Many athletes – from casual exercisers to Iron Man triathletes – don’t often fully understand the impact dehydration has on exercise performance. Simply put, dehydration is terrible for athletes, and the science is pretty clear.
Dehydration affects an athlete’s mind and body, and the more dehydrated they are, the more pronounced the decline in performance. Thus, preventing it is one of the most effective strategies for maximizing athletic output. Here are four ways dehydration affects your performance:
1. Fatigue Sets in Faster
Your body temperature rises more rapidly when you’re dehydrated. This happens because dehydration causes a drop in sweat rate and the flow of blood to the skin[i], and thus greatly reduces your ability to dissipate heat. Unfortunately, the higher your body temperature increases, the more fatigued you feel, especially nearing a core temperature of 103° F[ii].
2. You Lose the Mental Battle Easier
The adage goes, “exercise is 90 percent mental,” and that doesn’t bode well for dehydrated athletes. Why? A drop in cognitive performance has been observed numerous times in dehydrated athletes.
For instance, a 2012 study looked at 8 healthy athletes who were about 3-percent dehydrated due to heat stress or intense exercise[iii]. After a 90-minute recovery period, all participants experienced declines in motor-skills, memory and feelings of fatigue. That’s just one example. Another, a recent Tufts University study, found that college athletes had declines in mood and “vigilance attention” when dehydrated following practice[iv].
3. Aerobic Endurance Begins to Decline
Dehydration, however slight, tends to negatively impact an athlete’s “maximum aerobic power,” which directly correlates to capacity. In fact, at just 1 to 2 percent dehydration, slightly dehydrated distance runners experienced slower finishing times in a 1985 study[v]. For longer distances, the finishing times dropped even more, i.e. endurance erodes.
Greater levels of dehydration, though, wreak havoc on performance. For instance, 5 percent dehydration has been observed to cause up to a 30 percent reduction in performance[vi].