A dose of 3.6 to 7.2 grams of sodium, about 9 to 18 grams of normal kitchen salt may improve performance in hot conditions. This is the outcome of a study on well-trained cyclists who did an endurance test of 2 hours in warm and dry surroundings of about 33 degrees C. with an air humidity of 30%. As a higher dose does not lead to better effects it is not recommended to use more than 3.6 grams of sodium.
BODY FLUID AND SALT DURING PHYSICAL EFFORT
During physical efforts the blood supplies the muscles with oxygen. The quantity of blood per minute that runs through the muscles depends amongst others on the total volume of fluid within the body of the athlete. During exercise is warm surroundings the athlete loses fluid and salt (sodium chloride or NaCl) by sweating. Salt is an important agent in controlling the fluid balance within the body. The average recommended daily amount of salt per day is 1 to 2 grams. Most people get more than sufficient salt, the average is 8 to 10 grams per day. The investigators have tested whether the intake of salt prior to exercise in warm surroundings might have a positive effect on endurance performance.
Ten well-trained cyclists participated in the test. Average age 33 years, VO2max 60 ml/kg.min. Three identical tests were done in dry and warm surroundings of 33 degrees C with an air humidity of 30%. Between the tests was a resting period of 5 days.
Before the test each test person received 770 ml of water to drink. Before one test they got capsules containing a placebo. In the two other tests capsules with 3.6 and 7.2 grams of sodium.
Consequently an endurance effort of two hours at 63% of their VO2max, followed by a time trial. The workload during the time trial was determined individually, viz. 110% of the VO2max of each participant.
During the time trials in salt conditions the cyclists delivered a higher average performance. In both salt conditions 289 Watt and in the placebo condition 269 Watt. Therefore they had done the time trial faster, respectively 9min.57sec and 10min.00 sec against 10min.25sec in the placebo condition.
IN BOTH SALT CONDITIONS
A larger blood volume (5%), a larger heart minute volume (1.3 l/min) and a larger stroke volume 10 ml per heartbeat) compared to the placebo group.
Heart rate was lower prior to the time trial, 149 in both salt conditions, instead of 153 beats per minute with the placebo.
Conclusion: the volume of blood pumped through the body and the muscles was larger after the intake of salt
Performance improvement in hot conditions can be achieved by the intake of salt prior to the effort. The salt causes the blood volume to decrease less rapidly when the athlete perspires much. A sufficient amount of salt within the body is necessary to retain water in the blood and in the cells. The solution of 3.6 grams of sodium is as good as the higher dose of 7.2 grams of sodium in well-trained cyclists. With a view to the disadvantages of salt for health in general some restraint in the use of large amounts of salt is recommended.