***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: In 1987 I contributed a commentary that seriously evaluated the method ologic quality of studies promulgating the assumption that exercise has a role in the prevention of osteoporosis [ l ] . Along with a more comprehensive review published separately in 1989 121 , that commentary recommended r and omized controlled trials to confirm the well-recognized association between above average levels of physical activity and higher bone mineral density ( BMD ) [ l-4 ] . A recent literature search revealed eight reports published since 1989 that utilized a r and omized study design to determine the potential effects of various types of exercise interventions on BMD 15 - 121 . These studies had equivocal results ; some showed mild positive effects but others showed virtually no effect of exercise on BMD ( Table 1 ) . What is most disturbing about these studies is the generalIy high level of subject attrition reported . Indeed , subject dropout rates ranged from 4 % to 50 % . Five of the studies had attrition rates above 20 % ( Table 1 ) . Such high levels of attrition have serious implication s for analyzing and interpreting the results of these trials . In fact , not a single study presented a valid intention-to-treat ( ITT ) analysis to adjust statistically for significant subject attrition . Interestingly , a recent position statement on exercise and osteoporosis made no mention of this problem , its potential impact on the results of r and omized trials , or its statistical implication s 1131 . As articulated by a working group of the American Statistical Association , ITT analysis includes all r and omized subjects in the groups to which they were r and omly assigned , regardless of their compliance to the intervention and regardless of subsequent withdrawal from treatment or deviation from the protocol 1141 . ITT requires that all subjects initially r and omized into the study be included in the primary test statistics . Because this type of analysis may require imputation of data , its consequences can be profound in studies with attrition rates as high as many of these exercise studies . Some study reports stated that withdrawal rates were similar between groups ill ] , that reasons for withdrawal were not study related [ 9,11 ] , or that dropouts were not dissimilar to subjects who remained in the study on selected baseline variables 1121 . While these findings may To assess the effect of an exercise intervention using a weighted vest on perceived health status and bone density in older persons , we enrolled 36 seniors in a r and omized controlled trial . The vest-use group met weekly for 1 h for a low level exercise class . They wore a weighted vest during the class and as tolerated at home . The discussion controls met for 1 h weekly . At baseline and follow-up ( 20 weeks ) , subjects completed a question naire that incuded the 20 item MOS Short-Form Health Survey , Multidimensional Health Locus of Control Scale , and Philadelphia Geriatric Center Morale Scale , and bone density was measured by dual energy X-ray absorptiometry . Subjects also completed daily activity diaries . Subjects in the vest group reported a statistically significant dicrease in bodily pain , improved physical functioning , and increased internal health locus of control . Bone density increased by 1 % in the vest group and decreased by 0.6 % in the controls ( p=0.12 ) . We conclude that our exercise intervention had a positive effect on some measures of perceived health in older persons The objectives of this study were to evaluate ( 1 ) the effect of spinal muscle strengthening by loading exercises on the bone mineral density ( BMD ) of the spine , and ( 2 ) the effect of upper extremity loading exercises on the BMD of the midradius and femur in healthy , premenopausal women . The study design was a r and omized , controlled trial of 3 years ' duration . Ninety-six healthy , premenopausal , white women aged 30 - 40 years participated ; 67 completed the study . All subjects were in good health ( normal menses ) and were active , but not athletic ( that is , not involved in a regular sport activity ) . Subjects were r and omized to an exercise or control group . The exercise group performed a supervised , non-strenuous , weight-lifting exercise program . Exercise performance was supervised once a week at the medical facility . In addition , the subjects performed the exercises twice a week on their own . Dietary calcium intake was to be maintained at 1,500 mg/day in both groups . Bone density was measured at the lumbar spine and hip with dual-energy X-ray absorptiometry at 0 , 1 , and 3 years . BMD of the midradius was measured with single photon absorptiometry . Measurements of muscle strength were obtained at baseline and every 3 months for 3 years . Maximal oxygen uptake was measured , and the level of physical activity was recorded . Compliance with the exercise program was excellent during the first year of the study , but decreased thereafter . At the end of 3 years , subject withdrawal was about 34 % from the exercise group and about 22 % from the control group ( total subject withdrawal was about 30 % ) . Muscle strength in the exercise group increased significantly at all involved skeletal sites ( p values all < 0.001 ) . There was a modest positive correlation between the BMD of Ward 's triangle with spinal flexor strength ( r = 0.32 , p = 0.008 ) and with grip strength ( r = 0.38 , p = 0.001 ) . Comparing study groups , we found no significant effect of the loading and nonstrenuous strengthening exercises in the exercise group or free physical activity group ( our control group ) on BMD at the spine , hip , or midradius measurement sites . In active , but not athletic premenopausal women , additional moderate weight-lifting exercises showed no significant effect on BMD 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 OBJECTIVE The purpose of the study was to determine the effect of six months of heavy resistance training ( weightlifting ) on the bone density of premenopausal women . EXPERIMENTAL DESIGN A 6-month prospect i ve design with r and om assignment to groups . SETTING Measurements of bone mineral density ( BMD ) were obtained from the Radiology Clinic at North Carolina