Influence of fluid deficiency on muscle strength and muscle mass

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What role does water play in strength training, muscle strength, and muscle mass exactly? What are the consequences of dehydration? In this article, we delve deeper into athletic performance in relation to fluid intake.

Impact of Dehydration on Endurance

Several studies have shown the impact of dehydration on endurance performance, particularly in activities of longer duration at moderate intensity [1,2,3]. It has been demonstrated that dehydration negatively affects athletic performance, although there are significant individual differences [4].

Impact of Dehydration on Muscle Strength

However, when it comes to the influence of dehydration and fluid deficit on high-intensity efforts requiring short-term muscle strength, research results vary considerably. Some studies have demonstrated a negative impact on performance [5 to 10, 31]. Others show no effect and thus no difference in performance [7, 11 to 16]. If you’re keen on references, you might have noticed that one of these studies even noted both conclusions [7]. However, there were more studies among them showing conflicting results [12,13].

Additionally, the results of some studies cannot be directly attributed to water and fluid intake because researchers have not adequately controlled other variables [10,14,17]. For example, factors such as body temperature, menstruation, calorie intake, etc., were not taken into account.

Another drawback is that in many cases, studies focused on a single maximal effort [31]. This is not directly comparable to a typical training session involving multiple exercises with multiple sets and repetitions per set.

Hence, the challenge lies in finding studies that consider all these factors. In this regard, there are three studies we can examine. One of these dates back to 1979 [8], while the others are more recent, from 2007 and 2008 [18]. However, since I couldn’t find the full text of the 1979 study, I’ll limit discussion to the more recent ones.

“Dehydration Limits Performance in Strength Training”

Researchers from California State University initiated their study with seven young men familiar with the back squat exercise. However, this already poses a limitation as seven individuals do not represent a large population sample. They were not divided into groups with different fluid intake but instead underwent a training protocol under three different conditions:

1. Normal fluid balance (“euhydration”) – “EU”
2. Dehydration (2.5% body mass loss) – “HY25”
3. Dehydration (5% body mass loss) – “HY50”

There was a week’s gap between the different training protocols. Fluid balance was manipulated the day before the training through exercise, heat, and controlled fluid intake. The degree of deficit was determined by calculating the decrease in body mass and urine specific gravity [19].

Initially, the maximum weight for one squat repetition (1RM, one repetition maximum) was measured. The squats were performed on a Smith Machine to maintain controlled movement. The actual training began at the next visit, consisting of six sets of squats at 80% of 1RM intensity. They performed ten repetitions per set or the maximum achievable if ten reps were not completed. They rested for two minutes between sets and indicated their level of fatigue after each set.

In addition to squats, jump squats and vertical jumps were performed to assess the amount of force generated during a single effort.

The researchers made considerable efforts to account for all conditions such as calorie intake and body temperature.

Results and Conclusion:

On the maximum strength during single leg extensions, fluid balance had little effect. However, it significantly impacted the six sets of squats. The results of squatting under these conditions are shown on the right.

The primary findings of this study were that hypohydration 1) has little demonstrable effect on single, maximal-effort strength and power, but it 2) limited the ability of healthy, resistance-trained males to perform a six-set back squat protocol. These results suggest that hypohydrated individuals who complete isotonic, multiple-repetition, multiple-set, intermittent resistance exercise tasks will likely experience impaired performance.

…In conclusion, hypohydration up to 4.8% body mass loss 1) failed to affect vertical jump height, peak lower-body power, and peak lower-body force, but it 2) significantly compromised the ability to perform a resistance exercise bout. Preliminary results evaluating the effect of hypohydration on the ability of the central nervous system to maximally stimulate the musculature suggest further work should continue to investigate this plausible mechanism.

-D. Judelson, California State University

Thus, dehydration reduced performance when six sets of squats were performed.

“Drinking During Training Increases Testosterone and Reduces Cortisol”

The same researchers investigated a year later the effect of dehydration on hormone levels during training. They examined its effects on “good” hormones such as testosterone, insulin, IGF-1, and growth hormone, as well as cortisol, which we typically aim to keep low. They used the same setup as in the previous study, with seven participants and the same differences in fluid balance.

During sets of squats at 80%1RM, they observed hormonal responses. Some of the results are shown on the right. Clearly, dehydration has unfavorable effects on hormone levels.

Both testosterone and growth hormone decrease during training when there’s dehydration. However, this difference was not statistically significant in this study (thus could be due to chance). Cortisol, on the other hand, the stress hormone that promotes muscle breakdown, significantly increases with a 5% dehydration (the difference was not significant at 2.5%). There’s a substantial difference of over 46% compared to normal fluid balance.

Similar increases in cortisol due to dehydration have been observed in endurance sports and are likely caused by the rise in body temperature it induces [21 to 27].

What the researchers didn’t expect was the rise in the anabolic hormone IGF-1 during dehydration. They speculate this is a delayed response to the increase in growth hormone the day before when extensive running was done to lose fluid. Previous research has shown that prolonged low-intensity exercise increases growth hormone [28,29]. Due to prolonged dehydration-induced temperature elevation, more growth hormone may have been produced. Growth hormone elevates IGF-1, but with a delay [30]. The increased IGF-1 could thus be a reaction to the increased growth hormone a day earlier.

In conclusion, hypohydration up to 4.8% body mass loss significantly altered the endocrine and metabolic internal environments before and after intense resistance exercise. The stress of hypohydration significantly enhanced the exercise-induced increase in catabolic hormones and modified the anabolic hormonal response. Likely secondary to these hormonal shifts, hypohydration stimulated a large influx of metabolic substrates. These data demonstrate that body water status is an important consideration in modulating the hormonal and metabolic responses to resistance exercise.

-D. Judelson, California State University

This is the impact on a single training session. If every training session results in lower testosterone and growth hormone levels and higher cortisol levels, it’s conceivable that this will also affect muscle mass, which is largely regulated by these hormones. However, more research is needed in this regard.

It should also be noted that these studies from 2008 and 2007 were partially funded by The Gatorade Sports Science Institute. They have a commercial interest in demonstrating the adverse effects of dehydration since their sports drink would naturally prevent such problems. This doesn’t automatically mean the research is unreliable but should be kept in mind.

Dehydration and the Function of mTOR and Protein Synthesis

Looking at protein synthesis (the production of new proteins, a crucial process in muscle growth alongside hypertrophy), it’s useful to know about the influence of mTOR, mammalian target of rapamycin. mTOR plays a significant role in initiating protein synthesis under the influence of insulin [32]. However, this process in muscle cells can become inactive due to dehydration, even if there is sufficient insulin present [33].

Conclusion

Most studies are not ideally designed. Often, the conditions under which they are conducted leave much to be desired, making definitive statements challenging. Studies that come close to the right conditions seem to have the appearance of conflicts of interest.

If we were discussing a supplement or a pre-workout, I would probably say, “Save your money until the added value is better proven.” However, we are talking about water here. About fluid deficits and their effects on other aspects such as fat burning, as well as mental functions, I could write several more pieces, but summarily, dehydration almost never yields benefits. The only exception is those rare days when a bodybuilder wants to remove all the moisture from the skin for a competition, but otherwise, there’s no reason to drink too little.

What I will describe in the next article, however, is how to drink your water best by addressing the dangers of plastic water bottles.

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