The scientific literature on dehydration’s effect on anaerobic strength and power is contradictory. Some studies show a definite drop in strength because of dehydration, while others show little or no effect. One study found no effects on voluntary muscle contraction in the legs or arm muscles with an induced 4 percent loss of weight through dehydration. Another study found no ill effects of dehydration on one-rep-max bench presses. On the other hand, 30 minutes in a sauna resulted in a loss of leg press strength. Dehydration amounting to loss of 3.9 percent of body mass during moderately prolonged exercise reduced blood flow to active muscles; elevated carbohydrate oxidation, which leads to premature muscle glycogen depletion; and increased lactate production—all of which can cause muscle fatigue.
In a new study seven subjects, average age 27, did upper and lower Wingate anaerobic exercise tests before and after a 90-minute recovery from a heat stress trial of treadmill exercise. They lost about 3 percent of body mass through sweating. The severity of fatigue increased by 70 percent in the dehydrated condition. Mean power decreased 17.17 percent in the upper body and 19.20 percent in the lower body, which is consistent with past studies showing that lower-body muscles are more affected by dehydration than upper-body muscles. The results suggest that dehydration on that scale decreases the body’s ability to generate anaerobic power.
Loss of water leads to loss of intracellular potassium, which adversely affects calcium use during muscle contraction. Higher intramuscular temperature resulting from dehydration elevates cellular hydrogen ion acidity, which inhibits energy-producing enzyme activity. The net effect: muscle fatigue and a considerable drop in training intensity.
Studies show that on average, athletes replace only two-thirds of the water they lose during exercise. If you lose 3 percent or more of your weight from water loss, your anaerobic-exercise capacity is compromised. That suggests that you should drink water at regular intervals during training, since thirst is not a precise indicator of fluid requirements. That’s particularly true in hot and humid environments.