A brand new study in the Journal of Applied Physiology (July 10, 2008) reveals that being dehydrated can significantly impair the strength and body fat loss results you might be looking for from a resistance exercise program.

1. New Study - Dehydration is Detrimental to Resistance
Exercise Adaptations!
A brand new study in the Journal of Applied Physiology (July 10, 2008)
reveals that being dehydrated can significantly impair the
strength and body fat loss results you might be looking for from a
resistance exercise program.
Methods
The researchers from this brand new study looked at 7 healthy,
resistance-trained males and subjected them to 6 sets of squats (at
80% of 1RM) in three different hydrated states: euhydrated (normal),
dehydrated (-2.5% of body mass), very dehydrated (-5% of body
mass).
The subjects were asked to complete as many reps (over the 6 sets)
as they previously had completed during their pre-study test.
The Three Main Findings of The Study Were That:
1) dehydration significantly increases circulating concentrations of
stress hormones cortisol and norepinephrine,
2) dehydration attenuates the testosterone response to exercise, and
3) dehydration alters carbohydrate and fat metabolism
These are significant findings if resistance exercise is an integral part
of your fitness regimen (and it should be!) because it highlights the
importance of remaining adequately hydrated to get the most from
your strength training workouts.
Several other studies have shown the negative impact of dehydration
on endurance exercise but this study is one of the first to investigate
the importance of exercise hydration status for resistance training

2. individuals.
Discussion of Findings
The novel results from this study show that dehydration causes an
increase in catabolic stress hormones such as cortisol and
norepinephrine. These are hormones that are released during stressful
conditions and do not favour the maintenance or building of lean body
mass. Instead, as catabolic stress hormones, they are known to “break
down” reserves in the body for immediate energy needs.
The dehydrated exercise states likely stimulated these catabolic
hormones by increasing the body’s core temperature and
cardiovascular demand resulting from a decreased blood plasma
volume. Again, conditions such as an elevated core body temperature
and lower blood plasma volume result from having less water in the
body and represent a state of “stress”. Not a good thing if you want to
preserve your lean body mass.
Since, cortisol became elevated during the dehydrated state, there
was also a significant rise in blood glucose. Remember, cortisol breaks
down carboydrate reserves (ie. glycogen), leading to a rise in blood
sugar. Subsequently, this study also found that there was a rise in
insulin (to remove the excess glucose from the blood). This rise in
insulin (an anabolic hormone) is known to inhibit fat breakdown.
Does Dehydration Eat Away at Lean Body Mass?
One of the main ways that our muscles get stronger (and larger) is via
an increased release of testosterone after resistance training.
However, the current study demonstrates that resistance exercise in a
dehydrated state attenuates the resistance exercise-induced increases
in testosterone; therefore, reducing the efficacy of strength workouts
for strength and/or development of lean body mass.
In Conclusion

3. The results of this new and novel research indicate that dehydration
produces a less beneficial post-exercise hormonal milieu by increasing
catabolism (break down) and potentially decreasing anabolism (build
up). Therefore, these findings suggest that if you routinely complete
resistance exercises in a dehydrated state you are probably
compromising the strength and body fat loss results you may have
otherwise achieved!
What To Do?
To stay properly hydrated, be sure to drink 500ml to 1 liter of water 1-
2 hours before your workouts, as well as 150 ml of water every 15-20
minutes during your workout. Oh, and don’t forget to drink plenty of
water and a post-exercise recovery drink or smoothie after you’re
finished working out.
Make resistance exercise work for you!
YURI
Reference:
Judelson, A. et al. Effect of hydration state on resistance exercise-induced endocrine
markers of anabolism, catabolism, and metabolism. Journal of Applied Physiology.
July 10, 2008.