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4 Ways Dehydration Is Killing Your Workout

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, remedying 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].

4. Your Muscles Feel Weaker

Engaging your muscles for extended periods -- i.e. when cycling – becomes harder as dehydration progresses. Dehydration causes your muscles to feel weaker and can cause cramping. For example, a National Athletic Trainers’ Association position statement[vii], which cited 6 studies on the subject, noted that muscle endurance was adversely impacted starting at between 3- and 4-percent dehydration.

Image via Flickr.

Sources: [i] Sawka, M. N., Montain, S. J., & Latzka, W. A. (2001). Hydration effects on thermoregulation and performance in the heat. Comparative Biochemistry and Physiology Part A: Molecular & Integrative Physiology, 128(4), 679-690.
[ii] Jeukendrup, A., & Gleeson, M. (2010). Sport nutrition: an introduction to energy production and performance (No. Ed. 2). Human Kinetics.
[iii] Cian, C., Barraud, P. A., Melin, B., & Raphel, C. (2001). Effects of fluid ingestion on cognitive function after heat stress or exercise-induced dehydration. International Journal of Psychophysiology, 42(3), 243-251.
[iv] D'Anci, K. E., Mahoney, C. R., Vibhakar, A., Kanter, J. H., & Taylor, H. A. (2009). Voluntary dehydration and cognitive performance in trained college athletes 1, 2. Perceptual and motor skills, 109(1), 251-269.
[v] Armstrong L.E., Costill D.L., Fink W.J. (1985). Influence of diuretic-induced dehydration on competitive running performance. Med Sci Sports Exerc. (17(4):456-61.
[vi] Burke, L. M., & Maughan, R. J. (2000). Effects of Dehydration and Rehydration on Performance. Nutrition in sport, 405-414.
[vii] Casa, D. J., Armstrong, L. E., Hillman, S. K., Montain, S. J., Reiff, R. V., Rich, B. S. & Stone, J. A. (2000). National Athletic Trainers' Association position statement: fluid replacement for athletes. Journal of athletic training, 35(2), 212.

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