Bike New York water bottles


How important is being well hydrated – how significant can the effects of dehydration be on performance?

By Nicole Lund, MPH, RDN, Clinical Nutritionist

Making up much more than half our body, water plays a major role in regulating our temperature, helping with blood circulation, and assisting with many of our essential everyday bodily functions.  Not only is hydration essential to feeling good, but especially important when we engage in training and sports competition.  Daily water balance depends on the difference between water gained and water lost.  Apart from fever and illness, the primary way we lose water is through urine and sweat.  When physical activity creates heat in the body, increasing our core temperature, our body needs a way to transfer that heat and keep cool.  When we sweat, our body loses water and that water must be replaced to keep us feeling good. Dehydration, or losing more water than you have taken in, can decrease athletic performance with even as little as a 2% loss in body mass from water loss.  There is a lot of variation between people when it comes to just how much they sweat and factors like the environment, duration and intensity of the activity, your clothing, how often you train in the heat, and exercise economy can all play a role.


Research suggests dehydration affects the body in a few major ways: decreased cognitive function, mood changes, and risk of heat related illness (especially in warmer weather).  From a sports performance standpoint, there is strong evidence to show that dehydration impedes aerobic performance and may contribute to a decline in mental performance as well.  Dehydration also increases physical strain, giving you a higher perceived effort to perform the same physical activities. When we sweat, we also lose electrolytes. Electrolytes are essential minerals that are vital to many key functions of the body, including muscle contraction.  When the body is low on these minerals you may experience muscle cramps, muscle weakness, headaches, irregular heartbeat, and dizziness.  All of that is not good when you’re getting ready to compete!


So how do we manage this? There are 2 main ways to become dehydrated during physical activity. First, you start hydrated but sweat so much that you become dehydrated.  Secondly, and more commonly, you may begin training already under hydrated.  This is more likely to happen when training sessions are back to back, you do 2 a day training sessions, and in weight class sports where individuals may consciously dehydrate to compete.  When it comes to athletic performance, every inch of potential counts and hydration should be considered an essential component of any athletes training plan!


For more about staying hydrated and signs of dehydration, check out our fact sheet.

Want to speak with a sports health expert? As Bike New York’s official healthcare partner, NYU Langone has exclusive concierge service for our members.