By The Numbers
Water is an essential component for all processes the body completes each day. While most of these processes occur without our awareness, without adequate water availability they would not occur, and in cold weather, not enough water increases certain problems.
The human body is made up of 70% water; most of the water is found in and around tissues like skin and within the tiny individual cells that make up our body parts like organs. We lose water on a daily basis in the following ways:
- 1/2L lost through normal breathing
- 1/2L lost through perspiration
- 1.5L lost through urine and bowel excretion
- >2L lost through exercise
The loss of water throughout the day is usually replenished when we get thirsty. During warmer weather we are very aware of water loss because of the sweating mechanism our body uses to keep cool. But what about during colder weather; do we still lose water? Do we sweat as much during colder weather exercise?
How Does It Work?
The kidneys regulate the amount of fluid loss through urine output and actual water lost through exhalation is negligible. Food items containing caffeine (tea, chocolate and soft drinks) can increase output since caffeine acts as a diuretic. When our bodies have enough water on board to facilitate all the transactions each day, any excess can be expended through urine output.
What if there isn’t enough water on board throughout the day?
Dehydration can occur when we don’t take in enough water to compensate for the water lost during routine processes or exercise. How does one know if they are dehydrated?
The thirst mechanism is usually a slow reaction to an event that has already taken place and therefore not a reliable indicator of hydration.
Urinary markers for dehydration include a reduced urine volume, a high urine specific gravity, a high urine osmolality, and a dark urine color. Specific gravity and osmolality are measurements taken in a clinical setting by a healthcare professional. However, the individual easily assesses volume and color.
Other symptoms of dehydration can include:
- Irritability, headache, fatigue
- Weakness, dizziness, nausea
- Having a dry or sticky mouth
Dehydration and Performance
Dehydration negatively affects competition, training and recovery during. Exercise heart rate increases, blood flow to the skin decreases which helps cool the body during exercise and the core body temperature can increase more than it should during exercise. Performance decreases with a loss of 1-2% of bodyweight. Figure 1 illustrates the relationship between performance and body water lost.
Cold Weather Hydration
Awareness, recognition and education are the ways to help prevent dehydration during cold weather training.
While proper clothing is essential during cold weather, some of the same technology that keeps us comfortable may inhibit the ability to appreciate sweat rate or water loss during exercise.
The goal is to replace 100% of sweat and electrolytes lost during exercise outdoors. The recommendations are 1/2L of fluid per kg of weight loss. Use a simple weigh-in/weigh-out procedure to determine the amount of kg’s lost. The American College of Sports Medicine (ACSM) recommends ingesting 125 ml (5 ounces) every 20 minutes of exercise.
Understand that we continue to lose fluids, even during cold weather exercise, and the importance of replacing those fluids in order to stay healthy and have a positive effect on performance.
Nutritional Considerations in Cold Weather
By The Numbers
Energy expenditure is 2X greater on wet or snow covered surfaces than on regular surfaces and the heavier clothing essential to cold weather training increases energy expenditure. Vasoconstriction, which is a reaction to cold temperatures, reduces blood flow to peripheries and thereby decreasing fat utilization. Glycogen usage increases in colder weather, resulting in fatigue.
How Does It Work?
Exercise rate at the beginning of a session can maintain body temperature, however a prolonged training session will deplete stored reserves of fuel in the form of glycogen. The resulting effect is fatigue and subsequently blood glucose and cold intolerance.
As the intensity of training decreases, muscular activity decreases, accompanied by a lower body temperature. In extreme cases, the end result is hypothermia or even death.
Cold Weather Nutrition
Maintaining cold weather nutrition presents unique challenges that must be overcome in order to stay healthy and continue training. In extreme climates, food and drinks can freeze, making them difficult to handle and ingest during a training session, not to mention palatability.
The nutrition should be high in carbohydrate content, easy to carry and access during a training session. Taking in a small meal prior to cold weather exercise is recommended; 1-4 gram of carbohydrate per kilogram of bodyweight usually 2-3 hours prior to session. This will help replenish stored fuel reserves (glycogen) in the liver. During the actual training session, 30-60 grams of carbohydrates per hour is recommended in order to replenish blood glucose.
Breakfast (30 to 45 grams of Total Carb)
Lunch (30-45 grams of Total Carb)
Dinner (30-45 grams of total carb)
Snack (15 grams of total carb)