***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: PURPOSE The purpose of this prospect i ve study was to examine rates and risk factors for overuse injuries among 824 women during Marine Corps Recruit Depot basic training at Parris Isl and , SC , in 1999 . METHODS Data collected included training day exposures ( TDE ) , baseline performance on a st and ardized 1.5-mile timed run , and a pretraining question naire highlighting exercise and health habits . The women were followed during training for occurrence of stress fracture and other lower-extremity overuse injury . RESULTS There were 868 lower-extremity overuse injuries for an overall injury rate of 12.6/1000 TDE . Rates for initial and subsequent injury were 8.7/1000 and 20.7/1000 TDE , respectively . There were 66 confirmed lower-extremity stress fractures among 56 ( 6.8 % ) women ( 1.0/1000 TDE ) . Logistic regression modeling indicated that low aerobic fitness ( a slower time on the timed run ( > 14.4 min ) ) , no menses in six or more consecutive months during the past year , and less than 7 months of lower-extremity weight training were significantly associated with stress fracture incidence . Self-rated fair-poor fitness at baseline was the only variable significantly associated with other non-stress fracture overuse injury during basic training . CONCLUSIONS Among this sample of women , the risk of lower-extremity overuse injury was high , with a twofold risk of subsequent injury . The results suggest that stress fracture injury might be decreased if women entered training with high aerobic fitness and participated frequently in lower-extremity strength training . Furthermore , women reporting a history of menstrual irregularity at their initial medical exam may require closer observation during basic training Strenuously exercising young women with hypothalamic amenorrhea are hypoleptinemic and have low bone mineral density ( BMD ) and content ( BMC ) , which predispose them to increased fracture risk . Short-term leptin replacement in these women corrects many neuroendocrine abnormalities and increases circulating levels of bone formation markers . Whether treatment with recombinant methionyl human leptin ( metreleptin ) for a long period improves BMD and BMC remains unknown . We studied 20 strenuously exercising young women with hypoleptinemia ( leptin concentration < 5 ng/mL ) and hypothalamic amenorrhea of at least 6 months ' duration . Eleven were r and omized to metreleptin  ( initial dose , 0.08 mg/[kg·d ] for 3 months ; altered thereafter to 0.12 mg/kg for lack of efficacy or 0.04 mg/[kg d ] for more than 5 % weight loss ) and 9 were r and omized to placebo for 9 months . After a 3-month washout period , subjects were reexamined at the 1-year time point . Six subjects elected to continue on open-label metreleptin treatment for another 12 months . Two subjects dropped out after 18 months , and 4 completed the entire 2-year study . The BMD and BMC of the total body , lumbar spine ( L1-L4 ) , hip , and radius were assessed by using dual-energy x-ray absorptiometry at baseline and at 3 , 6 , 9 , 12 , 18 , and 24 months of treatment . Metabolic and hormonal parameters and bone markers were measured in blood and urine . Metreleptin  significantly increased BMC ( P = .034 ) and tended to increase BMD ( P = .069 ) at the lumbar spine at 9 months in the entire study group ( intention-to-treat analysis ) . In subjects who completed the entire 2-year study ( n = 4 ) , metreleptin  significantly increased BMD ( P = .024 ) and BMC ( P = .049 ) at the lumbar spine by 4 % to 6 % . Changes were not significant at the whole body , hip , and radius . Changes in hormonal and metabolic parameters and bone markers were moderate during the first year of treatment , but metreleptin further increased insulin-like growth factor 1 and decreased cortisol and cross-linked C-terminal telopeptide of type 1 collagen concentrations in serum during the second year of treatment ( P < .05 ) . The incremental area under the estradiol concentration curve over the 2-year course of the study correlated positively with the corresponding increase in lumbar spine BMD ( ρ = 0.42 , P = .039 ) . Long-term metreleptin administration in strenuously exercising young women with hypothalamic amenorrhea and hypoleptinemia  increases lumbar spine BMD and BMC and alters bone