Why Fighters Keep Getting Sick: The Hidden Physiology Behind Hard Training
If you’re a fighter who keeps getting sick every time training ramps up, you’re not “weak” and your immune system isn’t randomly broken.
What’s actually happening is that your immune system is working overtime in the background of your training. If you don’t respect that system, it will start throwing red flags at you: constant colds, sore throats, gut issues, random fatigue, performance crashes.
This article is here to explain what is going on under the hood in plain language and then give you practical ways to fix it.
1. Big picture: your immune system is more than “not getting sick”
Everyone thinks immune system = not catching the flu.
For fighters, your immune system is deeper than that. It is involved in:
Repairing damaged muscle and connective tissue after hard pads, clinch and strength work
Managing inflammation and body temperature
Keeping your gut barrier tight when you are smashing carbs, caffeine, weight cuts, and stress
Regulating sleep, fatigue and even mood
Exercise immunology as a field grew from this exact idea: training stress, the nervous system, hormones and immune cells are tightly connected.Physiology Journal
So every time you go to war in the gym, your immune system is in that fight with you.
2. The “open window” and why fighters get sick after hard blocks
You have probably lived this:
You push a brutal camp
You finally taper, fight, or take a few days off
Then you get nailed by a cold or throat infection right when you are supposed to be enjoying the break
This pattern is what researchers called the “open window” of immunodepression after prolonged, intense exercise. In that window (a few hours to maybe a couple of days after very hard work), some immune measures drop below baseline, which may make it easier for viruses to get a foothold.Physiology Journal
Epidemiology backs this up:
Moderate training tends to reduce illness risk compared with being sedentary
Very heavy or chronic high-intensity training pushes illness risk above normal again
That relationship is often drawn as a J-shaped curve: a little training is good, a lot is better, too much with not enough recovery starts to break you down.PubMed
For fighters constantly hovering in “camp mode” with no real off-season, it is easy to live on the wrong side of that J.
3. What actually happens to your immune cells when you train hard
Here is the simplified version, where i try break it down easily for you.
During hard training
A tough session (intense pads, conditioning, or long sparring) causes:
An increase in most white blood cells in the blood
Especially neutrophils and a class of fast-response lymphocytes like natural killer (NK) cells and certain T cells
This is driven by:
Adrenaline and noradrenaline
Blood flow and shear stress
Stress hormones like cortisol later on
It is your body saying, “We might be about to get injured or exposed to pathogens, send the troops.”
In the hours after
After the session, you see something interesting:
Neutrophils (front line “grenade throwers” that kill bacteria) often stay elevated for up to 6 hours after long efforts
Lymphocytes (T cells, B cells, NK cells) drop below baseline for several hours – this is called lymphopenia
That drop freaked people out at first, but what the data now show is:
Those “missing” lymphocytes have not died
They have left the blood and moved into tissues like lungs, gut and muscle, where infection risk and tissue damage are highestPhysiology Journal
In other words, your immune system is not simply “down”; it is being redeployed.
Where it becomes a problem is when:
The session is very long and very hard (think >90 minutes of heavy work)
You stack multiple brutal sessions with short recovery
You are under-fuelled, underslept and stressed
In that state, cell function (killing ability, cytokine production, etc.) can stay suppressed longer, which may reduce your ability to deal with viruses and bacteria in real life.Physiology Journal
4. Overreaching, overtraining and “camp sick”
There is a spectrum:
Functional overreaching - 1 to 2 weeks of heavy training, performance dips slightly, then rebounds higher if you deload correctly
Non-functional overreaching - you stay fatigued, performance drops, mood and hormones are off, and this can drag for weeks
Overtraining syndrome - full crash, months of issues, often with recurrent illness, mood problems and big performance loss Physiology Journal
What shows up immune-wise when fighters live in that non-functional zone?
