A circadian rhythm, or circadian cycle, is a natural oscillation that repeats roughly every 24 hours. Circadian rhythms can refer to any process that originates within an organism and responds to the environment. Circadian rhythms are regulated by a circadian clock whose primary function is to rhythmically co-ordinate biological processes so they occur at the correct time to maximise the fitness of an individual. Circadian rhythms have been widely observed in animals, plants, fungi and cyanobacteria and there is evidence that they evolved independently in each of these kingdoms of life.
Altitude is a distance measurement, usually in the vertical or "up" direction, between a reference datum and a point or object. The exact definition and reference datum varies according to the context. Although the term altitude is commonly used to mean the height above sea level of a location, in geography the term elevation is often preferred for this usage.
Acclimatization or acclimatisation is the process in which an individual organism adjusts to a change in its environment, allowing it to maintain fitness across a range of environmental conditions. Acclimatization occurs in a short period of time, and within the organism's lifetime. This may be a discrete occurrence or may instead represent part of a periodic cycle, such as a mammal shedding heavy winter fur in favor of a lighter summer coat. Organisms can adjust their morphological, behavioral, physical, and/or biochemical traits in response to changes in their environment. While the capacity to acclimate to novel environments has been well documented in thousands of species, researchers still know very little about how and why organisms acclimate the way that they do.
In mountaineering, the death zone refers to altitudes above a certain point where the pressure of oxygen is insufficient to sustain human life for an extended time span. This point is generally tagged as 8,000 m (26,000 ft), where atmospheric pressure is less than 356 millibars. The concept was conceived in 1953 by Edouard Wyss-Dunant, a Swiss doctor, who called it the lethal zone. All 14 peaks above 8000 m in the death zone are located in the Himalaya and Karakoram regions of Asia.
The Combat Capabilities Development Command Soldier Center, formerly the United States Army Natick Soldier Research, Development and Engineering Center, is a military research complex and installation in Natick, Massachusetts, charged by the U.S. Department of Defense with the research and development of food, clothing, shelters, airdrop systems, and other servicemember support items for the U.S. military. It is a component unit of the United States Army Combat Capabilities Development Command and is a tenant unit of the United States Army Natick Soldier Systems Center (SSC). The installation includes facilities from all the military services, not just the Army, and is so configured to allow cross-service cooperation and collaboration both within the facility and with the many academic, industrial and governmental institutions in the Greater Boston Area.
Aviation medicine, also called flight medicine or aerospace medicine, is a preventive or occupational medicine in which the patients/subjects are pilots, aircrews, or astronauts. The specialty strives to treat or prevent conditions to which aircrews are particularly susceptible, applies medical knowledge to the human factors in aviation and is thus a critical component of aviation safety. A military practitioner of aviation medicine may be called a flight surgeon and a civilian practitioner is an aviation medical examiner. One of the biggest differences between the military and civilian flight doctors is the military flight surgeon's requirement to log flight hours.
Altitude training is the practice by some endurance athletes of training for several weeks at high altitude, preferably over 2,400 metres (8,000 ft) above sea level, though more commonly at intermediate altitudes due to the shortage of suitable high-altitude locations. At intermediate altitudes, the air still contains approximately 20.9% oxygen, but the barometric pressure and thus the partial pressure of oxygen is reduced.
A hypobaric chamber, or altitude chamber, is a chamber used during aerospace or high terrestrial altitude research or training to simulate the effects of high altitude on the human body, especially hypoxia and hypobaria. Some chambers also control for temperature and relative humidity.
Performance-enhancing substances, also known as performance-enhancing drugs (PEDs), are substances that are used to improve any form of activity performance in humans. A well-known example of cheating in sports involves doping in sport, where banned physical performance-enhancing drugs are used by athletes and bodybuilders. Athletic performance-enhancing substances are sometimes referred as ergogenic aids. Cognitive performance-enhancing drugs, commonly called nootropics, are sometimes used by students to improve academic performance. Performance-enhancing substances are also used by military personnel to enhance combat performance.