remodeling milieu to favor bone accretion . Results from this pilot study should be confirmed by future , larger clinical trials and need to be extended by study ing bone microarchitecture and fracture risk PURPOSE To identify risk factors for stress fracture among young female distance runners . METHODS Participants were 127 competitive female distance runners , aged 18 - 26 , who provided at least some follow-up data in a r and omized trial among 150 runners of the effects of oral contraceptives on bone health . After completing a baseline question naire and undergoing bone densitometry , they were followed an average of 1.85 yr . RESULTS Eighteen participants had at least one stress fracture during follow-up . Baseline characteristics associated ( P<0.10 ) in multivariate analysis with stress fracture occurrence were one or more previous stress fractures ( rate ratio [ RR ] [ 95 % confidence interval]=6.42 ( 1.80 - 22.87 ) , lower whole-body bone mineral content ( RR=2.70 [ 1.26 - 5.88 ] per 1-SD [ 293.2 g ] decrease ) , younger chronologic age ( RR=1.42 [ 1.05 - 1.92 ] per 1-yr decrease ) , lower dietary calcium intake ( RR=1.11 [ 0.98 - 1.25 ] per 100-mg decrease ) , and younger age at menarche ( RR=1.92 [ 1.15 - 3.23 ] per 1-yr decrease ) . Although not statistically significant , a history of irregular menstrual periods was also associated with increased risk ( RR=3.41 [ 0.69 - 16.91 ] ) . Training-related factors did not affect risk . CONCLUSION The results of this and other studies indicate that risk factors for stress fracture among young female runners include previous stress fractures , lower bone mass , and , although not statistically significant in this study , menstrual irregularity . More study is needed of the associations between stress fracture and age , calcium intake , and age at menarche . Given the importance of stress fractures to runners , identifying preventive measures is of high priority CONTEXT Stress fractures are common in endurance athletes . Whereas studies have described distal tibia bone structure in athletes , there are few data regarding hip geometric parameters . Hip structural analysis ( HSA ) using dual-energy x-ray absorptiometry is a vali date d technique to assess hip bone structure . OBJECTIVES The purpose of this study was to compare hip geometry in young oligoamenorrheic athletes ( AAs ) , eumenorrheic athletes ( EAs ) , and nonathletes using HSA . We hypothesized that AAs would have impaired bone structure compared with that of EAs . DESIGN This was a cross-sectional study . SETTING The setting was a clinical research center . SUBJECTS We enrolled 55 AAs , 24 EAs , and 23 nonathletes of normal weight who were 14 to 22 years old . Athletes ran ≥20 miles/wk or were engaged in weight-bearing sports for ≥4 hours/wk . MAIN OUTCOME MEASURES Dual-energy x-ray absorptiometry was used for HSA and hip areal bone mineral density ( aBMD ) . RESULTS Hip aBMD Z-scores were lower in AAs and in nonathletes than in EAs ( P = .002 ) . A larger proportion of AAs than EAs and nonathletes had hip Z-scores < -1 ( 30.9 , 4.2 , 17.4 % , P = .01 ) . At the narrow neck , trochanteric region , and femoral shaft , subperiosteal width , cross-sectional moment of inertia , and section modulus were higher in EAs than in nonathletes ; values in AAs did not differ from those of nonathletes . Cross-sectional area was lower in AAs and in nonathletes than in EAs . Groups did not differ for cortical thickness or buckling ratio . Group differences were lost after adjustment for lean mass but not aBMD . CONCLUSIONS In an eugonadal state , athletic activity confers benefits for hip structure independent of aBMD . This advantage is lost in AAs , who do not differ from nonathletes for most parameters and fare worse than EAs for cross-sectional area Studies of stress fracture ( SF ) incidence are limited in number and geographical location ; this study determined the incidence of SF injury in female endurance athletes based in the United Kingdom . A total of 70 athletes aged between 18 and 45 years were recruited and prospect ively monitored for 12 months . Question naires at baseline and 12 months assessed SF , menstrual and training history , eating psychopathology , and compulsive exercise . Peak lower leg muscle strength was assessed in both legs using an isometric muscle rig .  