***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: Our aim is to analyse the effect on bone mass of : ( 1 ) physical fitness performance on a specific group of physical activity ( PA ) and , ( 2 ) PA on a specific physical fitness performance group . Bone mineral content ( BMC ) by dual energy X-ray absorptiometry ( DXA ) and PA by accelerometers was assessed in 373 Spanish adolescents ( 182 males ) . Adolescents were classified as : active and non-active ( ≥60 or < 60 min day−1 of moderate-vigorous PA ) . Fitness was assessed through speed/agility , strength and cardiorespiratory tests . Adolescents were classified by tertiles ( T1 , T2 and T3 ) . ANCOVA was used for the analysis with sex , height , lean mass , calcium intake and pubertal status as covariates . Adolescents with lower strength , speed/agility and cardiorespiratory fitness ( CRF ) showed lower BMC in the whole body and extremities compared with adolescents with better results in these tests , mainly those non-active adolescents . Non-active adolescents with high fitness levels showed higher BMC ( whole body and upper limbs ) than active ones . The conclusions included : ( 1 ) within the non-active group , lower levels of fitness were associated with lower BMC ; this might be through PA or trough an effect of PA on muscle mass . ( 2 ) Non-active adolescents with high level of fitness in most fitness tests showed higher BMC than their active peers , in spite of their lower PA levels . These unexpected results could be influenced by several factors such as genetics , nutrition , type of exercise or sport , hormones and skeletal age A higher bone mass may reduce the risk of osteoporosis and fractures . The role of maturational timing for optimizing bone mass is controversial due to the lack of prospect i ve evidence from childhood to adulthood . The purpose of this study was to examine the long term relationship between the onset of maturation and bone mineral content ( BMC ) development . Two hundred thirty individuals ( 109 males and 121 females ) from the Saskatchewan Pediatric Bone Mineral Accrual Study ( PBMAS ) were classified into maturity groups based on age of peak height velocity . BMC was serially assessed using dual energy X-ray absorptiometry ( DXA ) . Multilevel models were constructed to examine the independent development of BMC by maturity group . When age , body size , and body composition were controlled early maturing females had on average 3 - 4 % , 62.2 ± 16.8 g ( p<0.05 ) , more total body BMC than their average maturing peers by 20 years of age . In contrast , late maturing females had 50.7 ± 15.6 g less total body BMC . No maturational effects were found at either the lumbar spine or femoral neck ( p>0.05 ) in females . There were no significant differences in BMC development at any site among male maturational groups ( p>0.05 ) . In this group of healthy participants , there appears to be a sex-dependent effect on the relationship between maturational timing and total body BMC development . Early , average and late maturing males displayed similar BMC development . Late maturing females had compromised BMC accrual compared to their early and average maturing peers BACKGROUND Osteoporosis is a growing health problem . One of the proposed reasons for this is a more sedentary lifestyle . The aim of this study was to investigate the associations between muscle strength and total body bone mineral density ( TBMD ) in young adults at expected peak bone mass . METHODS Sixty-four women and 61 men ( total 125 ) 21 years of age were included .  H and grip strength , isokinetic knee-flexion and -extension muscle strength , TBMD , and body composition were measured . RESULTS Univariate regression analyses showed that knee flexion and extension explained almost 30 % of the variation in TBMD in women , whereas h and grip strength was not associated with TBMD . In men , no correlation between any measures of muscle strength and TBMD was evident . Stepwise regression analysis showed that knee-flexion and -extension muscle strength in women were associated with TBMD , R2=0.27 . In men , lean body mass , fat mass , weight , and height were predictors for TBMD , R2=0.43 , whereas muscle strength did not affect the prediction of TBMD . CONCLUSIONS Muscle strength at weight-bearing sites is related to TBMD in women , whereas body composition is related to TBMD in men . The association of lower limb strength on TBMD only in young women indicates a gender difference OBJECTIVE The aim of the study was to quantify the inter-relationship between bone mineral density and physical activity , muscle strength , and body mass composition in a group of healthy 16 - 20-year-old women . DESIGN A cross-sectional study . SETTING Reykjavik area . SUBJECTS Two-hundred and fifty-four Icel and ic Caucasian women aged 16 , 18 and 20 years , r and omly selected from the registry of Reykjavik . MAIN OUTCOME MEASURES Bone mineral content ( BMC ) and density ( BMD ) in lumbar spine , hip , distal forearm and total skeleton and lean mass and fat mass were measured with dual energy X-ray absorptiometry ( DEXA ) and compared with  grip strength measured with a dynamometer and physical activity as assessed by a question naire . RESULTS The lean mass had the strongest correlation with BMC and BMD , stronger than weight , height and fat mass , both in univariate analysis ( r = 0.41 - 0.77 ; P<0.001 ) and in linear regression analysis . The total skeletal BMD was logarithmically higher by hours of exercise per week ( P<0.001 ) ) . About 30 % of variability in total skeletal BMD in this age group can be predicted by lean mass and physical exercise . CONCLUSIONS Modifiable factors , such as exercise and adequate muscle seem to be significant predictors of the attainment of peak bone mass in women PURPOSE This study investigated the influence of different exercise types and differences in anatomical distribution of mechanical loading patterns on bone mineral density ( BMD ) in elite female cyclists , runners , swimmers , triathletes , and controls ( N = 15 per group ) . Associations between leg strength and BMD were also examined . METHODS Areal BMD ( g x cm(-2 ) ) was assessed by duel-energy x-ray absorptiometry ( DXA ) ( total body ( TB ) , lumbar spine ( LS ) , femoral neck ( FN ) , legs , and arms ) . Right knee flexion and extension strength was measured using a Cybex Norm isokinetic dynamometer at 60 degrees x s(-1 ) . RESULTS Runners had significantly higher unadjusted TB , LS , FN , and leg BMD than controls ( P < 0.05 ) ; higher TB , FN , and leg BMD than swimmers ( P < 0.05 ) ; and greater leg BMD than cyclists ( P < 0.05 ) . Absolute knee extension strength was significantly ( P < 0.01 ) correlated ( 0.33 < or = r < or = 0.44 ) with TB , FN , LS , and leg BMD for all groups combined . Weaker but still significant correlations ( 0.28 < or = r < or = 0.33 ) existed for normalized ( per leg lean tissue mass ) knee extension strength and all BMD sites , except FN BMD . There were no significant correlations between absolute or normalized knee flexion strength and any of the BMD variables . Absolute knee extension strength was entered as the second independent predictor for LS and leg BMD in stepwise multiple linear regression analysis ( MLRA ) , accounting for increments of 4 % and 12 % , respectively , in total explained variation . CONCLUSION We conclude that running , a weight bearing exercise , is associated with larger site-specific BMD than swimming or cycling , that the generalized anatomical distribution of loads in triathlon appears not to significantly enhance total body BMD status , and that knee extension strength is only a weak correlate and independent predictor of BMD in adolescent females OBJECTIVES To analyse the relationship between isokinetic strength of the lower limb muscles and bone mineral density and content ( BMD , BMC ) of adolescent male soccer players and age-matched controls not involved in sport ( 12 - 15 years ) . METHODS A r and om sample of 151 young males was divided into soccer players ( SG ; n=117 ) and control subjects ( CG ; n=34 ) .  