My DHPR test results — heart rate drift exposed my hidden dehydration

I ran a Dehydration to Performance Ratio (DHPR) test on myself: 85% hydration score at 80 bpm, but dropped to 70% at 175 bpm. Heart rate drift between 10 and 40 minutes of steady-state running was 8 bpm — above the 5 bpm threshold for dehydration.

I was drinking 16 oz of water per hour during runs, but sweating 28 oz/hour. The math was simple: I was losing 12 oz of fluid per hour. Over a 90-minute run, that's 1.4 lbs of water loss. The drift started at 25 minutes and got worse.

I increased pre-run hydration by 24 oz 2 hours before and added electrolytes during runs. Next test: HR drift dropped to 4 bpm, hydration score 92% at max HR. Perform better, feel better.