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Human Swimming
Swimming is the self-propulsion of a person through water, or other liquid, usually for recreation, sport, exercise, or survival. Locomotion is achieved through coordinated movement of the limbs and the body to achieve hydrodynamic thrust that results in directional motion. Humans can hold their breath underwater and undertake rudimentary locomotive swimming within weeks of birth, as a survival response. Swimming is consistently among the top public recreational activities, and in some countries, swimming lessons are a compulsory part of the educational curriculum. As a formalized sport, swimming is featured in a range of local, national, and international competitions, including every modern Summer Olympics. Swimming involves repeated motions known as strokes in order to propel the body forward. While the front crawl, also known as freestyle, is widely regarded as the fastest out of four primary strokes, other strokes are practiced for special purposes, such as for training. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Propulsion
Propulsion is the generation of force by any combination of pushing or pulling to modify the translational motion of an object, which is typically a rigid body (or an articulated rigid body) but may also concern a fluid. The term is derived from two Latin words: ''wikt:pro, pro'', meaning'' before'' or ''forward''; and ''wikt:pellere, pellere'', meaning ''to drive''. A propulsion system consists of a source of mechanical power, and a ''propulsor'' (means of converting this power into propulsive force). Plucking a guitar string to induce a vibration, vibratory translation is technically a form of propulsion of the guitar string; this is not commonly depicted in this vocabulary, even though human muscles are considered to propel the fingertips. The motion of an object moving through a gravitational field is affected by the field, and within some frames of reference physicists speak of the gravitational field generating a force upon the object, but for general relativity, deep the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Snorkel (swimming)
A snorkel is a device used for breathing air from above the surface when the wearer's head is face downwards in the water with the mouth and the nose submerged. It may be either separate or integrated into a swimming or diving mask. The integrated version is only suitable for surface snorkeling, while the separate device may also be used for underwater activities such as spearfishing, freediving, finswimming, underwater hockey, underwater rugby and for surface breathing with scuba equipment. A swimmer's snorkel is a tube bent into a shape often resembling the letter "L" or "J", fitted with a mouthpiece at the lower end and constructed of light metal, rubber or plastic. The snorkel may come with a rubber loop or a plastic clip enabling the snorkel to be attached to the outside of the head strap of the diving mask. Although the snorkel may also be secured by tucking the tube between the mask-strap and the head, this alternative strategy can lead to physical discomfort, mask leakage ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Vasoconstriction
Vasoconstriction is the narrowing of the blood vessels resulting from contraction of the muscular wall of the vessels, in particular the large arteries and small arterioles. The process is the opposite of vasodilation, the widening of blood vessels. The process is particularly important in controlling hemorrhage and reducing acute blood loss. When blood vessels constrict, the flow of blood is restricted or decreased, thus retaining body heat or increasing vascular resistance. This makes the skin turn paler because less blood reaches the surface, reducing the radiation of heat. On a larger level, vasoconstriction is one mechanism by which the body regulates and maintains mean arterial pressure. Medications causing vasoconstriction, also known as vasoconstrictors, are one type of medicine used to raise blood pressure. Generalized vasoconstriction usually results in an increase in systemic blood pressure, but it may also occur in specific tissues, causing a localized reduction in bl ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Reflex Bradycardia
Reflex bradycardia is a bradycardia (decrease in heart rate) in response to the baroreceptor reflex, one of the body's homeostatic mechanisms for preventing abnormal increases in blood pressure. In the presence of high mean arterial pressure, the baroreceptor reflex produces a reflex bradycardia as a method of decreasing blood pressure by decreasing cardiac output. Blood pressure (BP) is determined by cardiac output (CO) and total peripheral resistance (TPR), as represented by the formula BP = CO x TPR. Cardiac output (CO) is affected by two factors, the heart rate (HR) and the stroke volume (SV), the volume of blood pumped from one ventricle of the heart with each beat (CO = HR x SV, therefore BP = HR x SV x TPR). In reflex bradycardia, blood pressure is reduced by decreasing cardiac output (CO) via a decrease in heart rate (HR). An increase in blood pressure can be caused by increased cardiac output, increased total peripheral resistance, or both. The baroreceptors in the ca ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Apnea
Apnea, BrE: apnoea, is the temporal cessation of breathing. During apnea, there is no movement of the muscles of inhalation, and the volume of the lungs initially remains unchanged. Depending on how blocked the airways are ( patency), there may or may not be a flow of gas between the lungs and the environment, but if there's sufficient flow, gas exchange within the lungs and cellular respiration wouldn't be severely affected. Voluntarily doing this is called holding one's breath. Apnea may first be diagnosed in childhood, and it is recommended to consult an ENT specialist, allergist or sleep physician to discuss symptoms when noticed; malformation and/or malfunctioning of the upper airways may be observed by an orthodontist. Cause Apnea can be involuntary—for example, drug-induced (such as by opiate toxicity), mechanically / physiologically induced (for example, by strangulation or choking), or a consequence of neurological disease or trauma. During sleep, people with sev ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Mammalian Diving Reflex