Peak torque of knee extensors ( PTE ) and flexors ( PTF ) was measured during isokinetic knee joint movement ( 90 ° /s ) of the dominant and non-dominant lower limbs . BMD and BMC of the whole-body , lumbar spine , dominant/non-dominant lower limb were determined by dual-energy X-ray absorptiometry . Physical activity was monitored with accelerometers during 5 days . Estimated maturity offset was used as an indicator of biological maturity status . RESULTS Whole-body BMD ( 1.03±0.01 vs. 0.98±0.01 g/cm2 , P=0.003 ) and dominant ( 1.09±0.01 vs. 1.02±0.01 g/cm2 , P<0.001 ) and non-dominant ( 1.09±0.01 vs. 1.01±0.01 g/cm2 , P<0.001 ) lower limb BMD was greater in SG compared to CG . No significant differences were found for BMC . Compared to CG , SG performed better in the YY-IE2 test ( 780±40 vs. 625±31 m ) , exhibited higher PTE ( dominant limb : 155.2±30.3 vs. 123.4±37.0N m ; non-dominant limb : 156.2±36.1 vs. 120.4±41.1 N m ) and PTF muscles ( dominant limb : 79.0±25.3 vs. 57.1±25.3 Nm ; non-dominant limb : 73.3±20.7 vs. 57.0±24.2N m ) . Moreover , the PTE , soccer participation and maturity status were positively associated with the BMD at all body sites ( r2=0.57 - 0.73 , P<0.05 ) . CONCLUSIONS Muscle strength of knee extensors is associated with BMD and BMC at all body sites . Muscle-skeletal structures respond positively to the weight-bearing and impact-loading imposed by soccer practice . Soccer seemed to be a multilateral balanced sport activity The incidence of hip and forearm fracture in elderly men in the United Kingdom is a public health issue , but there is limited knowledge on lifestyle factors affecting male bone health . The aim of this cross-sectional study was to evaluate the relationships between whole body and regional bone mineral status and self-reported participation time in no- , low- , moderate- , and high-impact activities and fitness measurements in 16- to 18-year-old boys . One hundred twenty-eight boys underwent absorptiometry ( DXA ) measurements ( Hologic QDR 1000W ) of  bone mineral content ( BMC ) , bone area ( BA ) , and bone mineral density ( BMD ) at the whole body , hip , spine , and forearm . They also completed the EPIC ( European Prospect i ve Investigation of Cancer ) physical activity question naire , which allowed categorization of activities according to impact and aerobic intensity . Fitness and strength were assessed in each subject using estimated VO2 max , grip strength , and back strength . Significant positive relationships were found between BMC , BA , and BMD and the fitness and strength measurements and participation time in high-impact sports at most skeletal sites . The relationships were further examined after adjustment of BMC for height , weight , and bone area , thereby minimizing the influence of body and bone size on these relationships . VO2 max was a significant positive determinant of size-adjusted BMC at the whole body , the ultradistal and one-third radius , and all the hip sites , except the trochanter . Size-adjusted BMC at the forearm sites and trochanter was significantly positively associated with grip strength . Size-adjusted BMC at the whole body and all the hip sites was significantly positively associated with time spent at high-impact activities . Differences in size-adjusted BMC across thirds of time spent at high-impact activities were also examined . Boys in the highest third of high-impact activity had significantly greater size-adjusted whole body BMC and total hip BMC compared to subjects in the lowest third [ + 3.4 (1.2)% for whole body and + 8.5 (2.2)% for hip , both P = 0.001 ] . Boys in the highest third of high-impact activity spent most activity time jogging , playing tennis , football and rugby , basketball , and exercising with weights . Back strength and lean mass were significantly greater in subjects in the highest third compared to those in the middle ( P = 0.02 ) and lowest third ( P = 0.03 ) . No significant differences were found between subjects in each third of high-impact activity for potential confounders including TV viewing , calcium intake , body fat , and height . These findings indicate that participation of male adolescents in a range of high-impact activities for 1 h or more a day is associated with greater bone size and mineral content , especially at the hip Summary The National Academy of Medicine recommends the h and grip for school-based surveillance of muscle strength for bone health . We established grip strength cutpoints that are linked to bone health in both US and European youth . These cutpoints could serve as a potential set of st and ards for surveillance and clinical applications . Purpose The U 
    Output:
    
This systematic review and meta- analysis supports that muscular strength should be considered as a useful skeletal health marker during development and a target outcome for interventions aim ed at improving bone health