Hydration and Electrolytes
One of the major underlying factors of premature fatigue during exercise is excessive dehydration.
For every liter of fluid lost during prolonged exercise, body temperature rises by 0.3°C, heart rate elevates by about eight beats per minute, and cardiac output (the volume of blood pumped by the heart per minute) declines by 1 liter/min.
These cardiovascular changes can not only significantly impair your athletic performance, but can also lead to death.
The factors that influence dehydration are exercise intensity, environment, clothing and equipment, genetics, fitness and acclimatization.
Athletes who exercise very intensely in humid environments, wearing heavy clothing and equipment, and have overactive sweat glands, while being less fit or acclimatized (accustomed) to exercise in the heat, are most prone to dehydration.
Sports drinks were formulated to help prevent dehydration in athletes in conditions like these, and reduce the strains on their hearts and cardiac systems. These drinks replace the fluids and electrolytes that are normally lost through sweat and urine, so that athletic performance can be maintained.
Early scientific investigations showed that substantial quantities of sodium, chloride, and to a lesser extent, potassium (collectively known as electrolytes) are lost in sweat during prolonged exercise, especially exercise in the heat.
However, evidence of a beneficial effect of electrolyte replacement during exercise exists for only a small handful of endurance athletes – specifically those that compete in intense, humid, long-duration events.
It was later found that electrolytes in blood plasma often increase during exercise without fluid replacement (Costill et al., 1970, 1974, 1976, 1981) which indicates that electrolyte replacement is not always necessary.
Furthermore, during repeated exposures to prolonged physical exertion, our kidneys are very effective at conserving sodium and potassium so that body electrolyte balance is usually maintained when an athlete consumes a normal diet, or a diet low in potassium (Costill et al., 1976), or even a diet high or low in sodium (Armstrong et al., 1985).
Instances of endurance athletes experiencing dangerous low blood sodium concentrations (known as hyponatremia) during exercise usually occurs when they ingest large quantities of water, which dilutes their normal blood sodium concentrations and leaves them in a deadly condition.
For most people, normal amounts of plain water is adequate enough to maintain hydration during many athletic events because sweat is mostly composed of water, compared to the losses of electrolytes.
Therefore, replacing water during exercise is far more important than replacing sodium, potassium or other electrolytes – but make sure don’t overdo it. As you learned above, if you take in too much water, then you risk becoming hyponatremic.
Replacing fluids during resistance exercise (i.e., weight lifting) is also important too.
In 2008, University of Connecticut researchers showed that as resistance-trained men were dehydrated at 2.5% and 5% of their body weight before engaging in weight-lifting exercise, their testosterone response to exercise was diminished, and they had increased concentrations of cortisol and norepinephrine (the stress hormones) (Judelson DA et al, 2008).
This study suggests that being adequately hydrated before and during weight lifting is very important for a proper hormonal and metabolic response to resistance exercise – in other words, if you are dehydrated before and during a weight lifting session, you won’t able to build muscle and burn fat like you would if you were properly hydrated.
So, for the benefit of your heart, your muscles, and your athletic performance, staying hydrated with adequate ( but not excessive) water is the key to a healthy body and effective exercise success.
Dehydration, Cramping and ElectrolytesAnother reason sports drinks are so popular is that people feel that they need them to prevent muscle cramping during exercise (and if you’ve ever had a muscle cramp when you were lifting or running, you know it’s not pleasant).
Some athletes experience extreme, painful, muscle cramps while exercising intensely and they think it’s associated with low electrolyte status and/or dehydration.
However, a recent 2010 study argues that electrolyte imbalances have little to nothing to do with cramping.
Researchers from Cape Town, South Africa looked at risk factors associated with exercise-associated muscle cramping in 209 Ironman triathletes before and after a race, and tried to detect any differences between the 43 who developed muscle cramps and the 166 who didn’t (Schwellnus MP et al, 2010).
The major finding was that there was no significant difference in the levels of dehydration or electrolyte loss between the two groups, challenging the prevailing electrolyte-depletion hypothesis of cramps.
The cramping group lost 2.8% body mass compared to 3.1% in the non-crampers; cramper’s sodium levels dropped 0.1% (+/- 1.9%), while the non-crampers increased 0.4% (+/- 2.6%).
Researchers found that the three factors that predicted cramping were:
1. faster predicted race time
2. faster actual race time
3. previous history of cramping
Since training volumes and paces for the final week before the race were more or less identical in the two groups, it means that in this group of athletes, failing to taper exercise volume before the race was not to blame, like some people also suspect.
