This month's CompEat is taken from our book "Peak Performance: Training and Nutritional Strategies for Sport" by John A Hawley and Louise M Burke, to be published by Allen and Unwin, Sydney, in 1998.
You may have noticed dehydrated and heat-stressed athletes in the medical tents of marathons and triathlons receiving intravenous (IV) fluids for their medical problems. In the last year or two there has been a growing interest by athletes to use IV feedings as a recovery tool rather than a medical treatment. It has become trendy in tennis tournaments, stage cycle races and other multi-day sports events for athletes to request an IV to speed their recovery for the next day's performance. Athletes are even starting to walk into the medical tents of races like the Ironman triathlon and asking for an IV to boost their recovery.
Standard intravenous fluids provide saline (water and sodium) and sometimes a low concentration of glucose. In medical practice they are used to correct fluid, electrolyte and carbohydrate deficits in people who are unable to do this by eating and drinking. If someone is unconscious, asleep, or has a non-functioning gut (for example, has severe vomiting, diarrhea, or gastric shut-down), an IV drip provides an alternative and effective means of getting fluid and carbohydrate into the body. In rare medical cases, people may receive substantial nutrition via IV means. And the solution may contain also contain lipids, amino acids, vitamins, minerals and trace elements. The procedure is expensive, carries a high risk of infection, and may cause nutritional imbalances. Such nutrient-rich solutions generally have to be given via a large "central" vein rather than a peripheral arm vein, because the concentration may cause a small vein to collapse.
It might sound dramatic and "state of the art" for an athlete to receive intravenous fluids or intravenous nutrition after prolonged intensive exercise. Some athletes claim that it makes them feel better and recover more quickly. However most race medical directors say that it's nothing more than a placebo effect. They counter that the main benefits are the novelty and attention, and being forced to lie still for 1-2 hours after the event. Many won't provide the service to "well" athletes, particularly if it ties up resources for athletes with real medical problems arising from the race.
There is also the issue of fluid overload. Some athletes finish ultra-endurance events with low blood sodium levels, generally an effect of overhydration rather than dehydration. And in some cases the athlete appears to have a kidney malfunction, which stops excess fluid from being urinated out. It can be dangerous--even fatal--to pour liters of fluid into such athletes.
It's even possible that IV fluids aren't as good as low-technology drinking. A recent study (Riebe et al., 1997) addressed this question. Males were dehydrated by 4% of body mass by 2-4 hours of mild exercise in the heat, then rested for a couple of hours. During this recovery period they either received a 1900 ml IV infusion of dilute saline, drank 1900 ml of the saline, or received no fluid at all. Then it was back to exercise. The subjects rated the experience of exercise without fluid replacement as the hardest, and reported being very thirsty. Hardly surprising. But subjects reported feeling thirstier and having to work harder at the exercise following IV rehydration compared with oral rehydration. One explanation is that the sensation of drinking--having cool liquid pass from your mouth into your stomach--sends important signals to the brain about thirst. And this may impact on what you feel during subsequent exercise. So, it may not be enough top up plasma and other body fluids. Your whole body may need to join in the experience for the full benefit. Whether this conclusion holds true for athletes working at higher intensities, and whether it affects performance, need further investigation.
Here's the bottom line for someone who has just finished a marathon or ultra-distance triathlon without collapsing: forget about IV nutrition. You should have complete rest for up to a week afterwards, and that's plenty of time to eat, drink, and recharge your fluid and energy levels.
What about the athlete in the middle of Wimbledon or the Tour de
France? It is likely that this athlete has a lot on the line, is
severely fluid and fuel depleted from today's effort, and has a date
to do it all again the tomorrow. Some of the components of the secret
IV formulae reportedly used by pro cyclists are unstudied and of
dubious benefit. But there is still no proof that even the basic
ingredients of IV preparations are of special help in recovery.
Studies need to be undertaken to see if IV carbohydrate promotes
faster glycogen storage than dietary carbohydrate, or whether IV
fluids promote superior rehydration to post-event drinking. No doubt
there is a psychological edge from having an IV when recovery before
the next grueling day is in doubt. And there may also be a practical
edge. It is often hard to juggle the priority of eating and sleeping
during busy competition schedules. With an IV, the athlete can be
given a known amount of fluid and carbohydrate, and can recharge with
these while sleeping. The last word is that where IV recovery is
used, medical supervision and strict control over the conditions in
which it is given are essential.
Riebe D., Maresh C.M., Armstrong L.E. et al. (1997). Effects of oral and intravenous rehydration on ratings of perceived exertion and thirst. Medicine and Science in Sports and Exercise, 29, 117-124.