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 .
Low back joint loading and kinematics during standing and unsupported sitting
The aim was to examine lumbar spine kinematics , spinal joint loads and trunk muscle activation patterns during a prolonged ( 2 h ) period of sitting .  This information is necessary to assist the ergonomist in design ing work where posture variation is possible — particularly between st and ing and various styles of  sitting  . Joint loads were predicted with a highly detailed anatomical biomechanical model ( that incorporated 104 muscles , passive ligaments and intervertebral discs ) , which utilized biological signals of spine posture and muscle electromyograms ( EMG ) from each trial of each subject . Sitting result ed in significantly higher ( p < 0.001 ) low back compressive loads ( mean±SD 1698±467 N ) than those experienced by the lumbar spine during st and ing ( 1076±243 N ) . Subjects were equally divided into adopting one of two sitting strategies : a single ‘ static ’ or a ‘ dynamic ’ multiple posture approach . Within each individual , st and ing produced a distinctly diVerent spine posture compared with sitting , and st and ing spine postures did not overlap with flexion postures adopted in sitting when spine postures were averaged across all eight subjects . A rest component ( as noted in an amplitude probability distribution function from the EMG ) was present for all muscles monitored in both sitting and st and ing tasks . The upper and lower erector spinae muscle groups exhibited a shifting to higher levels of activation during sitting . There were no clear muscle activation level diVerences in the individuals who adopted diVerent sitting strategies . St and ing appears to be a good rest from sitting given the reduction in passive tissue forces . However , the constant loading with little dynamic movement which characterizes both st and ing and sitting would provide little rest/change for muscular activation levels or low back loading
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 .