Pro Teams Are Warming to a New Core Body Temperature Technology. Should You?
If you looked closely at the grand tour riders this past year, you’d have spied the outline of a little rectangular device sitting on the side of a handful of those in the peloton.
That’s a CORE Body Temperature Monitor, a brand new piece of technology that, like the heart rate monitor it’s paired with, is a “biohacking” device that claims to add another important metric to the training and competition picture.
Deceuninck Quick-Step wore the CORE sensors during the Giro d’Italia last year. The team’s “Wolfpack” is currently using the device during races, hoping to identify where riders get too hot and blow up—like when charging up long mountain passes in grand tours. And Bora-hansgrohe, after test driving the device in the 2020 Tour de France, is on board with CORE Body Temperature monitoring for 2021.
Pro coaches have also taken to manipulating body temperature via heat training to try to amplify performance gains.
There’s scientific evidence that elevating your core temperature during training—through layering, ambient temperature, and/or hot baths—can yield beneficial adaptations, including expanding blood plasma (the watery part of your blood that enables you to sweat and cool down); increasing production of hemoglobin (the protein in red blood cells that carries oxygen from your lungs to your working muscles), raising VO2 max and power output, as well as, perhaps, improving your energy-producing mitochondria function. One recent small study published in the Journal of Applied Physiology even found that soaking in a hot tub for 60 minutes may provide similar post-exercise cardiovascular benefits as 60 minutes of cycling.
Heat training enthusiasts believe those adaptations go beyond improving performance in hot conditions and provide an all-around fitness advantage (an assertion that has been debated for decades).
One such enthusiast is longtime World Tour pro coach Kevin Poulton, who started considering the benefits of heat training for performance while coaching Mathew Hayman in his run-up to his huge win at Paris Roubaix in 2016, just six weeks after a crash at Omloop Het Nieuwsblad that left him training indoors with a broken hand.
“You get more than the VO2 gains,” Poulton says. “The thermoregulation system becomes so much better, that riders come out of an indoor training period using heat training right into a race like Strade Bianche, which can be extremely cold and wet and windy, and tell me they’ve never felt so good riding in the cold.”
Historically, however, it’s been pretty tough to monitor core body temperature outside of a laboratory setting. You can swallow electronic pills, but they’re expensive and the monitoring equipment is cumbersome. Or you can use rectal probe thermometry, which— well, you’re probably not doing that during a training session.
CORE says it can change all that by allowing accessible core temperature monitoring via a lightweight wearable device. CORE gauges your core temperature by using a type of thermal energy transfer sensor that measures the heat leaving the body through the skin. The company claims the device is accurate within 0.21 degrees Celsius.
“This is going to open up a whole new world of training for people,” Poulton, who has no affiliation with the company, says. “This is a big one.”
Leading into a grand tour, Poulton uses the device as part of the taper. “We decrease overall training and have the riders raise their temperature during a short indoor training session and then finish in a hot bath, which effectively maintains the training session while the riders are being passive,” he explains. “The specific heat-training adaptations last four to six weeks.”
The coach also integrates heat training into his own indoor training sessions. “I don’t turn on my fan straight away when I get on the trainer,” he says. “I keep it off until I get my core body temperature to 38.5 degrees [C] and then I turn it on, and I hold that temperature. It’s a simple way to get heat training benefits during your typical indoor training session.”
What Scientists Say About the Benefits of Heat Training
This all sounds great. Even heat training and environmental physiology scientists agree that there are distinct benefits of training in the heat, but some remain skeptical regarding the use of this new technology.
“Our previous research has shown an increase in hemoglobin mass and minor, but significant, changes in parameters of exercise performance,” says heat training researcher Carsten Lundby, Ph.D., professor at Inland Norway University of Applied Sciences, who has conducted a series of heat training studies and is currently in the midst of one on 60 elite riders.
