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Heat adaptation for the contemporary soldier.

On the contemporary battlefield, Soldiers frequently endure intense heat typical of the desert environments in the Middle East where temperatures routinely exceed 120 degrees Fahrenheit. This extreme environment requires them to endure intense, daily heat while conducting dismounted patrols for six to 12 hours while covering 10 to 25 kilometers in urban areas, deserts, mountains or broken and wooded terrain.

In addition to the challenges posed by the regional climate, Soldiers wear interceptor body armor Interceptor is a type of body armor fielded by the U.S. military. It is more effective than traditional bulletproof vests and is currently replacing a previous version of body armor known as Personnel Armor System for Ground Troops (PASGT).  and the advanced combat helmet A combat helmet is a helmet designed specifically for use during combat. Helmets are among the oldest forms of personal protective equipment, and are known to have been worn by ancient Greeks and Romans, throughout the Middle Ages, and up to the end of the 1600s by many combatants.  for protection. Further, Soldiers carry a weapon with a combat load of ammunition (usually 210 rounds for an M4 carbine “M4A1” redirects here. For the World War II tank, see M4 Sherman.

The M4 Carbine is a family of firearms tracing its lineage back to earlier carbine versions of the M16, all based on the original AR-15 made by ArmaLite.
), a CamelBak or multiple canteens for proper hydration hydration /hy·dra·tion/ (hi-dra´shun) the absorption of or combination with water.

1. The addition of water to a chemical molecule without hydrolysis.

, a secondary weapon, first aid bags, casualty litters and other miscellaneous equipment dictated by each mission.

This equipment places an incredible amount of stress on the body, adding 50 to 75 pounds of weight and insulating heat around the core body. To mitigate the risks associated with severe environmental conditions and the weight that Soldiers must bear, leaders and Soldiers must understand the importance of heat adaptation to survive the current operating environment In computing, an operating environment is the environment in which users run programs, whether in a command line interface, such as in MS-DOS or the Unix shell, or in a graphical user interface, such as in the Macintosh operating system. .

Heat adaptation. Army units routinely deploy to southwest Asia Southwest Asia or Southwestern Asia (largely overlapping with the Middle East) is the southwestern portion of Asia. The term Western Asia is sometimes used in writings about the archeology and the late prehistory of the region, and in the United States subregion  in support of the ongoing operations in Iraq and Afghanistan. In preparation for their deployments, these units try to replicate every aspect of combat, using the latest training techniques and facilities available. The growing training resources essentially simulate every complex combat scenario imaginable, such as hostile villages, detainee de·tain·ee  
A person held in custody or confinement: a political detainee.

Noun 1. detainee - some held in custody
political detainee
 operations and forward operating base An airfield used to support tactical operations without establishing full support facilities. The base may be used for an extended time period. Support by a main operating base will be required to provide backup support for a forward operating base. Also called FOB.  procedures. Despite these advanced training resources, the extreme heat of the Middle East cannot be duplicated in the U.S. However, Soldiers can overcome this challenge through successful heat adaptation preparation.

Heat adaptation is a response to repeated stress application factors such as solar radiation solar radiation,
n the emission and diffusion of actinic rays from the sun. Overexposure may result in sunburn, keratosis, skin cancer, or lesions associated with photosensitivity.
, temperature, humidity, work and exercise intensity, clothing, fitness, etc. (1) Generally, the adaptation is a response to naturally occurring climatic changes in the environment (acclimatization acclimatization

Any of numerous gradual, long-term responses of an individual organism to changes in its environment. The responses are more or less habitual and reversible should conditions revert to an earlier state.
), heat exposure in an artificial climate (acclimation acclimation /ac·cli·ma·tion/ (ak?li-ma´shun) the process of becoming accustomed to a new environment.

) and training-induced elevations in body temperatures. (2)

This definition is important because heat adaptation essentially is the sum of acclimation and acclimatization, where the "former is induced experimentally in an artificial environment whereas the latter is induced by exposure to natural environments." (3) Thus, heat adaptation's objective, as an outcome of acclimation and acclimatization, is to achieve three primary physiological changes--a heightened sweat response with an increased sweat output, a lower heart rate and a lower core temperature.

