| Copyright (c) 2009 Neal Spruce | | | | and profuse sweating, we also lose electrolytes that |
| Experienced athletes generally have no trouble | | | | are involved in muscle and nerve function. Also with |
| properly hydrating while exercising or training. Most | | | | prolonged exercise, there is a significant decrease in |
| athletes are aware of the role hydration plays in their | | | | muscle and liver glycogen, the body's main energy |
| performance and will take all measures to insure | | | | sources. Replacing fluid, electrolytes and glucose is the |
| proper hydration before, during and after activity, | | | | formula for performance success, especially in longer |
| including acclimating to the environment in which they | | | | duration exercise (more than 60 minutes) in hot |
| will be competing. | | | | environments. |
| Heat acclimatization | | | | Children and older exercisers/athletes |
| It is well-known that exercising in a hot environment | | | | In young children, adolescents and in older (40+) |
| accelerates muscle fatigue, challenging the body to | | | | athletes, we find natural hydration mechanisms (thirst |
| regulate its core temperature and dissipate heat. As | | | | triggers, taste) and heat dissipation functions (skin blood |
| the core temperature rises, a change in muscle | | | | flow and sweat rates) are underdeveloped or |
| metabolism takes place (e.g. increase in lactate and | | | | diminished, making proper hydration strategies a bigger |
| free radical production, accelerated glycogen usage, | | | | concern. In these populations cognitive monitoring is |
| etc.). An acute episode of hyperthermia starts off | | | | generally required. |
| relatively mildly with symptoms like headache and | | | | The other side of the equation starts with "a little bit of |
| nausea. If activity continues and hydration and | | | | knowledge can be dangerous" |
| temperature regulation are not addressed, symptoms | | | | This is never more true than in the world of nutrition, |
| can progress to cramps, heat exhaustion (with | | | | and hydration is no exception. In recent years there |
| dizziness, profuse sweating and weak/rapid pulse), and | | | | has been so much attention focused on "water" intake |
| ultimately heat stroke which is very serious and can | | | | (especially with the increased marketing efforts from |
| cause a loss of consciousness or even in extreme | | | | makers of bottled water). The average, lightly active |
| instances death. In fact, among US high school athletes, | | | | person has no trouble replacing the approximate loss |
| heat illness is the third leading cause of death. It doesn't | | | | of two to three liters of fluids used daily, and it's often |
| help that many distance running races, triathlons and | | | | done without drinking one glass of pure water. In spite |
| football games occur in warmer times of the year. | | | | of this, the average person is exposed to a |
| When exercising intensely for prolonged periods and | | | | considerable amount of information/advertising that |
| or in hot, humid conditions, keeping a watchful eye on | | | | tells them they require considerably more. |
| hydration is crucial for optimal performance and health. | | | | Too much of anything can be bad for you |
| Steps in preventing dehydration or heat stroke include: | | | | Yes, this includes water. Though it may be the soup of |
| - Adequate fluid intake before and throughout practice | | | | life, water can actually be toxic if ingested in excessive |
| or competition | | | | amounts. When this occurs it is usually based on bad |
| - Monitoring of heart rate (any significant change in HR | | | | or incomplete advice. Inexperienced runners, including |
| to constant activity shows a poor response to the | | | | charity race participants, often function under the |
| demands of that activity) | | | | outdated notion that you can't get too much water. |
| - Monitoring of weight, replacing weight losses with fluid. | | | | Many participants are not competitive athletes and |
| Remember, a pint weighs a pound | | | | their pace/level of effort is not extreme; water losses |
| Fortunately, continued exposure to training in warm | | | | are not that great. Still, in their mind is the knowledge |
| environments leads to adaptations that make it easier | | | | that endurance athletes need to keep up on fluid intake |
| to perform in the heat. These adaptations include an | | | | during events. Hyponatremia occurs when blood |
| increased capacity to sweat, reduced salt losses in | | | | sodium concentration falls to an abnormally low level |
| sweat and a lower body temperature and heart rate | | | | prompting a rapid swelling of the brain that can result in |
| response during activity. The best part is that these | | | | seizures, coma and death. The key risk factor is |
| adaptations can take place in a little as 7-14 days. | | | | excessive drinking—especially non-electrolyte |
| The primary mechanism for the body's heat loss at | | | | fluids such as many types of water. |
| high levels of work in a normal environment, and at all | | | | First reported in 1985, this disorder was considered be |
| levels of work in a hot environment, is the evaporation | | | | a rare phenomenon but has become more common |
| of sweat which releases heat from the body. Sweat | | | | since the early 1990s. A post-race study done after |
| rates increase linearly with increased exercise intensity, | | | | the 2002 Boston Marathon found that 13 percent of |
| and in hot weather sweat losses can reach close to | | | | the participants experienced hyponatremia and point |
| 3.0 liters/hr. | | | | six percent had critical hyponatremia, a potentially |
| Fluids and performance | | | | deadly issue. Basically these people had gained weight |
| If you are not properly hydrated, you do not have the | | | | from excess water consumption going into the start of |
| potential to perform your best, even if exercise is only | | | | the event and continued to gain as they drank during |
| a few minutes long. The greater the duration of the | | | | the race, partially because their relatively long race |
| task, the greater decrease one will experience in | | | | times gave them enough time to ingest more fluids |
| performance with inadequate hydration. Many athletes | | | | than they lost. |
| and exercisers mistakenly think that their thirst will | | | | The risk of hyponatremia can be reduced by making |
| guide them to ideal hydration. Thirst typically occurs | | | | certain that fluid intake does not exceed sweat loss |
| when the one's water deficit is approximately two | | | | and by ingesting sodium-containing beverages or foods |
| percent of body mass. Performance begins to be | | | | to help replace the sodium lost in sweat. |
| impaired with a fluid loss of as little as 1%, suggesting | | | | For most athletes, dehydration is still the primary |
| our natural thirst mechanisms cannot keep up with | | | | obstacle to optimizing performance, not hyponatremia. |
| exercise-induced fluid losses. In other words, by the | | | | But the message regarding this increasing problem is |
| time we register we are thirsty, performance may be | | | | for the zealous, less experienced exercisers or |
| in decline. | | | | competitors: Make sure you start off with the |
| How can performance be affected by such small fluid | | | | accurate hydration recommendations. |
| deficits? It may be due in part to the decrease in | | | | Follow the proper hydration guidelines for before, during |
| plasma volume (any decrease in fluids will automatically | | | | and after training, including weighing yourself after the |
| decrease blood/plasma levels), impairing the delivery of | | | | workout/event, and make adjustments as necessary. |
| oxygen and nutrients in and out of muscles. Along with | | | | Additionally, weigh each morning. A stable weight |
| the loss of fluids, especially during prolonged exercise | | | | generally indicates proper fluid balance. |