Research in endurance and team athletes shows: Physiology Journal
Drops in salivary IgA (this is an antibody in your saliva that is literally your first line of defence in the nose and throat)
Reduced ability of monocytes, neutrophils and dendritic cells to produce cytokines and do their job
More frequent upper respiratory tract infections (URTIs) over long heavy blocks
Low or falling IgA over a season is consistently associated with higher URTI risk in elite athletes.PubMed
Now imagine fighter life layered on top of this:
Sparring in packed gyms
Humid, bacteria ridden environments
Weight cuts
Travel
Work, money, relationship stress
If you feel like every time training spikes, your throat goes scratchy, or you pick up “gym flu”, this is probably not random. It is chronic overreaching plus lifestyle plus exposure.
5. Sleep: the silent performance drug you keep under dosing
If you are sleeping 5 to 6 hours per night and wondering why you are always sick, you do not need a fancy supplement. You need to go to bed.
Classic research from Cohen and colleagues found that people sleeping less than 7 hours per night were about three times more likely to get a cold after being exposed to a virus than people sleeping 8 hours or more. PubMed
Poor sleep quality and irregular schedules are also linked to:
Higher inflammation (IL-6, CRP)
Blunted vaccine responses
Increased risk of infection in general ResearchGate
For fighters, that means:
Late night scrolling, Netflix, or gaming after pm sessions
Early-morning roadwork
Caffeine abuse to cover fatigue
All of that quietly drags your immune resilience down. When you then throw heavy training on top, the system cracks.
6. Under-fuelling, “train low” and why your immune system hates your diet
A lot of fighters live on coffee / M-150, vibes and two shitty meals a day in camp.
From an immune perspective, that is a problem.
Carbohydrates
During long or intense exercise, carbs do more than just fuel your muscles.
Carbohydrate intake before and during prolonged exercise has been shown to: Physiology Journal
Reduce spikes in stress hormones (adrenaline, cortisol)
Blunt huge swings in cytokines like IL-6
Reduce extreme shifts in some white cell populations
Over consecutive heavy days, higher daily carbohydrate intake helps reduce markers of immunodepression and cortisol and seems to reduce overreaching symptoms. Physiology Journal
General guideline ranges for hard-training athletes are:
5 to 7 g of carbohydrate per kilogram per day for moderate to high training
6 to 10 g/kg/day when you have multiple hard sessions or long endurance work PubMed
If you are constantly doing long, hard work on 2 to 3 g/kg and “train low” every day, you are not just limiting performance; you are stressing your immune and endocrine systems.
You can still use strategic “train low” sessions for adaptation, but they must be:
Planned
Limited in frequency
Surrounded by enough “train high” days with proper carbs Physiology Journal
Protein
Protein is not only for muscle; it is crucial for immune cells, antibodies, and recovery from tissue damage.
For hard-training athletes, the realistic sweet spot is around 1.6 to 2.2 g/kg/day of high-quality protein. PubMed
High-protein diets in intense training blocks have been shown to: Physiology Journal
Help maintain normal immune cell trafficking
Reduce self-reported respiratory illness in elite athletes
So, if you are a 70 kg fighter living on 60 to 80 g of protein per day, training twice daily, and shocked that you keep getting sick, you now know why!
Antioxidants and “immune” supplements
This is the harsh truth:
High-dose antioxidants and “immune” pills are not a magic shield
The evidence that things like mega-dose vitamins or phytochemicals prevent illness in athletes is mixed and often weak
Very high doses may even blunt training adaptations Physiology Journal
A diet built on whole foods, fruit, vegetables, quality fats and proteins will cover most needs better than a random cocktail of supplements.
7. So why are fighters sick so often? The usual pattern
When I look at fighters who are constantly sick, the pattern is usually some version of this:
Training volume and intensity are high, all the time
There is no true deload, only “oops I am sick, forced deload”
Sessions are stacked badly: hard sparring plus brutal conditioning on the same days, repeated
Food intake is too low, carbs are too low, protein is borderline
Sleep is broken, reduced, or all over the place
Life stress is high (money, family, relationships, work)
Hygiene in the gym is poor, and they are exposed to a lot of respiratory bugs and skin infections
Your immune system is extremely adaptable and actually benefits from training stress when the stimulus and recovery are balanced. Physiology Journal
The problem is not the training stress itself; it is the stacking of stress with no real support.