Thermal comfort is the condition of mind that expresses satisfaction with the thermal environment and is assessed by subjective evaluation. The human body can be viewed as a heat engine where food is the input energy. The human body will release excess heat into the environment, so the body can continue to operate. The heat transfer is proportional to temperature difference. In cold environments, the body loses more heat to the environment and in hot environments the body does not release enough heat. Both the hot and cold scenarios lead to discomfort. Maintaining this standard of thermal comfort for occupants of buildings or other enclosures is one of the important goals of HVAC design engineers.
The U.S. Army Pikes Peak Research Laboratory, or simply the "Pikes Peak Lab", is a modern medical research laboratory for the assessment of the impact of high altitude on human physiological and medical parameters of military interest. It is a satellite facility of the U.S. Army Research Institute of Environmental Medicine (USARIEM), located in Natick, Massachusetts. The Pikes Peak Lab is at the summit of Pikes Peak 14,115 feet (4,302 m) in central Colorado, USA. The summit is approximately 5 acres (2.0 ha) of relatively flat, rocky terrain and is directly and easily accessible by automobile via the Pikes Peak Highway.
The effects of high altitude on humans are mostly the consequences of reduced partial pressure of oxygen in the atmosphere. The medical problems that are direct consequence of high altitude are caused by the low inspired partial pressure of oxygen, which is caused by the reduced atmospheric pressure, and the constant gas fraction of oxygen in atmospheric air over the range in which humans can survive. The other major effect of altitude is due to lower ambient temperature.
The Doriot Climatic Chambers (DCCs) are a pair of very large, highly specialized wind tunnels/environmental chambers located at the U.S. Army’s Soldier Systems Center (SSC) in Natick, Massachusetts. Built in 1952, the Chambers are a unique facility, capable of simulating an extreme range of global weather conditions for the testing of both the physical properties of military equipment and the physiology and adaptations of human subjects.
Transient receptor potential cation channel subfamily V member 4 is an ion channel protein that in humans is encoded by the TRPV4 gene.
The Microgravity Centre, colloquially known as the "MicroG", at PUCRS university, Porto Alegre, Brazil, was initially created as a laboratory in 1999 by Professor Thais Russomano MD MSc PhD, as the first academic and research establishment dedicated to Space Life Sciences in Latin America. It evolved into a fully multidisciplinary centre in 2006, expanding its areas of research beyond aerospace medicine and engineering, to include pharmaceuticals, biomechanics and physiotherapy, among others.
The history of military nutrition in the United States can be roughly divided into seven historical eras, from the founding of the country to the present day, based on advances in food research technology and methodologies for the improvement of the overall health and nutritional status of U.S. military service members. Through the research and guidance of medical and military professionals, rations and packaging have been consistently and dramatically improved.
In aviation, a source of stress that comes from the environment is known as an environmental stressor. Stress is defined as a situation, variable, or circumstance that interrupts the normal functioning of an individual and, most of the time, causes a threat. It can be related not only to mental health, but also to physical health.
Harvard Fatigue Laboratory (1927–1947) was a research centre designed to investigate the physiological, sociological and psychological impacts of fatigue caused by daily activities, and those on the conditions that industry workers faced at the time.
Palm cooling is a type of recovery intervention that involves cooling the palm of the hand during rest periods between bouts of strenuous physical activity. The palm cooling modality can be used to moderate increases in core temperature resulting from the level of physical activity, the wearing of protective clothing or a combination of both, for example in the activities of military personnel or firefighters.
Stefan M. Pasiakos is a U.S. physiologist specializing in diet and supplemental nutrition, muscle physiology, and human performance. He has served as the director of the National Institutes of Health (NIH) office of dietary supplements since 2023. Pasiakos was previously chief of the military performance division at the United States Army Research Institute of Environmental Medicine.
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United States Army 