The diving reflex, also known as the diving response and mammalian diving reflex, is a set of physiological responses to immersion that overrides the basic homeostatic reflexes, and is found in all air-breathing vertebrates studied to date. It optimizes respiration by preferentially distributing oxygen stores to the heart and brain, enabling submersion for an extended time. The diving reflex is exhibited strongly in aquatic mammals, such as seals, otters, dolphins, and muskrats, and exists as a lesser response in other animals, including human babies up to 6 months old (see infant swimming), and diving birds, such as ducks and penguins. Adult humans generally exhibit a mild response, the dive-hunting Sama-Bajau people being a notable outlier. The diving reflex is triggered specifically by chilling and wetting the nostrils and face while breath-holding, and is sustained via neural processing originating in the carotid chemoreceptors. The most noticeable effects are on the cardio ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Diving Reflex
The diving reflex, also known as the diving response and mammalian diving reflex, is a set of physiological responses to immersion that overrides the basic homeostatic reflexes, and is found in all air-breathing vertebrates studied to date. It optimizes respiration by preferentially distributing oxygen stores to the heart and brain, enabling submersion for an extended time. The diving reflex is exhibited strongly in aquatic mammals, such as seals, otters, dolphins, and muskrats, and exists as a lesser response in other animals, including human babies up to 6 months old (see infant swimming), and diving birds, such as ducks and penguins. Adult humans generally exhibit a mild response, the dive-hunting Sama-Bajau people being a notable outlier. The diving reflex is triggered specifically by chilling and wetting the nostrils and face while breath-holding, and is sustained via neural processing originating in the carotid chemoreceptors. The most noticeable effects are on the cardiov ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Squat (exercise)
A squat is a strength exercise in which the trainee lowers their hips from a standing position and then stands back up. During the descent and knee joints flex while the ankle joint dorsiflexes; conversely the hip and knee joints extend and the ankle joint plantarflexes when standing up. Squats also help your hip muscles Squats are considered a vital exercise for increasing the strength and size of the lower body muscles as well as developing core strength. The primary agonist muscles used during the squat are the quadriceps femoris, the adductor magnus, and the gluteus maximus. The squat also isometrically uses the erector spinae and the abdominal muscles, among others. The squat is one of the three lifts in the strength sport of powerlifting, together with the deadlift and the bench press. It is also considered a staple exercise in many popular recreational exercise programs. Form The squat begins from a standing position. Weight is often added and is typically in t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hydrodynamics
In physics and engineering, fluid dynamics is a subdiscipline of fluid mechanics that describes the flow of fluids—liquids and gases. It has several subdisciplines, including ''aerodynamics'' (the study of air and other gases in motion) and hydrodynamics (the study of liquids in motion). Fluid dynamics has a wide range of applications, including calculating forces and moments on aircraft, determining the mass flow rate of petroleum through pipelines, predicting weather patterns, understanding nebulae in interstellar space and modelling fission weapon detonation. Fluid dynamics offers a systematic structure—which underlies these practical disciplines—that embraces empirical and semi-empirical laws derived from flow measurement and used to solve practical problems. The solution to a fluid dynamics problem typically involves the calculation of various properties of the fluid, such as flow velocity, pressure, density, and temperature, as functions of space and time. Bef ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Swimming Stroke
Human swimming typically consists of repeating a specific body motion or swimming stroke to propel that body forward. There are many kinds of strokes, each defining a different swimming style or crawl. In high school, collegiate, and Olympic swimming, there are two undulating strokes (breaststroke and butterfly stroke) and two alternating strokes (front crawl and backstroke). Most strokes involve rhythmic and coordinated movements of all major body parts — torso, arms, legs, hands, feet, and head. Breathing typically must be synchronized with the strokes, too. It is possible, however, to swim by moving only legs without arms or only arms without legs; such strokes may be used for special purposes, for training or exercise, or by amputees (paralympians) and paralytics. Swimming styles Within a competitive sense particularly, swim stroke techniques are continuously changing to become either easier or more efficient as more people explore the activity. * Front crawl: the fastes ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Viscosity
The viscosity of a fluid is a measure of its resistance to deformation at a given rate. For liquids, it corresponds to the informal concept of "thickness": for example, syrup has a higher viscosity than water. Viscosity quantifies the internal frictional force between adjacent layers of fluid that are in relative motion. For instance, when a viscous fluid is forced through a tube, it flows more quickly near the tube's axis than near its walls. Experiments show that some stress (such as a pressure difference between the two ends of the tube) is needed to sustain the flow. This is because a force is required to overcome the friction between the layers of the fluid which are in relative motion. For a tube with a constant rate of flow, the strength of the compensating force is proportional to the fluid's viscosity. In general, viscosity depends on a fluid's state, such as its temperature, pressure, and rate of deformation. However, the dependence on some of these properties is ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hydrostatic Weighing
Hydrostatic weighing, also referred to as underwater weighing, hydrostatic body composition analysis and hydrodensitometry, is a technique for measuring the density of a living person's body. It is a direct application of Archimedes' principle, that an object displaces its own volume of water. Method The procedure is based on Archimedes' principle, which states that: ''The buoyant force which water exerts on an immersed object is equal to the weight of water that the object displaces.'' Example 1: If a block of solid stone weighs 3 kilograms on dry land and 2 kilogram when immersed in a tub of water, then it has displaced 1 kilogram of water. Since 1 liter of water weighs 1 kilogram (at 4 °C), it follows that the volume of the block is 1 liter and the density (mass/volume) of the stone is 3 kilograms/liter. Example 2: Consider a larger block of the same stone material as in Example 1 but with a 1-liter cavity inside of the same amount of stone. The block would still wei ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