The body's sweat response supports the body's cooling mechanism by maximizing evaporative cooling Evaporative cooling is a physical phenomenon in which evaporation of a liquid, typically into surrounding air, cools an object or a liquid in contact with it. Latent heat describes the amount of heat that is needed to evaporate the liquid; this heat comes from the liquid itself and , which lowers the temperature of the peripheral blood peripheral blood Cardiology Blood circulating in the system/body  before its return to the deeper tissues or the body's core. Likewise, a lower heart rate results from a more powerful heart-stroke volume, which enables the heart to regulate the body's plasma levels more efficiently.

As an outcome, the cardiovascular system cardiovascular system: see circulatory system.
cardiovascular system

System of vessels that convey blood to and from tissues throughout the body, bringing nutrients and oxygen and removing wastes and carbon dioxide.
 is more stable when blood is pumped to the skin and muscles or during a significant loss of fluids. These two physiological adaptations drive down the core temperature, which is the final objective of heat adaptation. Therefore, to achieve the physiological responses necessary to complete heat adaptation, an analysis of acclimation and acclimatization must be conducted.

Heat acclimation. Heat acclimation refers to adaptation that can be induced experimentally, while its purpose is to exercise the physiological mechanisms that facilitate adaptation. Physically fit subjects or highly trained individuals exhibit many of the characteristics of heat acclimation.4 Researchers commonly refer to this as partial acclimation and credit the result to repeated bouts of exercise. (5)

Repeated exercise applications yield elevated internal body temperatures, causing an increase in the sweat drive and a subsequent boost in evaporative cooling. The desired results of acclimation are increased heart-stroke volume, blood flow to the working muscles and skin, and increased sweat response during exercise or heat exposure. These results mirror and directly relate to those physiological changes of heat adaptation.


The most important consideration of acclimation for military professionals, though, can be developed in any environment, even cool climates.6 This implies that acclimation can be controlled and achieved at any installation or in any environment before deployment. Soldiers can acclimate through targeted physical training at their home stations. Specifically, morning PT and frequent road marches (foot marches) provide sufficient opportunities to exercise the acclimation responses. To achieve the desired acclimation and its physiological side effects Side effects

Effects of a proposed project on other parts of the firm.
, units and Soldiers can implement some simple training techniques.

Increased stroke volume. An increased stroke volume is achieved through interval training Interval training is broadly defined as repetitions of high-speed/intensity work followed by periods of rest or low activity.

This training technique is often practiced by long distance runners (800 meters and above) although some sprinters are known to train using this
. Conducted properly, interval training stresses the heart through exertion and, ultimately, strengthens it during recovery. A stronger heart enables a more powerful heart-stroke volume, increasing its efficiency with a slowed heart rate.

Eight repetitions of 400 meters (at or below a Soldier's established two-mile run pace) on a track using a three-minute cycle is an entirely realistic option during morning PT. This means that an entire platoon starts a 400-meter sprint together every three minutes "Three Minutes" is the 46th episode of Lost. It is the twenty-second episode of the second season. The episode was directed by Stephen Williams, and written by Edward Kitsis and Adam Horowitz. It first aired on May 17, 2006 on ABC. , but slower runners will get less recovery between sprints. A platoon conducting interval training at least once a week will obtain an increased stroke volume quickly.

Increased blood flow to working muscles and skin. Increased blood flow to the working muscles and skin is accomplished through longer periods of physical activity, stressing the aerobic system and causing the heart to push more blood to the working muscles and skin. In the muscles, more capillaries will open to generate greater blood flow within the muscle fibers. Likewise, larger quantities of blood pump to the skin and cool through evaporation evaporation, change of a liquid into vapor at any temperature below its boiling point. For example, water, when placed in a shallow open container exposed to air, gradually disappears, evaporating at a rate that depends on the amount of surface exposed, the humidity . This process returns cooled blood to the inner organs and allows the core temperature to remain more stable.

