ISSN:0195-9131    

出版商:OVID    

年代:1998

数据来源: OVID

摘要:

Juvenile obesity is a serious, increasingly prevalent problem in technologically developed societies. Almost one-quarter of U.S. children are now obese, a dramatic increase of over 20% in the past decade. It is intriguing that the increase in prevalence has been occurring while overall fat consumption has been declining. Body mass and composition are influenced by genetic factors, but the actual heritability of juvenile obesity is not known. A low physical activity (PA) is characteristic of obese children and adolescents, and it may be one cause of juvenile obesity. There is little evidence, however, that overall energy expenditure is low among the obese. There is a strong association between the prevalence of obesity and the extent of TV viewing. Enhanced PA can reduce body fat and blood pressure and improve lipoprotein profile in obese individuals. Its effect on body composition, however, is slower than with low-calorie diets. The three main dietary approaches are: protein sparing modified fast, balanced hypocaloric diets, and comprehensive behavioral lifestyle programs. To achieve long-standing control of overweight, one should combine changes in eating and activity patterns, using behavior modification techniques. However, the onus is also on society to reduce incentives for a sedentary lifestyle and over-consumption of food. To address the key issues related to childhood weight management, the American College of Sports Medicine convened a Scientific Roundtable in Indianapolis.

ISSN:0195-9131    

出版商:OVID    

年代:1998

数据来源: OVID

摘要:

Purpose:Thirty four HIV+patients participated in a 6-wk aerobic exercise training program to determine whether exercise improved aerobic fitness, immune indices, and quality of life.Methods:Subjects were assigned to three groups: control (no regular aerobic exercise), moderate exercise, and heavy exercise training. At study entry and exit (in each subject) we evaluated aerobic function with a symptom limited cardiopulmonary exercise test, immune indices with CD4 counts and Candida skin tests, viral replication with plasma HIV RNA measurements, and quality of life with a HIV+population validated questionnaire.Results:Aerobic fitness increased significantly in both exercise groups relative to the control group; immune indices changed very little among all three groups; however, the Candida skin tests (mm2) increased significantly in the moderate group; viral replication was essentially unchanged in all three groups; quality of life (QOL) markers improved in both exercising groups but not the control group. There were no opportunistic infections during the study.Conclusions:Exercise training resulted in a substantial improvement in aerobic function while immune indices were essentially unchanged. Quality of life markers improved significantly with exercise. Exercise training is safe and effective in this patient group and should be promoted for HIV+patients

ISSN:0195-9131    

出版商:OVID    

年代:1998

数据来源: OVID

摘要:

Purpose:To study the ventilatory effects of closely monitored cycle ergometer conditioning (HR target, 145-150 beats·min-1; 25 min/session; three sessions per week) during the second and third pregnancy trimesters(TMs) in healthy human pregnancy.Methods:Subjects were 27 previously sedentary pregnant women (exercised group, EG). A sedentary control group (CG,N= 20) was also studied. Subjects were tested at rest and during upright cycle ergometry at three steady-state power outputs (≈20, 45, and 65 W) at the start of the second TM (ENTRY), at the end of the second and third TMs (post-training), and 3 months postpartum(PP, nonpregnant control).Results:Significant reductions in exercise HR were observed in the EG at each exercise level, confirming achievement of an aerobic conditioning effect. In both groups the ventilatory equivalent for oxygen(˙VE/˙VO2) was significantly higher at all work rates during pregnancy compared with that during PP. This effect was caused by significantly higher exercise tidal volumes (VT) at each work rate in both groups during pregnancy versus PP. Respiratory sensitivity as reflected by the ventilatory equivalent for carbon dioxide(˙VE/˙VCO2) and calculated arterial carbon dioxide tension (PaCO2) was significantly increased at all three work rates in late gestation versus PP and increased slightly with advancing gestational age in both groups. The main effects of physical conditioning were attenuation of increases in ˙VE/˙VO2observed at all exercise levels between the end of TM2 and TM3 and reductions in respiratory perception of effort (RPEr) between ENTRY and the end of TM3. Attenuation of increases in˙VE/˙VO2during TM3 in the EG was attributed to the combined effects of enhanced fat versus carbohydrate utilization (resulting in reduced CO2output and drive to ventilate) and attenuation of pregnancy-induced increases in dead space ventilation in late gestation.Conclusion:The study results support the hypothesis that physical conditioning reduces both ventilatory demand and respiratory perception of effort in late gestation.

