Sweat-sniffing sensor could make workouts smarter

If you have ever pushed yourself to the edge in a workout — legs on fire, lungs burning — you have probably crossed what physiologists call a lactate threshold. It is the point where muscles cannot clear a metabolic by-product called lactate fast enough, and performance starts to nosedive.

Athletes train for years to raise that threshold. But knowing exactly when it is crossed still requires lab gear, blood samples and a big interruption to your workout.

A research team at KAUST aims to change that. Atif Shamim and members of his group built a noninvasive sweat sensor that can detect lactate levels in real time using nothing more than microwaves and enzyme-coated glass beads^[1]

No blood. No needles. No power source. Just stick on a cheap, disposable patch, sweat it out and let the physics do the rest.

Here’s how it works: the sensor uses a circuit design technology called a complementary split-ring resonator — essentially a microwave component that is finely tuned to detect subtle chemical shifts. With sweat, lactate molecules react with enzymes inside the sensor, producing hydrogen peroxide. That tiny chemical change shifts the way the sensor reflects microwave signals, creating a digital fingerprint of how hard the body is working during physical activity.

In tests, the device nailed its readings, tracking lactate in sweat across a range of exercise intensities and comparing favorably to more involved chemical analyses in the lab. Even better, it held up across different skin types, fitness levels and environments. Volunteers with higher endurance had lower sweat lactate spikes, while less fit individuals saw sharp climbs, as expected.

The device is still in an early prototype stage, tethered to a benchtop reader. But with further design optimization, the researchers expect it should be made fully compatible with passive, wireless technology. Ideally it will be wearable patches that beam lactate data to nearby radio frequency-powered readers, uploading measurements to the cloud and making them accessible via an online portal or smartphone app.

“This should allow both athletes and trainers to monitor real-time lactate levels throughout training sessions,” says lead author, Firas Fatani, a Ph.D. student in Shamim’s lab.

What’s more, because the platform uses enzymes to drive specific reactions, it could be retooled to detect other components of sweat associated with health and performance — biomarkers such as glucose, cortisol or hydration levels. Since it relies on microwaves instead of chemical dyes or electrical currents, it is robust, scalable and surprisingly simple, notes Sakandar Rauf, a research scientist on the team.

“We are expanding the sensor’s capabilities to monitor additional biomarkers,” Rauf says — starting with a dual-sensor system for simultaneous glucose and lactate monitoring.

Discussions are under way with Saudi hospitals, gyms and football clubs to pilot the technology. According to Shamim, these partnerships could aid the Kingdom in achieving its Vision 2030 goals for health innovation and wellness.

“This will help improve the quality of fitness plans by designing personalized exercises not only for professional athletes but also for anyone who is interested in pushing their physical limits,” he says, noting that “such sensors will have substantial acceptance as people are becoming more invested in physical health.”