Most physiologists and researchers agree that 60 to 90 minutes of continuous physical activity during the warmest hours of the day sufficiently familiarizes the body to such a redistribution of blood. (7) Long, steady distance running throughout a PT session or constant physical activity (a foot march at a pace greater than 15 minutes per mile) for 60 minutes or longer satisfactorily achieves this result.

In addition, some investigations indicate that the same effect can be achieved through shorter duration, moderately intense, continuous running for 30 to 35 minutes. (8) This method adjusts to the time constraints for PT. There is no prescribed frequency or limit on long, steady distance, so platoons should incorporate this activity into PT as frequently as possible.

Increased sweat response. Increasing the sweat rate during exercise allows for greater evaporation on the skin. Through evaporation, the subcutaneous blood cools, returns to the inner organs and regulates the core temperature. Achieving the sweat response is the easiest of the acclimation responses because it is practiced during any activity that results in sweating.

Therefore, most PT sessions will yield an increased sweat response. The body can attain an increased sweat response by training or working in the heat of the day or through exposure to a climate controlled environment.

Although more controversial, wearing extra layers of clothes to create a microclimate microclimate

Climatic condition in a relatively small area, within a few feet above and below the Earth's surface and within canopies of vegetation. Microclimates are affected by such factors as temperature, humidity, wind and turbulence, dew, frost, heat balance,
, inducing a greater sweat response, is an another method. (9) The concern is the additional stress from thermal strain on a subject wearing additional layers.

However, such elite athletes as Meb Keflezighi Mebrahtom "Meb" Keflezighi (Ge'ez: መብራህቶም ክፍልእዝጊ mebrāhtōm kifl'igzī, Tigrinya "their lamp, part of the Lord";) born May 5 1975 in Asmara, Eritrea province, Ethiopia, (modern Eritrea) is , the 2004 Athens Olympic Games Olympic games, premier athletic meeting of ancient Greece, and, in modern times, series of international sports contests. The Olympics of Ancient Greece

Although records cannot verify games earlier than 776 B.C.
 Silver Medalist in the marathon, advocate this method. In preparation for the 2004 Olympic Games, Keflezighi trained by wearing additional layers to prepare his body for the humidity of Athens, Greece. (10) This method supports continuous training in IBA IBA
International Bar Association

IBA (in Britain) Independent Broadcasting Authority

IBA n abbr (Brit) (= Independent Broadcasting Authority
; it creates a microclimate around the body's core area similar to wearing extra layers of clothing.

Acclimation is achieved primarily through work or exercise. It is obvious, then, that PT is paramount to acclimation. Still, it only represents a part of the adaptation process since repeated PT exercises the mechanisms for adaptation but does not result in physiological changes.

Simply put, acclimation is analogous to a runner who trains for the 800 meter run, but then decides to run a marathon. The athlete worked the mechanisms to run, but is not fully prepared for the length of a marathon. To prepare for the longer marathon, the athlete requires considerably more endurance training Endurance training is the deliberate act of exercising to increase stamina and endurance. Exercises for endurance tends to be aerobic in nature versus anaerobic movements. Aerobic exercise develops slow twitch muscles. .

Likewise, Soldiers exercise the mechanisms for heat adaptation through acclimation training. However, they still require exposure to the real elements of the regional environment over a longer, more consistent period of time to complete adaptation. This final phase in adaptation is known as acclimatization.

Heat acclimatization. Exposure to the natural environment induces heat acclimatization and results in improved heat tolerance and decreased physiological strain. The purpose of heat acclimatization is to transfer heat efficiently from the body's core to the skin--ultimately to the external environment--and improve cardiovascular functioning to deal with the stressors of dehydration and a decreased blood volume from an increased skin blood flow. (11)


The primary difference from heat acclimation is that acclimatization requires continuous, long-term exposure to heat. Subsequently, the desired results of acclimatization are somewhat similar to acclimation, yet even more critical and more effective for the adaptation process.

Therefore, the desired results of heat acclimatization are improved blood flow to the skin, decreased heart rate, decreased perception of work exertion and increased sweat output and more effective distribution of sweat. Similar to acclimation, these results reflect the physiological changes necessary for adaptation.