ISSN:0195-9131    

出版商:OVID    

年代:1998

数据来源: OVID

摘要:

Muscle blood flow (Q) and metabolic response to exercise can very within species and may depend upon whether measurements were madein vivoorin situ. It has been suggested that to some extent these variations in muscle Q and metabolism may be the result of a reduction in muscle performance after the surgery ofin situpreparations. In contrast, the development of the novel humanin vivopreparation often described as dynamic knee-extensor exercise by Andersen and Saltin in 1985 is only minimally invasive. This preparation has revealed human muscle Q which far exceed those previously measured and allows the metabolic response of a single dynamically exercising muscle group to be studied. The use of this human exercise model was not the focus of this symposium, but each contributing author has worked extensively with this and other preparations to investigate muscle blood flow and metabolism in exercise. Thus, the purpose of this symposium was to bring together these new insights into muscle Q and metabolism in exercising muscle studiedin vivoandin situ.

ISSN:0195-9131    

出版商:OVID    

年代:1998

数据来源: OVID

摘要:

This review considers four experimental models for studying the dynamics of ammonia and amino acid metabolism in skeletal muscle: the rat hindlimb, the isolated dog gastrocnemius, the leg extensor for humans, and the traditional approach of humans performing two-legged exercise. The rat hindlimb is well suited for studying intense exercise with fast-twitch white fibers, but it is poorly suited for studying prolonged exercise because of rapid fatigue of major portions of the muscle and the restrictions of taking multiple blood samples. The traditional human model is limited because of the inability to quantify accurately the active muscle mass and to determine the true blood flow to the entire active tissue. Despite species differences and the various limitations of the paradigms, there are numerous consistencies in the literature. For example, human muscle and the canine gastrocnemius demonstrate similar magnitudes of efflux of ammonia, glutamine, and alanine (when indexed for the active mass) during prolonged exercise. Muscle has a large ammonia producing capacity during either intense or prolonged exercise. In prolonged exercise this is accompanied by similar productions of alanine and glutamine as well as a large uptake of glutamate. Despite the latter, the intramuscular glutamate concentration rapidly declines by more than 50% and remains constant throughout the exercise period. The leg extensor model and the canine gastrocnemius offer the greatest opportunities to quantify these responses during prolonged exercise.

ISSN:0195-9131    

出版商:OVID    

年代:1998

数据来源: OVID

摘要:

Anaerobic energy production during supramaximal exercise has been estimated from muscle metabolic changes. Based on such measurements the anaerobic energy production was determined to be 63 and 189 mmol ATP·kg-1d.w. for 60 and 142 s of exhaustive cycling exercise, respectively. These estimations do not, however, include release of lactate from the exercising muscles. Furthermore, the anaerobic production cannot be related to the work performed since the muscle biopsy sample may not be representative for the muscles involved in the exercise, and the total anaerobic energy production during whole body exercise cannot be determined because the mass of the muscles used is unknown. When a single muscle is exercised, the problems are minimized. With a one-legged knee-extensor exercise model, which uses a defined muscle mass, the anaerobic energy production has been estimated to be 370 mmol ATP·kg-1d.w. for a 192-s exhaustive exercise period. Estimated pulmonary oxygen deficit based on an energy demand extrapolated from a linear relationship between exercise intensity and oxygen uptake at submaximal exercise does not appear to represent the anaerobic energy production during whole body exercise.

