As a public safety provider in Las Vegas we repeatedly heard the phrase, “It is a dry heat.” When summer temperatures soar above 100 degree and stay there overnight radiating into the next day, it is common to retreat to a chilled dayroom in the fire station.
Company officers push their crews to pre-hydrate as at any time a vehicle crash or fire during the midday desert heat would tax even the most physically fit firefighters. This is compounded in areas where humidity decreases the efficiency of the turnout ensemble’s vapor barrier.
While most rehab efforts focus on what to do after the exertion or during the event, science is now revealing that conditioning with heat may make a firefighter more resilient to the heat stresses of firefighting. In the past, working out, running or doing drills in the heat was seen as reckless and for the “animal crews.”
The discovery of heat and cold shock proteins has given us a look at how the body adjusts to temperature fluctuations. Heat shock proteins are a family of proteins that are produced by cells in response to exposure to stressful conditions.
They were first described in relation to heat shock by exercise physiology labs. However, they are now known to also be expressed during other stresses including exposure to cold, UV light and during wound healing or tissue remodeling.
Proteins at work
Exercise causes heat shock (muscle temperatures of up to 45 degrees C or 113 degree F and core temperatures of up to 44 degrees C or 111 degrees F) and oxidative stress or the generation of peroxide or hydrogen peroxide. The concentrations of at least 15 possible heat shock or oxidative stress proteins are increased in skeletal muscle, heart and liver by exercise.
These proteins peak in an hour after exertion and heat stress and return to normal approximately six hours later.
It may seem trivial to worry about the degree of heat or cold you are subjected to in the course of daily operations. However, much the same way we are concerned about the daily exposures to benzene, carbon monoxide, cyanide and host of other free-radical chemicals, temperature fluctuations can have the same damaging effects — particularly on proteins.
Proteins are one of the key building blocks for all things important, from the myelin sheath coating nerves and brain cells to more heat-sensitive organs like the kidney, pancreatic tissue, heart muscle and a host of circulating proteins in the blood, lymph and interstitial fluid. The human body is in a constant state of need for proteins to replace or repair these systems.
For a protein to be functional it has to be folded correctly; think of it as piece of origami where the geometry of the protein is key to how it integrates into a targeted location in the body. Heat and cold can cause proteins to change their folding and become dysfunctional.
Improperly folded
When a protein is dysfunctional, it is either identified as defective and eaten by the immune system or, in the presence of an immune system overwhelmed by stress or inflammation, goes unrecognized and becomes cancer.
In the absence of properly folder proteins, other diseases like muscular dystrophy and neuromuscular disease can arise.
Consider an improperly folded hemoglobin molecule (protein) that we commonly see after carbon monoxide exposure. Carbon monoxide changes its geometry by attaching to the hemoglobin in a slightly different way than oxygen, effecting the folding as it locks on and decreases the hemoglobin’s ability to carry oxygen.
Even more dangerous is the increase agglutination or clotting ability of hemoglobin when it is folded in this manner.
An increase in temperature also decreases hemoglobin’s ability to carry oxygen. This could be a contributing factor to firefighters’ high rate of sudden death.
This trifecta of impacts — carbon monoxide, dehydration and now heat stress — thickens the blood and enables a clot to form and do the damage for what is commonly seen as a cardiac death.
Heat shield
Enter in the heat shock protein. When the body senses heat stress, it can secrete a protective protein to compensate for the heat. The most common heat shock proteins are 40, 70 and 90. There are other smaller heat shock proteins and similar molecules called chaperonins.
Their job is very simple: protect the formation of proteins to ensure it folds correctly and makes it to the cellular apparatus that properly delivers it to the target organ.
Malformed proteins often trigger an immune response. An immune response in turn usually involves inflammation.
This very detailed protein science is important to the fire service because inflammation is often the fuse that triggers cancer. Heat shock proteins are part of the body’s protective mechanism to defend against heat and some other triggers of inflammation. More important is the ability for heat shock proteins to protect and ensure the correct protein construction.
The science is now indicating that heat-related conditioning can improve fitness and alter the circulating heat shock proteins.
One study from the University of Oregon tracked the performance of cyclists over a 10-day training period in 100-degree heat. Another control group did the exact same exercise regimen in a much more comfortable 55-degree room. Both groups worked in 30 percent humidity.
Get results
The results showed that the cyclists who worked through the heat improved their performance by 7 percent, while the control group did not show any improvement.
The experimental group not only achieved a level of heat acclimation, but the training also helped them to function better in cooler environments. The profile for a cyclist is similar to a firefighter requiring a combination of strength and endurance.
What it means from a rehab perspective is the need for workouts that use heat for acclimation verses cooled gyms and low air-conditioning settings in the station. Acclimatizing to heat can take anywhere from seven days to three weeks depending on a person’s risk factors for heat stress.
Programs like P90X or Cross Fit may be helpful, yet there is little research on these workouts involving firefighters. However, studies on animals showed that using a treadmill for 15 to 40 minutes at a 4 percent grade in a warm or hot environment is enough to trigger heat shock proteins.
Yet the effects of acclimatizing can be lost in a short period of time and declines in as little as two to three days. After seven days out of a hot environment, a person is no longer acclimatized and must restart the process.
In the future, we may see a finger-stick test or some sort of testing process much like the way endurance athletes use lactate meters to identify when they have reached a point where muscle breakdown is occurring.
Until then, acclimating in a warm environment with a cardio workout in short increments may be a lifesaver and maximize the benefits of the rehab process.
