The Latest Olympic Science
by Pete Pfitzinger, M.S.
The Sydney Olympics have already started. In fact, for coaches and sports medicine doctors, the Olympics began last November, when the International Olympic Committee held a World Congress on Sport Science in Sydney. More than 1,200 delegates attended, with many of the most renowned sport scientists and sports medicine practitioners from around the world giving presentations.
You don’t have to be an Olympian to benefit from this research. Three presentations have special significance for competitive-minded recreational runners.
The real cost of running hot and dry
In a culture of carbo loading, it may surprise you to learn that lack of food energy isn’t your biggest problem during a distance race. According to Ed Coyle, Ph.D., in races from 5K through the half marathon, dehydration and overheating are bigger factors than glycogen depletion in limiting performance. For marathoners, glycogen depletion is equally critical.
Conventional wisdom has been that running performance suffers if you lose more than 2% of your body weight because of dehydration. Coyle says that any amount of dehydration will affect performance. Dehydration reduces blood volume, so less blood reaches your working muscles. Your heart beats faster because there’s less blood to pump. Overheating exacerbates the problem; to cool itself, your body sends blood to the skin. The result: even less blood is available for your working muscles. The competition between your muscles and your cooling mechanism for blood becomes greater as you become progressively more dehydrated.
Your best bet: Enter races fully hydrated and dressed properly to stay cool. Slow down at aid stations for fluid intake on warm days. If you wait until you feel the need to drink, it is likely that your performance will already have been compromised.
Running, stress and infection
You’ve probably figured out that running boosts your immune system, helping you resist colds and flu. But you’ve probably also learned–the hard way–that too much running or too many intense workouts can leave you open to infection. Bente Pedersen, Ph.D., of the University of Copenhagen, examined the literature in order to accurately measure the open window, the time after intense exercise when an athlete is at increased risk of infection.
Pedersen found that, for healthy, well-trained runners, the immune system is only suppressed following exercise lasting longer than one hour at an intensity greater than 80% of VO2 max (about marathon pace). It appears, therefore, that you’re at increased risk for infection after only very hard training runs or races of longer than an hour. For example, marathon runners were found to be six times more likely to have an upper respiratory tract infection during the week after a marathon. This open window typically lasts from 12 up to 72 hours. To protect yourself from infection, you should not do another race or long high-intensity training run until your immune function recovers.
Fortunately, training appears to strengthen our immune systems. So, though a single hard run may temporarily suppress your immunities, the overall effect of training is generally positive.
Pedersen also looked at the nutritional supplements that some researchers think may prevent immune suppression following high-intensity exercise. She found that, despite the claims of supplement vendors, five separate studies find no effect of the amino acid glutamine on immune function. There is no data yet on the role of prostaglandin inhibitors, although studies are underway. The results of studies on antioxidant supplementation are mixed, with some finding a benefit with vitamin C or vitamin E in preventing post-exercise infections, and others finding no effect.
The evidence is clearer concerning carbohydrate supplementation. Reduced blood-glucose levels lead to the release of stress hormones, which are known to alter immune function. By consuming carbs before, during and immediately after exercise, you can prevent your blood-sugar levels from dropping, which may prevent the dip in immune function and close the window.
What happens during a marathon
During a marathon, you get tired–that’s a given. But why? In a unique set of experiments, Paavo Komi, Ph.D., of the University of Jyvaskyla, Finland, had well-trained runners complete a marathon during which they ran over a force platform every 5K.
He saw that, as fatigue set in over the 26.2 miles, the runners had to deal with increased impact forces and had to do more work to maintain a given pace. It seems that as fatigue increases, runners’ muscles have less ability to tolerate impact forces. This reduces the ability to use the stretch-shortening cycle to bounce into the next step, so more work must be done in the push-off phase of the stride. These effects generally kick in after 20K to 25K.
Komi suggests (only partly tongue-in-cheek) that marathoners change shoes during the race as the stretch-shortening cycle sensitivity in their legs decreases. An easier strategy might be to select your marathon shoes for the second half when your legs have lost their spring. He also suggests taking about four days off from running after a marathon to let muscle function return to normal and prevent injury.