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A small microneedle device that monitors lactate continuously in real time could help coaches make smarter decisions about pitcher fatigue and recovery.

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The modern pitcher throws harder than ever, with explosive bursts of power under intense stress and minimal recovery in between. Fastball speeds have climbed since the early 2000s, and with them, injury rates. Yet one variable has remained hard to measure: muscle fatigue levels.

A new study published in Biosensors and Bioelectronics from Omeed Djassemi, Joseph Wang and their team at UC San Diego used a minimally invasive wearable device, about the size of a postage stamp, to continuously measure lactate levels in the fluid between cells. Lactate is a widely used marker of metabolic stress. When muscles work hard, lactate accumulates. That’s why it’s used as a biomarker of fatigue. Measuring it typically requires a blood draw, but that only provides a snapshot, not a continuous picture of what is happening inside a pitcher’s body.

With the researchers’ wearable device, they were able to assess lactate levels continuously in 11 Division I collegiate pitchers at UC San Diego.  Each pitcher wore the sensor on their non-dominant arm. During the fifteen-minute pitching session, lactate levels rose on average by around 4 mmol/L from resting baseline levels, while heart rate climbed to roughly ninety percent of age-predicted maximum.

So what did the continuous data reveal that blood samples would have missed? There were transient spikes in lactate tied to individual pitches, rises that appeared and resolved within minutes, tracking closely with pitch intensity and ball velocity. That means it is possible to see which pitches are costing the most metabolically, in real time.

Recovery told its own story. Heart rate returned to near-baseline within ten to fifteen minutes of finishing. Lactate took twenty to twenty-five minutes to clear. That gap may matter for coaches. A pitcher can look recovered, breathing normal and composure intact, while his muscles are still under metabolic stress. Sending him back out too early could mean pushing him too soon, before he has fully recovered. 

The results are promising, but the authors are clear about the study’s limitations. It is a pilot study with eleven pitchers, controlled conditions, and a small number of blood reference points for comparison with the wearable sensor measurements.  Larger studies in live game settings are needed to achieve the long-term goal of establishing lactate-guided thresholds for fatigue and using these sensors to help manage workload for athletes across all levels of the sport.

For coaches and athletic trainers, that future could change how decisions get made during a game and how much time a pitcher has to recover. The implications extend beyond baseball too, with most sports benefiting from real-time metabolic data that offer coaches a clearer picture of how fatigued athletes may be.

This study was conducted as part of the Triton Center for Performance and Injury Science, a Wu Tsai Human Performance Alliance Innovation Hub 

Co-authors include Oscar Vila Dieguez, Maria Reynoso, Byungjin Kim, Taylor La Salle, Nicolette Agajanian, Justhine Kaye Placio, Evan Kroll, Chochanon Moonla, An-Yi Chang, Arnel Aguinaldo, Samuel Ward.