Sports
Real-Time Physiological Monitoring in Endurance Sports
Sports physician José Cruvinel Neto explains how glucose, sweat, and core temperature sensors optimize training and racing.
Wearables measuring interstitial glucose, electrolyte loss, and core temperature are transforming endurance sports. Sports physician José Cruvinel Neto breaks down how to interpret biometric data to optimize nutrition, hydration, and overall performance.
Wearable technology in high-performance sports has evolved far beyond tracking GPS pace and distance. Real-time physiological monitoring—including interstitial glucose levels, sweat rate with mineral loss, and core body temperature—now drives strategic training, nutrition, and recovery decisions in endurance sports. In a conversation on Stemma Performance, triathlete and host Bruna Mahn welcomed sports physician and surgeon José Cruvinel Neto to demystify how athletes can leverage these devices.
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Interstitial glucose monitoring with the Libre
Originally developed for diabetes management, the Freestyle Libre continuous glucose sensor measures glucose in interstitial fluid and has gained significant traction among endurance athletes looking to fine-tune their carbohydrate intake. According to José Cruvinel, the primary goal in sports is not just avoiding performance drops during exertion, but preserving muscle and liver glycogen stores to accelerate post-workout recovery.
The physician emphasizes that analysis should focus on the overall glycemic trend throughout the workout rather than isolated readings. Subclinical hypoglycemia—where glucose levels drop without triggering immediate symptoms—forces the body to tap internal stores prematurely, impairing subsequent protein synthesis. Continuous monitoring also helps pinpoint individual responses to carbohydrate intake rates (whether 60 g/h, 90 g/h, or over 100 g/h) and highlights the risks of fasted training for athletes without high fat oxidation capacity (Fat Max).
Sweat tracking and sodium loss with Nix
Adhesive biosensors like the Nix (and alternatives such as HDrop) analyze sweat in real time to quantify fluid volume and electrolyte and sodium losses per hour. Cruvinel notes that these assessments must account for weather conditions and exercise intensity, serving as a reliable benchmark to calibrate precise fluid and electrolyte replenishment during hot-weather races.
From a general medical safety perspective, standard guidance remains drinking to thirst, which prevents both severe dehydration and exercise-associated hyponatremia (a critical drop in blood sodium caused by drinking excessive plain water). However, for athletes targeting peak performance, knowing exact sweat rates enables precise fueling without carrying unnecessary fluid weight during competition.
Core body temperature and heat acclimation with the CORE sensor
Among the latest innovations, the CORE sensor—clipped onto a heart rate strap—continuously monitors core body temperature during exertion. When internal temperature rises excessively (hyperthermia), ventilatory thresholds decouple: sustainable power output plummets, and the athlete burns through anaerobic reserves unknowingly, heading toward premature exhaustion or heat collapse.
Cruvinel explains that the device helps identify an athlete's functional thermal training zones through progressive ramp protocols (such as the Heat Ramp Test). Structured sessions in this targeted temperature zone stimulate heat adaptation. In competitive settings, detecting that core temperature has breached a critical threshold signals the athlete to ease pace, unzip jerseys, and apply external cooling before bonking or overheating.
Heart rate: chest strap vs. optical wrist sensors
While heart rate is a responsive metric influenced by heat, psychological stress, and hydration status, measurement accuracy depends heavily on the hardware. Cruvinel points out that chest straps (notably Polar models recognized as benchmarks in research and laboratory settings) detect direct cardiac electrical signals, outperforming wrist-based optical watch sensors that often lag during rapid cadence changes and recovery intervals.
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