Field Notes
Sports Beverages
Carbohydrate and electrolyte beverages or sports drinks help maintain performance, cognitive ability, and immune function while they address fluid replacement requirements. The electrolytes replace sweat loss and minimize urinary fluid loss. Electrolytes may also reduce muscles' tendency to cramp during hours of work in the heat. Sports drinks are recommended for fluid replacement during work and for recovery after the shift.
During Work—Fluid replacement during work requires a balance between restoring critical fluids and the need for energy. Most sports drinks contain between 5 and 8 percent of carbohydrates per liter of fluid. Higher levels of carbohydrates may seem too sweet or syrupy for use during work. High levels of carbohydrates can slow absorption of the fluid. All the major brands of sports drinks include moderate levels of sodium and potassium, and a few contain small amounts of magnesium. A powdered drink mix allows each firefighter to mix the drink to personal taste. Up to half of an individual's fluid needs should be replaced with a sports drink, and the balance should be water. Firefighters should take frequent drinks to ensure consumption of 1 liter of fluid per hour of work.
After Work—Rehydration or recovery drinks may contain more carbohydrates and some protein (1 gram of protein per 4 grams of carbohydrates). The carbohydrates restore muscle and liver glycogen levels and the protein aids muscle recovery. Electrolytes in the beverage minimize urinary water loss. A firefighter should consume about 2 liters of the beverage in the 2 hours immediately after work. Solid food containing carbohydrates, protein, and some electrolytes will also aid muscle recovery. Water also aids rehydration, but unless the water contains electrolytes, about one-third of the water will be lost in the urine.
High-Fat Diet?
Is prolonged work or endurance training possible on a high-fat diet? In an experiment reported in 1928, researchers studied the effects of 11 days of exercise performance on a high-fat diet as compared to a high-carbohydrate diet. The authors described the subject's ability to handle the exercise:
"After the first two to three days the subject felt very tired and sleepy, in fact did sleep several hours between experiments, and had no desire to work or to do anything else. The work seemed harder, although it was the same as in the previous series. In the last few experiments the subject became dizzy on the ergometer (bicycle) toward the end of the work period and afterward expressed the fear that he might have fallen off. But he stuck pluckily until the series was completed. The very last experiment had to be discontinued at the end of 6.4 minutes because of dizziness."
In contrast, when the subject consumed the carbohydrate diet, all exercise tests were performed without problems.
An earlier study (1920) found that some subjects experienced excessive fatigue during exertion after 3 days on a very high-fat diet, while a few failed to observe an appreciable difference. Current studies on the topic are equally equivocal, suggesting the possibility of an individual response to a high-fat diet. However, since high-fat intake suppresses the immune response and has serious health consequences (heart disease, obesity, diabetes), a firefighter has no reason to consume a high-fat diet.
Krogh and Lindhard. 1920. Bio-chemical Journal, 14: 290–363. Marsh and Murlin. 1928. Journal of Nutrition, 1: 105–137.
