Q: I know hydration is important, but how does dehydration negatively impact my strength training session?

A: The importance of proper hydration is well known.  Proper hydration supports all bodily function.  Every cell, tissue, and organ in your body needs water to work properly.  Therefore it is not surprising that dehydration can negatively impact performance in endurance sports (running), team sports (football), sports taking place in hot temperatures, or sports requiring heavy gear.

However, there is very little research on the impact of dehydration on strength / resistance training.

A study published in the European Journal of Applied Physiology evaluated the effects of dehydration on resistance training performance. Ten trained males completed two resistance training protocols under the following conditions:

  • dehydration (3% of body mass) followed by rehydration preceding a full body workout
  • dehydration (3% of body mass) without rehydration preceding a full body workout

The full body resistance training protocol was comprised of three sets to failure across six activities.  Resistance was based on the subject’s 12 repetition maximum, and two minutes of rest was given between each set.  Total repetitions were counted for all sets and compared between conditions.

The results showed that the males performed significantly more total repetitions when they were hydrated (average of 169 reps) versus when they were dehydrated (average of 144 reps).  On average, the males performed one to two reps less per set than when they were hydrated.  Conclusion: as little as 3% dehydration was enough to impair resistance exercise performance.

The following website was used in answering the question: