The IOC recently published consensus documents addressing training load in sport and risk of injury (part 1) and illness (part 2), which summarises the findings from a group of experts following their evaluation of the scientific evidence on the relationship between load and health outcomes in sport. Considered in the appraisal was the impact on injury and illness risk of rapid changes in training and competition load, an over packed competition calendar, psychological load and travel. Practical guidelines were produced which are useful for both elite and recreational athletes alike.
This article is a brief summary of some of the findings from the consensus statements, with a focus on the nutritional elements of illness prevention highlighted from the practical guidelines.
Factors influencing the risk of injury and illness
Training volume and intensity is pushed to the limits in elite and developing athletes to elicit maximal adaptation in an attempt to improve performance. Evidence is mixed regarding injury risk and training loads in athletes, in that high loads can have either positive or negative influences on injury risk. However an imbalance between loading and recovery may lead to chronic fatigue and abnormal responses to training thus increasing the risk of both illness and injury.
The J shaped curve relationship between absolute training load and risk of illness is well established in recreational and sub elite athletes (i.e. both low and very high training loads being associated with higher risk of illness). However evidence suggests that increased illness risk with higher training loads may not be applicable to the elite level athlete perhaps due to inherent self-selection.
Changes in training load
Large and rapid week-by-week changes in training load may place an athlete at risk of injury. If the program allows athletes to reach high training loads in a gradual and regulated manner then hard training appears to offer protection against injuries due to development of robust physical qualities.
In terms of the relationship between risk of illness and changes in training load only a few studies have been conducted. These suggest that increases in training volume or intensity increased the risk of illness but it was not possible to quantify the amount of training load increase related to the risk of a specific illness in a given sport.
Competition, which is a high acute load, can place greater demands on the athlete than their usual training blocks. Injury rates across sports are typically found to be higher in competition compared to training. Calendar congestion – many events over a shorter period than usual can increase acute load and may increase injury risk.
Participation in single or multiple competitions is associated with increased risk of illness but data is too sparse to quantify the risk. Several studies have demonstrated an increased risk of illness during the precompetition and competition period.
Data from several Olympic games and international competitions across a variety of sports reveals that in shorter duration international games (<4 weeks) 6-17% of registered athletes are likely to experience an episode of illness. 50% of all acute illness in athletes during competition affects the respiratory tract.
Despite the sparse number of studies, it is recognised that frequent long distance air travel across several time zones leading to travel fatigue and jet lag can negatively influence performance and increase risk of illness. However no link has been found with injury risk.
In elite rugby union players competing in a 16-week tournament, travelling across more than 4 time zones was associated with 2-3 x increased risk of illness.
Several psychological factors may influence injury risk e.g. life event stressors, anxiety and type A behaviours. Other variables such as lack of sleep or severe psychosocial stress may impact immunity and also increase risk of illness.
Practical guidelines for preventing illness in athletes
Regular athlete monitoring is fundamental to assess the relationship between load and risk of injury and illness. A variety of methods can be used such as recording training load, mood profiles, RPE and psychological screening. Subjective load measures have been found to be particularly beneficial.
A well-executed illness prevention strategy can have a significant impact. For example an illness prevention program in the Norwegian Olympic Winter Games (OWG) reduced illness rate from 17.3% of athletes competing in Turin OWG to 5.1% of athletes in Vancouver OWG, which may have contributed to the improved performance and overall results.
Outlined below are some of the nutrition and hygiene strategies that are recommended from the IOC document to help prevent illness in athletes:
- Introduce personalised nutrition programs to avoid deficiencies of essential micronutrients
- Encourage athletes to consume carbohydrate during and after exercise and to consume both carbohydrate and protein after exercise
- Measure and monitor the vitamin D status of athletes and supplement if required
- Consider advising athletes to ingest a probiotic such as lactobacillus probiotics on a daily basis
- Consider advising athletes on the regular consumption of fruits and plants, polyphenol supplements (e.g. quercetin) or foodstuffs (non alcoholic beer and green tea) that may reduce risk of illness
- Consider zinc lozenges (> 75mg zinc/day; high zinc content) at the onset of upper respiratory symptoms as there is some evidence that the number of days with illness can be reduced
- Ensure an athletes schedule has adequate recovery, particularly after intensive training periods, competitions and travel, including nutrition and hydration, sleep and rest, active rest, relaxation strategies and emotional support
- Wash hands regularly and effectively with soap and water especially before meals and after direct contact with potentially contagious people, animals, blood, secretions, public places and bathrooms
- Carry insect repellent, antimicrobial foam/cream or alcohol based hand washing gel with them
- Do not share drinks bottles, cups, cutlery, towels etc. with other people
- Choose drinks from sealed bottles, avoid raw vegetables and under cooked meat, wash and peel fruit before eating, while competing or training abroad
- Avoid excessive drinking and binge drinking of alcohol as this impairs immune function for several hours, particularly after strenuous training or competition