***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 
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    ***EXAMPLES*** 
    Input: CONTEXT Physical activity can reduce the risk of  hip fractures in older women , although the required type and duration of activity have not been determined . Walking is the most common activity among older adults , and evidence suggests that it can increase femoral bone density and reduce fracture risk . OBJECTIVE To assess the relationship of walking , leisure-time activity , and risk of hip fracture among postmenopausal women . DESIGN , SETTING , AND PARTICIPANTS Prospect i ve analysis begun in 1986 with 12 years of follow-up in the Nurses ' Health Study cohort of registered nurses within 11 US states . A total of 61,200 postmenopausal women ( aged 40 - 77 years and 98 % white ) without diagnosis of cancer , heart disease , stroke , or osteoporosis at baseline . MAIN OUTCOME MEASURES Incident hip fracture result ing from low or moderate trauma , analyzed by intensity and duration of leisure-time activity  and by  time spent walking , sitting , and st and ing  , measured at baseline and up date d throughout follow-up . RESULTS From 1986 to 1998 , 415 incident hip fracture cases were identified . After controlling for age , body mass index , use of postmenopausal hormones , smoking , and dietary intakes in proportional hazards models , risk of hip fracture was lowered by 6 % ( 95 % confidence interval [ CI ] , 4%-9 % ; P<.001 ) for each increase of 3 metabolic equivalent (MET)-hours per week of activity ( equivalent to 1 h/wk of walking at an average pace ) . Active women with at least 24 MET-h/wk had a 55 % lower risk of hip fracture ( relative risk [ RR ] , 0.45 ; 95 % CI , 0.32 - 0.63 ) compared with sedentary women with less than 3 MET-h/wk . Even women with a lower risk of hip fracture due to higher body weight experienced a further reduction in risk with higher levels of activity . Risk of hip fracture decreased linearly with increasing level of activity among women not taking postmenopausal hormones ( P<.001 ) , but not among women taking hormones ( P = .24 ) . Among women who did no other exercise , walking for at least 4 h/wk was associated with a 41 % lower risk of hip fracture ( RR , 0.59 ; 95 % CI , 0.37 - 0.94 ) compared with less than 1 h/wk . More time spent st and ing was also independently associated with lower risks . CONCLUSION Moderate levels of activity , including walking , are associated with substantially lower risk of hip fracture in postmenopausal women Summary This study showed that combination of strength , balance , agility and jumping training prevented functional decline and bone fragility in home-dwelling elderly women . The finding supports the idea that it is possible to maintain good physical functioning by multi-component exercise program and thus postpone the age-related functional problems . Introduction This 1-year r and omized , controlled exercise intervention trial assessed the effects of two different training programs and their combination on physical functioning and bone in home-dwelling elderly women . Methods One hundred and forty-nine healthy women aged 70–78 years were r and omly assigned into : group 1—resistance training ( RES ) , group 2—balance-jumping training ( BAL ) , group 3—combination of resistance and balance-jumping training ( COMB ) , and group 4—controls ( CON ) . Self-rated physical functioning , leg extensor force , dynamic balance , and bone mass and structure were measured . Results Self-rated physical functioning improved in the COMB group , but was reduced in the CON group ; the mean inter-group difference was 10 % ( 95 % CI : 0–22 % ) . Mean increase in the leg extensor force was higher in the RES ( 14 % ; 4–25 % ) and COMB ( 13 % ; 3–25 % ) compared with the CON groups . Dynamic balance improved in the BAL ( 6 % ; 1–11 % ) and in the COMB ( 8 % ; 3–12 % ) groups . There were no inter-group differences in BMC at the proximal femur . In those COMB women who trained at least twice a week , the tibial shaft structure weakened 2 % ( 0–4 % ) less than those in the CON group . Conclusions Strength , balance , agility , and jumping training ( especially in combination ) prevented functional decline in home-dwelling elderly women . In addition , positive effects seen in the structure of the loaded tibia indicated that exercise may also play a role in preventing bone fragility 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 INTRODUCTION Exercise can increase bone strength , but to be effective in reducing fracture risk , exercise must be feasible enough to be adopted into daily life and influence potentially vulnerable skeletal sites such as the superolateral cortex of the femoral neck , where thinning is associated with increased fracture risk . Brief , high-impact exercise increases femoral neck bone density but the optimal frequency of such exercise and the location of bone accrual is unknown . This study thus examined ( 1 ) the effectiveness of different weekly frequencies of exercise on femoral neck BMD and ( 2 ) whether BMD change differed between hip sites using a high-impact , unilateral intervention . METHODS Healthy premenopausal women were r and omly assigned to exercise 0 , 2 , 4 , or 7 days/week for 6 months . The exercise intervention incorporated 50 multidirectional hops on one r and omly selected leg . BMD was measured by DXA at baseline and after 6 months of exercise . Changes in the exercise leg were compared between groups using ANCOVA , with change in the control leg and baseline BMD as covariates . RM-MANOVA was conducted to determine whether bone changes from  exercise  differed between hip sites . RESULTS 61 women ( age 33.6+/-11.1 years ) completed the intervention .  