ISSN:0112-1642    

DOI:10.2165/00007256-199519020-00001

出版商:Springer International Publishing    

年代:2012

数据来源: ADIS

摘要:

SummaryThe fitness and physical activity levels of children and youth are commonly questioned, but the evidence cited is both equivocal and methodologically diverse. The amount and type of physical activity undertaken during childhood that is appropriate for optimal health is unknown, although it has been suggested that, in the absence of such criteria, activity levels known to confer health benefits in adults are also appropriate for children. The measurement of activity in children is problematical, and there is currently no valid method of assessing activity levels that is feasible for use in large studies. Therefore, studies may lack either internal validity or wider applicability.Studies using self-report methods indicate relatively high levels of activity with 60 to 70% of children taking sufficient ‘appropriate’ physical activity. However, a variety of activity thresholds have been used. Studies that use more objective methods report much lower levels of activity, especially when cardiovascular fitness criteria are applied. The use of less stringent health-related thresholds results in higher levels of ‘appropriate’ activity. Nearly all studies of teenagers report a decline in activity with age during this period. Data from the large population studies indicate that activity levels peak in children at around 13 to 14 years of age, and then markedly decline. Boys are normally reported to be more active than girls, but this difference is greatly reduced when moderate activity alone is compared, indicating that boys participate in more vigorous exercise than girls. The health effects of low levels of vigorous activity in children are unclear.There is a need to identify more clearly the quantity and type of activity which is appropriate for children’s health and well-being, and to improve assessment techniques. There is a particular need to assess the value of, and measure the prevalence of, low to moderate intensity activity below the level normally considered appropriate for cardiorespiratory fitness improvement.

ISSN:0112-1642    

DOI:10.2165/00007256-199519020-00002

出版商:Springer International Publishing    

年代:2012

数据来源: ADIS

摘要:

SummaryA decrease in physical activity may lead to an increased loss of bone and an increase in the incidence of osteoporotic fractures. Studies have demonstrated increases in bone formation in animals and increases in bone mineral density in humans. Studies of animals show that bone has enhanced physical and mechanical properties following periods of increased stress. Strains which are high in rate and magnitude, and of abnormal distribution, but not necessarily long in duration, are best for inducing new bone formation, resulting in the strengthening of bone by increased density. Cross-sectional studies show that athletes, especially those who are strength-trained, have greater bone mineral densities than nonathletes, and that strength, muscle mass and maximal oxygen uptake correlate with bone density. Longitudinal training studies indicate that strength training and high impact endurance training increase bone density.Strain induction, the deformation that occurs in bone under loading, may cause a greater level of formation and an inhibition of resorption within the normal remodelling cycle of bone, or it may cause direct activation of osteoblastic bone formation from the quiescent state.Various mechanisms have been proposed for the transformation of mechanical strain into biochemical stimuli to enhance bone formation. These include prostaglandin release, piezoelectric and streaming potentials, increased bone blood flow, microdamage and hormonally mediated mechanisms. These mechanisms may act on their own or in concert, depending on the loading situation and the characteristics of the bone.

ISSN:0112-1642    

DOI:10.2165/00007256-199519020-00003

出版商:Springer International Publishing    

年代:2012

数据来源: ADIS

摘要:

SummaryHealth is determined not only by the absence of disease, but also by an individual’s resistance to pathogenic factors. In turn, resistance depends on the effectiveness of specific homeostatic regulation and the mechanism of general adaptation. Through the change in adaptivity, health may be increased or reduced. While it is difficult to predict which specific homeostatic mechanism will be necessary in various stages of life in the individual, it is more reliable to try to improve health, thereby increasing the effectiveness of the mechanism of general adaptation.Physical training results in a variety of changes in individuals. There are several changes which are essential both for increased exercise performance and for increasing adaptivity, by favouring the effectiveness of the mechanism of general adaptation. These changes: improve central nervous regulation and central nervous system functions; increase endocrine system capacity; increase energy potential; improve the capacity of the oxygen transport system; improve oxidation processes; increase metabolic and functional economy; increase functional stability; and increase the number of Na+,K+-pumps.The influence of these changes on adaptivity is accomplished by the influence of exercise training on immunoactivities, and by the antisclerotic effect of training. The latter may be considered to be metabolic (actualised through the training effect on lipoprotein metabolism and aging-related calcium distribution) or mechanical (protection of tissues from sclerotic changes by their activities) effects.The training effects are specifically dependent upon performed exercises. Endurance exercise is considered to be the most important and widely recommended form of exercise for health improvement. Most of the training benefits (listed above) for increased adaptivity are induced by aerobic endurance training. Gymnastic exercises are indispensable in regard to mechanical antisclerotic effect. They are also essential influences on the central nervous system. Aerobic dance or aerobic rhythmic gymnastics are ways by which the positive effects of endurance and gymnastic exercise can be combined.

ISSN:0112-1642    

DOI:10.2165/00007256-199519020-00004

出版商:Springer International Publishing    

年代:2012

数据来源: ADIS

摘要:

SummaryThe increasing frequency of injury in young athletes over the last 2 decades reflects the increases in sports participation of children of a young age. Physical injury is an inherent risk in sports participation at any age. In general, the factors causing sports injuries can be grouped in 2 separate broad categories: extrinsic and intrinsic factors. However, the great majority of injuries which are sustained are minor and self-limiting, suggesting that children and youth sports are safe. However, a increasing number of children undergo treatment because of the effects that injuries may have on their developing bodies. A child’s skeletal system shows pronounced adaptive changes to intensive sports training. Sports injuries affect both growing bone and soft tissues, and could result in damage of the growth mechanisms with subsequent life-lasting damage.Adolescents are particularly vulnerable to injuries, at least partially due to an imbalance in strength and flexibility. During growth there are significant changes in the biomechanical properties of bone. In young athletes, as bone stiffness increases and resistance to impact diminishes, sudden overload may cause bones to bow or buckle. Epiphyseal injuries occur at the epiphyseal growth plates. They are usually due to shearing and avulsion forces, although compression also plays a significant role. Given the remarkable healing potential of bone in youngsters, fractures that initially united with some deformity can completely remodel and appear totally normal in later life. As the risk of injuries sustained by young athletes can be significant, it is essential that training programmes take into account their physical and psychological immaturity, so that the growing athlete can adjust to their own body changes.

ISSN:0112-1642    

DOI:10.2165/00007256-199519020-00005

出版商:Springer International Publishing    

年代:2012

数据来源: ADIS

摘要:

SummaryLoss of motion following knee ligament surgery is a common and potentially serious complication. Loss of extension is most common following anterior cruciate ligament reconstruction, and loss of flexion is most common after posterior cruciate ligament reconstruction. The aetiology of loss of motion is multifactorial and includes impingement and capsulitis. The risk for loss of motion can be minimised by appropriate preoperative, intraoperative and postoperative intervention. Management of loss of motion depends on the cause and length of time following surgery.

ISSN:0112-1642    

DOI:10.2165/00007256-199519020-00006

出版商:Springer International Publishing    

年代:2012

数据来源: ADIS