Cold & Flu & Training

Exercising Sick – good or bad idea?
Winter is nearly upon us and the risk of getting colds, flus and infections starts to impact athletes training schedules.  I have therefore been prompted to do a little research on whether the advice I give my athletes is sound or not.  I’m happy to see that not only has my cautious approach got plenty of merit but there is increasing evidence that exercising when you have certain systemic illnesses is potentially harmful in the long term.

What type of illness?
In this article I am referring to common winter ailments such as colds and flus with symptoms such as runny nose, sore throat, fever, aching muscles, headaches & coughs.

Obviously these ailments have varying degrees of discomfort and how we treat each of them is dependent on their severity.  A simple cold without systemic symptoms is a far cry from a full blown flu presenting itself as fever and aching bones.

What to do when you get sick?
Now if you are reading this and you are a weekend warrior who only rides once or twice a week you may be thinking, “What is he on about?  I just wouldn’t go out riding, simple”.  Well, for those a little more serious about their sport or training harder than ever before for a major goal in the near future, the thought of having a day or two off or missing a “key session” is unthinkable.  How will they possibly achieve their goals if they miss training sessions?

Here are my general Rules of Thumb:

  • If you think that you have a simple cold without systemic symptoms (above neck), exercise at a low heart rate and easy level of perceived exertion (long-slow-distance pace or easier) for a short period of time. If you are any sicker than a stuffy-nose-sick, you should skip the ride altogether.  If the sickness is just in your head, then a gentle spin will release those endorphins you are used to and may actually make you feel a bit better temporarily.  If this easy spin makes you worse over the next 24hrs, have complete time off for a few days before resuming gentle exercise.
  • If you have a fever, lower respiratory tract infection or muscle aches and/or chills then don’t exercise at all.  This includes anything in the lungs (cough, chest tightness).  Hang the bike up for 3 days minimum and don’t get out again until feeling 95%.
  • Do not ignore symptoms that could be attributable to the heart, including shortness of breath, irregular heartbeat, fainting, chest pain or light headedness. See a doctor immediately if you have any question about the health of your heart.

Resuming Training

  • Take your time.  If you just have a head-cold, ride easy for 3 days, nothing long and then if feeling 95% it may be OK to try a light tempo session.  Nothing above threshold.  Extend that 3 days for as long as it takes to feel at least 95%.
  • If you have anything worse than a head cold, complete the above suggestion first, and then proceed gradually.
  • Lower your pre-sickness fitness / performance expectations for 10-14 days.  Rushing back into it can very easily lead to a relapse as having the cold / flu can weaken your immune system.

Risks of ignoring my advice

  • Prolonged sickness.  Without giving the body the energy it needs to ward off infection, a simple cold can linger for weeks.  Better to eradicate it in 3-5 days and then continue as normal than to keep training at 70% for 2-3 weeks.
  • Post viral syndrome.  In some cases this can lead to chronic fatigue like symptoms which in severe cases can last 2-3 years.  There are plenty of documented cases of this occurring when athletes exercise intensely whilst sick.  Scared yet?
  • Myocarditis is an inflammation of the heart muscle.  This is one of the more common and most serious side effects of an acute infection, often accompanied by a fever.  Vigorous exercise during acute sickness worsens this affliction, resulting in increased viral spread in the heart muscle and can result in more inflammation and destruction of heart muscle.  Long term consequences can include scarring of the heart muscle which can in turn cause arrhythmias.  That made you think eh?


  • Sweating it out will be good for me.  In the case of a mild head cold, the endorphins released during exercise may well make you feel better, briefly relieving symptoms but if you are not careful to hydrate more than usual you may make matters worse.  If you have a fever, then your core temperature is already high and with exercise raising it further it can actually be dangerous.  The risk of dehydration is high.

While moderate exercise is good for our general health and well-being, vigorous training routines can actually have a negative effect on immune function, elevate stress hormones and increase cortisol production.  Unfortunately, these very same stressors are necessary to cause the body to adapt and become fitter.  It’s the key to improvement in every competitive athlete.

This is why I advocate a gradual progression in all aspects of training with every athlete I coach and never is this more important than when recovering from a cold / flu.  Rest, then take it back a step from where you were pre-illness, and gradually build back into it over the next 10-14 days based on a day to day analysis of how you feel.

Caution is best.