***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: 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 Background . The effect of physical training on bone mineral density ( BMD ) in women with endometriosis treated with gonadotropin‐releasing hormone ( GnRH ) analogs  was studied Summary The purpose of this study was to determine the optimal intensity of exercise necessary to prevent the postmenopausal bone loss on the basis of anaerobic threshold ( AT ) . Thirty-three postmenopausal women were r and omized to control ( group C : n=12 ) or two exercise groups ( group H and group M ) . All women performed a treadmill exercise test , and the AT was measured by expired gas analysis . The exercise regimen consisted mainly of walking at a speed that kept the exercise heart rate above the AT ( group H : n=12 ) or below the AT ( group M : n=9 ) . Exercise was performed for 30 minutes , three times a week for 7 months . The bone mineral density ( BMD ) of the lumbar vertebrae was measured using dual energy X-ray absorptiometry . The BMD level in group C decreased by 1.7±2.7 % , but there was a significant increase of 1.1±2.9 % in group H. In group M there was a decrease of 1.0±3.1 % which did not differ from group C. In group C , serum osteocalcin and urinary hydroxyproline excretion were significantly increased , but no changes were seen in either of the exercise groups . Urinary calcium significantly decreased in the exercise groups . We conclude that short-term ( 7 months ) exercise with intensity above the AT is safe and effective in preventing postmenopausal bone loss Abstract . Several meta-analyses confirm that physical exercise can slow down postmenopausal bone loss , but it is not clear whether physical exercise alone can increase bone mass . Our intent was to evaluate high-impact exercises ( including jumping ) and combined balance and leg-strength training , with and without raloxifene treatment , in three healthy elderly women , age 68–71 years . The 40-week study period consisted of two 17-week exercise periods with a 6-week rest period in between . The jumping exercises were performed both vertically and in different directions . Effects were measured in bone mineral density ( BMD ) , balance , maximal gait speed , and leg extensor strength . BMD ( g/cm2 ) was measured with dual-energy X-ray photon absorptiometry ( DXA ) at the proximal femur , lumbar spine , and total body . After the first exercise period , large losses of trochanteric BMD ( 8.1%–10.8 % ) were seen in all subjects . After both 6 weeks of rest and the second exercise period , which included both exercise and raloxifene , BMD increased in all subjects . During both exercise periods , the balance , gait speed , and leg extensor strength increased in all subjects . The results show that this kind of high-impact exercise had limited effects on BMD , but had large positive effects on balance , gait speed , and leg extensor strength . In conclusion , high-impact exercise in elderly women improves their fall risk factors , but , at least without raloxifene treatment , the trochanteric fracture risk might even increase because of reduction in the regional bone mass 1 . This study examined the influence of brisk walking on skeletal status in post-menopausal women . 2 . Subjects were 84 healthy women aged 60 - 70 years . Who were previously sedentary and at least 5 years post-menopausal . Subjects were r and omly assigned to walking ( n = 43 ) and control ( n = 41 ) groups . Walkers followed a 12-month , largely unsupervised programme of brisk walking . The bone mineral density of the lumbar spine , femoral neck and calcaneus and broadb and ultrasonic attention of the calcaneus were measured at baseline and after 12 months . 3 . Forty control subjects and 38 walkers completed the study .  Walkers built up to 20.4 + /- 3.8 min/day ( mean + /- SD ) of brisk walking .  Body mass increased in control subjects relative to walkers [ mean change ( SE ) + 0.9 ( 0.3 ) and -0.1 ( 0.3 ) kg respectively ; P = 0.04 ] . Predicted maximum oxygen uptake increased in walkers by 2.1 ( 0.9 ) ml min-1 kg-1 ( P = 0.02 ) . Bone mineral density in the lumbar spine and calcaneus fell in control subjects [ -0.005 ( 0.004 ) and -0.010 ( 0.004 ) g/cm2 , respectively ] but not in walkers [ + 0.006 ( 0.004 ) and + 0.001 ( 0.004 ) g/cm2 ] . The difference in response between groups was significant in the calcaneus ( P = 0.04 ) but not in the lumbar spine ( P = 0.08 ) . Mean femoral neck bone mineral density did not change significantly in either group , although changes in walkers were related to the amount of walking completed ( r = 0.51 , P = 0.001 ) . The change in broadb and ultrasonic attenuation of the calcaneus differed between groups [ control subjects , -3.7 ( 0.8 ) ; walkers , -0.7 ( 0.8 ) dB/MHz ; P = 0.01 ] . 