Andrew Hamilton looks at optimum fueling strategies for a half marathon, and explains why one size doesn’t fit all MORE
Seven secrets of hydration
Drink your way to winning performances
If you want to perform at a high level, you need to drink. Water, that is. For each per cent of body weight lost due to dehydration, your performance slips by about two per cent, and a meagre two-per cent loss in weight can force your heart rate and body temperature to spiral upward, making strenuous exercise almost impossible to carry out.
If you’re going to be exercising for 20 minutes or less, dehydration is not usually a problem, but difficulties can arise during longer exertions. For example, copiously sweating athletes can flush about 1.5 Iitres of fluid per hour through their sweat glands, a total of three pounds per hour. If these heavily perspiring individuals weight 150 pounds, that’s a two-per cent loss in weight after just one hour, producing a four-per cent dip in performance if no fluid is taken on board. The downturn in performance would be smaller, about two per cent, after 30 minutes, but that’s still enough to make a difference to serious athletes who are interested in winning.
But what are the rules for fluid intake? How much do you really need and what should your drink be like? To make it easy for you, we’ve listed the seven rules of fluid intake during exercise below. If you follow these rules, you’ll keep your body water intact during exercise and perform at a much higher level.
RULE NO. 1: The rate of passage of water from your stomach into your small intestine depends on HOW MUCH fluid is actually in your stomach. If there’s lots of water there, fluid flow from stomach to intestine is like a springtime flood; if there’s little water, the movement resembles a lightly dripping tap. Therefore, to increase stomach-intestinal flow (and overall absorption of water) you need to deposit a fair amount of liquid in your stomach just before you begin your exercise. In fact, 10-12 ounces of fluid is a good start. This will feel uncomfortable at first, so practise funnelling this amount of beverage into your ‘tank’ several times before an actual competition.
RULE NO. 2: To sustain a rapid movement of fluid into your small intestine during your exertions, take three to four sips of beverage every 10 minutes if possible, or five to six swallows every 15 minutes.
RULE NO. 3: If you’re going to be exercising for less than 60 minutes, don’t worry about including carbohydrate in your drink; plain water is fine. For more prolonged efforts, however, you will want the carbohydrate.
RULE NO. 4: Years of research have suggested that the correct concentration of carbohydrate in your drink is about 5-7 per cent. Most commercial sports drinks fall within this range, and you can make your own 6-per cent drink by mixing five tablespoons of table sugar with each litre of water that you use. A bit of sodium boosts absorption; one-third teaspoon of salt per litre of water is about right. Although 5-7 per cent carbohydrate solutions seem to work best for most individuals, there is evidence that some endurance athletes can fare better with higher concentrations. In research carried out recently at Liverpool John Moores University, for example, cyclists who ingested a 15-per cent maltodextrin solution improved their endurance by 30 per cent compared to individuals who used a 5-percent glucose drink. The 15-per cent drink also drained from the stomach as quickly as the 5-per cent one, though many other studies have linked such concentrated drinks with a slowdown in water movement.
RULE NO. 5: A 6- per cent ‘simple sugar’ drink will empty from your stomach at about the same rate as a fancy, 6-per cent ‘glucose polymer’ beverage, so don’t fall for the idea that the latter can boost water absorption or enhance your performance more than the former, and don’t pay more for the glucose-polymer concoction.
RULE NO 6: Contrary to what you’ve heard, cold drinks aren’t absorbed into your body more quickly than warm ones. However, cold drinks are often more palatable than warm ones during exercise, so if coldness helps you to drink large quantities of fluid while you exert yourself, then keep your drinks cool.
RULE NO. 7: Swilling drinks during exercise does NOT increase your risk of digestive-system problems. In actuality, most gut disorders that arise during exercise are caused by dehydration, not from taking in fluid. Dehydration induces nausea and discomfort by reducing blood flow to the digestive system, so by all means keep drinking!
