***TASK*** the task is to summarize an input biomedical literature in six sentences 
    ***INPUT*** the input is a biomedical literature 
    ***OUTPUT*** the output is the summary of an input biomedical literature in six sentences 
    ***DOCUMENTATION*** 
    ***EXAMPLES*** 
    Input: BACKGROUND Osteoporosis may be prevented or delayed by maximizing peak bone mass through diet modification and physical activity during adolescence . OBJECTIVE We studied whether increases in calcium intake and physical activity effectively increase the bone mineral status of adolescent girls aged 16 - 18 y. DESIGN We conducted a 15.5-mo study of calcium supplementation ( 1000 mg Ca/d as carbonate ) in 144 adolescent girls aged 17.3 + /- 0.3 y ( + /- SD ) . The subjects were r and omly allocated to an exercise ( three 45-min exercise-to-music classes/wk during term time ) or nonexercise group . Dual-energy X-ray absorptiometry of the whole body , spine , forearm , and hip was performed before and after intervention . RESULTS The mean ( + /- SD ) percentage of subjects compliant with supplement taking was 70 + /- 27 % and with exercise class attendance was 36 + /- 25 % . Baseline calcium intake was 938 + /- 411 mg/d . Calcium supplementation significantly increased size-adjusted bone mineral content . The effect was stronger in subjects with good compliance ( percentage difference + /- SE ) : whole body , 0.8 + /- 0.3 % ( P < or = 0.01 ) ; lumbar spine , 1.9 + /- 0.5 % ( P < or = 0.001 ) ; ultradistal radius , 1.3 + /- 0.6 % ( P < or = 0.05 ) ; total hip , 2.7 + /- 0.6 % ( P < or = 0.001 ) ; femoral neck , 2.2 + /- 0.7 % ( P < or = 0.001 ) ; trochanter , 4.8 + /- 0.9 % ( P < or = 0.001 ) . Attendance at > 50 % of the exercise sessions was significant at the total hip ( 1.4 + /- 0.7 % ; P < or = 0.05 ) and trochanter ( 2.6 + /- 1.2 % ; P < or = 0.05 ) . CONCLUSIONS Calcium supplementation and exercise enhanced bone mineral status in adolescent girls . Whether this is a lasting benefit , leading to the optimization of peak bone mass and a reduction in fracture risk , needs to be determined Exercise during growth has a positive influence on bone mineral accrual , yet little is known about how bone geometry and strength adapt to loading during growth . Our primary objective was to compare changes in proximal femur bone geometry and strength between 31 prepubertal ( Tanner Stage 1 ) boys who participated in a school-based , high-impact circuit intervention ( 12 min , three times a week ) for 20 months and 33 maturity-matched controls . Our secondary objective was to compare changes in total body ( TB ) , proximal femur ( PF ) , and lumbar spine ( LS ) bone mineral content ( BMC ) and bone area ( BA ) in these groups . We assessed geometric variables and bone strength at the narrow neck ( NN ) , intertrochanteric ( TR ) region , and femoral shaft regions by applying the Hip Structure Analysis program to proximal femur dual energy X-ray absorptiometry scans ( DXA , Hologic QDR 4500 ) . Further , we assessed total body , lumbar spine , and proximal femur BMC and BA by DXA and derived total body lean mass and fat mass from total body scans . Intervention ( 10.2 + /- 0.5 years ) and control boys ( 10.1 + /- 0.5 years ) had similar baseline height ( 140.8 vs. 141.3 cm ) and weight ( 36.9 vs. 35.4 kg ) , and average 20-month physical activity scores ( Physical Activity Question naire for Children , PAQ-C ) and calcium intakes ( 861 vs. 852 mg/day , food frequency question naire ) . Twenty-month height and weight changes were not significantly different between groups ; lean mass changed more ( P < 0.05 ) in intervention boys ( 22.8 % ) than control boys ( 18.6 % ) . At the NN region , intervention boys had greater bone expansion on both the periosteal ( + 2.6 % , P = 0.1 ) and endosteal ( + 2.7 % , P = 0.2 ) surfaces , result ing in significantly greater changes in section modulus ( bone bending strength ) ( + 7.5 % , P = 0.02 , ANCOVA , adjusting for height change , final Tanner Stage , and baseline bone values ) . Changes at the intertrochanteric and femoral shaft regions were not significantly different between groups . Femoral neck ( FN ) BMC changes were significantly greater in intervention boys ( + 4.3 % , P < 0.01 ) ; changes in BA and BMC for other regions were not significantly different between groups . In summary , a school-based , high-impact exercise intervention implemented three times a week for 12 min is an effective strategy for site-specific gains in bone strength at the narrow neck region of the proximal femur Cross-sectional studies of elite athletes suggest that growth is an opportune time for exercise to increase areal bone mineral density ( BMD ) . However , as the exercise undertaken by athletes is beyond the reach of most individuals , these studies provide little basis for making recommendations regarding the role of exercise in musculoskeletal health in the community . To determine whether moderate exercise increases bone mass , size , areal , and volumetric BMD , two socioeconomically equivalent schools were r and omly allocated to be the source of an exercise group or controls . Twenty boys ( mean age 10.4 years , range 8.4 - 11.8 ) allocated to 8 months of 30-minute sessions of weight-bearing physical education lessons three times weekly were compared with 20 controls matched for age , st and ing and sitting height , weight , and baseline areal BMD . Areal BMD , measured using dual-energy X-ray absorptiometry , increased in both groups at all sites , except at the head and arms . The increase in areal BMD in the exercise group was twice that in controls ; lumbar spine ( 0.61 + /- 0.11 vs. 0.26 + /- 0.09%/month ) , legs ( 0.76 + /- 0.07 vs. 0.34 + /- 0.08%/month ) , and total body ( 0.32 + /- 0.04 vs. 0.17 + /- 0.06%/month ) ( all p < 0.05 ) . In the exercise group , femoral midshaft cortical thickness increased by 0.97 + /- 0 . 32%/month due to a 0.93 + /- 0.33%/month decrease in endocortical ( medullary ) diameter ( both p < 0.05 ) . There was no periosteal expansion so that volumetric BMD increased by 1.14 + /- 0.33%/month , ( p < 0.05 ) . Cortical thickness and volumetric BMD did not change in controls . Femoral midshaft section modulus increased by 2.34 + /- 2 . 35 cm3 in the exercise group , and 3.04 + /- 1.14 cm3 in controls ( p < 0.05 ) . The growing skeleton is sensitive to exercise . Moderate and readily accessible weight-bearing exercise undertaken before puberty may increase femoral volumetric BMD by increasing cortical thickness . Although endocortical apposition may be a less effective means of increasing bone strength than periosteal apposition , both mechanisms will result in higher cortical thickness that is likely to offset bone fragility conferred by menopause-related and age-related endocortical bone resorption Abstract : The maximum amount of bone a person can obtain during the first two decades of life is an important determinant of bone mass in later life , and an increase in peak bone mass has been associated with decreased risk for osteoporotic fractures . It is known that growth of bone and thus development of peak bone mass are strongly controlled by genetic factors , but information on the role of environmental factors , such as exercise and nutrition , ( e.g. , exercise ) on growing bone is limited . We tested a hypothesis that in growing girls the benefit of mechanical loading on bone mineral mass and bone strength is better before rather than after the menarche . Sixty-four girls ( 25 premenarcheal , 39 postmenarcheal ) carried out a supervised 9-month step-aerobic program ( two sessions per week ) , each session complemented with additional jumps .  Sixty-two girls ( 33 premenarcheal , 29 postmenarcheal ) served as controls . Bone mineral content ( BMC ) at the lumbar spine and proximal femur was measured by dual-energy X-ray absorptiometry ( DXA ) . In addition , the cortical density ( CoD , mg/cm3 ) and cortical cross-sectional area ( CoA , mm2 ) and the density-weighted polar section modulus ( BSI , mm3 ) of the tibial midshaft were determined by peripheral quantitative tomography ( pQCT ) . In the premenarcheal girls , BMC increased statistically significantly more in the trainees than controls at the lumbar spine ( p= 0.012 ) ( 8.6 % vs 5.3 % ) and femoral neck ( p= 0.014 ) ( 9.3 % vs 5.3 % ) . In the tibial midshaft , the intergroup differences ( CoD , CoA and BSI ) were not significant . The postmenarcheal girls showed no significant post-training