ISSN:0112-1642    

DOI:10.2165/00007256-199111020-00001

出版商:Springer International Publishing    

年代:2012

数据来源: ADIS

摘要:

SummaryIn addition to the direct energy cost of physical activity, exercise may influence resting energy expenditure in 3 ways: (a) a prolonged increase in postexercise metabolic rate from an acute exercise challenge; (b) a chronic increase in resting metabolic rate associated with exercise training; and (c) a possible increase in energy expenditure during nonexercising time.It seems apparent that the greater the exercise perturbation, the greater the magnitude of the increase in postexercise metabolic rate. An exercise prescription for the general population that consists of exercise of low (<50% V̇O2max) or moderate intensity (50 to 75% V̇O2max) does not appear to produce a prolonged elevation of postexercise metabolic rate that would influence body-weight. Inconsistent results have been found with respect to the effects of exercise training and the trained state on resting metabolic rate. Whereas some investigators have found a higher resting metabolic rate in trained than untrained individuals and in individuals after an exercise training programme, other investigators have found no chronic exercise effect on resting metabolic rate. Differences in experimental design, genetic variation and alterations in energy balance may contribute to the discrepant findings among investigators. A relatively unexplored area concerns the influence of exercise training on energy expenditure during nonexercising time. It is presently unclear whether exercise training increases or decreases the energy expenditure associated with spontaneous or nonpurposeful physical activity which includes fidgeting, muscular activity, etc. The doubly labelled water technique represents a methodological advance in this area and permits the determination of total daily energy expenditure. Concomitant with the determination of the other components of daily energy expenditure (resting metabolic rate and thermic effect of a meal), it will now be possible to examine the adaptive changes in energy expenditure during nonexercising time.A plethora of studies have examined the combined effects of diet and exercise on body composition and resting metabolic rate. The hypothesis is that combining diet and exercise will accelerate fat loss, preserve fat-free weight and prevent or decelerate the decline in resting metabolic rate more effecively than with diet restriction alone. The optimal combination of diet and exercise, however, remains elusive. It appears that the combination of a large quantity of aerobic exercise with a very low calorie diet resulting in substantial loss of bodyweight may actually accelerate the decline in resting metabolic rate. These findings may cause us to re-examine the quantity of exercise and diet needed to achieve optimal fat loss and preservation of resting metabolic rate.

ISSN:0112-1642    

DOI:10.2165/00007256-199111020-00002

出版商:Springer International Publishing    

年代:2012

数据来源: ADIS

摘要:

SummaryPlasma glucose is an important energy source in exercising humans, supplying between 20 and 50% of the total oxidative energy production and between 25 and 100% of the total carbohydrate oxidised during submaximal exercise. Plasma glucose utilisation increases with the intensity of exercise, due to an increase in glucose utilisation by each active muscle fibre, an increase in the number of active muscle fibres, or both. Plasma glucose utilisation also increases with the duration of exercise, thereby partially compensating for the progressive decrease in muscle glycogen concentration. When compared at the same absolute exercise intensity (i.e. the same V̇O2), reliance on plasma glucose is also greater during exercise performed with a small muscle mass, i.e. with the arms or just 1 leg. This may be due to differences in the relative exercise intensity (i.e. the %V̇O2peak), or due to differences between the arms and legs in their fitness for aerobic activity.The rate of plasma glucose utilisation is decreased when plasma free fatty acid or muscle glycogen concentrations are very high, effects which are probably mediated by increases in muscle glucose-6-phosphate concentration. However, glucose utilisation is also reduced during exercise following a low carbohydrate diet, despite the fact that muscle glycogen is also often lower.When exercise is performed at the same absolute intensity before and after endurance training, plasma glucose utilisation is lower in the trained state. During exercise performed at the same relative intensity, however, glucose utilisation may be lower, the same, or actually higher in trained than in untrained subjects, because of the greater absolute V̇O2and demand for substrate in trained subjects during exercise at a given relative exercise intensity.Although both hyperglycaemia and hypoglycaemia may occur during exercise, plasma glucose concentration usually remains relatively constant. Factors which increase or decrease the reliance of peripheral tissues on plasma glucose during exercise are therefore generally accompanied by quantitatively similar increases or decreases in glucose production. These changes in total glucose production are mediated by changes in both hepatic glycogenolysis and hepatic gluconeogenesis. Glycogenolysis dominates under most conditions, and is greatest early in exercise, during high intensity exercise, or when dietary carbohydrate intake is high. The rate of gluconeogenesis is increased when exercise is prolonged, preceded by a restricted carbohydrate intake, or performed with the arms. Both glycogenolysis and gluconeogenesis appear to be decreased by endurance exercise training. These effects are due to changes in both the hormonal milieu and in the availability of hepatic glycogen and gluconeogenic precursors.Hepatic glucose production during exercise is stimulated by glucagon and the catecholamines and suppressed by insulin or an increase in plasma glucose concentration. In contrast to earlier suggestions, it appears that a decrease in insulin and an increase in glucagon are both required for hepatic glucose production to increase normally during moderate intensity, moderate duration (40 to 60 minutes) exercise. Changes in the catecholamines. however, may still prove to be important, especially during more intense or more prolonged exercise.

ISSN:0112-1642    

DOI:10.2165/00007256-199111020-00003

出版商:Springer International Publishing    

年代:2012

数据来源: ADIS

摘要:

SummaryDislocation of the acromioclavicular joint is a common joint injury in sport, especially those in which there is the risk of falling on to the point of the shoulder. There is controversy regarding the early management of such a dislocation but recent literature strongly favours a conservative approach, because no single surgical procedure has produced results which are consistently better than those achieved following conservative management. In addition the few studies which document late results suggest that in most instances the outcome following conservative treatment is very satisfactory with good power and movement of the shoulder.

ISSN:0112-1642    

DOI:10.2165/00007256-199111020-00004

出版商:Springer International Publishing    

年代:2012

数据来源: ADIS