By Aaron Vaughan & Eliza Parker
With the hot weather upon us, every level of athlete should consider their hydration status and how it can affect their performance and recovery. As one sweats during exercise, both water and salts are lost, which can lead to a reduction in blood volume, an increase in the amount of work on the heart and a reduction in the efficiency at which nutrients and oxygen are delivered to the working muscles.
These increased stresses can lead to prolonged recovery time, exhaustion, cramping, and in severe cases dehydration and death. A few main factors should be taken into consideration when accounting for one’s hydration needs:
- Duration of exercise
The greater the intensity of the exercise, the greater the fluid loss. Simply put, intensity is the difficulty of or level at which exercise is performed. A faster run or a run including an incline would be considered of higher intensity. The body needs to use more energy to accomplish these activities, which result in an increase in core temperature.
Increased temperatures with enhanced humidity increases sweat rate and output. With increased environmental humidity, your body is less able to lose heat to the environment through sweating due to the amount of water that is already in the air. Therefore, the act of sweat evaporation is decreased, preventing cooling of the body. Clothing makes a difference on hot humid days. Sweat-wicking material is important, as it pulls sweat away from the skin promoting cooling.
Over time, the body can adapt and become fit to perform in certain stressful environmental conditions. This adaptation or acclimatization takes roughly 7-14 days. Once this happens you begin sweating earlier, sweat more and lose less electrolytes. This adaptation promotes cooling and allows for better performance and recovery.
Hydration is a key aspect of performance. If one does not take in sufficient fluids before, during and after exercise it can have a negative effect on the body. When you sweat, water and salts are pulled out of the blood. This results in a reduction in blood volume and an increase in osmolality (concentration of salts and electrolytes). This reduction in blood volume in turn causes the heart to work harder, increases blood pressure and decreases the efficiency at which oxygen and nutrients are transported to the body tissues, resulting in fatigue, lengthened recovery and increase risk of injury. In severe cases, dehydration can result in exhaustion, cramps, fainting and even death.
How much water do you need?
The National Academy of Sports Medicine recommends an intake of roughly 2/3 fluid ounces of water a day per pound of body weight. Determining water loss through exercise is tracked through pre- and post-exercise weight checks. It is recommended that 20-24 fl oz of water should be taken in for every pound lost during activity within 2 hours of activity (USATF Advisory). A 5 percent loss of body weight during exercise is a sign of serious dehydration.
Dark urine color can also suggest a dehydrated state. Medical intervention is needed if dehydration leads to an alteration in mental processes or gastrointestinal distress. It is important to focus on hydration prior to activity or competition to reach a state of adequate or slightly over-hydration. Hydration strategies should begin several days prior to an event.
Sports drinks – what’s the skinny?
Another component of hydration is electrolyte balance. Salt and electrolytes are needed for muscles contractions. The body operates at an ideal blood electrolyte concentration. Electrolyte concentrations change when fluid levels in the body change. Sports drinks and electrolyte tablets can be beneficial for endurance athletes. If only water is taken into account for fluid loss, electrolyte concentrations will decrease.
The ideal concentration of a sports drink is (per 8 fl oz.):
- 14 g carbohydrates
- 28 mg of potassium
- 100 mg of salt
It is more important to know when and how to use sports drinks. If taking part in endurance exercise lasting longer than 45 minutes to an hour an 8 – 12 fl oz sports drink will provide electrolyte and blood sugar to assist you in sustaining and recovering from performance. The more you sweat, the more replenishment you will require.
In summary, remember to hydrate. Consider your level of conditioning as well your environment stressors and supplement, and replenish appropriately.
Aaron Vaughan, MD, is the Director of Primary Care Sports with Mission Orthopedics and a non-operative physician with Asheville Orthopaedics Associates. Eliza Parker, MS, ATC, LAT, is a corrective exercise specialist and interactive metronome provider with Mission Sports Medicine.