Memorial Hospital . Exercise sessions were completed in the Physical Education Department facilities at the University of North Carolina , Chapel Hill , NC . PARTICIPANTS Thirty-five premenopausal women , 40 - 50 years of age , were r and omly assigned to either a resistance training ( RT ) and sedentary control ( CON ) group . The study finished with 12 women exercising and 14 in the control group . INTERVENTION The resistance training consisted of three days per week of high-intensity weightlifting specifically design ed to place strain on the spine and hips . MEASURES Bone density of the lumbar vertebrae , femoral neck , and distal radius , were determined prior to and at the end of the exercise program using dual energy X-ray absorptiometry ( DEXA ) . RESULTS Resistance-training produced strength gains : overhead press = 125 % , leg press = 86 % , and calf raises = 91 % ( p < 0.001 ) . RT tended to increased lumbar BMD 1.03 % , while the CON decreased 0.36 % ( p = 0.072 ) . Both groups lost radial BMD ( CON = -0.45 % ; RT = -1.04 % ) . Both groups gained femoral neck BMD ( CON = 1.26 % ; RT = 1.22 % ) . CONCLUSIONS These results suggest that even a short-term weight training program can either maintain or improve the BMD of the femoral neck and lumbar vertebrae in premenopausal women A substantial body of cross-sectional data and a smaller number of intervention trials generally justify optimism that regular physical activity benefits the skeleton . We conducted an 8 month controlled exercise trial in a group of healthy college women ( mean age = 19.9 years ) who were r and omly assigned to a control group or to progressive training in jogging or weight lifting .  We measured the following variables : bone mineral density ( BMD ) of the spine ( L2 - 4 ) and right proximal femur using dual-energy x-ray absorptiometry , dynamic muscle strength using the 1-RM method , and endurance performance using the 1.5 mile walk/run field test . A total of 31 women completed the 8 month study . For women completing the study , compliance , defined as the percentage of workout sessions attended , was 97 % for the runners ( range 90 - 100 % ) and 92 % ( range 88 - 100 % ) for the weight trainers . Body weight increased by approximately 2 kg in all groups ( p less than 0.05 ) . Weight training was associated with significant increases ( p less than 0.01 ) in muscle strength in all muscle groups . Improvement ranged from 10 % for the deep back to 54 % for the leg . No significant changes in strength scores were observed in the control or running groups . Aerobic performance improved only in the running group ( 16 % , p less than 0.01 ) . Lumbar BMD increased ( p less than 0.05 ) in both runners ( 1.3 + /- 1.6 % ) and weight trainers ( 1.2 + /- 1.8 % ) . These results did not differ from each other but were both significantly greater than results in control subjects , in whom bone mineral did not change . ( ABSTRACT TRUNCATED AT 250 WORDS A r and omized controlled trial was carried out to determine whether calcium supplementation and load-bearing exercise can increase or maintain bone mass in the elderly . Fifty Chinese women , aged 62–92 years , living in a hostel for the elderly in Hong Kong were r and omized to enter one of four treatment groups : ( I ) calcium supplementation of 800 mg ( as calcium lactate gluconate ) daily ; ( II ) load-bearing exercise four times a week plus a daily placebo tablet ; ( III ) calcium supplementation daily and load-bearing exercise four times a week ; ( IV ) a placebo tablet daily . The interventions went on for 10 months . The bone mineral density ( BMD ) was measured at three sites in the hip ( femoral neck , Ward 's triangle and intertrochanteric area ) and the L2–4 level of the spine . The percentage change in BMD in 10 months was used as the main outcome measurement . The parathyroid hormone level and indices of bone metabolism were also measured before and after 10 months of intervention . The BMD at Ward 's triangle and the intertrochanteric area increased significantly in subjects on calcium supplement ( p<0.05 ) , but there was no significant change at the spine and femoral neck . Exercise had no effect on bone loss at any site . However , the results of two-way analysis of variance showed a significant joint effect of calcium supplements and exercise  at the femoral neck ( p<0.05 ) , but not at the other sites . The parathyroid hormone levels fell significantly in subjects on calcium supplements (p<0.01).Calcium supplement in the form of calcium lactate gluconate was adequately absorbed in elderly Chinese women with a calcium intake of less than 300 mg per day . It was effective in reducing bone loss at the hip , and there may be interaction effects with exercise in maintaining bone density The effect of two structured exercise programmes on the bone mass of 48 healthy postmenopausal white women aged 50 - 62 was studied after one year . Volunteers were r and omised to group 1 ( control ) , group 2 ( aerobic exercise ) , or group 3 ( aerobic and strengthening exercises ) . Before and after the training programme each subject had evaluations of bone mass ( determined by neutron activation analysis and expressed as calcium bone index ) and maximum oxygen uptake attained on a multistage exercise treadmill test . After one year both exercise groups had higher levels of fitness and greater bone mass than controls . Mean values ( 2 SEM ) for changes in the calcium bone index were -0.011 ( 0.037 ) , 0.039 ( 0.035 ) , and 0.066 ( 0.036 ) for groups 1 , 2 , and 3 , respectively . Analysis of variance on the observed data and analysis of covariance adjusting changes to the initial mean value for the whole group showed significant differences between each exercise group and the controls but no difference between the exercise groups themselves . Both exercise groups showed a significant improvement in maximum oxygen uptake . This study suggests that exercise may modify bone loss in healthy postmenopausal women 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 
    Output:
    
This systematic review of r and omized trials shows that both impact and non-impact exercise have a positive effect at the lumbar spine in pre- and postmenopausal women .
Impact exercise probably has a positive effect at the femoral neck .