Article Review
The purpose of this study was to examine the effect of commercially available sports drinks on rehydrating capacity and anaerobic performance following exercise in the heat. Other variables of interest included drink palatability, thirst, feeling of stomach fullness, and urine output during exercise.
The sample group consisted of seven endurance trained cyclists. Prior to the experimental intervention, each participant underwent a pre-experimental and heat acclimatization training period. Initially, each subject completed an incremental cycling test to exhaustion to determine Vo2 Max. Then for 9 consecutive days each subject partook in heat acclimatization training, consisting of steady state cycling at 63% Vo2max for 90 minutes (35 ± 0.1 degrees Celsius and 27% ± 3% relative humidity). Four sessions each were devoted to proper execution of maximal cycling power (Pmax) and maximal voluntary isometric contraction (MVC) of the knee extensors of the right leg (measures of dependent variables).
Three hours prior to the experimental intervention the participants consumed a high carbohydrate meal (4gkg body mass). Two hours prior to the trial, each participant consumed 500ml of water. Preceding exercise, each participant urinated in a graduated cylinder for urinalysis, inserted a rectal thermometer, and received a cannula in their arm for blood sampling. Warm up consisted of each participant entering the hot room, and pedaling for 10 minutes. After this warm-up, each participant was measured for MVC, followed by a 15 minute rest-period. Two sweat patches were attached to the participants’ lower back and a 5 ml blood sample was collected. Then the subjects began pedaling for 120 min at 63% Vo2 Max. Each subject participated in 5 trials separated by 2-4 days. In one of these trials there was no fluid intake during the exercise period (DEH). “In the remaining four trials, 100% sweat loss (2.4 ± 0.1 L) was replaced by the following: (i) ingestion of mineral water (San Benedetto1, i.e., WAT trial); (ii) ingestion of a sports drink with 6% carbohydrate and 22 mmolL–1 sodium (Gatorade1 lemon, Quaker Oats Co.); (iii) ingestion of a sports drink with 8% carbohydrate and 22 mmolL–1 sodium (Powerade1 Citrus Charge, Coca-Cola Co.); (iv) ingestion of a sports drink with 8% carbohydrate and 10 mmolL–1 sodium (Aquarius1 orange, Coca-Cola Co.).” In addition to a MVC, nude weight and urine samples were collected prior to and immediately following exercise. At 24, 54, 84, and 114 minutes into the trial, maximal cycling power tests were administered. They consisted of 3 X 4sec bouts of all out sprint cycling, followed by 2 minutes of cycling at a low work rate. Sport drinks were divided into four equal portions and consumed at 8, 30, 60, and 90 mins.
Based on the data, rehydrating with Gatorade and PowerAde yielded significantly higher MVC of the knee extensors, compared to DEH. Whereas, rehydrating with water or Aquarius did not yield significantly higher MVC compared to DEH. There was no significant difference in maximal cycling power between trials. Sweat rates were significantly higher in drink trials compared to DEH. Consuming water lead to significantly higher amounts of urine volume. Sodium balance was significantly higher in the Gatorade trial compared to DEH and water trials (PowerAde trended the same way). Plasma volume was significantly higher in all rehydrating groups compared to DEH.
This study examined the effect of commercially available sport drinks on anaerobic performance following prolonged exercise in the heat. The results suggest that some sports drinks yielded higher peak force outputs following prolonged exercise in the heat, when compared to no fluid consumption. Despite waters effect to prevent fluid deficit and hyperthermia it did not yield higher MVC compared to no fluid intake during exercise.
Reference
Coso J, Estevez E, Baquero R, Mora-Rodriguez R. Anaerobic performance when rehydrating with water or commercially available sports drinks during prolonged exercise in the heat. Applied Physiology, Nutrition & Metabolism [serial online]. April 2008;33(2):290-298.
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