Bone mineral density ( BMD ) of total body , spine , hip , and radius was assessed using dual X-ray absorptiometry . Among the 61 athletes who completed the 12-month monitoring , two sustained a SF diagnosed by magnetic resonance imaging , giving an incidence rate ( 95 % confidence intervals ) of 3.3 ( 0.8 , 13.1 ) % of the study population sustaining a SF over 12 months . The SF cases were 800 m runners aged 19 and 22 years , training on average 14.2 h a week , eumenorrheic with no history of menstrual dysfunction . Case 1 had a higher than average energy intake and low eating psychopathology and compulsive exercise scores , while the reverse was true in case 2 . BMD in both cases was similar to mean values in the non-SF group . The incidence of SF in our female endurance athlete population based in the United Kingdom was 3.3 % , which is lower than previously reported . Further work is needed to confirm the current incidence of SF and evaluate the associated risk factors Introduction Osteoporosis is associated with increased risk for fracture . However , most postmenopausal women have bone mineral density ( BMD ) within the normal or osteopenic range . The aim of this study was to determine the proportion of the population burden of fragility fractures arising from women at modest risk for fracture . Methods We measured baseline BMD in a population -based r and om sample of 616 postmenopausal women aged 60–94 years and followed these individuals for a median of 5.6 years ( IQR 3.9–6.5 ) to determine the incidence of fractures according to age , BMD and the presence of a prior fracture . Results Based on WHO criteria , 37.6 % of the women had normal total hip BMD , 48.0 % had osteopenia and 14.5 % had osteoporosis . The incidence of fracture during follow-up was highest in women with osteoporosis , but only 26.9 % of all fractures arose from this group ; 73.1 % occurred in women without osteoporosis ( 56.5 % in women with osteopenia , 16.6 % in women with normal BMD ) . Decreasing BMD , increasing age and prior fracture contributed independently to increased fracture risk ; in a multivariate model , the relative risk for fracture increased 65 % for each SD decrease in BMD ( RR=1.65 , 95%CI 1.32–2.05 ) , increased 3 % for every year of age ( RR=1.03 , 95%CI 1.01–1.06 ) and doubled with prevalent fracture ( RR=2.01 , 95 % CI 1.40–2.88 ) . A prevalent fracture increased the risk for fractures such that women with osteopenia and prevalent fracture had the same , if not greater , risk as women with osteoporosis alone . Conclusions Reducing the population burden of fractures requires attention to women with osteopenia , as well as osteoporosis , because over half of the fragility fractures in the population arise in these individuals , and women with osteopenia plus a prevalent fracture have the same fracture risk as women with osteoporosis A prospect i ve study of 295 infantry recruits has shown that the mediolateral width of the tibia measured radiographically at each of three different levels in the bone had a statistically significant correlation with the total incidence of stress fractures as well as with those in the tibia alone or the femur alone . A narrow tibial width was shown to be a risk factor , but cortical thickness was not found to be significant UNLABELLED The cumulative effect of the female athlete triad ( Triad ) risk factors on the likelihood of low bone mineral density ( BMD ) in exercising women is unclear . PURPOSE This study aim ed to determine the risk of low BMD in exercising women with multiple Triad risk factors . METHODS We retrospectively examined cross-sectional data from 437 exercising women ( mean ± SD age of 18.0 ± 3.5 yr , weighed 57.5 ± 7.1 kg with 24 
    Output:
    
Bone area and cortical thickness at the tibia were identified as altered both in women with menstrual disturbances and in women with stress fractures ; however , there was inconsistency in the results observed for all bone parameters .
The majority of skeletal parameters of the lower extremities were not significantly different between exercising women with and without stress fractures and between those with and without menstrual disturbances .
The lack of observed differences in skeletal parameters suggests that risk factors other than bone geometry and structure may be the primary causes of stress fracture in these women