Compliance amongst exercisers was 86.7+/-10.6 % . Peak ground reaction forces during exercise increased from 2.5 to 2.8 times body weight . The change in femoral neck BMD in the exercise limb ( adjusted for change in the control limb and baseline BMD ) differed between groups ( p=0.015 ) , being -0.3 % ( -1.2 to 0.6 ) , 0.0 % ( -1.0 to 1.0 ) , 0.9 % ( -0.1 to 2.0 ) and 1.8 % ( 0.8 to 2.8 ) in those exercising 0 , 2 , 4 and 7 days per week , respectively . When BMD changes at upper neck , lower neck and trochanter were compared using RM-MANOVA , a significant exercise effect was observed ( p=0.048 ) , but this did not differ significantly between sites ( p=0.439 ) despite greatest mean increases at the upper femoral neck . CONCLUSIONS Brief , daily hopping exercises increased femoral neck BMD in premenopausal women but less frequent exercise was not effective . Brief high-impact exercise may have a role in reducing hip fragility , but may need to be performed frequently for optimal response The POWER PE study was an 8-mo , r and omized , controlled , school-based exercise intervention design ed to apply known principles of effective bone loading to practical opportunities to improve life-long musculoskeletal outcomes . A total of 99 adolescents ( 46 boys and 53 girls ) with a mean age of 13.8 + /- 0.4 yr ( peri- to postpubertal ) volunteered to participate . Intervention subjects performed 10 min of jumping activity in place of regular physical education ( PE ) warm up . Control subjects performed usual PE warm-up activities .  Bone mass ( DXA and QUS ) was assessed at baseline and follow-up along with anthropometry , maturity , muscle power , and estimates of physical activity and dietary calcium . Geometric properties ( such as femoral neck [ FN ] moment of inertia ) were calculated from DXA measures . Boys in the intervention group experienced improvements in calcaneal broadb and ultrasound attenuation ( BUA ) ( + 5.0 % ) and fat mass ( -10.5 % ) , whereas controls did not ( + 1.4 % and -0.8 % , respectively ) . Girls in the intervention group improved FN BMC ( + 13.9 % ) and lumbar spine ( LS ) BMAD ( + 5.2 % ) more than controls ( + 4.9 % and + 1.5 % , respectively ) . Between-group comparisons of change showed intervention effects only for whole body ( WB ) BMC ( + 10.6 % versus + 6.3 % ) for boys . Boys in the intervention group gained more lean tissue mass , trochanter ( TR ) BMC , LS BMC , and WB BMC and lost more fat mass than girls in the intervention group ( p < 0.05 ) . Ten minutes of jumping activity twice a week for 8 mo during adolescence seems to improve bone accrual in a sex-specific manner . Boys increased WB bone mass and BUA , and reduced fat mass , whereas girls improved bone mass at the hip and spine BACKGROUND Physical exercise affects many risk factors and diseases and therefore can play a vital role in general disease prevention and treatment of elderly individuals and may reduce costs . We sought to determine whether a single exercise program affects fracture risk ( bone mineral density [ BMD ] and falls ) , coronary heart disease ( CHD ) risk factors , and health care costs in community-dwelling elderly women . METHODS We conducted a r and omized , single-blinded , controlled trial from May 1 , 2005 , through July 31 , 2008 , recruiting women 65 years or older who were living independently in the area of Erlangen-Nuremberg , Germany . In all , 246 women were r and omly assigned to an 18-month exercise program ( exercise group ) or a wellness program ( control group ) . The exercise group ( n = 123 ) performed a multi purpose exercise program with special emphasis on exercise intensity ; the controls ( n = 123 ) focused on well-being with a low-intensity , low-frequency program . The main outcome measures were BMD , the number of falls , the Framingham-based 10-year CHD risk , and direct health care costs . RESULTS For the 227 women who completed the 18-month study , significant exercise effects were observed for BMD of the lumbar spine ( mean [ 95 % confidence interval ( CI ) ] percentage of change in BMD [ baseline to follow-up ] for the exercise group : 1.77 % [ 1.26 % to 2.28 % ] vs controls : 0.33 % [ -0.24 % to 0.91 % ] ; P < .001 ) , femoral neck ( exercise group : 1.01 % [ 0.37 % to 1.65 % ] vs controls : -1.05 % [ -1.70 % to -0.40 % ] ; P < .001 ) , and fall rate per person during  
    Output:
    
Conclusions The findings from our meta- analysis of RCTs indicate that exercise can significantly enhance bone strength at loaded sites in children but not in adults .