While heat acclimation can occur in any region or environment given certain training conditions, heat acclimatization must take place in the region of interest. Therefore, the only way to achieve heat acclimatization is to live in the environment. Specifically, Soldiers must experience the discomfort of the heat by training, exercising and feeling the physiological strain.

Physiologists and researchers recommend a minimum of 10 to 14 days of living, training and exercising in the environment to acclimatize. The number of days is based on physiological adaptations during heat acclimatization (the point at which approximately 95 percent of adaptation occurs) for variables such as a decreased heart rate, expansion of plasma volume, a decreased rectal temperature, a decreased perceived exertion and an increased sweat rate. (12) This information explains why Army units train in Kuwait for a few weeks before moving into Iraq.

Successful acclimation allows for more efficient acclimatization. (13) First, a higher level of fitness (acclimation) allows subjects to function with a lower heart rate while carrying a greater relative workload compared to unfit subjects. This enables fit subjects to use less energy to complete a greater amount of work and experience less cardiovascular strain during work in the heat. (14)

Second, acclimation improves acclimatization efficiency because a fit subject arrives in the new environment with an already improved skin blood flow and decreased heart rate due to his exercise regime. (15) This suggests that the most important response during acclimatization is the increased sweat output and the distribution of sweat.

It is true that the sweat mechanisms are exercised during acclimation, but only for short durations. Once introduced into the new environment, the body requires the sweat system (as part of the cooling system cooling system: see air conditioning; internal-combustion engine; refrigeration.
cooling system

Apparatus used to keep the temperature of a structure or device from exceeding limits imposed by needs of safety and efficiency.
) to work continuously--day after day, week after week. This is a critical consideration because few locations in the Army can replicate this process.

To acclimatize the sweat system, physiologists initially recommend light exercise during the coolest hours of the day, followed by subsequent daily increases in the intensity of PT and Army training. In no more than 14 days, Soldiers should be ready to conduct training at near normal levels. (16)

One decisive facet of heat acclimatization involves the importance of hydration and its relationship to sweat output. Although hydration is important during acclimation, it is not vital because repeated bouts of exercise rarely last longer than 90 minutes. Thus, once a subject cools down and the sweat system shuts off, lost fluids can be replaced quickly.

Contrary to acclimation, acclimatization does not offer the opportunity to restore lost fluids quickly because the sweat system works continuously. The sweat response may be stimulated as a result of work, yet it does not stop once the work is complete due to intense heat and the body's efforts to cool itself through the evaporation process. In fact, sweat losses in extreme heat often exceed rehydration rehydration /re·hy·dra·tion/ (-hi-dra´shun) the restoration of water or fluid content to a patient or to a substance that has become dehydrated.

 rates. (17) The effect is constant sweat output, challenging the body's ability to maintain healthy plasma levels.

The body's plasma level (fluid levels) declines without adequate hydration (dehydration). This drop in the plasma level yields a less powerful heart stroke, which decreases the heart's ability to pump an ample quantity of blood to the skin. Subsequently, this cycle impairs the body's cooling system.

The heart attempts to push more blood from a lower total volume to the skin by pumping more rapidly. In doing so, the heart rate increases, which consequently elevates the body's core temperature. Ultimately, this negates any previous advantages of acclimatization and potentially can lead to a severe heat injury.

Yet, even with continuous fluid intake, dehydration may be unavoidable. Recent studies conducted in Iraq indicate that "a threshold may exist for water consumption above which additional consumption may not prevent dehydration." (18) Still, dehydration's impacts are so severe that constant hydration is imperative to remain functional in the new environment and complete acclimatization.

There may be no substitute for living, training and fighting under hot conditions in the regional environment to improve performance in the heat. However, through heat acclimation, Soldiers reap the benefits of intense home station PT--especially endurance exercises--to develop the critical response mechanisms needed to improve heat tolerance and advance acclimation. Acclimatization then promotes a reduction in Soldiers' physiological strain when they live in the environment, yet, it is critical to recognize that all Soldiers acclimatize and adapt at different rates.

Finally, Soldiers gain confidence by embracing the discomfort while working in the heat and learning the value of hydration to complete the adaptation process. Properly conducted, these two steps complete heat adaptation, ultimately enabling Soldiers to execute their missions on the contemporary battlefield more safely.

