Medicine and science in sports and exercise
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Med Sci Sports Exerc · Oct 1996
ReviewClinical aspects of the control of plasma volume at microgravity and during return to one gravity.
Plasma volume is reduced by 10-20% within 24-48 h of exposure to simulated or actual microgravity. The clinical importance of microgravity induced hypovolemia is manifested by its relationship with orthostatic intolerance and reduced maximal oxygen uptake (VO2max) after return to one gravity (1G). Since there is no evidence to suggest that plasma volume reduction during microgravity is associated with thirst or renal dysfunctions, a diuresis induced by an immediate blood volume shift to the central circulation appears responsible for microgravity-induced hypovolemia. ⋯ Fluid-loading and lower body negative pressure (LBNP) have not proved completely effective in restoring plasma volume, suggesting that they may not provide the stimulus to elevate the CVP operating point. On the other hand, exercise, which can chronically increase CVP, has been effective in expanding plasma volume when combined with adequate dietary intake of fluid and electrolytes. The success of designing experiments to understand the physiological mechanisms of and development of effective counter measures for the control of plasma volume in microgravity and during return to IG will depend upon testing that can be conducted under standardized controlled baseline conditions during both ground-based and space flight investigations.
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Med Sci Sports Exerc · Oct 1996
ReviewClinical models of cardiovascular regulation after weightlessness.
After several days in microgravity, return to earth is attended by alterations in cardiovascular function. The mechanisms underlying these effects are inadequately understood. Three clinical disorders of autonomic function represent possible models of this abnormal cardiovascular function after spaceflight. ⋯ In acute and complete baroreflex failure, there is usually severe hypertension and tachycardia, while with less complete and more chronic baroreflex impairment, orthostatic abnormalities may be more apparent. In orthostatic intolerance, blood pressure fall is minor, but orthostatic symptoms are prominent and tachycardia frequently occurs. Only careful autonomic studies of human subjects in the microgravity environment will permit us to determine which of these models most closely reflects the pathophysiology brought on by a period of time in the microgravity environment.
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Humans experience significant physiological stresses while diving, which can result in disease on occasion. With the increasing popularity of sports diving, it is critical that both physicians and divers be aware of the spectrum of illness associated with diving. An overview of common diving-related disorders is presented. ⋯ This is followed by a discussion of the pathophysiology, clinical settings, and manifestations of pulmonary barotrauma along with a review of the pathophysiology and presentation of decompression illness. Initial emergency measures and referral procedures for decompression related disorders are addressed. A brief discussion of recompression therapy is included.
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In this 3-yr longitudinal study we investigated the occurrence of low-back pain and anatomic changes in the low back in relation to loading and injuries among 98 adolescents: 33 nonathletes (16 boys, 17 girls), 34 boy athletes (17 ice hockey, 17 soccer players), and 31 girl athletes (17 figure skaters, 14 gymnasts). During the 3-yr follow-up, low-back pain lasting longer than 1 wk was reported by 29 (45%; 95% CI, 32%-57%) athletes and by 6 (18%; 95% CI, 7%-35%) nonathletes (P = 0.0099). ⋯ Among 43 girls participating in baseline and follow-up MRI examinations of the lumbar spine, new MRI abnormalities were found in 6 of 8 reporting acute back injury (75%; 95% CI, 35%-97%) and in 8 of the remaining 35 girls (23%; 95% CI 10% to 40%) (P = 0.018). In conclusion, excessive loading that involves a risk for acute low-back injuries during the growth spurt is harmful to the lower back.
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Med Sci Sports Exerc · Jan 1996
Review Practice Guideline GuidelineAmerican College of Sports Medicine position stand. Exercise and fluid replacement.
It is the position of the American College of Sports Medicine that adequate fluid replacement helps maintain hydration and, therefore, promotes the health, safety, and optimal physical performance of individuals participating in regular physical activity. This position statement is based on a comprehensive review and interpretation of scientific literature concerning the influence of fluid replacement on exercise performance and the risk of thermal injury associated with dehydration and hyperthermia. Based on available evidence, the American College of Sports Medicine makes the following general recommendations on the amount and composition of fluid that should be ingested in preparation for, during, and after exercise or athletic competition: 1) It is recommended that individuals consume a nutritionally balanced diet and drink adequate fluids during the 24-hr period before an event, especially during the period that includes the meal prior to exercise, to promote proper hydration before exercise or competition. 2) It is recommended that individuals drink about 500 ml (about 17 ounces) of fluid about 2 h before exercise to promote adequate hydration and allow time for excretion of excess ingested water. 3) During exercise, athletes should start drinking early and at regular intervals in an attempt to consume fluids at a rate sufficient to replace all the water lost through sweating (i.e., body weight loss), or consume the maximal amount that can be tolerated. 4) It is recommended that ingested fluids be cooler than ambient temperature [between 15 degrees and 22 degrees C (59 degrees and 72 degrees F])] and flavored to enhance palatability and promote fluid replacement. ⋯ This rate of carbohydrate intake can be achieved without compromising fluid delivery by drinking 600-1200 ml.h(-1) of solutions containing 4%-8% carbohydrates (g.100 ml(-1)). The carbohydrates can be sugars (glucose or sucrose) or starch (e.g., maltodextrin). 7) Inclusion of sodium (0.5-0.7 g.1(-1) of water) in the rehydration solution ingested during exercise lasting longer than 1 h is recommended since it may be advantageous in enhancing palatability, promoting fluid retention, and possibly preventing hyponatremia in certain individuals who drink excessive quantities of fluid. There is little physiological basis for the presence of sodium in n oral rehydration solution for enhancing intestinal water absorption as long as sodium is sufficiently available from the previous meal.