The Role of Dehydration in Sport Performance

Physical therapist becomes board certified

By Dr. Chad M. Pens

As the start of the fall sport season begins and athletes young and old are in the midst of their preseason training, I thought it pertinent to discuss the role of hydration in athletic performance. Exertional heat stroke (EHS) is a condition whereby an individual’s body loses the ability to dissipate heat when exercising in extreme heat situations, and it is extremely dangerous. Keeping the body well hydrated can help prevent EHS from occurring, and can relatively enhance performance in one’s given sport.

There is an increasing body of evidence growing regarding the effect of hydration on thermoregulation, which is the body’s ability to maintain a safe temperature. The latest evidence comes from one of my mentors when I studied sports medicine at the University of Connecticut. Douglas Casa, PhD is an associate professor at UConn in the Department of Kinesiology, and he is a nationally renowned expert in the field of exertional heat stroke. His research findings are significant because it refutes some fairly recent field studies that suggesting that hydration is of minimal importance. Casa’s study was published in the May issue of Medicine and Science and Sports and Exercise, the official journal of the American College of Sports Medicine.

Casa’s most recent study involved running at “all-out speed” and at submaximal intensity in 85-degree heat, with and without fluid replacement. Each subject ingested an adjustable thermistor, a large pill with a sensor inside, that allowed researchers to measure core body temperature throughout these tests.

The athletes exercising at sub-maximal intensity in a dehydrated state measured a body temperature of 102.5, which is a full degree Fahrenheit higher than the group that was well hydrated. Likewise, the dehydrated athletes average heart rate was 15 beats per minute higher, and required greater time for the heart to return to resting levels. Casa stated, “Your heart works much harder when it is working closer to its maximum. It therefore does not leave much room for error when performing at a higher level at the end of a race or a game.”

The hydrated group exercising at an “all-out” pace recorded lower core body temperatures, despite running harder. “Being properly hydrated allowed them to run faster and stay safer,” stated Casa. Hopefully, this information will help change attitudes of athletes and coaches alike to be more pro-active when it comes to hydration. For example, encouraging athletes to hydrate well at home and during the day, as well as providing adequate breaks during practices and games will facilitate opportunities for athletes to stay well hydrated.

Practices such as weighing in pre and post practice, especially on days where temperatures are in the 80’s and high humidity, are recommended. A loss of a pound during an exertional bout equates to a re-hydration demand of one pint of fluids. The re-hydration saying states “a pint a pound, the world around.”

It is also a fact that once an individual experiences a sense of being thirsty, he or she is already in a state of dehydration. Therefore, it is important to drink often. Making it a habit of carrying around a water bottle throughout the day will help keep the athlete well hydrated.

Particularly for athletes, I encourage the use of commercial drinks that are fortified with electrolytes given that when we sweat these electrolytes are lost through the skin. Most people are familiar with the fact that sweat is salty. Therefore, if we lose these electrolytes through the skin via sweating, it is essential that they are replenished. Sodium, chloride and potassium are the essential electrolytes for proper muscle physiology. When muscle is forced to exercise when these are deficient, muscles are prone to cramping.

So as athletes return to the playing fields this fall season, they should make it a point to be well hydrated at all times to optimize their overall performance. Coaches should provide frequent water breaks and encourage good hydration throughout the athlete’s day. By staying well hydrated, athletes will be able to perform at their best and recover faster, leading to satisfaction on the part of both the athlete and coach with the overall performance of the individual and team.