This article is reprinted from the November-December 2008 edition of Armor.


See: Carriage Paid To
 Russell G. Nowels, AR, CPT Coley coley

Brit an edible fish with white or grey flesh [perhaps from coalfish]
 D. Tyler, FA, and Dr. Phillip L. Henson


(1.) Nigel A. Taylor and James D. Cotter cot·ter  
1. A bolt, wedge, key, or pin inserted through a slot in order to hold parts together.

2. A cotter pin.

[Origin unknown.
, "Heat Adaptation: Guidelines for the Optimization of Human Performance," International SportMed Journal, Vol. 7, No.1, (2006),36.

(2.) E.R. Nadel, et al., "Mechanisms of Thermal Acclimation to Exercise and Heat," Journal of Applied Physiology, Vol. 37, No. 4, (October 1974), 517-519. Carl Gisolfi and Sid Robinson, "Relations between Physical Training, Acclimatization, and Heat Tolerance," Journal of Applied Physiology, Vol. 26, No 5, (1969),533-534.

(3.) Lawrence E. Armstrong, Performing in Extreme Environments, (Champaign, IL: Human Kinetics kinetics: see dynamics.
Kinetics (classical mechanics)

That part of classical mechanics which deals with the relation between the motions of material bodies and the forces acting upon them.
), 2000, 3.

(4.) Op Cit Op Cit Opere Citato (Latin: In the Work Mentioned) , Gisolfi and Robinson, 533-534.

(5.) Op Cit, Nadel, et al., 517-519.

(6.) Carl V. Gisolfi, "Work-Heat Tolerance Derived from Interval Training," Journal of Applied Physiology, Vol. 35, No. 3, (1973), 349.

(7.) Ron Maughan and Susan Shirreffs, "Exercise in the Heat: Challenges and Opportunities," Journal of Sports Sciences, Vol. 22, (2004), 919.

(8.) Joseph A. Houmard, et al., "The Influence of Exercise Intensity on Heat Acclimation in Trained Subjects," Medicine and Science in Sports and Exercise, Vol. 22, No. 5, (1990), 618-620.

(9.) Brian Dawson, "Exercise Training in Sweat Clothing in Cool Conditions to Improve Heat Tolerance," Sports Medicine sports medicine, branch of medicine concerned with physical fitness and with the treatment and prevention of injuries and other disorders related to sports. Knee, leg, back, and shoulder injuries; stiffness and pain in joints; tendinitis; "tennis elbow"; and , Vol. 17, No. 4, (1994), 233-243.

(10.) Peter Pfitzinger, "Simulating Race Conditions for Optimal Performance," Running Times, (January-February 2006).

(11.) Op Cit, Armstrong, 28.

(12.) Lawrence E. Armstrong and Carl M. Maresh, "The Induction and Decay of Heat Acclimatization in Trained Athletes," Sports Medicine, Vol. 12, No. 5, (1991), 304.

(13.) Kent B. Pandolf, "Effects of Physical Training and Cardiorespiratory car·di·o·res·pi·ra·to·ry  
Of or relating to the heart and the respiratory system.

Adj. 1. cardiorespiratory - of or pertaining to or affecting both the heart and the lungs and their functions; "cardiopulmonary
 Physical Fitness on Exercise Heat Tolerance: Recent Observations," Medicine and Science in Sports, Vol. 11, No. 1, (1979), 65.

(14.) Christine L. Wells, et al., "Training and Acclimatization: Effects on Responses to Exercise in a Desert Environment" Aviation, Space, and Environmental Medicine, Vol. 51, No. 2, (1980), 106.

(15.) K.B. Pandolf, et al., "Role of Physical Fitness in Heat Acclimatization, Decay and Reinduction," Ergonomics, Vol. 20, No. 4, (1977), 403-406.

(16.) Op Cit, Armstrong, Performing, 28-29.

(17.) Op Cit, Taylor and Cotter, 40.

(18.) Edward Manning and Bradley Wilson, "Dehydration in Extreme Temperatures While Conducting Stability and Support Operations Stability and support operations involve military forces providing safety and support to friendly noncombatants while suppressing and threatening forces.

