CORE Sensor
For us ultramarathoners, pushing the limits of human endurance is, quite simply, what we do!!! For those of us who are managing to cover the bases of our training and do the basics right, those marginal gains can make a significant difference. One such gain comes from heat acclimation—a process that has a long list of potential benefits, ranging from the obvious improvement in toleration of warmer conditions, through to improved lactate threshold, lowered metabolic rates, and several more!
In this blog, we’ll explore the scientific backing of heat acclimation, its benefits in ultramarathon contexts, specific protocols used in studies, and my personal experience testing the CORE Sensor body temperature monitor designed for endurance athletes.
The Science Behind Heat Acclimation
Heat acclimation involves exposing the body to elevated temperatures over a period, prompting physiological adaptations that improve thermoregulation and performance. Key adaptations include:
- Increased Plasma Volume: Enhances cardiovascular stability and sweating capacity.
- Improved Sweat Response: Earlier onset of sweating and increased sweat rate help dissipate heat more effectively.
- Reduced Heart Rate: Lowers cardiovascular strain during exercise in the heat.
Julien Periard is a researcher that is at the very forefront of environmental physiology in sports and has published a large handful of papers on heat acclimation and the focus of his current research is on developing policies for safely exercising in hot environmental conditions and using exercise to maintain or improve resilience to rising global temperatures.
Benefits in an Ultramarathon Context
Ultramarathons often involve prolonged exposure to the elements, making heat acclimation particularly beneficial. The adaptations from heat training can lead to:
- Enhanced Endurance: Improved thermoregulation delays fatigue as well as improved muscle glycogen sparing
- Better Hydration Management: Efficient sweating conserves electrolytes.
- Adaptability to Temperature Fluctuations: Prepares the body for unexpected weather changes during races.
Research indicates that even in cooler environments, heat-acclimated athletes outperform their non-acclimated counterparts, gaining that “extra 1%” that can be pivotal in competitive settings (bear this “competitive” comment in mind for some of my thoughts later in this article!)
Specific Protocols Used in Studies
Effective heat acclimation protocols typically span 7-14 days and involve daily heat exposure sessions, although longer, slower protocols can be done. Key components include:
- Duration: 60-90 minutes of exercise per session. Which is what CORE recommends for the most part
- Intensity: Moderate exercise (50-75% VO2 max) to elevate core temperature sufficiently.
- Environment: Training in hot conditions (e.g., 35-40°C with 40-50% humidity).
For example, a protocol used in a study by Périard et al. (2015) had athletes perform cycling sessions in a heat chamber at 40°C for 10 consecutive days, resulting in significant performance improvements.
My Experience with the CORE Body Temperature Monitor
To put theory into practice, I tested the CORE Sensor body temperature monitor over the past month, the device is aimed at optimizing heat acclimation training.
Firstly, I tried to put myself into the shoes of a typical excited person with a new toy and I got the CORE Sensor right out the box, quickly scanned the instructions, attached it to my chest HR monitor, and went for an 80-minute run, which just so happened to be an interval session done at 10km effort, so pretty intense. I got back to see that I had barely gotten into the middle of the first heat training zone, of which there are 4 and you need to be in zone 3 to get the benefits from the session! It also fell off… twice!
The next “session” I did, was on my treadmill. Partly because I was scared that I was going to lose it, but also because I have a thermometer on the wall next to my treadmill (from doing previous heat acclimation protocols) and ensured the heating was on, doors closed, no fans… this time it was a 12×5 minute threshold treadmill hills at 8%… pretty brutal! This time I did get into zone 3, but only just and not for long!
Third time, I got myself a heat suit! An RDX one from Amazon and jumped on the treadmill again… this is clearly the way to do it, because after that brutal treadmill session where I emptied the tank and had my HR just about as high as I have seen it, it had to be warmer! This time, it worked a treat as I got into the 3rd heat zone within 20 minutes and spent the next 60 mins at a quite easy intensity and HR in low zone 2 and it stayed there without having to destroy myself!
I have since used the CORE Sensor on several occasions, apart from one long run outside (where it fell off my HR strap and I had to run an extra 3 miles trying to find it. Luckily, I did!!), all indoors on my treadmill and on one Zwift bike session, and have been seeing the Heat Adaption score on the CORE app (which is very simple to use and easy to understand) increase steadily and, crucially, my tolerance for heat has, anecdotally, been improving… I am normally one for “enjoying” inclement weather conditions and some of my own best ultra performances have come during torrential rain, wind, cold and Welsh mountains or the Lakes!