Overall, cramping during an event seems to be one of the many unavoidable risks associated with getting as close as possible to your limits, especially if you happen to have a history of cramping.
Dehydration and Performance
According to the American Academy of Sports Medicine - one of the leading authorities on sports nutrition, health and performance - if you lose more than 2% of your body weight, presumably due to water losses from sweat and urine, dehydration will impair your performance.
But it turns out that there is some debate about this claim.
Another scientific investigation by South African researchers published Dec 2010 (Zouhal H et al, 2010) looked at 643 runners at the Mont Saint-Michel Marathon and weighed them before and after a race. They found that the fastest finishers lost the most weight, with those under 3:00 hours averaging 3.1% weight loss, compared to 2.5% for 3:00-4:00 hours and 1.8% for greater than 4:00 hours.
Results showed that there was a significant linear relationship (P<0.001) between the degree of weight loss and race finishing times.
Thus, body weight loss greater than 2% during a race may not always confer decreased performance or dehydration.
This may be explained in part by two observations:
1) A genetic ability to withstand dehydration. A genetic variant of a gene called AQP-1 has recently been associated with superior endurance performance, and this gene variant was linked to a type of protein that transports water across cellular membranes. People with this gene variant are able to tolerate higher levels of dehydration while sustaining greater athletic performances (Rivera MA et al, 2011).
2) Body weight loss during exercise does not always equate to water loss. In a recent investigation, soldiers who marched for 14.6 km drank 0.85 liters of water per hour, but sweated 1.289 liters per hour. In other words, they technically should have lost fluid. However, results showed that their total body water (the marker of hydration status) did not change at all (in fact, it increased by 0.53%), meaning that using body weight losses to estimate dehydration is not entirely accurate and does not mean decreased performance (Nolte HW et al, 2010).
Carbohydrates, Glycogen and Blood GlucoseOne of the major ingredients of sports drinks is carbohydrate (a.k.a., pure sugar, or high fructose corn syrup) because it was thought that another reason for decreased athletic ability was due to depleted muscle carbohydrate content…and this is partly true.
As you exercise, whether it be endurance or strength events, you deplete carbohydrate stores from your muscle (known as glycogen) and this often leads to decreased ability to exercise at the same intensity. At the same time, blood glucose levels may drop, leaving you yearning for energy.
However, these effects often do not set in until at least 60 minutes of consistent and challenging exercise.
If you happen to have blood sugar or muscle glycogen drops during exercise of a shorter duration than 60 minutes, it could be because you started out with low blood sugars or muscle glycogen to begin with, or because you ate a carbohydrate food before exercise that caused your blood sugars to fall from an over-sensitive insulin response.
For people training for more than an hour, such as a marathon or resistance training for several hours, you probably do need to ingest some carbohydrates during the session to maintain your performance (adding protein is also very beneficial too as researchers have shown that carbs + protein can benefit exercise performance even more than carbs alone (Valentine RJ et al, 2008)).
For exercisers training for about ½ hour to 1 hour at a time (if you exercise less than this, you definitely don’t need anything during your exercise session), research experts have had conflicting recommendations of what you should consume during exercise.
Some say you need carbohydrate (and protein) during this time, whereas others say it’s not needed. Some of it is personal preference and goals, while recent research may offer more insight:
A study by researchers from Loughborough University in Britain (Rollo I and Williams C, 2010) showed that carbohydrate and/or protein during exercise shorter than one hour in duration is only required under certain conditions.
In their study 10 trained runners did two running trials in which they ran as far as they could in one hour. In both cases, the runners ate a high-carbohydrate breakfast three hours before the run. Before and during the run, they drank either a sports drink containing 6.4% carbohydrates or a placebo (colored water).
The results: there was no difference whatsoever in their performance, blood glucose, lactate, respiration, carbohydrate burning, perceived exertion, or anything else they measured.
Previously, these same researchers showed that if athletes running for one hour were fasted (not eaten for more than 6 hours) before a run, the ones who drank a sports drink before and during exercise significantly outperformed the runners who only drank a placebo drink (Rollo I and Williams C, 2009).
This means that you really only need supplemental nutrition during a one-hour (or less) endurance/cardio exercise bout if you haven’t topped up your body energy supplies beforehand either from a overnight fast, or from not eating several hours before you begin exercising.
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