SASO operations can occur in everything from natural disaster areas (earthquakes, storms and flooding) to insurgencies
 in a Combat Zone," Military Medicine, Vol. 172, (2007), 975.

Captain Russell G. Nowels, Armor, is a Military Movement Instructor, Department of Physical Education at the U.S. Military Academy, West Point, N.Y. He has served as Commander, A Troop, 1st Squadron, 10th Cavalry (A/1-10 Cav), Fort Carson Fort Carson is a United States Army installation and a Census Designated Place located immediately south of Colorado Springs in El Paso County, Colorado, United States and just north of Pueblo, Colorado in Pueblo County Colorado. , Colo.; Assistant S3, 3-3 Armored Cavalry Regiment An armored cavalry regiment (ACR) is a regiment of the United States Army or United States National Guard organized for the specific purposes of reconnaissance, surveillance, and security. , Fort Carson; Adjutant ADJUTANT. A military officer, attached to every battalion of a regiment. It is his duty to superintend, under his superiors, all matters relating to the ordinary routine of discipline in the regiment. , Regimental Headquarters and Headquarters Troop, 3rd ACR See riser card. , Fort Carson; and Executive Officer, G/2-3 ACR, Fort Carson; deploying to Iraq in support of Operation Iraqi Freedom in each assignment. He holds a master's degree master's degree
An academic degree conferred by a college or university upon those who complete at least one year of prescribed study beyond the bachelor's degree.

Noun 1.
 in Kinesiology kinesiology

Study of the mechanics and anatomy of human movement and their roles in promoting health and reducing disease. Kinesiology has direct applications to fitness and health, including developing exercise programs for people with and without disabilities, preserving
 from Indiana University Indiana University, main campus at Bloomington; state supported; coeducational; chartered 1820 as a seminary, opened 1824. It became a college in 1828 and a university in 1838. The medical center (run jointly with Purdue Univ.  in Bloomington.

Captain Coley D. Tyler, Field Artillery, is a Military Movement Instructor, Department of Physical Education at the U.S. Military Academy, West Point, N.Y. He has served in several positions in 3rd Brigade, 1st Cavalry Division, Fort Hood Fort Hood, U.S. army post, 209,000 acres (84,580 hectares), central Tex., near Killeen; est. 1942 on the site of old Fort Gates and named for Confederate Gen. John Hood. It is one of the army's largest installations and a major employer of the area. , Texas, including Commander, Headquarters and Headquarters Company, 3rd Brigade Special Troops Battalion A Special Troops Battalion (STB) has companies from different branches of the Army under a Headquarters & Headquarters Company (HHC).

In an Infantry Brigade Combat Team, the STB has an HHC, an Military Intelligence, a Signal, and an Engineer Company.
; Assistant S3, 2-82 FA; Battalion Fire Support Officer, 2-7 Cav; Battalion S2, 2-82 FA and Company FSO (Free Space Optics) Transmitting optical signals through the air using infrared lasers. Also known as "wireless optics," FSO provides point-to-point and point-to-multipoint transmission at very high speeds without requiring a government license for use of the spectrum. , D/3-8 Cav; deploying in support of OIF OIF Operation Iraqi Freedom
OIF Organisation Internationale de la Francophonie (French: International Organization of Francophonie)
OIF Office for Intellectual Freedom (American Library Association) 
 in each assignment. He holds a master's degree in Kinesiology from Indiana University.

Dr. Phillip L. Henson is an Assistant Professor in the Department of Kinesiology at Indiana University. His activities and research center on understanding and improving human athletic performance, especially through the sport of track and field. He served as the Competition Director for the 1996 Olympic Games in Atlanta, Georgia, dealing with the potential heat issues involving the track and field events, such as the marathons and the 50K walk. He holds a Ph.D. in Human Performance from Indiana University.
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Title Annotation:Transformation: today & tomorrow's Soldier
Author:Nowels, Russell G.; Tyler, Coley D.; Henson, Phillip L.
Article Type:Reprint
Date:May 1, 2009
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