So what did they think?

I just got one of these myself to begin experimenting with (not part of the study).

So far VERY interesting...

I've done the following so far with it
1 x 2:45 long run outside
1 x 30 min easy treadmill run
1 x 90 min endurance ride

i'm looking forward to the improved integration into Training Peaks and looking forward to seeing what the testers have had to say!

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Merge Multisport Founder & Head Coach
USAT Level 2 - Short & Long Course
Ironman Certified
Brevard, NC

I was one of them:

Bottom line up front: First of all it works as advertised. It's small, unobtrusive, and easy to use. The data is quite handy to and easy to understand. The ramp test is easy to do. I used it as a decision making tool.

I live in a hot and humid environment where the dew point stays high enough in the summer that sweat will not evaporate so while I get hot I'm always wet meaning I can't really tell how hot is "hot" until it's too late. This is especially true on the bike and where I get the most benefit from the Core.

I can see the Core data on my Garmin 530 and the data screen is pretty simple. (I like simple). On "hot days", like I said that is almost a constant where I live, I have seen my core body temp reach 103.5 F on the bike and 105F running. More on running in a little bit.

On the bike without Core I know it's hot but I have been fooled by the wind and the breeze generated by riding thinking that I'm not that hot until my performance declines and I don't know why. However with Core it takes the guess work out. I know when I have to use cooling strategies while riding now, dump water over my body, grab some ice at a stop, etc. because Core gives me a number. Being proactive in cooling has increased my performance or in other words decreased the debilitating effect of the heat.

Running is a different matter. Prior to the Core I had to use feel for the heat and HR. When sweat doesn't evaporate it's super hard to guess how hot you are. With a lot of training you can figure out the effect of heat on your HR but there is still a little guess work there. Core gives you a number, tracks histories, and you can see trends. Its a simple processes on my Garmin 945. Before Core I would go by HR and feel. I sweat, I'm wet, I feel ok, so I must be ok until the wheels come off. Now I know when to use a cooling strategy proactively.

The device itself, phone app, and widgets on my two Garmin's are all easy to use. It complements the other data that I track and again it takes the guess work out for me.

For me (and yes, this part is personal) the biggest win for the Core is on the bike. Its really good to know how hot I'm getting and watch the numbers go down when I cool. Its a good mental check for me other than telling myself "This heat sucks". I'm no longer fooled by the conditions. Running is just hard in the heat period and you can only cool so much and keep running. Core is super handy in that endeavor but on the bike, at least for me, it's become essential.

Ok, so this isn’t a cooling device….it’s a monitoring device??

Anything you can say you'd do differently in training based on what you saw?

I started a pretty novice topic on here a year ago or so asking about heat adaptation and also optimizing gains from training. So, basically trying to pinpoint what power zones to train in hot and which to train in indoors or optimally cool like early morning.

Consensus I thought I got from asking that was lower zones when hot and threshold area zones when optimally cooled.

Funny though how it works out that all my free time from family stuff it winds up being that weeknight worlds is super hot or my free time for cooler rides in the AM on weekends is when I can get in more time instead of more intensity. Exact opposite of how I'd prefer it.

Ha... I just ordered based on this thread. Score one for ST driving revenue for Core. I am a sucker for cool tech devices. Plus, I live in a hot & humid climate, and I really want to objectively know how my core temperature is affected by tough conditions and in turn how both correlate with performance.

Very cool! Can’t quite justify the spend, given that HR, wattage (or run pace), RPE, and the occasional post-workout thermometer probably get me close…but let me know if CORE needs Kona guinea pigs. Would love to try it out.

Interesting and useful commentary. I’m on coastal SE USA and have the same issue as the lows will not drop below 75 for the entire summer with a ridiculous dew point. I’ll wait for a few more comments but I’m leaning heavily towards buying one as I’ve been curious about it since hearing Kevin Poulton on various podcasts discussing the product.

I certainly understand being wet and not knowing you’re on the ledge until it’s too late. I’m 6’2, 168 prior to any weight loss and on Sunday I went out for my long 13 mile easy run - it felt cooler than normal, and technically it was, I stopped halfway at just short of 50 minutes and had 16oz of precision hydration. Finished the run and had a 20oz Gatorade on the drive home - shower, get on the scale and boom - 157lbs. That sweat loss is typical for me, but this time it didn’t feel like I’d lost much - I had no idea how close I really was to doing the walk, jog, sit under tree, repeat process.

What actionable items come from it? Or just the nice feeling of knowing you’re getting hot? Have you found anything like a 30sec walk break gets temp down?

Interested to hear more how you use it.

Also - chest or arm? Website makes it sound like chest is preferred but they sell an arm strap. I haven’t worn a chest strap in years.

Correct. Just like a HR strap monitors your HR.

