Overtraining and the Immune System. How Much is Too Much?

Overdoing it, burning the candle at both ends, cooking the goose. Athletes are notoriously bad for knowing when to back off and take a break, but why is it that going just a little too hard on the training track can lead to illness that can destroy an athlete’s whole season?

Image Credit: Geraldt via Pixabay

It’s no secret that athletes need hours upon hours of training to improve or maintain their level of performance. There are three markers generally used to assess the total load on an athlete during training and competition. Intensity (how hard each session is), frequency (how often an athlete is training) and duration (the length of each session). Given most professional athletes, cyclists included, will typically train 6-7 times a week year-round (excluding rest periods) the main influences on load are the intensity and duration of training.

Increases in intensity and duration, whether due to a heavy training period or a competition, ramp up production of cortisol, commonly known as the stress hormone. Cortisol along with other hormones released during excessive training suppress the immune system, increasing the risk of illness.




Most studies indicate that about 50% of these illnesses in athletes affect the respiratory tract, a tract that happens to be quite important for … respiration. The fluid loss associated with such infections also causes a temporary reduction in stroke volume and cardiac output. The resultant decrease in maximal oxygen uptake reduces endurance capacity. Not only is less oxygen making it to the muscles but some of these illnesses have also been shown to impair muscle enzyme activity and metabolic function.

Image Credit: StockSnap via Pixabay

These studies are great, but they’ve basically just confirmed what we all knew ourselves: cop a nasty cold or flu and you’ll be feeling rubbish and going slow. A fact uncovered by research that people seem less likely to accept on their own is that the decrease in performance related to these Upper Respiratory Tract Infections can last for up to 4 days after full recovery from the illness itself.

The outlook so far isn’t great and you’d be forgiven for thinking of giving training a miss for the next year or two, just in case… However, studies on load have found that there is an optimal level of training to maximise immune function and prevent illness, do nothing and you’re putting yourself at the same risk as someone driving themselves into the ground. An interesting find in the last few years is that athletes at the top of their sport often don’t experience the same number of infections as the weekend warrior would with the same load. Part of this may be the years of progressively increasing their training to get to that level. Another hypothesis is that simply to be that good you must be naturally good at handling heavy training load.





The relationship between training load and illness isn’t quite as straightforward as the above diagram may suggest. Psychological stressors within or external to an athlete’s sport (e.g. lack of sleep, keeping the wife/husband happy, missing the rent deadline for the 4th week in a row) also have a similar effect on cortisol to exercise, only this stress won’t give you any long-term physiological gains (if only). Another major contributor to illnesses in elite athletes is frequent and prolonged international travel, with travel across more than four time zones causing 2-3 times the risk of infection.

Image Credit: JeSHOOTS-com via Pixabay

With these studies in mind there’s a few easy ways to give yourself less chance of getting sick:

  • Avoid contact with sick people (No s***)
  • Wash hands before eating
  • Avoid sharing drink bottles/cups/cutlery/towels with others
  • Avoid excessive alcohol consumption as this impairs immune function
  • Carry a disinfectant soap with you during international travel
  • Avoid sudden dramatic changes (>10% difference) in training load
  • Reduce training load if there are high levels of psychological/exterior stress

Even if you’ve taken in all the information, planned your training out with a coach and think everything’s gone right there’s going to be times you’re straight up unlucky and get sick the week before your big event, that’s sport. It’s important to remember the physiological changes from a few days off are a lot smaller than those from a full-blown virus attacking an immune system that’s defeated from heavy training. There’s no point rushing straight back into hard efforts or a race in the few days after an illness as your cardiovascular system will still be stuck on struggle street. Rest up, ‘take your medicine’ and wait until the day after you feel like you’re ready to go again before getting back into it. You’ll likely find you’ve lost a lot less fitness than you’d expect, and your immune system will thank you later.

2018 U23 Road World Championships, Innsbruck, Austria. I’d come off a big race block in Belgium and received a last minute call-up to worlds. I then had to find a bike to hire the day before flying out as my current training bike wasn’t rideable with parts left in Belgium. This stress followed by a few long travel days meant I wound up sick in the week leading up to the race and was a long way off my best.

Further reading:



Funnily enough I did most of the research on this topic during back to back tours in New Zealand and the Herald Sun Tour. Sifting through the papers I decided it would definitely be a good idea to take an easy week after a big January. A few tantalising ride invitations from mates later and I ended up doing three five-hour rides, two in the rain, ending up crook as a dog by Sunday. I’ll be locking myself in the house the next few days to properly recover and be good to go come Melb-Warrnie this Saturday. Until then, I’ll keep reading the research papers so you can spend more time on the bike.

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