As we continue our Perform Better module, we need to consider the link between exercise, recovery, and the immune system. 

Imagine you've trained tirelessly for more than a decade. You've thought of everything and prepared endlessly to make sure you have the best chance of reaching your potential. Then on the plane to your event, you pick up a virus and get sick. Even an infection as simple as the common cold can disrupt your performance and end your dreams.

A fascinating paradox in human physiology is the concept of the J-shaped relationship between exercise training and health. The “J-shaped hypothesis” suggests that, in general, people who exercise regularly experience fewer illnesses and infections than those who do not. However, increasing the amount of exercise beyond moderate levels does not improve immunity further. Quite the opposite happens. When athletes train at volumes and intensities excessively higher than normal for extended periods, they experience a significant increase in illnesses. I'm sure you've experienced this on many occasions during periods of high-intensity and high-volume training.

Immunoglobulins, also known as antibodies, are proteins produced by white blood cells that identify specific pathogens. Research on soccer players suggests that exhaustive exercise may cause a temporary suppression of these antibodies. This immune suppression is temporary and may last from a few hours to a few days, depending on the volume and intensity of the exercise. In this situation, a lower immunoglobulin level presents an "open window", or an opportunity for viruses, bacteria or other microbes to gain access to the body. 

As an elite athlete you are under tremendous physical and mental stress. You're probably intuitively aware of the J-shaped relationship, even if you haven't read the research. So how can you prevent getting sick in periods of high training? The good news for you is that great advances are being made in our knowledge of how to keep athletes healthy during stressful training, intense competition, and while traveling. Here are some simple but effective suggestions:

1) Refuel. Your muscles and immune system are competing for nutrients after exercise, so make sure you're refuelling with proper carbohydrates and protein, especially after a really hard workout. 

2) Fruits and vegetables. Make sure you're eating a balanced diet, including lots of fruits and vegetables. 

3) Supplements. Eating foods that are high in nutrients is ideal, but supplements can help ensure you’re getting what you need to keep yourself healthy during training or periods of high stress. Many athletes take L-glutamine, an amino acid used by the body to repair muscle tissue, and to fuel white blood cells. Taking an antioxidant supplement containing vitamin C, vitamin E and beta-carotene is also suggested.

4) Hygiene. Wash your hands and avoid touching your eyes, especially during the first hour after exercising.

5) Sleep. Make sure to get extra rest and sleep after periods of really hard training or competitions.

Today's POWER-UP: Vitamin C to Improve Immune Health

How to treat the common cold, and specifically the use of vitamin C to do so, has been a source of controversy for decades. Dr. Robert M. Douglas and Dr. Harri Hemilä looked at studies of elite athletes and determined that in those participating in physically stressful events such as marathon running, cross-country skiing or physical training, vitamin C supplementation decreased the risk of infection by 50%.

They also noted that one study, which had a very large sample size, indicated that treatment of the common cold with 8 grams of vitamin C per day after the onset of symptoms had a beneficial effect on the symptoms experienced.

So, although I am sure there will be more research and debate on this topic, for now it appears that you should be taking some vitamin C regularly—and that you should increase the amount you take if you get a cold or participate in some serious physical activity.

Excellent food sources of vitamin C include broccoli, bell peppers, kale, cauliflower, strawberries, lemons, mustard and turnip greens, brussel sprouts, papaya, chard, cabbage, spinach, kiwi, snow peas, cantaloupe, oranges, grapefruit, limes, tomatoes, zucchini, raspberries, asparagus, celery, pineapple, lettuce, watermelon and fennel.