intergroup differences in any of the bone parameters ( BMC increased in the lumbar spine 6.0 % vs 4.9 % ; femoral neck 3.4 % vs 3.2 % ; and trochanter 2.6 % vs 3.5 % ) . Although a large proportion of bone mineral increase in the growing girls of this study was attributable to growth itself , this 9-month exercise intervention showed that a clear and large additional bone gain could be obtained in exercising premenarcheal girls , but not in exercising postmenarcheal girls . In other words , exercise seemed more beneficial for additional bone mineral acquisition before menarche ( i.e. , during the growth spurt ) rather than after it Physical activity during childhood is advocated as one strategy for enhancing peak bone mass ( bone mineral content [ BMC ] ) as a means to reduce osteoporosis-related fractures . Thus , we investigated the effects of high-intensity jumping on hip and lumbar spine bone mass in children . Eighty-nine prepubescent children between the ages of 5.9 and 9.8 years were r and omized into a  jumping  ( n = 25 boys and n = 20 girls ) or  control group  ( n = 26 boys and n = 18 girls ) . Both groups participated in the 7-month exercise intervention during the school day three times per week . The jumping group performed 100 , two-footed jumps off 61-cm boxes each session , while the control group performed nonimpact stretching exercises .  BMC ( g ) , bone area ( BA ; cm2 ) , and bone mineral density ( BMD ; g/cm2 ) of the left proximal femoral neck and lumbar spine ( L1-L4 ) were assessed by dual-energy X-ray absorptiometry ( DXA ; Hologic QDR/4500-A ) . Peak ground reaction forces were calculated across 100 , two-footed jumps from a 61-cm box . In addition , anthropometric characteristics ( height , weight , and body fat ) , physical activity , and dietary calcium intake were assessed . At baseline there were no differences between groups for anthropometric characteristics , dietary calcium intake , or bone variables . After 7 months , jumpers and controls had similar increases in height , weight , and body fat . Using repeated measures analysis of covariance ( ANCOVA ; covariates , initial age and bone values , and changes in height and weight ) for BMC , the primary outcome variable , jumpers had significantly greater 7-month changes at the femoral neck and lumbar spine than controls ( 4.5 % and 3.1 % , respectively ) . In repeated measures ANCOVA of secondary outcomes ( BMD and BA ) , BMD at the lumbar spine was significantly greater in jumpers than in controls ( 2.0 % ) and approached statistical significance at the femoral neck ( 1.4 % ; p = 0.085 ) . For BA , jumpers had significantly greater increases at the femoral neck area than controls ( 2.9 % ) but were not different at the spine . Our data indicate that jumping at ground reaction forces of eight times body weight is a safe , effective , and simple method of improving bone mass at the hip and spine in children . This program could be easily incorporated into physical education classes OBJECTIVE To evaluate the effects of an elementary school-based physical education exercise intervention program on bone mineral accrual in prepubertal and early pubertal girls . STUDY DESIGN A total of 14 schools were r and omly assigned to control ( C ) and intervention ( I ) groups . Girls in the I group completed a 10-minute , 3 times per week circuit of varied jumping activities over 7 months . We measured total body , lumbar spine , proximal femur , femoral neck , and trochanteric bone mineral content and areal bone mineral density and estimated femoral neck volumetric bone mineral density at baseline and final measurement in 87 girls in the I group and 90 girls in the C group . Girls were between 8.7 and 11.7 years at baseline . Tanner stage 1 girls were considered prepubertal ; Tanner stages 2 and 3 girls were considered early pubertal . We 
    Output:
    
Although weight-bearing exercise appears to enhance bone mineral accrual in children , particularly during early puberty ; it remains unclear as to what constitutes the optimal exercise programme .
In addition , the measurement of bone quality parameters and volumetric BMD would provide a greater insight into the mechanisms implicated in the adaptation of bone to exercise