Want to leverage wearable tech like a World Cup athlete? Here are the metrics to track

By Jacqueline Howard and Andrew Quimby, CNN

(CNN) — Millions of people around the world wear smart rings and fitness trackers to keep tabs on their sleep, workouts, heart rate and even body temperature, all in the name of better understanding their health. But at the World Cup, that same technology is being pushed to an elite level.

In a tournament where the margin between winning and losing can be razor-thin, players are not only tracking biometric data, they’re leveraging it to fine-tune recovery, manage fatigue and unlock even the smallest performance gains.

Players have been spotted training and competing with commercial devices – such as sweat patches, WHOOPs, Oura Rings and performance vests – highlighting how consumer wearables continue to reshape the science of elite sports and, in turn, influence how athletes at every level train.

‘Technology as part of the game’

Most professional athletes are looking for every percentage point of data that might help give them a competitive advantage on a world stage, said Dr. Justin Mullner, sports medicine physician at Orlando Health Jewett Orthopedic Institute, who is the head primary care sports physician for Orlando City SC in the MLS and the Orlando Pride in the NWSL.

“These data points can then be used to follow trends and help the athlete know when their sleep is suffering or when they are not recovering as well as they usually do, so that they can intervene and change behaviors to get back on track,” Mullner said in an email.

“The data set produced by the wearables is likely more than enough for the casual athlete or weekend warrior, but it is only one small piece of the puzzle used by athletes at the highest levels,” he added.

For elite athletes, Mullner said, commercial wearables are often used in tandem with other monitoring systems such as clinical examinations by athletic trainers or physicians, and blood and urine tests.

Sweat patches

Many professional soccer players started using commercial wearables long before the World Cup kicked off.

Leading up to the tournament, a high-tech “sticker” that measures sweat played a major role in helping players on the Brazilian team train and prepare.

“Earlier this year, the Gatorade Sports Science Institute worked extensively with the Brazilian national team, conducting sweat testing with players to generate personalized hydration insights, including individual sweat rate and electrolyte loss profiles,” said Roozbeh Ghaffari, CEO and co-founder of Epicore Biosystems, which partnered with Gatorade to deploy the Gx Sweat Patches.

The Gx Sweat Patch sticks to the body and works by measuring sweat rate, fluid loss, sodium concentration and sodium loss. The patches are single-use, and they connect to a smartphone app where users can monitor metrics and gain insights on hydration needs and recovery during high-intensity workouts.

“Think of it as a smart sticker. You apply it to your skin, and it contains tiny micro-channels – almost like swim lanes – that fill with very small amounts of sweat. That’s where the science happens,” Ghaffari said.

“The patch has built-in chemistry that analyzes the composition of your sweat. It measures both the sodium concentration and the amount of sweat that’s been collected,” he said. “Those two pieces of information are incredibly valuable to sports scientists because they help personalize hydration strategies for both elite athletes as well as everyday athletes.”

Fitness bands

One wearable device that some players have been sporting during World Cup matches is the WHOOP fitness band. Worn snug against the skin on the wrist, bicep or other WHOOP Body locations, it monitors health metrics including sleep, strain, stress and heart rate.

“While we don’t have a commercial partnership with any national team, many organisations and individuals choose WHOOP to help maximize their performance during such an intense competition. … England is one of those teams,” Greg Grosicki, a data scientist at WHOOP, said in an email.

“England will cross multiple time zones as they progress through the tournament,” he said, which means players may struggle with jet lag and fatigue.

Travel and sleep disruptions can have a significant impact on any athlete’s performance. Grosicki said that WHOOP data – not collected from the players but in research studies – shows that on days users log travel or jet lag, heart rate variability can drop about 9%, sleep performance may fall by up to 6 points, and sleep consistency can be up to 19% lower.

“For a squad that’s flown from the UK to North America and onwards, those numbers are meaningful,” Grosicki said.

Smart rings

Another fitness tracker hitting the World Cup stage is Oura Ring. The US Men’s team received Oura Rings through a partnership that the wearable tech brand has with US Soccer, said Doug Sweeny, Oura’s chief marketing officer.

The players are not required to wear the Oura Rings, according to US Soccer, but if they choose to do so, some of the health data could help them more closely monitor sleep patterns, skin temperature, blood oxygen, recovery and their readiness score, a metric that considers resting heart rate, heart rate variability and body temperature.

