Wednesday, February 27, 2013

Is running really good for your health? (An immunologist's perspective)

There seems to be a general acceptance in the running community that we will spend a certain amount of time suffering with injuries, and this is particularly true of marathoners pushing themselves through week after week of high mileage and intensive training. There are a number of things that can be done to minimise injury risk, including the use of adequate rest and nutrition strategies, general strengthening work and physiotherapy/soft tissue treatment. However, many runners will still find themselves injured at some point in the season. Or at the very least, resorting to cross-training for a few days in order to prevent a minor 'niggle' from progressing into a full-blown injury. This has often led to conversations between myself and fellow athletes in which we jokingly wonder why we put our bodies through all of the trauma, which is a question that my knees in particular would like to know the answer to as they seem to have born the brunt of most of my marathon training cycles!

Setting the issue of injuries aside, the general opinion of running and other forms of exercise is in terms of a positive impact on health. This is a logical viewpoint to take, as are the recommendations that organisations such as the NHS and CDC give for regular physical activity in order to improve general health and well-being. The picture changes somewhat if we move from considering a moderate level of exercise undertaken with the aim of staying fit and healthy, and into the world of elite endurance athletes pushing their bodies to the limit in pursuit of their perfect performances. My own experiences in the athletics world have caused me to associate high training volumes with an increased incidence of illness, and I personally seem particularly sensitive to developing a sore throat as I approach the end of a hard training block, or even after a tough race (particularly in cold weather). I am not alone in having developed this perception of the side-effects of intense training, and several reviews of the subject (including the 2011 Exercise Immunology Review Position Statement1) note that athletes and coaches generally believe that there is an increase in upper respiratory tract infections (URTI) associated with intensive exercise.

Having spent several years studying for a PhD in the field of immunology, I could come up with a reasonably educated guess about some of the potential immunological explanations for a link between hard training and increased vulnerability to infections. However, I have also occasionally wondered how many of my own symptoms were really signs of infection, and to what degree they  were due to running-related allergy and other inflammatory effects. Recently, after finally taking the plunge and beginning to carry out some research on a subject with which I should probably already be much more familiar, it was comforting to discover that even among experts there is a degree of uncertainty about the level of URTI in athletes versus non-infection-related Upper Respiratory Symptoms (URS). A large part of this uncertainty is due to a lack of investigation into the causes of symptoms reported by athletes, of which sore throats are the most common1. There is a greater amount of published scientific literature concerning the more general effects that endurance training has on the functioning of the immune system, which is likely to have an impact on susceptibility to disease. So much literature, in fact, that these effects will have to be the subject of future blog posts.

Regardless of whether the URS experienced by athletes are caused by infection or other inflammatory stimuli, evidence from several studies does indicate that symptoms are more prevalent in endurance athletes during high intensity training or competition2. Further research needs to be carried out to determine the level of any impact that URS have on an athlete's performance in training and racing, in order to gain a better understanding of any potential negative consequences from this side-effect of extended intensive training.

You'll be pleased to know that there's no need to hang up your trainers just yet, well not for your immune system's sake anyway. In addition to the well-publicised general health benefits of regular, moderate, exercise, there is  also evidence of a positive impact on the immune system and possible reduction in URTIs (more on this in future posts). These findings have led to  the hypothesis of a J-shaped relationship between exercise and upper respiratory infection3:

As with so many of my favourite things in life, it seems that moderation is also the key to getting the maximal health benefits from exercise. I don't think I'll be letting that stop me from running a few more marathons in the future though (or occasionally having that extra glass of red wine and piece of dark chocolate)!

1 Walsh, N et al. Position Statement Part one: Immune function and exercise. Exercise Immunology Review 17: 6-63, 2011.
2 Shephard, R Overview of the epidemiology of exercise immunology. Immunology and Cell Biology 78: 485-495, 2000.
3 Nieman, D Exercise, infection, and immunity. International Journal of Sports Medicine. 15: S131-141, 1994.

No comments:

Post a Comment