If you follow the research around sports hydration, then you may have heard reports based on research, which claims that being “dehydrated” prior to competition is okay and will have no impact on performance outcomes. The research goes on to suggest that it may actually be beneficial in some athletes.

This research claims to finally offer the real truth, despite decades of data on sports hydration going back to the 1980s, which clearly shows that dehydration prior to and during competition leads to a reduction in endurance and poor performance outcomes.

A study published last year by Lewis James and colleagues at the School of Sport, Exercise and Health Sciences, Loughborough University, in the United Kingdom, puts the sword to this myth once and for all.

In the study, these researchers acknowledge that the general scientific consensus is that starting exercise with a 2% loss of body mass due to dehydration (a condition called hypohydration) impairs endurance performance and capacity, but the problem is that most the previous sports hydration studies were just observational and lacked a blind control; ie they lacked scientific rigor, until now….

This UK study examined the effect of hypo-hydration prior to a race on athletic performance, in a single-blind manner, which means that the athlete is unaware of their treatment.  Using a combination “fluid by mouth” and  “fluid by intragastric tube” researchers were able to rehydrate and manipulate each athletes hydration status.

Seven trained and active males, with an average age of 25 years, completed two randomized trials.

Trials involved an intermittent exercise preload 8, 9, 15 min exercise with 5 min rest between each set. This was followed by a 15-min all-out performance test on a cycle ergometer. During the preload period, water was given orally every 10 minutes.

Additional water was also infused into the stomach via a gastric feeding tube to replace sweat loss or withheld induce to induce dehydration of ~2.5% body mass

Blood samples were drawn and thirst sensation rated before, during, and after exercise.

The work completed during the performance test was lower (152+/-  24 kJ  vs. 165 +/-  22 kJ;   P < 0.05) during the periods of dehydration.

These results provide a novel way of showing that impairs cycling performance in trained and active athletes is impaired by hypohydration by 2.4% or more loss in body mass due to dehydration, even when subjects are blinded to the intervention.