ISSN:0195-9131    

出版商:OVID    

年代:1998

数据来源: OVID

摘要:

The series of drops in PO2which comprise the oxygen cascade from the air to mammalian tissue can provide useful information about O2transport during exercise in both health and disease, but the complete cascade has been challenging to studyin vivo. This paper reviews a series ofin vivohuman knee-extensor studies which focus on the determinants of maximal O2consumption (˙VO2max) in exercising muscle and concludes with a characterization of the complete O2cascade in maximally exercising human muscle. Specifically, three issues have been addressed: 1) determinants of O2extraction under conditions of very high muscle blood flow; 2) the role of O2diffusivity in determining the maximum O2flux rate(˙VO2max); and 3) myoglobin associated PO2as a indicator of O2transport and cellular respiration rate. In summary, these investigations demonstrate that in humans O2extraction can be uncompromised despite high mass specific blood flows, perhaps in part because of an increased capillary density in exercise trained subjects. Exercise in hypoxia reduces ˙VO2max, but as calculated diffusability of O2from blood to muscle is constant this suggests that a fixed O2diffusivity plays a key role in limiting maximal O2uptake. Supporting evidence of a substantial PO2gradient from blood to myoglobin also suggests a resistance to the diffusion of O2between red cell and sarcolemma, which may be present even at submaximal exercise. Finally, the proportionate relationship between myoglobin associated PO2and ˙VO2maxin conditions of normoxia and hypoxia additionally supports the hypothesis that maximal respiratory rate of muscle cells is limited by O2supply.

ISSN:0195-9131    

出版商:OVID    

年代:1998

数据来源: OVID

摘要:

Aerobic training-induced changes in vascular reactivity have been evaluated in vessels of a variety of sizes and tissue origins. In trained animals large coronary arteries have increased responses to adenosine (Ad) and decreased responses to norepinephrine (NE) and nitroprusside (Np). Smaller coronary arterioles have increased responses to bradykinin (Bk) but not Ad; intermediate size vessels have enhanced responses to both Ad and Bk. A similar size dependence has been found in the vascular bed of the rat spinotrapezius muscle. The terminal feed arteries of trained animals demonstrate increased dilation in response to Np and increased constriction in response to epinephrine (Epi) and NE. Smaller arterioles demonstrate increasedβ-dilation at low doses of Epi and decreased constriction at higher doses. Intermediate size vessels demonstrate adaptive responses that appear to be a combination of those in larger and smaller vessels. These vascular alterations are evident despite the fact that blood flow does not increase in this muscle during treadmill running and the oxidative capacity of this tissue is not enhanced by treadmill training. Recently, training-induced vascular adaptations have also been observed in the rat intestine; these adaptations include decreased responses to NE and acetylcholine and increased responses to Np. Experimental evidence suggests that vascular smooth muscle adaptations to training are highly dependent on the size and tissue location of the vessel and occur in tissues other than those activated during the training bout. Potential mediators of these adaptations are discussed.

ISSN:0195-9131    

出版商:OVID    

年代:1998

数据来源: OVID

摘要:

The purposes of this investigation were to see whether free radical production changed with high intensity resistance exercise and, secondly, to see whether vitamin E supplementation would have any effect on free radical formation or variables associated with muscle membrane disruption. Twelve recreationally weight-trained males were divided into two groups. The supplement group (S) received 1200 IUs of vitamin E once a day (3 × 400 IU·d-1) for a period of 2 wk. The placebo group (P) received cellulose-based placebo pills once a day for the same period of time. Creatine kinase activity was significantly elevated between preexercise and immediately postexercise, 6 h postexercise, and 24 h postexercise for both groups. The placebo group also had a significant increase in creatine kinase activity at 48 h postexercise. There was a significant difference in creatine kinase activity between the groups at 24 h after exercise. Plasma malondialdehyde significantly increased from preexercise levels for the P group at 6 and 24 h postexercise. Plasma malondialdehyde concentrations significantly increased in the S group between preexercise and immediately postexercise levels. This study indicates that high intensity resistance exercise increases free radical production and that vitamin E supplementation may decrease muscle membrane disruption.

ISSN:0195-9131    

出版商:OVID    

年代:1998

数据来源: OVID