***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: The effect of exercise training , particularly relatively brief periods , on bone turnover markers in adolescents has been poorly studied . Thirty-eight healthy males ( 16+/-0.7 years ) participated in a 5-week  summer school program in which 20 subjects were r and omly assigned to a training group consisting of 2 h/day , 5 days/week of endurance exercise , and 18 subjects were assigned to a control group .  Bone formation was assessed by measurements of circulating osteocalcin , bone-specific alkaline phosphatase ( BSAP ) , and the C-terminal procollagen peptide ( PICP ) . Bone resorption was assessed by urinary levels of free deoxypyridinoline cross-links ( dPYR ) and the C-(CTX ) and N-terminal ( NTX ) telopeptide cross-links . Prior to training , there was a weak positive correlation between fitness and PICP ( r = 0.27 , p < 0.05 ) , but no correlations were observed between fitness and either the other markers of bone formation or bone resorption . Training led to a significant increase in ( 1 ) osteocalcin ( 15+/-4 % , p < 0.03 ) , ( 2 ) BSAP ( 21+/-6 % , p < 0.02 ) , and ( 3 ) PICP ( 30+/-11 % , p < 0.03 ) and to a significant decrease in NTX ( -21 + /- 3 % , p < 0.05 ) . These bone turnover markers did not change in the control subjects ( osteocalcin , 0+/-4 % ; BSAP , 2+/-4 % ; PICP , -4 + /- 6 % ; NTX , -6 + /- 4 % ) . There was no change in urinary dPYR and CTX in either control or trained subjects . Fitness is only weakly , if at all , correlated with bone formation , but a relatively brief period of endurance training leads to a substantial increase in bone formation markers in adolescent males . School-based , short-term exercise training programs could play a role in enhancing bone formation in adolescents Summary Twenty-two sixth- grade girls who participated in a 7-month school-based resistance-training program were compared to 22 controls . In a sub analysis of Tanner breast II ( T2 ) and III ( T3 ) subjects ( n = 21 controls subjects ( CON ) , n = 17 subjects in the high-intervention (INT)-dose group ( HI ) ) , T2 HI had greater narrow neck ( NN ) width gains than T2 CON ( p < 0.05 ) and T3 HI had greater L3 bone mineral density ( BMD ) gains than T3 CON ( p < 0.05 ) . Introduction Physical activity modulates bone growth during adolescence , but an effective activity has not been identified for general use . The purpose of this study was to examine the effect of a school-based resistance-training program on skeletal growth in pre-menarcheal females . Methods Sixth- grade girls participated in a 7-month , resistance-training program ( INT ) embedded in physical education ( PE ) classes .  Age- and maturity-matched CON from a neighboring school participated in the st and ard PE classes . INT dose defined high ( HI ) and low ( LO ) groups . At baseline ( BL ) and follow-up ( FU ) , non-INT organized physical activity ( PA , hours per week ) and maturity status were recorded ; DXA scans assessed total body , distal radius , proximal femur , and lumbar spine . Regression models analyzed growth in bone outcomes for HI versus CON , accounting for age , Tanner stage , height , and PA . Results Forty-four girls ( 22 HI , 22 CON ) were 11.7 ± 0.3 years of age at BL ; all were ≤6 months postmenarche and did not differ in bone growth over the course of the intervention ( p > 0.05 ) . However , in a sub analysis limited to subjects who were T2 or T3 at BL ( n = 21 CON , n = 17 HI ) , T2 HI had greater gains in NN width ( p = 0.01 ) compared to T2 CON , while T3 HI had greater gains in L3 BMD ( p = 0.03 ) compared to T3 CON . Conclusions In a group of T2 and T3 sixth- grade girls  , a school-based resistance-training intervention produced maturity-specific differential gains for HI versus CON at the hip and spine Objective : To explore potential factors that could be associated with low bone mineral density ( BMD ) in female endurance runners . Methods : Fifty two female endurance runners ( 1500 m to marathon ) , aged 18–44 years , took part . Body fat percentage , lumbar spine BMD , and femoral neck BMD were measured using the Hologic QDR 4500w bone densitometer . Data on training , menstrual cycle status , osteoporosis , and health related factors were obtained by question naire . Dietary variables  were assessed from a prospect i ve seven day dietary record of macronutrients and micronutrients . Results : The mean ( SD ) lumbar spine and femoral neck BMD were 1.11 ( 0.11 ) and 0.89 ( 0.12 ) g/cm2 respectively . A backward elimination regression analysis showed that age , body mass , body fat , distance run , magnesium , and zinc intake were the variables significantly associated with BMD . Lumbar spine BMD ( g/cm2 ) = −1.90 + ( 0.0486 × age ( years ) ) + ( 0.342 × log