Hydration plays a crucial role in how accurately someone can estimate their Reps in Reserve (RIR), which is a measure used in strength training to gauge how many more repetitions a person can perform before reaching failure. When the body is well-hydrated, muscle function and cognitive processes involved in self-assessment tend to be more reliable. Dehydration, even at mild levels, can impair physical performance and mental clarity, leading to less accurate judgments about how many reps remain before exhaustion.
When dehydrated, muscles fatigue faster due to reduced blood flow and electrolyte imbalances, which can cause a person to feel more fatigued earlier than they actually are. This premature fatigue sensation can make someone underestimate their true capacity, resulting in a lower RIR estimate than is accurate. Additionally, dehydration affects the brain’s ability to process signals related to effort and fatigue, further reducing the precision of self-assessment during exercise.
Research on physical fitness and dehydration suggests that fitter individuals may better maintain performance and possibly RIR accuracy under mild dehydration, but this does not eliminate the negative effects of fluid loss. Staying hydrated supports both the physical and neurological functions necessary for accurate perception of effort and endurance during workouts.
In summary, hydration status influences the accuracy of Reps in Reserve by affecting muscle endurance and cognitive function. Proper hydration helps maintain clearer self-awareness of physical limits, while dehydration tends to cause earlier fatigue signals and less precise estimation of remaining reps.
Sources
https://medicalxpress.com/news/2025-10-physically-drier-world.html
https://www.goodrx.com/well-being/diet-nutrition/what-is-dry-scooping-pre-workout