These metrics could help inform when players may benefit from more recovery before or after training and when their bodies may be primed for more intense workouts.

Officials at US Soccer said they are being “mindful” about educating athletes on how to gain insights from their devices in a healthy way, for both psychological and physical health. For instance, if a player has a bad night’s sleep before a match and their readiness score is down, that could get into their head and erode confidence. Sports scientists and coaches encourage players to not treat a single metric as a final verdict on how they will perform.

Players were previously forbidden from wearing any jewelry on the pitch, but as of Wednesday, the International Football Association Board’s Laws of the Game have loosened FIFA’s restrictions: “Accessories are permitted if they are not dangerous and if safely and securely covered.”

Performance vests

Twelve nations have been utilizing GPS tracking systems from the sports technology company STATSports throughout the World Cup, primarily in a performance vest that monitors physical data in real time, including speed, heart rate and distance.

England is using STATSports technology to provide live in-game GPS performance data at a World Cup for the first time. The system enables coaches and sports scientists to monitor player workloads and physical performance throughout the tournament.

“GPS data is measured through small units within vests that players wear. The unit is situated on the players upper back to ensure optimal signal from the military grade satellite navigation system,” Phil Keehne, director of sport science with the MLS team FC Cincinnati, who is affiliated with STATSports technology, said in an email.

“England are among those teams whose performance staff will have a live dashboard updating in real time as the game unfolds,” Keehne said. “As a result, the metrics at practitioners’ fingertips are endless, enabling them to be proactive – instead of waiting for a player to look tired, staff can see fatigue accumulating in the data before it shows on the pitch.”

For instance, if a player’s real-time metrics may indicate excessive workload, injury risk or fatigue, the staff may decide to replace them with a substitute in order to preserve them – a decision made considering that this year’s World Cup features more matches than ever.

Other teams using this technology during the World Cup include Scotland, Belgium, Bosnia and Herzegovina, Croatia, Curaçao, Ecuador, Ghana, Jordan, Portugal, Qatar and Saudi Arabia.

“We are now at a level where a number of players have reached the World Cup stage with access to multiple forms of technology throughout their careers,” Keehne said. “With that being said, players have now become accustomed to technology as part of the game, and they are just as intrigued with their GPS numbers as sports scientists.”

The metrics you can leverage

Whether the goal is competing on the world’s biggest stage or simply feeling healthier and more energized each day, the same insights that support elite athletes are increasingly helping everyday people better understand their own bodies.

Sleep

Sleep has become one of the most closely monitored performance variables in professional sports. Research has shown that not getting enough quality sleep may sabotage muscle recovery, compromise cognitive performance, impair reaction time and raise the risk of injury.

“For most people, very simple changes to sleep habits can make an enormous difference,” Chris Danforth, professor of mathematics and statistics at the University of Vermont, who has published more than a dozen papers on wearable devices, said in an email.

“Focus on the consistency of when you’re going to bed each night, and on not eating in the few hours prior,” he said. “And if you have a habit of becoming a bit obsessed with data, I suggest only opening the app once a day.”

For the average weekend warrior or casual athlete, the “most accessible” data points to help improve performance and well-being include metrics related to stress and recovery, which can help you know when to do high-intensity workouts versus when to take an extra rest day, Mullner said.

For instance, if your wearable indicates that you slept well the night before, your body may be more primed to take on an intense workout, versus if you had a low sleep score.

“I’m a huge fan of sleep monitoring,” said licensed athletic trainer Dr. Douglas Casa, board of trustees distinguished professor at the University of Connecticut and chief executive officer of the Korey Stringer Institute, where he studies the impacts of heat on the body.

“There’s no question it helps with fitness and having an idea of the ebbs and flows of people knowing if there’s impending illnesses or how much stress particular events have caused them,” he said. It also can help encourage athletes to pay closer attention to any behaviors that may affect the quality of their sleep.

“There’s no question sleep quality is influenced by if you’re in the heat versus not. And if you don’t rehydrate well after an event, you’re not going to sleep as well. If your body temperature is higher after an event, you’re not going to sleep as well,” Casa said. “So the sleep monitoring is super helpful to kind of reinforce to the athletes the importance of getting temperature down and being hydrated.”

