Page 71 - Journal of Special Operations Medicine - Summer 2016

Effects of a New Cooling Technology on
Physical Performance in US Air Force Military Personnel

Reginald O’Hara, PhD; Christopher Vojta, MD; Amy Henry, BS; Lydia Caldwell, MS;
Molly Wade, MS; Stacie Swanton, BS; Jon K. Linderman, PhD; Jason Ordway, MS

ABSTRACT

Introduction: Heat-related illness is a critical factor satisfactorily complete specified duties required during
for military personnel operating in hyperthermic envi- SUSOPS missions.
ronments. Heat illness can alter cognitive and physi-
cal performance during sustained operations missions. Humans cool themselves in hyperthermic environments
Therefore, the primary purpose of this investigation was by increasing blood flow to the periphery to shed heat
to determine the effects of a novel cooling shirt on core through radiation at rest. However, during physically
body temperature in highly trained US Air Force person- demanding tasks, blood flow to the periphery is further
nel. Methods: Twelve trained (at least 80th percentile increased to release heat through evaporation, and by
for aerobic fitness according to the American College convection, if air movement is present. Prolonged work
of Sports Medicine, at least 90% on the US Air Force (e.g., in excess of 8 hours) in hyperthermic environments
fitness test), male Air Force participants (mean values: typically results in dehydration from excessive sweat
age, 25 ± 2.8 years; height, 178 ± 7.9cm; body weight and associated sodium chloride losses. Ultimately, the
78 ± 9.6kg; maximal oxygen uptake, 57 ± 1.9mL/kg/ competition between demands for blood flow to work-
min; and body fat, 10% ± 0.03%) completed this study. ing skeletal muscle and to regulate body temperature, as
Subjects performed a 70-minute weighted treadmill well as dehydration from sweat loss, result in physical
walking test and 10-minute, 22.7kg sandbag shuttle test and mental exhaustion as well as thermal injury. 1–6
under two conditions: (1) “loaded” (shirt with cooling
inserts) and (2) “unloaded” (shirt with no cooling in- The most serious form of thermal injury, heat stroke, re-
serts). Results: Core body temperature, exercise heart sults from the body’s inability to dissipate heat, which
rate, capillary blood lactate, and ratings of perceived ex- induces an excessive rise in core body temperature.
7,8
ertion were recorded. Core body temperature was lower A high core body temperature, defined as greater than
(p = .001) during the 70-minute treadmill walking test 41°C, may result in mental confusion, dry skin, delir-
in the loaded condition. Peak core temperature during ium, convulsions, and unconsciousness. 9,10 The estimated
the 70-minute walking test was also significantly lower death rate for subjects suffering from heat stroke is 20%. 7
(p = .038) in the loaded condition. Conclusion: This
lightweight (471g), passive cooling technology offers Precautionary measures included in a military train-
multiple hours of sustained cooling and reduced core ing program include acclimatization procedures, and
and peak body temperature during a 70-minute, 22.7kg ingestion of fluids before and during vigorous physical
weighted-vest walking test. activity. Failure to train troops correctly or use the ap-
11
propriate cooling devices in hot, humid environments
Keywords: cooling; Special Forces; physical activity; hyper- may result in mission mishaps. For example, when heat
thermia; fatigue, volitional accumulation exceeds removal, brain temperatures may
exceed 40°C, resulting in central fatigue, and impairing
the ability of SOF to sustain normal cognitive function
and physical work intensity.
Introduction
Special Operations Forces (SOF) are exposed to aus- Brain temperature is a critical factor affecting motor
tere environments during training and sustained opera- skill ability during exercise in hyperthermic conditions,
tions (SUSOPS) missions. Operations in hyperthermic during which there is an estimated 7% ± 2% greater
environments may impair physical performance and heat production in the brain. Based on these results, the
even result in death. Impaired physical performance mean brain temperature is estimated to be 0.2°C higher
can limit the ability of SOF to adequately sustain and than core body temperature during sustained aerobic

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