Several studies that used DXA or quantitative ultrasound suggested that objective ly measured SB was negatively associated with lower extremity bone outcomes , such as femoral neck bone mineral density .
The magnitude of this negative association was small and independent of moderate-to-vigorous physical activity .
In contrast to the lower extremities , there was insufficient evidence for an association of lumbar spine bone outcomes with objective ly measured SB .
In high- quality studies that used DXA , no association was observed between objective ly measured SB and total body bone outcomes .
In studies using question naires , none of these relationships were observed .
Sedentary  behaviour ( SB ) is increasing in Western societies and some studies suggest a deleterious effect of SB on bone .
The aim of this systematic review was to examine the association between  SB and bone health in children , adolescents and young adults .
Size-corrected BMD decreases during peak linear growth: implications for fracture incidence during adolescence.
UNLABELLED Peak adolescent fracture incidence at the distal end of the radius coincides with a decline in size-corrected BMD  in both boys and girls . Peak gains in bone area preceded peak gains in BMC in a longitudinal sample of boys and girls , supporting the theory that the dissociation between skeletal expansion and skeletal mineralization results in a period of relative bone weakness . INTRODUCTION The high incidence of fracture in adolescence may be related to a period of relative skeletal fragility result ing from dissociation between bone expansion and bone mineralization during the growing years . The aim of this study was to examine the relationship between changes in size-corrected BMD ( BMDsc ) and peak distal radius fracture incidence in boys and girls . MATERIAL S AND METHODS Subjects were 41 boys and 46 girls measured annually ( DXA ; Hologic 2000 )  over the adolescent growth period and again in young adulthood . Ages of peak height velocity ( PHV ) , peak BMC velocity ( P BMC V ) , and peak bone area ( BA ) velocity ( PBAV ) were determined for each child . To control for maturational differences , subjects were aligned on PHV . BMDsc was calculated by first regressing the natural logarithms of BMC and BA . The power coefficient ( pc ) values from this analysis were used as follows : BMDsc = BMC /BA(pc ) . RESULTS BMDsc decreased significantly before the age of PHV and then increased until 4 years after PHV . The peak rates in radial fractures ( reported from previous work ) in both boys and girls coincided with the age of negative velocity in BMDsc ; the age of peak BA velocity ( PBAV ) preceded the age of peak BMC velocity ( P BMC V ) by 0.5 years in both boys and girls . CONCLUSIONS There is a clear dissociation between P BMC V and PBAV in boys and girls . BMDsc declines before age of PHV before rebounding after PHV . The timing of these events coincides directly with reported fracture rates of the distal end of the radius . Thus , the results support the theory that there is a period of relative skeletal weakness during the adolescent growth period caused , in part , by a draw on cortical bone to meet the mineral dem and s of the exp and ing skeleton result ing in a temporary increased fracture risk
Several studies that used DXA or quantitative ultrasound suggested that objective ly measured SB was negatively associated with lower extremity bone outcomes , such as femoral neck bone mineral density .
The magnitude of this negative association was small and independent of moderate-to-vigorous physical activity .
In contrast to the lower extremities , there was insufficient evidence for an association of lumbar spine bone outcomes with objective ly measured SB .
In high- quality studies that used DXA , no association was observed between objective ly measured SB and total body bone outcomes .
In studies using question naires , none of these relationships were observed .
Sedentary  behaviour ( SB ) is increasing in Western societies and some studies suggest a deleterious effect of SB on bone .
The aim of this systematic review was to examine the association between  SB and bone health in children , adolescents and young adults .