Acclimating to hot conditions has always been an intriguing part of triathlon given our crown jewel event takes place in Kona, Hawaii. The first time I qualified to race on the Big Island was in 2003 and was living in Minnesota. I scoured the forum to see how others living in cooler climates prepared for the heat and humidity of Hawaii (trainer in enclosed room with air heater blasting, multiple layers of clothes, sauna, etc).

Fast forward 18 years, I was ecstatic to learn there was a device like CORE to measure body temperature, and in a simple way, not by having to swallow a pill or sticking a thermometer up the backside (neither of which I would be willing to do, for the record). The device clips onto a heart rate monitor band to be worn on your ribs under your armpit.

Why is heat training important? Yes it helps you perform in hot environments but heat training also helps trigger an increase in blood volume and plasma. According to one of the many cool blogs on CORE's site many of the top coaches they work with suggest 101.3-F is the ideal body temperature to trigger this physiological benefit.

The first thing CORE suggests you do is perform a Heat Ramp Test (somewhat similar to a FTP Test). CORE suggests you do this in a somewhat old fashioned way, on the trainer wearing layers of cloths and without fans for cooling, in order to more quickly pinpoint when the body temperature hits 101.3-F at which time you could determine a Heat Training Zone of between 101.1-F - 101.5-F for subsequent training. This test was uncomfortable but is not nearly as difficult as a FTP test.

Once a Heat Training Zone is established, CORE suggests a 2-4 week dedicated heat training block followed by adding in 2-4 heat training workouts into your regular training in order to retain those adaptations.

I've been living in The Woodlands, Texas (NW of Houston) since 2013 and conditions are nearly always hot and humid. In much the same way those living at altitude experience physiological benefits, I noticed the same training in the heat, though I had no way of measuring or monitoring, only what I perceived. Using the CORE has given me insight into my body temperature at various efforts and how that correlates to other measurements like heart rate and power too. For me, this has become a far more useful number to keep an eye on, as once body temperature climbs past a certain threshold, performance is guaranteed to suffer.

The only downside I experienced was having some initial difficulty connecting the CORE device to my Garmin device, though I am a luddite so this was likely a "me problem". Once connected though, it was easy to use. Keep in mind out of the box the device takes 4+ hours to fully charge, so don't expect to use it directly after opening.

While I have rarely worn a heart rate monitor or used power in years I will continue using this CORE device as a key metric during training and racing.

Happy to answer any specific questions anyone has.

Lars

The answer is yes. Zone 4-5 workouts in the heat is really hard to do and cool. Zone 2 is much more doable and easier to manage but with Core you can figure this out with a number vs feel. And of course my training time availably is like yours.....is always hot during the weekdays when I get off work.....sadly.

Ditto, and why I ordered just based on a few. Most of my runs are ~75° F and at least 90% humidity. My 70.3 runs are typically above 80° and 80%. Saturday I ran a race that was 98% humidity. I can usually wring a small puddle of sweat from my shirt after a run.

I want something that can help me objectively correlate how I am feeling to run performance and my nasty summer weather. So, rather than waiting until I feel super crappy and slowing down involuntarily, I am hoping that this can show me core temperature trends early so that I can back off, hydrate, or pack ice sooner than I might ordinarily and preserve a strong finish.

We must be the same person. I'm 6'2, 167lbs and ran 13 miles last weekend. Heat index was 103....it sucked. I lost 5.7lbs during the run and that was drinking a lot. I live in the SE USA so from June-Oct it's hot and humid 24/7.

I think that's the whole question mark...what actionable items are there to take?

first off it shows me that even trying to run at a very low HR outside in the current climate, my core blows up. So my legs don't get the mechanical loading / stimulus I want for training...so time to go inside to get that load.

I'm hoping to see that I can take structured walk breaks along with ice / cooling towel and can keep my core temp down. but at 102.2 I was done. my Hr very quickly went from staying under 140 up to 160 as the temp climbed over 101.6

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Merge Multisport Founder & Head Coach
USAT Level 2 - Short & Long Course
Ironman Certified
Brevard, NC

I was also part of the Slowtwitch team, and was quite honored to be included in this cool review. Pairing the CORE was relatively easy through Garmin ConnectIQ, and I got it set up as a new data field on my watch and bike computer. The device slides onto a HR strap with a couple of clips or can also be worn with included patches. I've only used it on my HR monitor strap. Once it's on, you don't notice it's there while working out.

I live outside of Boston, and while we don't get the sweltering heat of other parts of the country, the humidity is often very high. My first race of the season was Eagleman, and I was interested to see what my internal body temp was during the race. I got the CORE a couple of weeks prior to the race, so I was able to test it out a bit, but I didn't do the heat ramp test prior to the race. One thing that the CORE validated for me was that once your core temp is elevated, it is pretty hard to reduce quickly. It's not like HR, where easy spinning or coasting down a hill drastically lowers HR. Your core temp may go down .1 degrees F on a 2-3 minute downhill without pedaling. Having this metric and getting to know your temp zones is definitely great for racing. I think many of us have gone past that point of no return, sometimes without realizing it, and the internal temp gets too high to do much of anything. The CORE allows you to monitor your temp and back off a bit to try and stabilize your internal temp on hot days.

