Sweat Science with Precision Fuel & Hydration's Emily Arrell and Dr. Lindsey Hunt

On our way to ÖTILLÖ this year, we take a side quest to Precision Fuel & Hydration headquarters, pull on our swimrun wetsuits, and run on a treadmill in their heat lab. We want to answer a question every swimrunner feels on a long run leg: how much more do you sweat in a wetsuit? This week we finally get the full breakdown of what we found.

Joining us are Emily Arrell and Dr. Lindsey Hunt from the PF&H sports science team. Emily started at Precision as a sports science intern and now advises triathletes, ultrarunners and swimrunners on fuel and hydration, including collecting race data at world championships. Lindsey holds a PhD in environmental physiology from the University of Sydney and specializes in heat stress, heat training and predicting sweat rates.

We cover our results. Chris's lighter suit pushes his sweat rate about 20% above predicted, while Chip's full neoprene suit nearly doubles his. We also get into why sweat rate and sweat sodium concentration are two separate pieces of the puzzle, the 2% body mass rule, heat acclimation sessions you can do at home with a few extra layers, choosing a sleeveless or sleeved suit by conditions, preloading for salty sweaters, the "you don't need electrolytes" internet takes, and how to spread caffeine across an 11-hour race.

We also kick things off with a preview of ÖTILLÖ Swimrun Austin, our seventh straight year at Pace Bend Park. Plus a shout-out to friend of the show Dr. Yael Schonbrun, whose new book Why Don't You Understand Me? is out now. And yes, we're in it.

This episode is brought to you by Precision Fuel & Hydration. Head to their website to book a free fuel and hydration consultation call with their team.

00:00:00 Intro: our wetsuit sweat test results
00:00:53 Our Precision Fuel & Hydration headquarters side quest
00:03:30 Dr. Yael Schonbrun's new book
00:04:54 ÖTILLÖ Swimrun Austin preview
00:06:49 Meet Emily Arrell and Dr. Lindsay Hunt
00:10:26 The wetsuit treadmill test and our results
00:13:00 Why you should measure sweat rate in a range of conditions
00:13:47 Why sweat rate matters and the 2% body mass rule
00:15:43 What dehydration does to heart rate, pace and cramping
00:17:16 Sweat rate vs. sweat sodium concentration
00:18:49 Can you change your sweat rate? Fitness and heat training
00:21:45 Hot runs, cold water and why core temperature matters
00:23:46 Designing a safe wetsuit test
00:25:26 What the next round of swimrun testing could look like
00:27:44 How many sweat rate data points athletes collect
00:29:46 Kona, heat acclimation and how long it lasts
00:33:09 Building a heat acclimation protocol for a hot race
00:35:36 Heat training for amateurs: layers, garages and zone two
00:40:20 Can you train yourself to handle the cold?
00:42:03 Fueling when you sweat more than you can drink back
00:44:19 Sleeveless suits, arm sleeves and sweat rate
00:46:05 Preloading with extra sodium for salty sweaters
00:48:26 Are electrolytes a scam?
00:51:06 Does your daily diet matter for race hydration?
00:52:59 Caffeine dosing and timing for long races
00:55:10 Fuel and hydration as the low-hanging fruit
00:58:22 What Precision Fuel & Hydration learned surveying athletes in Nice

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