As the science of quantifying human performance becomes more common, biometric tracking services have burst onto the athletic field as a tool to optimize player performance. Increasingly, research shows that monitoring certain biomarkers, such as hormone and glucose levels, yields data that can be used to personalize training and custom-tailor athletes’ nutrition and workout regimens. Dozens of players in the NBA, NFL, and MLB, as well as U.S. olympic athletes, are using DNA and blood tests to gain insight into their genes and biochemistry.

The term biometrics refers to the science and technology of measuring and analyzing biological data, including hormone and glucose levels. A handful of startups are making inroads in the sports biometrics market: Catapult, Insidetracker, DNAFit, Whoop, and Agewell are arguably the most publicized.

Though each company differs in its approach to biometrics tracking, all of these startups offer services that include a blood test and screening. Following bloodwork, each user receives a personalized report providing an inside look at his or her biochemistry. The reports—usually an analysis of 30 to 40 biometric markers—contain detailed information about users’ internal organs and functioning. Typically, the biometric markers in the analyses include (but are by no means limited to) the body’s glucose levels, hormonal levels, cholesterol, vitamin D and vitamin B levels, and red blood cell count.

Metrics Mean More Home Runs

Athletes who pay attention to these analytics do so to maximize their health, energy, and preparedness for competition. Players apply the data in more granular ways, too. Within Major League Baseball, veteran Pittsburgh Pirates pitcher Mark Melacon is among a growing number of players who use biometrics to inform their training. Melacon uses the data from InsideTracker to keep an eye on his cortisol levels.

Notably, the Playing Rules Committee for MLB approved two devices for use during the 2016 season: the Motus Baseball Sleeve, which measures stress on elbows, and Zephyr Bioharness, a kind of smart sensor patch that monitors heart and breathing rates.

Better Cycling Through Biometrics

And baseball is just one of many sports in which biometrics monitoring has become trendy.  At the 2012 Summer Olympics in London, the U.S. women’s track cycling team won the silver medal. The team says their use of biometrics data helped them accomplish the feat. Data provided by InsideTracker identified cyclist Sarah Hammer’s vitamin D deficiency. Another member of the team, Dotsie Bausch, learned she had what’s known as “the sprinter’s gene.” The knowledge about Bausch’s DNA resulted in a revision of the women’s race strategy, as well as a total overhaul of Bausch’s individual olympic training.

More than a dozen NBA teams are using products made by the sports biometrics company Catapult, according to a report written in July 2015 in Reach magazine. The Bulls, Mavericks, and Spurs are interested in monitoring players’ exhaustion levels, in particular.

There’s no question the growing popularity of biometrics tracking among pro athletes is notable. But why is this trend so significant?

Athletes’ interest in biometrics data is part of a larger trend:

The recent interest among athletes represents the tip of the personalized medicine iceberg. With growing interest and rapidly advancing technology, we can expect the cost of biometrics screening to decrease and become more popular among mainstream consumers within the next few years.

What about privacy issues?

Blood contains a lot of personal information. The same biometrics data that can optimize an athlete’s performance is also the most personal data imaginable: records of heart rate, speed, strength, their ability to withstand blows. It’s not far-fetched to think an NFL or MLB team might consider this data before trading a player, or before renewing a veteran’s contract. For MLB players especially, blood tests are fraught with the sport’s long history of steroid and amphetamine use.

For sports franchises, athletes are investments:

Team owners and trainers have a financial incentive to encourage this kind of monitoring. In an article published in The Atlantic, Leslie Saxon, the director of USC’s Center for Body Computing, discusses the power of money to incentivize in this way. Professional athletes, Saxon points out, are “the most expensive human real estate in the world,” and in the future, coaches and trainers will undoubtedly rely on biometrics to safeguard athletes’ health and prevent player injuries.

Still, some critics remain skeptical of biometrics and of the performance optimization trend. They believe its potential to improve performance is overemphasized. And yet, athletes who monitor their biochemistry aren’t expecting their earned run average to plunge, or their points per game numbers to skyrocket. Players appreciate that the import of biometrics data is subtle.

It will be interesting to see what the performance optimization trend will look like several years down the road. Once biometrics tracking is ubiquitous among serious athletes, it’s likely that its usage will become more widespread and mainstream. Sure, biometrics tracking could be a fad. But it might also be the key to achieving wellness—for athletes and ordinary folks alike.