Hydration

Hydration is another important metric for athletes, as it can influence regulating body temperature, endurance and even cognitive function.

“Monitoring of hydration can be extremely beneficial to the everyday athlete when doing intense exercise in the heat because it serves as a valuable reminder about the need to rehydrate,” Casa said. “When not exercising, they should follow the WUT principle: Weight, urine color and thirst are excellent indicators to assess every morning, but during activity, the objective data of a hydration wearable can be critical to stay on top of the rehydration process.”

Body temperature

Maintaining a healthy body temperature and staying hydrated remain critical for any athlete. And while the weather this summer was always expected to be a challenge, the heat wave sweeping the US has made monitoring the temperatures of World Cup players an even higher priority.

Tracking skin or body temperature with wearables can provide insights into heat stress and recovery, but they also may offer early warning signs of illness, since an increasing body temperature could signal a looming fever.

“For example, individuals who catch a virus often learn from the Oura ring that their body is dealing with something several days before the first symptoms appear, allowing them to focus on sleep, nutrition, and recovery much sooner. The benefit to the team comes from players being able to be at their best when it counts,” Danforth said.

Heart rate variability

Heart rate variability, another key metric, provides insight into how well the body’s nervous system is adapting to physical and mental stress, helping athletes balance training intensity with recovery.

As a data point, heart rate variability is the measurement of how much the time between your heartbeats may slightly fluctuate. These variations are common, as the heart rate tends to speed up and get more regular during periods of stress, and become slower and allow more irregularity when relaxed.

Heart rate and heart rate variability can indicate how resilient your body is, said Benjamin Smarr, a professor in the Department of Bioengineering and the Halicioglu Data Sciences Institute at UC San Diego, who has used the Oura Ring to study health outcomes.

Low resting heart rate and higher heart rate variability “are good indicators” for cardiovascular health, he said. A higher heart rate variability number could be around 60 to 80, but metrics much higher than that, such as 200, mean someone probably has irregular heart rhythms, which would be a health concern. “Higher is better only to a point,” Smarr said.

For resting heart rate, the average for adults tends to be between 60 and 100 beats per minute, but the more fit you are, the lower it is. Highly conditioned athletes often have resting heart rates around 40.

“For me, my resting heart rate is usually sort of in the mid- to low 40s. That’s pretty good,” Smarr said. “I know that if I go off my exercise or stress is getting to me at work, it’ll creep up, and I know that I can do things about it, and it’ll creep back down.”

Research shows that quality sleep and regular exercise both can benefit heart rate variability as well as resting heart rate in healthy adults.

You know your body best

Monitoring trends in your own health data over time can be helpful in revealing whether you may benefit from changes in your exercise or sleep schedules, said Jud Ready, adjunct professor and principal research engineer in the Georgia Tech Research Institute.

“We’re talking over many weeks, several months and ultimately years, so that you can see, ‘Oh, wow, my resting heart rate is going down, so that means my exercise is working.’ Or ‘it’s going up; that means I need to do more exercise,’” Ready said.

Along with tracking heart rate, Ready suggests quantifying the amount of exercise you get each day, your sleep performance and any emergency medical situations that the wearable device may have detected, such as falls or elevated blood pressure, which you may want to discuss with a doctor.

Similarly, “wearables can also be helpful to detect early changes in health. Big changes in heart rate or respiratory rate or body temperature can be a signal of acute illness or emerging chronic disease which could be more easily mitigated if detected early,” Mullner said.

“They can also improve exercise consistency. The process of collecting and organizing data at your fingertips often motivates you to then continue collecting data and helps to gain momentum in a training plan,” Mullner said. “At the end of the day, good health is the sum of your behaviors, consistency and habits.”

But when using any kind of wearable tech, users should remember that no algorithms are perfect for everyone – so if you personally feel like something is off, you know your own body the best, Smarr said. And to leverage health data from wearables, you still need to take action to make adjustments in your sleep patterns, regular exercise and other behaviors.

“Assuming they’ll make you sleep better or they’ll make your health better, that’s not what they do,” Smarr said. “They’re able to help you navigate, they’re able to make the windshield less blurry, but you’re the driver.”

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