The Hydration Mistake That Ruins Long Runs

Hydration might be one of the most underestimated limiters in long distance running. In this video, we break down how sweat rate, sodium loss, and fluid replacement influence endurance performance using real world data. Chris and elite trail runner Vlad Shatrov head back out on the trails to test their usual long run fuelling strategies. On the first effort, we hydrate the way we normally would. On the second, we begin rebuilding our hydration plan using sweat sensor data to calculate fluid loss and sodium concentration. We compare sweat rate, sodium replacement, and perceived effort to see what changes when hydration is adjusted. This is not about extreme dehydration or dramatic blow ups. It is about the small physiological shifts that accumulate over 90 minutes or more. Reduced blood volume, impaired fluid retention, and rising cardiovascular strain can quietly turn strong running into a slow fade. If you are training for ultras, long trail races, or simply trying to stop fading in long runs, this deep dive into hydration strategy and sodium balance gives you practical data you can apply immediately. 📱 Our Channel Partner Whether you’re building to your first 5K or an ultramarathon, RunMotion gives you one system that grows with you as your goals change. RunLab viewers get a free month of premium here: https://bit.ly/RunMotion-RunLab 📌 Chapters 00:00 Intro 01:20 Baseline Fuelling 02:31 Run #1 (What Is Sweat) 04:23 The Hydration Gap (Results) 07:05 Sweat Rate Often Drops 07:45 Hydration Plans Should Change With Effort 08:43 Run #2 Updated Fuelling 10:54 Results 11:59 Lab Tests vs Worn Sensors 🤝 Thanks to Nix Nix kindly sent us their sweat sensors to test for this experiment. They did not pay for this coverage and this video is not sponsored. If you are considering trying a Nix sensor, you can support the channel by using our affiliate link below: https://alnk.to/d3FYiNO 📺 Related Videos Why Elites Run Further https://youtu.be/3uc2QO3CPC8?si=UMtCQxX3rNt_pKmW How Elites Beat Pain https://youtu.be/zKFoSe-j5TA?si=WRW3c4-PybqP0xFW 🏃‍♂️ Follow Vlad Strava https://www.strava.com/athletes/12387974 Instagram https://www.instagram.com/vlad_protrailrunner/ 🎥 Follow Chris Strava https://www.strava.com/athletes/28291087 Instagram https://www.instagram.com/chrisbeavon/ 🎬 Follow RunLab Media Instagram https://www.instagram.com/runlabmedia/ 📩 Business enquiries info@runlab.media