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.

Request a Topic

Want to know the results of research on a particular topic of interest? Any questions about a supplement, food or intervention you’ve heard is the next big thing? Leave a question or a topic suggestion in the comments and I’ll sift through the papers for you.


Finnish Saunas to Finish First. Could passive heat acclimation build the freeway to form?

Saunas have been a hot health topic for decades now, with a bucket load of claimed benefits ranging from improving skin, sleep and general relaxation. Research on athletes shows that the adaptations from sweating are even sweeter for endurance performance than expected.


Image Credit: monika1607 via Pixabay


The most significant impact of saunas for athletes is the increased oxygen delivery to working muscles. There are two key components of blood most important for this job: red blood cells (RBCs) and blood plasma. You can think of a blood vessel from the heart to the muscles as a freeway from a city towards towns. In order to move more people (oxygen) you can either put more cars (RBCs) on the road or build more lanes (plasma) for the cars to move quickly along.


Image Credit: qimono via Pixabay


The sweating that occurs in a sauna results in substantial dehydration which ramps up the renin-angiotensin-aldosterone system in the kidneys. This causes reabsorption of sodium into the blood vessels which leads to an increase in blood plasma, more lanes on the freeway. Repeat sauna sections can increase plasma volume by around 10%.


Image Credit: Free-photos via Pixabay


Not only can saunas help aid in the transport of RBCs but they may also result in more RBCs being produced, more cars on the road. The increase in plasma results in hemodilution (aka thinner blood) which can lead to a natural secretion of erythropoietin (EPO) and higher RBC count. The higher blood volume leads to heart adaptations including a greater stroke volume and hence lower heart rate at a given power output for cyclists. More cars on the road and more lanes to move those cars means a lot of people can leave the city, a lot more oxygen is reaching the muscles. This is shown in athlete studies by increased VO2max, peak power outputs over given intervals and even time trial performance after passive heat acclimation.

Outside of the blood vessels, repeat exposure to passive heat stress also provides more widespread physiological benefits. Elevated body temperature increases expression of heat shock proteins (my second favourite kind of HSP) which can upregulate circulating factors, increasing cellular protection and triggering the release of human growth hormone. Anyone who has paid attention to professional cycling since the turn of the millennium understands a natural means of boosting EPO and growth hormone release is going to make more than just your arm strong.


Image Credit: Dale Frederick via Flickr


The most obvious benefit of heat acclimation is … acclimation to heat. Heat adaptation broadens the critical range at which an athlete’s core temperature can lie without affecting performance. Athletes also develop improved thermoregulatory responses including better circulation and higher sweat rate, aiding in cooling. Plus, there’s no doubting the psychological benefit of getting comfortable being bloody hot.

World University Championships, Philippines, 2016. Hot

Saunas seem a sure-fire way to boost your cardiovascular fitness, ability to deal with heat and your general health and well-being and there’s no strong evidence for any health risks for healthy adults.

Hot tips for best results:

  • A typical Finnish sauna is 80-90°C and 10-15% humidity.
  • Heat stimulus should ideally be at least 30min per session (this can be in multiple bouts).
  • Avoid drinking any water in the sauna or in between bouts, the dehydration is a key player in the benefits!
  • Ideally heat acclimation should take place as soon as possible after an exercise session.
  • Heat-acclimatised athletes will need to hydrate more after sauna sessions or training/races than regular athletes due to increased sweat response.
  • Only 6-7 exposures are required to produce physiological and performance benefits.
  • Heating sessions should not be undertaken by athletes who have acute injuries, oedema, vascular disease, wounds, or infections.


I’m currently writing this on the bus ride with the team from Palmerston North to Cambridge, NZ. EvoPro just finished our first race and it couldn’t have gone much better, getting teammate Luke Mudgway up for the win in his home town and myself in third. Read all about it on my facebook page. Next up is the 5-day New Zealand Cycle Classic starting tomorrow. I won’t be hitting the sauna in between stages but hopefully the adaptations from heat acclimation sessions back home before heading over the ditch will hang around and we can get some more results this week. Until then, I’ll keep reading the research papers so you can spend more time on the bike.



Request a Topic

Want to know the results of research on a particular topic of interest? Any questions about a supplement, food or intervention you’ve heard is the next big thing? Leave a question or a topic suggestion in the comments and I’ll sift through the papers for you.