It could be rightly argued that you simply don’t need sophisticated physiological tests to achieve your athletic goals. Roger Bannister didn’t know how much salt he had in his sweat when he ran the world’s first sub-4-minute mile in 1954. California ultra-distance runner Zach Bitter, on the other hand, who in 2013 set the world record for the farthest distance ever run in 12 hours at 101.66 miles, knows exactly how many calories he’s burning at a 7-minute pace, and what percentage of that comes from fat.
Physiological tests are becoming more affordable, scientifically rigid and specialized for the citizen athlete. But what can a few tests tell you that you don’t already intuitively know? If you knew more precisely about how your body works, could you change up your training or alter your diet and run a better marathon? I got pricked, prodded and pushed in order to find out.
At the headquarters of Skratch Labs in Boulder, Colo., famed sports scientist Allen Lim straps a patch of pilocarpine to my forearm to test the sodium content of my sweat. This drug, induced into my pores by a 9-volt battery, forces a small area of my skin to begin to sweat at a rate somewhere between a lactate threshold and race-pace running effort.
At some point, every long distance runner has to consider their electrolyte needs. To ignore this is to court catastrophe, and leaving it to luck will eventually ruin a race that was important to you. As runners, our customary way of knowing who needs more salt was simply who had the nastiest sweat streaks on their clothes after a race.
“You primarily lose sodium in your sweat, and although people make a big deal of other electrolytes, it’s the salt that has the greatest performance and physiological consequences,” says Lim, co-author of “The Feed Zone Cookbook” and “The Feed Zone Table,” and sports science consultant to numerous elite endurance athletes. Sweat, however, is not the same across individuals. “I’ve seen people as low as 400 milligrams to 2,000mg of sodium per liter of sweat,” he says. “That’s like a shoe salesman carrying sizes 4 to 200.”
Lim has the rare ability to explain complicated science to anyone, a skill honed over years in the trenches of the Tour de France. The company he subsequently founded, Skratch Labs, makes electrolyte drink mixes that favor whole food ingredients. The suitcase-sized device he’s using to test me was originally designed to screen newborns for cystic fibrosis. Babies who have inherited the disorder have very salty sweat, around 3,500mg per liter.
After 20 minutes he removes the armband and extracts my sweat. As it turns out I’m average, at 864mg per liter. “Tour de France athletes are in the 700s; normal people are around 1,000,” Lim says. And this jibes with what I’ve figured out through trial and error over more than a decade of endurance racing.
Lim stresses that this isn’t about constantly making calculations or trying to be an athlete-chemist. Those at either end of the spectrum should pay closer attention to what they ingest during long training sessions and races, but it’s less critical for someone like me. “We want people to know basically if they are low, medium or high salt sweaters,” Lim says. “And you are right in the middle.”