I am going to continue to use this device, especially as I am looking to run a championship time for London marathon which is then fairly closely followed by a tilt at the South Downs Way 100 and Lakeland 50. All 3 of these events will need me to be finding that “extra1%”.
Do you need to find that extra 1%?
Which kind of leads me to my next point, and, I believe, an important one.
There is a list of other things you should be nailing before even thinking about a device like this; your training load; training structure; strength training; mobility work; sleep; nutrition; hydration (which is also VERY important in heat training… you will get very thirsty!) I would say it is important to make sure you are nailing all the above before you start thinking about a device like this.
Sure, heat training will help anyone get used to the heat they might experience in a race. But we know that heat training is a stress, and when you add that on top of training, which is a stress, these heated training sessions can be exhausting due to adding stress on top of stress. It’s a lot of stress for folks who probably also have a lot of other stress, like kids, jobs, etc
If you are competitive and looking for that extra 1%, then I absolutely think a device like this could be helpful, and potentially even necessary, and you and your coach who can help you manage your stress load can add this into your training.
Summary on the CORE Body Temp Monitor
- Recommendation for Warm Race Training – If you’re preparing for a warm race or seeking marginal gains in your training, I would recommend using the Core monitor. It provides real-time data on your core temperature (which I found to be quite accurate having monitored it against a digital thermometer), helping you stay within optimal training zones.
- Get a coach, if you don’t already have one – I would highly recommend working with someone who understands the concept of heat training with this device. Whilst CORE provide good educational content, there is some serious balancing to do with regards to stress load
- It falls off, a lot – If you do wear the device outside, make sure it is well secured. It came off my HR monitor 3 times, one of which I had to retrace my steps and luckily found it!
- Cost Considerations – In my opinion, the device is expensive at £230. For many athletes, this is a significant investment, and it’s essential to consider whether the potential benefits justify the cost. Add in to the fact I laid out another £60 on a sauna suit which helped me achieve the desired training zone. In retrospect, wearing extra layers could have been a more cost-effective solution… having said that, I heard David Roche talk about his heat training “suit” (a puffer jacket and hoodie!) stank bad in the build-up to Javelina Jundred!!!
- Challenges in Achieving Desired Training Zones – Training in adequately warm conditions is crucial. Simply wearing the device indoors isn’t enough to reach the optimal heat acclimation zones recommended by Core (Zone 3 of 4). During a rigorous session—12 intervals of 5 minutes at threshold pace on an 8% incline treadmill—I was drenched in sweat but only reached halfway into Zone 2.
Final Thoughts
There are absolutely no doubts that heat acclimation is a scientifically supported method to enhance endurance performance, offering significant benefits for ultramarathoners, and I will absolutely be using my CORE sensor for my training. While devices like the CORE body temperature monitor can aid in optimising training, they come with practical limitations and additional costs.
Considerations Before Investing
- Are you nailing the basics of your training? – as above mentioned, training load, specificity, nutrition, sleep, hydration. All aspects you should be 100% on top of before looking for the “fancy” stuff like this
- Assess the Cost-Benefit Ratio: Weigh the device’s price against the potential performance gains.
- Indoor vs. Outdoor Training: Be prepared to use the device primarily indoors… especially in the UK. It simply doesn’t get warm enough here to use it outside!
- Additional Equipment: You may need to create artificial heat stress (e.g., sauna suits, extra clothing).
- Alternative Approaches: If investing in a
high-costdevice like the CORE sensor isn’t feasible, traditional heat acclimation methods—like training in warmer environments or wearing extra layers—can also be effective. A preference of mine, which is less stress load and shown to be highly effective, is a passive approach using a sauna protocol of 7-10 sessions of 20-30 minutes in the two weeks prior to your race.
Nick Hancock is a UESCA Qualified Ultra Running Coach and Performance Nutrition Coach, UKA licensed and has coached many people to successful ultramarathon races such as UTMB, Arc of Attrition, Ultra-Trail Snowdonia, Dragons Back, The Spine, CCC, Canal Corridor, Race to The Stones, Endure24, Chiltern Wonderland, Wendover Woods and many more