As Lars mentioned, the heat ramp test isn't nearly as draining as an FTP test. You essentially eliminate any cooling and ride inside. I wore winter attire - tights, socks, jacket, hat & gloves. The basic idea is that once you hit 38 degrees C you try to hold your HR constant for a period of time. Over time, your power begins to drop as the heat builds up, and eventually you reaching a stopping point. For me, I got to just over 39 degrees C or around 103 degrees F. There is no specified time limit like 20 minutes in an FTP test - more of you know when you are cooked (kind of literally). Then you can go back and look at the data to find your heat training zone for acclimation.

Getting back to the race at Eagleman, unfortunately I crashed coming out of T1 - completely my own error. At that point my core temp was right around 103 degrees. As a result of the crash, I smashed my lower left leg and was unsure of how the rest of the race would go. My power was 30-40 watts lower than planned because of the crash, and this led to my temp dropping over the course of the bike. Down to around 101.8 at the end of the bike. The run was a hobble due to the crash and my core temp pretty much stayed constant a bit under 102. Race conditions were perfect for Eagleman, with cooler temps and lower humidity than normal. I wish I could have seen how I could have gone without the crash, but it was good to see that backing off a bit does get the internal temp down to a lower level.

I've been using CORE on pretty much every run and ride since Eagleman, and I really feel that being able to monitor internal temp is extremely valuable for any training or racing in hot/humid conditions. Having another metric that you can get to track over time to pair with HR and power allows me to begin noticing trends. As I've built back into the training and am getting a bit more heat acclimated I'm noticing that the CORE is giving me slightly lower internal temps at running paces and power compared to a month ago. I've also noticed that even with fans inside, the body temp gets elevated more rapidly than outside. This is kind of a no brainer, but being able to track and monitor the internal temp can help make indoor training even better.

I'm racing in St. George in September, and I definitely plan to do several of the heat acclimation sessions. The gym I belonged to that had a sauna closed during the pandemic, so that isn't an option. I'm happy to try answering any specific questions others have.

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Blog: http://262toboylstonstreet.blogspot.com/
https://twitter.com/NateThomasTri
Coaching: https://bybtricoaching.com/ - accepting athletes for 2023

This is very useful, thanks Nate and others for contributions so far.

Prior to reading this I was curious if anyone had done any sort of protocol, be it sauna, cycling with no fans and extra clothes, etc and could measure a before and after difference. Apparently you’re seeing that. Much appreciated

Excuse my ignorance as I'm not very strong in human physiology. I believe a person's HR increases when their body temperature increases to carry more blood to the skin for cooling. I'm assuming wearing a HR monitor is a lagging metric, i.e. the core body temperature has already increased and what this device provides is an ample warning that action needs to be taken to reduce your core temperature before the HR increases and you bonk. Is that correct? Were you able to study and quantify an approximate time lag between an increase in body temperature and HR increase? On the order of tens of seconds or minutes? Everyone's different but it'd be nice to have a range of what was observed, if any.

If it can be integrated with Garmin devices, I assume you can set it up to alert you at various temperatures...is that correct? Thanks.

Wow! How many minutes was the run? 11 lbs + 1.25 lbs + 1 lb = 6 kg. Assuming you were under two hours, your either not far from a world-record sweat rate (unlikely, given that it was an easy run), or there’s some measurement error.

As a fellow sweaty guy, I feel your pain. Wishing us both good luck and no hyponatremia!

If you include the water/precision hydration stop, run was around 1:45 - run time of 1:42. I’ll say the time to scale also included a 15 minute drive home and shower where additional perspiration definitely occurred.

And while I’ve never had it measured in a lab, I’ve had some pretty big problems over the years with heat in both races and training. To the point that this spring I purchased a pvc sauna suit to not only race prep, but also make the onset of summer more tolerable. I also have a treadmill arriving Thursday as i finally crossed the point of being tired of having everything in the summer be a game of hydration catch up.

ETA: unfortunately not a measurement error. I actually wasted $ on a Garmin scale last year because I didn’t trust the #s on our other cheap digital scale - now I have 2 sources of truth, unfortunately.

With the clip to HRM strap option, is there anything consumable about the device? Or are the pads only consumables if you go with the stick on route?

Ordered!

Same. Will deal with the wife complaining about more purchases whenever she sees it.

Nothing consumable if you put it on a hr strap.

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Blog: http://262toboylstonstreet.blogspot.com/
https://twitter.com/NateThomasTri
Coaching: https://bybtricoaching.com/ - accepting athletes for 2023