‘The Maintenance of Fluid Balance during Exercise’, International Journal of Sports Medicine, vol. 15(3), pp. 122-125, 1994, and ‘The Effect of Different Forms of Fluid Provision on Exercise Performance’, International Journal of Sports Medicine, vol. 14, p. 298, 1993)
Ergogenic aids: is it time for competitive athletes to scrap carnitine?
Carnitine (also called L-carnitine) is one of the most popular nutritional supplements used by athletes, and the idea that the chemical might boost performance is not an implausible one. Often mistakenly called a B-vitamin, carnitine is an important energy-producing compound which is naturally found inside muscle cells. Basically, carnitine latches on to fatty acids which have moved into muscle fibres and carries these fats into the mitochondria, which are tiny structures inside muscles in which fats and carbohydrates are broken down to provide energy. An increased dietary intake of carnitine might raise muscle-carnitine levels, leading to better transportation of fat into the mitochondria, greater energy production during exercise, and higher performances.
That all sounds reasonable enough, but there’s just one problem – scientific studies which demonstrate an actual ergogenic effect from carnitine are as scarce as hen’s teeth, and those that do portray a ‘warm and fuzzy’ role for carnitine are fraught with difficulties.
For example, a few years ago a team of Italian researchers found than when carnitine was given to a group of athletes before a rugged exercise test, the supplement boosted both maximal aerobic capacity(V02max) and muscle power. Unfortunately, other researchers subsequently showed that it takes at least 3.5 hours for blood-carnitine levels to rise appreciably after carnitine is ingested. Since exercise took place just one hour after carnitine ingestion in the Italian study, it seemed unlikely that carnitine was the cause of the heightened athletic prowess.
At Ball State University in the United States, carnitine was recently given a chance to redeem itself. Ten experienced collegiate swimmers routinely consumed a citrus drink which provided four grams of carnitine per day, while 10 other athletes imbibed a carnitine-free citrus drink. At the end of one week, members of each group warmed up by swimming 1000 yards (914 metres) at a moderate pace and then completed an interval workout consisting of five 100-yard (91m) intervals at close to top speed, with two minutes of rest between intervals.
The carnitine-laced citrus drink did a nice job of raising blood-carnitine levels, boosting their concentrations by about 40 per cent (the placebo group had no change in blood carnitine). Unfortunately, the surplus carnitine led to no increase in performance; average swimming speed during the intervals was about 1.56 metres per second, before AND after the carnitine supplementation. This was also the same swimming speed attained by the carnitine-free athletes.
Why didn’t the carnitine work? First, actual muscle-carnitine levels weren’t measured, so there was no assurance that at least some of the augmented blood carnitine had actually made its way into the muscles, where it might have made a real difference. In fact, although huge quantities of carnitine are sold to athletes each year, only one published study has shown that carnitine supplementation can actually lift muscle-carnitine concentrations.
Second, the athletes involved in the study were extremely well trained and therefore might already have reached their upper limits of performance. Since the athletes were already at a physiological peak, pushing more carnitine into their blood or muscles simply may not have made any difference (training by itself tends to raise muscle-carnitine concentrations; at the beginning of the study the swimmers’ blood-carnitine levels were already about 14 per cent higher than the average man in the street).
Finally, it’s possible that the Ball State study didn’t employ the kind of exercise which would show carnitine in its best light. The intensity of the swim intervals was about 120% V02max, a fiery level of exertion in which fat metabolism has no role to play at all. Since one of the supposed benefits of carnitine is enhanced fat burning, it’s not too surprising that the chemical didn’t win a blue ribbon at Ball State.
To summarise, it’s safe to say that carnitine probably doesn’t bolster performance during high-intensity exercise carried out by highly trained athletes; we’ll have to wait to see whether it can provide benefits during more moderate efforts. It’s also important to mention that carnitine should not be confused with creatine, another popular nutritional supplement which HAS been linked with improved performance during short-duration intense exercise.
‘The Effects of L-Carnitine Supplementation on Performance during Interval Swimming’: International Journal of Sports Medicine, vol. 15(4), pp. 181-185, 1994)