blog

Apr 17

According to my smartwatch, I hadn't fully recovered from my last workout when I started my run on Tuesday. I assumed this was why my legs felt heavy and stiff. Thankfully, things began to loosen up after half a mile. Feeling a bit more like myself, I glanced at the screen and found my pace was slow and steady, just as intended; however, my heart rate was 15-20 beats higher than typical. With the temperature approaching 85 degrees in mid-April, and my heat acclimation estimated at 3%, this all made perfect sense... If only it were summer. The physiological effect of heat is one of the most predictable risks our clients face each year, so we always make a special point to review it, along with recent trends and findings, as the summer months approach. Although April is supposed to be solidly "Spring," temperatures approaching 90 degrees in several of our clients' territories this week suggest 2026 might have other plans.

At the highest level, three key points regarding our ability to work or perform athletically in the heat are worth reinforcing. (a) Heat increases cardiovascular demand, leading to early fatigue, (b) full adaptation requires about 2 weeks of repeated exposure, and (c) effective mitigation strategies are a critical bridge while our bodies adapt. Let's break down each of these points further.

First, as we point out every year, "heat stress is heart stress". This cannot be overstated. As the body temperature rises, our hearts pump faster to circulate blood closer to the surface, prompting us to sweat and allowing heat to radiate more easily into the environment. This explains the heart rate increase I saw during my run, which is the expected response in the heat for healthy individuals not on heart rate-stabilizing medications (e.g., beta blockers). While an elegant solution to the immediate heat problem, the trade-off is that it is also energy-intensive, shortening our fatigue and therefore risk timeline. Next, while adaptation induces a variety of positive physiological changes that improve performance in hot conditions, it requires 10 days to 2 weeks of steady exposure at temperatures high enough to create an adequate demand, at or above 75 degrees F, according to most sources. This time of year can be especially tricky in that regard because fluctuating temperatures make the physiological "ask" unclear.  Therefore, slowing down, taking breaks, staying hydrated, using cooling strategies to maintain core temperature, and prioritizing sleep are all critical to staying healthy and mitigating risk. Simply put, if we respect the process and acclimate safely, we stand to benefit. Recent studies of elite athletes suggest that training in the heat or even just repeatedly sitting in a hot bath can improve physical performance. In some cases, this improvement is comparable to training at altitude, a well-known and widely studied tactic.

While important, none of this is new or wildly different from best practices used for years. The classic plan for most individuals who must perform in the heat, whether wildland firefighters or special warfare trainees, is very similar to those used in athletics: closely monitor and actively manage risks until acclimatization (acclimation under real-world conditions rather than in a controlled setting) takes place. This must all be done while acknowledging that body size and sex differences can significantly impact the time required for heat adaptation; larger bodies may take longer to adapt.

So what can we do now to prepare for the dog days on the horizon? Start early and use the early-season fluctuations to our advantage. Lower temperature days can act as built-in recovery days, allowing for a longer readiness ramp-up before the steady heat arrives. This recent study showed that a longer acclimatization period produced better results in cognitive performance, reducing the likelihood of critical errors for those who leverage it. Consistent with other protocols, such as the one used by the Indian Military, both training variables (like duration and intensity) and situational variables (such as uniform type and PPE) can be adjusted upward during the two-week protocol to more closely mimic real-world conditions and maximize the effort's benefit.

Whether it's the best cooling strategies or the proper use of sunscreen according to leading dermatologists, there is, of course, so much more to this topic. However, this week's hot shot arrived early enough to give us all a head start; now it's up to us to use it. Get out there and start getting ready, Summer will be here in a blink...

Have a great weekend,

Mike E.