mass ( kg ) ) − ( 0.000861 × age2 ( years ) ) − ( 0.00128 × distance ( km/week ) ) , with an R2 = 30.1 % ( SEE = 0.089 ( 95 % confidence interval ( CI ) 0.05 to 0.23 ) ; p<0.001 ) . Femoral neck BMD ( g/cm2 ) = −2.51 − ( 0.00989 × age ( years ) ) + ( 0.720 × log mass ( kg ) ) + ( 0.000951 × magnesium ( mg/day ) ) −(0.0289 × zinc ( mg/day ) ) − ( 0.00821 × body fat ( % ) ) − ( 0.00226 × distance ( km/week ) ) , with an R2 = 50.2 % ( SEE = 0.100 ( 95 % CI 0.06 to 0.22 ) ; p<0.001 ) . The negative association between skeletal BMD and distance run suggested that participants who ran longer distances had a lower BMD of the lumbar spine and femoral neck . Further , the results indicated a positive association between body mass and BMD , and a negative association between body fat and BMD . Conclusions : The results suggest a negative association between endurance running distance and lumbar spine and femoral neck BMD , with a positive association between body mass and femoral neck and lumbar spine BMD . However , longitudinal studies are required to assess directly the effect of endurance running and body mass on BMD , and to see if the addition of alternative exercise that would increase lean body mass would have a positive effect on BMD and therefore help to prevent osteoporosis Objectives We investigated whether musculoskeletal fitness of school children aged 8–10 years was affected by frequent intense PE sessions . Design and participants 295 Danish school children aged 8–10 years were cluster r and omised to a small-sided ball game group ( SSG ) ( n=96 , four schools , five classes ) , a circuit strength training group ( CST ) ( n=83 , four schools , four classes ) or a control group ( CON , n=116 , two schools , five classes ) . Intervention SSG or CST was performed 3 × 40 min/week over 10 months . Whole-body dual-energy X-ray absorptiometry ( DXA ) scans were used to determine areal bone mineral density ( aBMD ) , bone mineral content ( BMC ) and lean body mass ( LBM ) . Flamingo balance , st and ing long jump and 20-m sprint tests were used to determine muscular fitness . Results Analysis of baseline-to-10 months change scores showed between-group differences in favour of the interventions in whole-body aBMD ( SSG vs CON : 8 mg/cm2 , 95 % CI 3 to 13 ; CST vs CON : 7 mg/cm2 , 95 % CI 2 to 13 , p<0.05 ) and leg BMC ( SSG vs CON : 11 g , 95 % CI 4 to 18 ; CST vs CON : 11 g , 95 % CI 3 to 18 , p<0.05 ) . SSG had higher change scores in leg aBMD compared with CON and CST ( SSG vs CON : 19 mg/cm2 , 95 % CI 11 to 39 , p<0.05 ; SSG vs CST : 12 mg/cm2 , 95 % CI 3 to 21 , p<0.05 ) , and CST had higher change scores in whole-body BMC compared with CON ( CST vs CON : 25 g , 95 % CI 10 to 39 , p<0.05 ) . Both training types result ed in higher change scores in postural balance ( SSG vs CON : 2.4 fewer falls/min , 95 % CI 0.3 to 4.5 , CST vs CON : 3.6 fewer falls/min , 95 % CI 1.3 to 5.9 , p<0.05 ) and jump length ( SSG vs CON : 10 % , 95 % CI 5 to 16 % ; CST vs CON : 9 % , 95 % CI 3 to 15 % , p<0.05 ) . No between-group differences were observed for sprint performance or LBM ( p>0.05 ) . Conclusions In conclusion , 3 × 40 min/week with SSG or CST over a full school year improves bone mineralisation and several aspects of muscular fitness of children aged 8–10 years , suggesting that well-organised intense physical education classes can contribute positively to develop musculoskeletal health in young children . Trial registration number NCT02000492 , post results 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 PURPOSE The specific aims of the study were to 1 ) determine what effects dose-dependent rope jumping had on os calcis stiffness index ( OCSI ) and 2 ) determine whether OCSI values measured by  quantitative ultrasound ( QUS ) were dependent or independent of the values of bone mineral content ( BMC ) determined by dual energy x-ray absorptiometry ( DXA ) at the lumbar spine and proximal femur ( femoral neck ; greater trochanter ) . METHODS Upon study entry , girls were r and omly assigned to either one of two treatment groups ( high volume ; low volume ) or a control group .  Thirty-seven high school girls were recruited to participate in the study .  QUS and DXA measurements were made at baseline and at 4-month follow-up . Students in the high-volume and low-volume groups jumped rope for 10 and 5 min , respectively . RESULTS The follow-up mean OCSI values for the high-volume , low-volume , and control conditions were 103.95 + /- 
    Output:
    
Results An increase in PBM in adolescence was effective for preventing osteoporosis and fractures in older age .
Exercise programs as part of vigorous physical activity ( VPA ) including resistance and impact exercise at least 5 to 6 months were effective for improving PBM in adolescents .