4 . Walking decreased bone loss in the calcaneus and possibly in the lumbar spine . It also improved functional capacity and enabled walkers to avoid the increase in body mass seen in control subjects OBJECTIVE to evaluate the effects of brisk walking on bone mineral density in women who had suffered an upper limb fracture . DESIGN r and omized placebo-controlled trial . Assessment s of bone mineral density were made before and at 1 and 2 years after intervention . St and ardized and vali date d measures of physical capacity , self-rated health status and falls were used . SETTING district general hospital outpatient department . SUBJECTS 165 women drawn from local accident and emergency departments with a history of fracture of an upper limb in the previous 2 years . Women were r and omly allocated to intervention ( self-paced brisk walking ) or placebo ( upper limb exercises ) groups . INTERVENTION both groups were seen at 3-monthly intervals to assess progress , measure physical capacity and maintain enthusiasm . The brisk-walking group were instructed to progressively increase the amount and speed of walking in a manner that suited them . The upper limb exercise placebo group were asked to carry out a series of exercises design ed to improve flexibility and fine h and movements , appropriate for a past history of upper limb fracture . RESULTS drop-outs from both intervention and placebo groups were substantial ( 41 % ) , although there were no significant differences in bone mineral density , physical capacity or health status between drop-outs and participants . At 2 years , among those completing the trial , bone mineral density at the femoral neck had fallen in the placebo group to a greater extent than in the brisk-walking group [ mean net difference between intervention and placebo groups 0.019 g/cm2 , 95 % confidence interval ( CI ) -0.0026 to + 0.041 g/cm2 , P = 0.056 ] . Lumbar spine bone mineral density had increased to a similar extent ( + 0.017 g/cm2 ) in both groups . The cumulative risk of falls was higher in the brisk-walking group ( excess risk of 15 per 100 person-years , 95 % CI 1.4 - 29 per 100 person-years , P < 0.05 ) . There were no significant differences in clinical or spinal x-ray fracture risk or self-rated health status between intervention and placebo groups . CONCLUSION the promotion of exercise through brisk-walking advice given by nursing staff may have a small , but clinical ly important , impact on bone mineral density but is associated with an increased risk of falls . Self-paced brisk walking is difficult to evaluate in r and omized controlled trials because of drop-outs , placebo group exercise , limited compliance and lack of st and ardization of the duration and intensity of walking . Further work is needed to evaluate the best means of safely achieving increased activity levels in different groups , such as older women and those at high risk of fractures Abstract . Osteoporosis is one of the most common skeletal disorders affecting postmenopausal women . The purpose of this study was to investigate whether a 24-week program of aerobic high-impact loading exercise was beneficial for enhancing physical fitness and bone mineral density ( BMD ) in osteopenic postmenopausal women . Forty-three postmenopausal women aged 48–65 years participated in this study . The BMD of the spine ( L2–L4 ) and right femoral neck of each woman was below 1 SD of the mean of premenopausal women , as examined by dual X-ray absorptiometry . The assignment of subjects into exercise or control group was not r and omized but based on each subject 's anticipated compliance to the 6-month long exercise program . Twenty-two subjects joined the  exercise group and attended the training programs and 21 served as the  control group . Exercise programs included treadmill walking at an intensity above 70 % of maximal oxygen consumption ( VO2max ) for 30 minutes , followed by 10 minutes of stepping exercise using a 20-cm-high bench . The program was conducted three times per week for 24 weeks . Physical fitness measurements included testing of flexibility , muscular strength and endurance , body composition , and cardiopulmonary fitness . The results showed that the quadriceps strength , muscular endurance , and VO2max in the exercise group had significant improvements , whereas no improvement was found in any of the physical fitness parameters in the control group . The BMD of the L2–L4 and the femoral neck in the exercise group increased 2.0 % ( P > 0.05 ) and 6.8 % ( P < 0.05 ) and those in the control group decreased 2.3 % ( P < 0.05 ) and 1.5 % ( P > 0.05 ) , respectively . In conclusion , aerobics combined with high-impact exercise at a moderate intensity was effective in off setting the decline in BMD in osteopenic postmenopausal women The separate and combined effects of weight-bearing exercise and hormone replacement therapy ( HRT ) on bone mineral density ( BMD ) were studied in 32 women , 60 to 72 years of age .  HRT consisted of continuous conjugated estrogens 0.625 mg/day and trimonthly medroxyprogesterone acetate 5 mg/day for 13 days . Exercise consisted of 2 months of low-intensity exercise followed by 9 months of more vigorous weight-bearing exercise approximately 45 minutes/day , > or = 3 days/week , at 65 - 85 % of maximal heart rate . Lumbar spine and proximal femur BMD were significantly increased in response to exercise and to HRT , and total body BMD was significantly increased in response to HRT ; neither exercise nor HRT had an effect on wrist BMD . The combination of exercise + HRT result ed in increased BMD at all sites except the wrist , with effects being additive for the 
    Output:
    
We conclude that regular walking has no significant effect on preservation of BMD at the spine in postmenopausal women , whilst significant positive effects at femoral neck are evident .
Other forms of exercise that provide greater targeted skeletal loading may be required to preserve bone mineral density in this population