Hydration has a pervasive effect on physiological function. Even mild dehydration of 1 to 2 percent of body weight produces measurable decrements in strength, power, cognitive function, and perceived exertion. In the context of training and recovery, the most common hydration mistake is not extreme dehydration but chronic mild dehydration from inadequately meeting daily fluid requirements.
The Performance Effects of Mild Dehydration
- Strength reduction of 2 to 4 percent at 1 percent body weight dehydration
- Endurance performance reduction of 10 percent or more at 2 percent body weight dehydration
- Significant cognitive impairment including reduced concentration, increased reaction time, and reduced working memory at 1.5 percent dehydration
- Increased perceived effort at any given exercise intensity, making training feel harder without any change in the actual workload
The Recovery Effects
Muscle protein synthesis occurs in an aqueous environment. Dehydration reduces the efficiency of this process. Nutrient delivery to recovering muscle tissue depends on adequate plasma volume. Dehydration reduces plasma volume and therefore reduces the rate of substrate delivery to recovering tissue. Glycogen resynthesis, the process of refuelling muscle energy stores after training, is also impaired by dehydration.
Practical Hydration for Active Adults
- Baseline: 35ml per kilogram of body weight per day in temperate conditions
- Training day addition: an additional 500 to 750ml for each hour of moderate-intensity training
- Monitor urine colour: pale yellow indicates adequate hydration, dark yellow or amber indicates significant deficit
- Electrolytes: if training exceeds 60 minutes, sodium and other electrolytes lost in sweat should be replaced, particularly in warm conditions