time off. Let your tendons, joints and tissues adapt.

4. Muscle damage and delayed recovery

Your legs bear the brunt: muscle fibres strain, connective tissue loads, and inflammation sets in. That “dead legs” feeling days post-run is your body giving you feedback.

Tip: Use active recovery and targeted strength work. Don’t just log long K’s — build resilience on the ground.

5. Nutritional blind spots

Long runs burn glycogen, deplete iron stores, and can dent vitamin D or electrolyte levels. Over time, that adds up.

Tip: Ensure your diet supports the distance: lean proteins, leafy greens (iron), sunshine or supplement vitamin D, and salt or electrolyte support. Aim for nutrient‐rich fuel, not just carb loading.

6. Positive “dangers” you should welcome

If you plan your long runs with all of what I’ve just gone through in mind, then you’re in danger of:

👍Improved cardiovascular health

👍 Endurance that translates to everyday ease

👍 Mental toughness that shows up off the trail

👍New routes, new places, new people

These benefits remain the reason you lace up — so don’t let the risks overshadow the benefits.

7. Your Long-Run Danger-Proof Checklist

✅ Plan your run: route, weather, gear

✅ Pre-hydrate & carry fluids + electrolytes

✅ Wear gear suited to conditions (shoes, clothing)

✅ Use a conversational pace for most of it — save the “kick” for the final K’s

✅ Monitor how the body feels afterwards — soreness beyond 48 hrs? Review

✅ Give yourself rest days before and after large efforts

8. Ready to run safe and strong?

Take a moment to ask yourself: Are you stepping into your next long run with a simple plan for these risks?

If yes — good.

If no — pause, use the checklist, and show yourself the love and care you need to thrive.

Go chasing the horizon… but make sure you can come back ready to go again.

Yours in running and life,
Daniel Lucchini

References

Perry C, Pick M, Bdolach N et al. Endurance exercise diverts the balance between Th17 cells and regulatory T cells. PLoS One. 2013;8(10):e74722. PubMed Central
Nieman DC, Wentz LM. The compelling link between physical activity and the body’s defence system. Journal of Sport and Health Science. 2019;8(3):201-217. PubMed+1
Nielsen RO, et al. Excessive progression in weekly running distance and risk of running-related injuries. J Sci Med Sport. 2014;17(2):117-124. PubMed

The Hidden Dangers Of Long Runs – and How to Avoid Them