8. Practical checklist: how to train hard without falling apart
Here is where we get actionable.
A. Structure your training week for immune resilience
A simple framework:
2 to 3 hard days per week (hard sparring, very heavy conditioning, or hard S&C)
2 to 3 moderate days (technical, volume, or strength work that is tough but not maximal)
At least 1 full rest day or very low-intensity active recovery
Avoid:
Three or more “all-out” days in a row
Heavy S&C plus hard sparring plus hard conditioning stacked on the same day, week after week
Think in blocks:
2 to 3 weeks of push
Then a deload week with slightly less volume and intensity so your immune and endocrine systems can catch up
B. Protect the 24 to 48 hours after your hardest sessions
That “open window” after big efforts is where smart habits matter most: Physiology Journal
After a brutal day:
Do not hang out in crowded, germ-heavy spaces for hours
Do not stay at the gym touching every pad and handle if you do not need to
Wash hands properly, especially before eating
Eat carbs and protein soon after training
Hydrate, add electrolytes if you sweat a ton
Prioritise sleep that night like your performance depends on it (because it does)
C. Fuel like someone who actually wants to win
Aim for:
Carbs: roughly 5 to 7 g/kg/day in normal in-camp weeks, higher on days with very heavy work or two sessions
Protein: 1.6 to 2.2 g/kg/day from meat, fish, eggs, dairy (if tolerated) and quality powders
Anchor carbs around sessions:
1 to 4 g/kg of carbs in the 1 to 4 hours before key sessions
A mix of faster carbs and protein in the hour after PubMed
Stop pretending you can do three intense sessions on black coffee and a 7/11 sandwich.
D. Sleep like a professional
Non-negotiables:
Aim for 7 to 9 hours per night
Keep a consistent sleep and wake time where possible
Reduce screens and stress exposure in the last hour before bed
Use caffeine earlier in the day, not at night
If you are in a heavy block, think of sleep as part of the training prescription, not “optional life time”.
E. Watch for early warning signs
Red flags your immune system and nervous system are not coping:
You are getting ill more than 3 or 4 times per year
Every time you increase training volume, you get sick in the next 1 to 2 weeks
Resting heart rate is higher than normal for days on end
Mood is flat or irritable, motivation is low
Small cuts, skin issues or mouth ulcers take longer to heal
Saliva feels thicker, throat scratchy, or you wake up with mild cold symptoms frequently
That is the moment to adjust training and lifestyle, not push harder.
9. Supplements, recovery tools and what is actually worth it
Tools that may help indirectly:
Carb and protein shakes - to make it easier to hit macros around sessions
Electrolytes - when sweat losses are high (especially in hot climates and heavy sessions)
Basic micronutrients - if your diet is poor or you are cutting hard
Things that are not magic bullets:
High-dose antioxidants
Random “immune booster” blends
Overuse of NSAIDs to smash soreness daily
The evidence for massage, cryotherapy, compression, etc., on immune function specifically is weak and inconsistent, but these can still be useful for how you feel, how you sleep, and how well you mentally handle training. Physiology Journal
Use them as support, not as a crutch to keep overtraining.
10. The mindset shift fighters need
The takeaway is not “training makes you sick, so train less.”
The real message is this:
Training is a controlled stress
Your immune system is designed to handle stress, adapt and come back stronger
When you manage training, food, sleep and life like a professional, your immune system becomes a weapon, not a weakness
If you are always the fighter who “gets sick every camp”, that is not your fate. It is a systems problem.
Refine with:
Smarter programming
Better fuelling
Better sleep
Cleaner hygiene and environment
And you stack the deck in your favour.
Don't just fight - Fight by desigN
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