Not all running events are the same. The duration of events vary from less than 10 seconds to numerous hours, and runners may have to compete more than once a day, with warm up and cool down time in between. The physique of runners changes from the highly muscular sprinters, through to the lean and low muscled distance runners, ensuring a wide variation in sweat losses. The preparation required to compete in these different events also varies considerably. Acknowledging all of these factors, this information will provide some strategies for each type of event which will help in reducing the risk of dehydration. As with all sports, the onus remains on the athlete to assess their own fluid requirements and trial different strategies in order to determine the most effective means of staying hydrated under a range of different training and competition conditions.
The athletics season for sprinting is typically in summer here in New Zealand. During competition, the focus should be very much on starting the event hydrated, as there is clearly no time, nor need, to consume fluid during the event. There are no published reports on sweat rates during sprint events, although with such short distances the total volume of sweat lost would still be small1. More importantly, in competitive environments, there are often multiple events in one day, involving a bit of "waiting around", as well as time spent warming up and cooling down. Therefore, it's important to work on maintaining consistent fluid intake throughout the day, especially after races. In hot environments, try to avoid excessive exposure to the sun and heat. It may be necessary to consider alternative ways to warm down from the previous event (e.g. stretching, ice baths, hot/cold showers), rather than sustained jogging which would contribute further to dehydration. Similarly, during training, although each effort itself may be brief, the total number of efforts undertaken over the duration of training can result in an accumulation of sweat losses which may result in substantial dehydration1. Hence, fluid should always be consumed throughout training sessions, even if the environment is relatively cool since generally warmer clothes are worn, resulting in fairly similar sweat losses to warmer conditions.
Fluid intake recommendations are to consume 6-8 ml/kg (ie. for a 60kg runner, 360 - 480mL) of a sodium-containing fluid like POWERADE ION4 (or water with food) around two hours before your event1. Fluid intake at other times will depend upon duration and intensity of training / competition, and environmental conditions, but should never be so much that body weight is increased above "normal" over the session.
For those competitive runners who are very focused and train regularly, these events are very intense affairs usually lasting less than 30 minutes and fluid intake during the event is not normally required (or possible). Research into the effects of dehydration on middle distance running events is limited, however, one older study showed an increase in running times (i.e. poorer performance) over 1.5 km, 5 km and 10 km events when approximately 1.4 kg (~1.9%) was lost through dehydration prior to the event2. Therefore, optimising the state of hydration prior to the event is of chief concern, with the primary recommendation being the same as that stated above for sprint events. However, backing up for events in a few days time does mean significant attention should be paid to recovery protocols.
For the general public participant who may want to stay fit and participate in a one-off event such as a half marathon, some of the issues may differ. Being adequately hydrated would be a goal in the preparation phase. The less serious individual will have greater time and opportunity to make use of drink stations that are likely to be situated at points throughout the event, and should, therefore, be encouraged to consume fluid at a rate that is just below the rate of sweat loss during the event. (See "How can POWERADE help me during sport?" and the "How to Determine Your Personal Sweat Rate" for more information.)
Generally, this is classed as distances of half marathons or longer, and include race walking, requiring at least one hour to complete even in elite level runners. Naturally, just as it is important for a race or event, hydration is an important consideration throughout training for endurance running in order to help ensure optimal training capacity and promote training adaptations afterwards. Training sessions present a perfect opportunity to practice drinking during running events, something which many runners find difficult to do. Not only does this help runners learn how much fluid they can drink without getting stitches and gastric upsets, it can also help teach people how to "drink on the run" without spilling it all over yourself!
Reports of elite level marathon runners indicate sweat losses from 2-8% body mass through the course of a marathon, depending on environmental conditions1. While world class male athletes may race the half marathon in about one hour and a few minutes, the average runner who has still prepared well may take between 50 and 100% longer, turning the event into a significant endurance task. With reported sweat rates for a half marathon being as least 1.5 L/hr even in winter conditions3, this difference in length of event can be very significant physiologically, as dehydration greater than 2% body mass (e.g. a 1.6kg loss for an 80 kg runner) has been shown to negatively impact on performance3,4. The longer you spend running at these levels of dehydration, the worse your performance will be, especially in a warm to hot environment. Fortunately, provisions are made for fluid intake during such events, so opportunities to drink should be taken throughout the course of the run. A combination of water and sports drink, such as POWERADE ION4, should be taken based on your fluid loss (see "How to Determine Your Personal Sweat rate" or "Hydration Calculator" for more details). The carbohydrate and electrolytes available in sports drinks will support fuel provision, as well as allow for better absorption and retention of ingested fluid. If food or gels are consumed, then water is the most suitable fluid to use with this1. (For further information, refer to "Hydration strategies for endurance events".
The most important issue for kids is hydration. Many children in New Zealand take part in "Little Athletics" or similar programs, where they can be outdoors training or competing in a variety of events over a whole day. Dehydration is more detrimental to children than it is to adults5. Their ability to control body temperature isn't as responsive or effective as an adult so they are more vulnerable to heat-related problems especially in summer5. As a result, greater care must be taken with children to ensure they both maintain hydration and have a mechanism to cool themselves. In particular, most children don't drink as effectively as adults, so it is important to monitor total fluid intake during exercise and be actively encouraged to drink5,6. For children, water is usually the best fluid to give them.
Shirreffs SM, Casa DJ, Carter R. 2007. Fluid needs for training and competition in athletics. J. Sports Sci., 25: S83-S91.
Armstrong LE, Costill DL, Fink WJ. 1985. Influence of diuretic-induced dehydration on competitive running performance. Med. Sci. Sports Exerc. 17: 456-461.
Sawka MN, Burke LM, Eichner ER, Maughan RJ, Montain SJ, Stachenfeld NS. 2007. Exercise and fluid replacement. Med. Sci. Sports Exerc. 39: 377-390.
Cheuvront SN, Carter R, Sawka MN. 2003. Fluid balance and endurance exercise performance. Curr. Sports Med. Reports, 2: 202-208.
Meyer F, O'Connor H, Shirreffs SM. 2007. Nutrition for the young athlete. J. Sports Sci., 25: S73-S82.
Wilk B., Bar-Or O. 1996. Effect of drink flavour and NaCl on voluntary drinking and hydration in boys exercising in heat. J. Appl. Physiol. 80: 1112-1117.