We often focus on hydration when training in warm, humid conditions due to increased thirst, sweat and electrolyte losses. It’s often recommended to drink 16-24 ounces of fluid per hour containing electrolytes when training longer than an hour, but is this also needed when training in colder, drier air?
Using Thirst As Your Guide?
Unless you are measuring your sweat rate or using a latest technology to determine how much you sweat, you are primarily relying on your thirst sensation as your guide to hydration during longer training sessions in the winter. Unfortunately, using thirst to determine how much to drink is not reliable in cold climates. Cold weather actually reduces your thirst sensations by up to 40% at rest and during moderate-intensity exercise. This is caused by blood vessel constriction, leading to increased central blood volume and stimulation of central blood receptors, making you think you are well-hydrated.
Increased Sweat Losses
Contrary to what you may think, you lose a significant amount of sweat in cold weather when training longer than 60 minutes. Wearing extra layers and increasing metabolic rates to keep you warm outside contribute to higher sweat rates to help regulate your core body temperature.
You may not think you are sweating as much as if you were training in hot, humid conditions, but sweat evaporates more quickly in cold temps. You may not see the sweat and think you don’t need fluids, contributing to dehydration. In addition, breathing in cold air causes you to lose more water through respiration. When we can see our breath on a cold day, that is actually water vapor.
Urine Production Changes
Training in the cold can increase urine production, making us think we are well-hydrated. This is caused by blood volume being redistributed from our extremities to our core to keep us warm and protected. Normally, when we sweat a lot, antidiuretic hormone AVP signals the body to slow down urine production to conserve water losses. But in cold weather, the body decreases blood flow to our extremities to decrease heat loss. The brain does not detect blood volume decreases, therefore AVP will not increase, causing increased urination and leading to further dehydration.
Hydration Tips When Training in Cold Temperatures (longer than 60 minutes)
Start out well-hydrated: consider drinking 16 oz fluid 2 hours before and 8 oz 30 minutes before a long run.
Pre-hydrate with an electrolyte beverage before exercise.
Have a hydration plan: take small sips (2-3) every mile during long training sessions even when not thirsty.
Take electrolytes on your runs: suggest using products with 200-400 mg sodium per hour.
Drink warm fluids: start runs with warmer liquids to help regulate body temps (this will also help prevent fluids from freezing).
Limit alcohol: alcohol is dehydrating, so avoid it the night before long training sessions.
Monitor your urine: pale yellow urine indicates being well-hydrated. If it’s darker than pale yellow after long runs, drink more fluids.
Enjoy the outdoors safely during the winter, but have a hydration plan when training longer than an hour to prevent dehydration and to be able to perform your best!