ReviewWeight-bearing exercise and bone mineral accrual in children and adolescents: A review of controlled trials
Introduction
Osteoporosis is a systemic, skeletal disease characterised by low bone density and micro-architectural deterioration of bone tissue, with a consequent increase in bone fragility [1]. It is a serious disease that is increasing at an epidemic rate and it is predicted that osteoporosis and osteoporotic fractures will rise exponentially over the next 50 years, as the population ages [2]. Thus, there is a large emphasis on preventative measures to combat or offset osteoporosis and fracture. One major preventive measure is the optimisation of peak bone mass in the early years. Peak bone mass can be defined as the greatest amount of bone mass achieved during life at a given skeletal site and is based on observations that bone mass increases during childhood and puberty, consolidates during young adulthood and declines with age [3], [4]. One strategy to increase peak bone mass is through regular, weight-bearing exercise [5], [6], [7]. The definition of weight-bearing exercise that has been adopted for this review is that of a structured, force-generating activity that provides loading to skeletal regions, above that provided by activities of daily living [8]. Weight-bearing exercises can include aerobics, circuit training, jogging, jumping, volleyball and other sports that generate impact to the skeleton. There is evidence to suggest that the years of childhood and adolescence represent an opportune period during which bone adapts particularly efficiently to such loading [9], [10].
Evidence supporting the role of weight-bearing exercise in bone health has accumulated from cross sectional, retrospective, prospective and intervention studies. Cross sectional studies report higher bone mass in athletes than non athletes [11], [12], and in highly active children compared to those who are more sedentary [13], [14]. Retrospective studies report greater bone mass in retired dancers compared to controls [15], and an increase in physical education (PE) within the school curriculum is associated with positive skeletal effects in children [16]. Prospective studies following children with different physical activity levels also report greater increases in the bone mass of active children compared to those who are less active [17], [18], [19]. Although such studies have contributed to the literature, they do not provide robust and causal inferences between exercise and bone mineral accrual. As such, there is a need to assess randomised controlled trials (RCT), which are regarded as the primary source for more valid and reliable evidence. The number of investigations has increased over the last 5 years [20], [21], [22], [23], [24], [25], [26], [27], [28], [29], [30], [31], [32], [33] therefore the purpose of this review was to evaluate this literature to date.
Section snippets
Search strategy to identify relevant trials
The aim of the literature search was to identify all available RCTs and controlled studies concerning the effects of weight-bearing exercise on bone mineral accrual in children and adolescents, aged 8 and 17 years. To do so, a computerised search of the MEDLINE database was performed on articles published between the years 1964 and 2005. The keywords entered were: ‘exercise, children, girls, boys, adolescents, bone, bone mineral and bone mass’. A total of 573 articles were found, and their
Results
Table 2 summarises the design, execution and outcomes of the studies reviewed. These are grouped according to the participants' Tanner Stage because maturity status is critical when evaluating the effects of exercise on growing bone [8], [9]. Results are given as the percentage increase in bone mass parameters (bone mineral content (BMC), areal bone mineral density (aBMD) and volumetric BMD (vBMD) in exercisers compared to controls. When provided by the authors, absolute changes in bone mass
Optimal exercise intervention for bone mineral accrual
It is known that the skeletal response to weight-bearing exercise is site-specific and studies to date support this, reporting the most significant effects at the femoral neck (Table 2). However, a major question arising from this review is what constitutes the optimal exercise programme to improve bone mineral accrual in children?
Intervention trials that have achieved successful results have used a range of exercise protocols. These have included (a) activities such as aerobics, football and
Conclusions
To conclude, positive skeletal effects from weight-bearing exercise can be attained in girls and boys. The long term effects are unknown, but maximising peak bone mass is likely to offset future development of osteoporosis and bone fragility. The evidence indicates that early puberty potentially represents an opportune maturity stage to augment bone mineral accrual through exercise, although definitive conclusions cannot yet be made. Many studies to date have a high risk for bias, with only a
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