The Wrong Kind of Sweat: Lactate Sensors and the Sport Horse

At a standardized exercise test, the needle goes in at the jugular. A vein is drawn, the sample run, a number comes back in millimoles per liter, and a trainer decides how hard the horse can work next week. It is routine, it works, and no one particularly likes it, least of all the horse standing still for a blood draw moments after being asked to gallop. So when a wearable patch promised to read the same number from sweat instead of blood, the appeal was immediate. A new study out of Ghent University's Faculty of Veterinary Medicine, published in the Equine Veterinary Journal, looked at whether that promise holds up. The short answer is not yet, and the reason is written into the horse's own skin.

Lactate is the standard currency of fitness testing in sport-horse barns for a reason. As a horse works harder, muscle metabolism shifts toward the anaerobic pathway and lactate accumulates in the blood; how quickly that happens, and at what workload, tells a trainer where the horse's aerobic ceiling sits. A 2022 field study by researchers at the German Olympic Committee for Equestrian Sports measured this directly in competing show jumpers: mean post-exercise blood lactate rose from about 4.1 mmol/L after 1.40 m (4 ft 7 in) classes to about 5.2 mmol/L after 1.50 m (4 ft 11 in) classes, climbing further as the horses aged. The same study found that a jumping-course-specific field test picked up performance differences between horses that a generic, non-jumping field test missed entirely. In other words, the number is real, it moves with the work a horse is actually doing, and it is specific enough to shape a conditioning program. None of that is in question. What is in question is whether you can get that number without the needle.

The Pitch

Annelies Decloedt, Maarten Gijssel, Maria Cuartero, and Gastón A. Crespo set out to answer exactly that in a "science-in-brief" published this year in the Equine Veterinary Journal, testing a wearable sweat lactate sensor on horses at Ghent's veterinary faculty. The device came from IDRO B.V., a company that has built its business on wearable sweat lactate sensors for human endurance athletes, letting a runner or cyclist estimate their lactate levels without stopping to draw blood. Horses sweat profusely under hard work, visibly so, which is part of why the leap to an equine version looked, on paper, like a short one.

It was not. The authors' own review of the human sports-science literature found that even in people, the relationship between sweat lactate and blood lactate is inconsistent: the two don't reliably track each other, and the absolute concentrations differ. Layer a horse on top of that unresolved human problem and the complexity compounds. The paper's blunter finding was practical rather than theoretical: most current sweat-sensing techniques cannot take a repeatable reading without interfering with the exercise test they are meant to monitor, which defeats the purpose of a continuous, non-invasive tool in the first place.

Latherin is the detail worth sitting with. Identified and characterized by researchers including Rhona McDonald and Malcolm Kennedy, whose structural work on the protein was published in PLoS ONE, latherin acts as a wetting agent that lets a horse's coat carry sweat outward and evaporate it efficiently, which is part of why a horse under hard work visibly lathers where human skin would simply glisten. That same protein-dense, detergent-like fluid is what any sweat lactate sensor built for human skin now has to read through. The Ghent paper does not dwell on this specific biochemistry, but it is the underlying physiological reason a device that works on people was never guaranteed to transfer cleanly to a horse.

The Part Worth Naming Directly

One of the four authors, Gijssel, was employed by IDRO B.V. at the time of writing. IDRO B.V. owns the patent on the sensor the paper tested and supplied the units used in the pilot at Ghent. That is a direct financial interest in the technology's success, disclosed plainly in the paper itself, and it deserves equal plain statement here: a company that makes the product helped test the product. Credit where it is due, the paper's actual conclusion is not a marketing one. It reads as a careful, hedged "not yet" rather than a launch announcement, which is the opposite of what an uncritical read of a conflicted study would predict. That caution is worth noting. It does not substitute for independent replication, and none yet exists for horses.

For a sport that already pays real money for anything promising a training edge, the instinct to want this to work is understandable. Riders who track their own training load with wearable sensors, the same instinct behind the data-driven rider fitness programs now common in the sport, will recognize the appeal of applying the same logic to the horse. But wanting a tool to work is not evidence that it does, and the researchers best positioned to know, including one paid by the company selling it, are telling the sport-horse market to wait. Until a study validates sweat lactate against blood lactate in horses specifically, with sponsors other than the device's manufacturer, the vein stays the standard. The number from that blood draw at the in-gate is still the only one with the data behind it.