His most recently completed study, published in Experimental Physiology, found that riders who heat trained for five hours a week for five weeks boosted their hemoglobin mass by about 5 percent.
When comparing altitude training to heat training, for example, Lundby says heat training works a little better, “which was a bit of a surprise. It may also be more efficient, cheaper, and easier to do.”
It’s worth noting that, though he believes in the potential benefits of heat training, Lundby, who has not used the CORE sensor, is skeptical about the validity of thermal energy transfer sensor technology like that used by CORE. His team uses rectal thermometers on the athletes they test. “They would like it much more if we used something else. But we have not found another sensor that works,” he says.
It’s also important to bear in mind that most of the research and real-life results from using heat training are coming from elite athletes who are already trained up to their upper-performance limits. Most recreational athletes are not as close to their full potential and could easily make gains simply by training more or smarter through structured coaching.
“The question is whether most riders would find it worth it to engage in five sessions of heat training for one hour for five weeks, or if they’d rather just go out and ride more,” Lundby says. “Maybe, if they’re already training inside anyway because of the weather.”
The problem there is that unless you’re racing cyclocross or concentrating on Zwift racing, incorporating heat-training blocks during the cold, indoor training months makes little sense, Lundby says. “Red cells will return to the values they were before you started heat training within a few weeks, so it doesn’t make sense to do this in the off-season,” he says.
In general, heat training makes the most sense for riders who need to prepare for racing in the heat, says Michael Sawka, Ph.D., chief scientific officer of Environmental Physiology and Hydration Associates, and adjunct professor of biological sciences at Georgia Institute of Technology.
For example, a 2016 study published in Scandinavian Journal of Medicine and Science in Sports found that athletes who took a hot bath after exercise for six days improved their sweat response and boosted their 5K running performance in hot conditions by about five percent. They did not run faster in moderate temperatures, however.
“So if you’re heading somewhere hot for a big event, heat training for acclimatization is important,” Sawka says.
Sawka advocates traditional heat training methods (as opposed to hot water baths). That means taking seven to 14 days and going out and riding at your race intensity for about an hour in the heat. “But that’s a supplement to your traditional training, not a substitute,” Sawka says.
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So What About Monitoring Core Temp in Real-Time?
Both scientists question the value of monitoring core temperature in real-time during competition.
“The harder you work, the higher your core temperature is going to be,” Sawka says. “You can get a very high core temperature if you’re biking. It could be safe. It could not be safe. It really depends on a lot of things, like skin temperature.”
If you’re sweating and the conditions allow that sweat to evaporate to keep your skin cool, you can get your core temperature higher before running into trouble, he says.
“If my skin gets too warm in [hot and humid] Kona, I’ll be lying on the ground well before my core temperature gets to 38.5 [101.3 F; the temperature target often used in heat training],” he says.
Like Lundby, Sawka, who also has not tested the CORE specifically, is skeptical of the validity of thermal energy transfer sensor technology, which he likens to tympanic [ear] temperature readings.
“It might be representative [of core temperature] in some conditions; under others, it’s probably not,” he says.
So Should You Buy In?
Having tested the CORE Body Temperature Monitor for several weeks, I can say it’s intriguing. You can sync it to your Wahoo or Garmin to watch your temperature changes in real-time. A companion app lets you analyze your data after the fact. The monitor is still very new and they’re making improvements to how it interfaces with your devices as well as to their own companion app.
As to questions of validity, CORE has conducted its own laboratory testing against ingested e-pills, rectal thermometers, bladder catheters, and heart catheters. They also have tested CORE versus e-pills in the field with UCI World Team riders during a training camp. Independent studies are underway, but the results are not yet available.
Given what we know (and what we don’t know) at this time, we’d recommend keeping an eye on this emerging trend and seeing how the testing and real-world application in the pro ranks shakes out before buying in. Eager to be an early adopter? There’s no harm in adding a CORE device to your training routine, aside from the fairly steep price: It retails for around $275.
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