Dehydration is known to negatively affect performance and contribute to cardiac strain in endurance sports like running and cycling. Dehydration can also become an issue for team-sport athletes, particularly when competing outside in hot temperatures for prolonged periods of time. Factors such as high body mass and heavy equipment (i.e., football pads and helmets) can also contribute to higher sweat rates during play. As a result, more and more teams are monitoring hydration status in athletes. Some teams use a simple approach with pre and post-training weigh-ins while others use more sophisticated methods such as urine specific gravity. Despite the substantial amount of research available evaluating the effect of dehydration on endurance performance, there is comparably less research pertaining to its impact on resistance training.
A recent study published in the European Journal of Applied Physiology evaluated the effects of dehydration on resistance training performance. Ten resistance trained males completed two protocols involving 1) dehydration (3% of body mass) followed by rehydration or 2) dehydration (3% of body mass) without rehydration preceding a full body workout. Dehydration was induced via hot water bath. The full-body resistance training protocol was comprised of 3 sets to failure with their predetermined 12 repetition maximum in the bench press, lat pull down, overhead press, barbell curl, triceps press and leg press. Two-minute rest periods were provided between sets. Total repetitions were counted for all sets and compared between conditions. In addition, ratings of perceived exertion (RPE) and recovery heart rate was recorder for all sets and compared between conditions.
The results showed that the subjects performed significantly more total repetitions when they were hydrated (average of 169 reps) versus when they were dehydrated (average of 144 reps). When dehydrated the subjects performed on average 1-2 reps less than when they were adequately hydrated. Though not statistically significant RPE’s following bench press, lat pull down and triceps press were meaningfully higher when dehydrated versus when hydrated, as was the case for total session RPE. Finally, recovery heart rate was significantly higher (average of 116 bpm) when dehydrated versus when hydrated (average of 105 bpm). The authors concluded that 3% dehydration was enough to impair resistance exercise performance, increase perceived exertion and delay recovery heart rate. Therefore, the negative of effects of dehydration can be extended to strength training.
Kraft, J. A., Green, J. M., Bishop, P. A., Richardson, M. T., Neggers, Y. H., & Leeper, J. D. (2010). Impact of dehydration on a full body resistance exercise protocol. European journal of applied physiology, 109(2), 259-267.