***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: BACKGROUND Female adolescent runners have an elevated prevalence of low bone mass for agemdashan outcome that may be partially due to inadequate energy intake . OBJECTIVE The objective was to evaluate diet , menstrual history , serum hormone concentrations , and bone mass in female adolescent runners with normal or abnormal bone turnover . DESIGN Thirty-nine cross-country runners ( age : 15.7 plusmn 0.2 y ) participated in the study , which included a 7-d dietary assessment with the use of a food record and daily 24-h dietary recalls ; serum measures of insulin-like growth factor I , estradiol , leptin , parathyroid hormone , progesterone , triiodothyronine , 25-hydroxycholecalciferol , bone-specific alkaline phosphatase ( BAP ) , and cross-linked C-telopeptides of type I collagen ( CTX ) ; an evaluation of height , weight , bone mass , and body composition with the use of dual-energy X-ray absorptiometry ; and a question naire to assess menses and sports participation . Age- and sex-specific BAP and CTX concentrations of at least the 97th percentile and no greater than the third percentile , respectively , were considered abnormal . RESULTS All abnormal BAP and CTX concentrations fell within the elevated ( ge 97 % ) range . Runners with an elevated bone turnover ( EBT ) ( n = 13 ) had a lower body mass , fewer menstrual cycles in the past year , lower estradiol and 25-hydroxycholecalciferol concentrations , and a higher prevalence of body mass index lt 10 % for age , vitamin D insufficiency , amenorrhea , and low bone mass . Girls with EBT consumed less than the recommended amounts of energy and had a higher prevalence of consuming lt 1300 mg Ca than did those with normal bone turnover . CONCLUSIONS Runners with EBT had a profile consistent with energy deficiency . Nutritional support to increase energy , calcium intake , and 25-hydroxycholecalciferol concentrations may improve bone mineral accrual in young runners with EBT . This trial was registered at clinical trials.gov as NCT01059968 PURPOSE This investigation examined the effect of variations in protein intake on whole-body protein turnover ( WBPTO ) after exercise in endurance-trained males . METHODS Five male runners ( 21.3 + /- 0.3 yr , 179 + /- 2 cm , 70.6 + /- 0.1 kg , 8.7 + /- 0.4 % body fat , 70.6 + /- 0.1 VO2peak ) participated in a r and omized , crossover- design diet intervention , where they consumed either a low- ( 0.8 g.kg(-1 ) ; LP ) , moderate- ( 1.8 g.kg(-1 ) ; MP ) , or high-protein ( 3.6 g.kg(-1 ) ; HP ) diet for 4 wk . WBPTO ( Ra , leucine rate of appearance ; NOLD , nonoxidative leucine disposal ; and Ox , leucine oxidation ) were assessed after a 75-min run at 70 % VO2peak after each diet-intervention period . RESULTS Leucine Ra ( indicator of protein breakdown ) and leucine Ox were greater on the HP diet than on the LP diet ( Ra , 123.4 + /- 6.9 vs 97.9 + /- 6.0 micromol.kg(-1).h(-1 ) ; Ox , 23.9 + /- 0.5 vs 17.0 + /- 0.8 micromol.kg(-1).h(-1 ) , P < 0.05 ) . No differences were noted in NOLD ( an indicator of protein synthesis ) across diets . Plasma branched chain amino acids ( BCAA ) at rest were greater for MP and HP than for LP , and nonessential amino acids ( NEAA ) were greater for LP than MP at rest and greater than MP and HP after exercise . CONCLUSION Findings from this study show that variations in protein intake can alter plasma amino acid levels and modulate rates of WBPTO after exercise . Additionally , a lower protein intake was associated with decreased rates of WBPTO after exercise Background : Current literature shows conflicting results regarding the possible direct role of exercise on leptin concentrations , mainly because of a non-homogeneous level of energy expenditure ( EE ) and the lack of st and ardization of energy balance . Aim : The aim of the study was to evaluate the effect of exercise duration and its corresponding EE on leptin levels , during prolonged treadmill exercise , in a well-controlled laboratory setting . Material s and methods : Seven young trained males underwent a 4-h treadmill exercise . The starting intensity was set at 65 % of maximal oxygen consumption . At the start of the test and throughout the exercise , venous blood sample s were drawn for the assays of leptin , glucose , free fatty acids ( FFA ) , cortisol , epinephrine ( E ) and norepinephrine ( NE ) . Hourly and total EE was monitored with gas analysis . Results : Plasma leptin levels decreased from 1.10±0.15 to 0.85±0.26 µg/l ( p<0.01 ) at the end of the exercise , reaching a significant reduction already after the second hour . FFA and cortisol showed a progressive significant increase , while glucose did not significantly change throughout the test . Plasma E and NE significantly increased at all sampling times compared to basal values ( 48.1±30.3 to 352.3±187.7 pg/ml , p<0.001 and 238.1±118.9 to 1798.7±413.5 pg/ml , p<0.001 ) . The r and om-effects model for panel data analysis showed negative correlation between leptin , NE and the values of progressive EE ( r2=0.745 , p<0.05 ) . Conclusions : Our data demonstrate that , during a prolonged moderate intensity exercise , leptin decrease is significantly related to the total EE . Further , NE concentrations seem to play an important role in the inhibition of leptin secretion In order to compare the influence of a single bout of exercise on HDL-C metabolism with normal variability , 12 male runners ( mean age : 24.9 + /- 4 yr ) who ran 15 - 30 miles per week underwent exercise ( E ) and control ( C ) experimental conditions . During the E trial subjects ran on a motor driven treadmill at 75 % ( 42.5 + /- 4.7 ml.kg-1.min-1 ) VO2max until 800 Kcals were expended . The C trial consisted of no exercise . Subjects were instructed to follow the same diet and keep a four d food diary during each experimental condition . Fasted blood sample s were obtained at the same time of day in each condition at time points corresponding to 24 h pre-exercise ( 24 PRE ) , 6 h post- ( 6 h ) and 24 h post-exercise ( 24 h ) . Plasma was analyzed for HDL-C , HDL2-C and HDL3-C ( mg.dl-1 ) . In addition post-heparin plasma sample s were analyzed for lipoprotein lipase ( LPL ) and hepatic lipase ( HL ) activity ( mumol . FFA-1.ml-1 ) . All values were adjusted for changes in plasma volume and compared to Baseline . HDL-C levels were unaltered following the C trial . However , following the E trial , HDL-C increased ( p < 0.01 ) above baseline values at 24 h. The increase in HDL-C was reflected in the HDL3-C subfraction ( p < 0.05 ) . Analysis of lipolytic activity revealed an overall greater LPL activity ( p < 0.05 ) in the E trial vs the C trial . In addition , a decrease in HL was observed at 24 h ( p < 0.05 ) but was not different between experimental conditions . These data suggest that exercise and not normal variability are responsible for alterations in lipolytic activity and corresponding increases in HDL-C levels Objective : To explore potential factors that could be associated with low bone mineral density ( BMD ) in female endurance runners . Methods : Fifty two female endurance runners ( 1500 m to marathon ) , aged 18–44 years , took part . Body fat percentage , lumbar spine BMD , and femoral neck BMD were measured using the Hologic QDR 4500w bone densitometer . Data on training , menstrual cycle status , osteoporosis , and health related factors were obtained by question naire . Dietary variables  were assessed from a prospect i ve seven day dietary record of macronutrients and micronutrients . Results : The mean ( SD ) lumbar spine and femoral neck BMD were 1.11 ( 0.11 ) and 0.89 ( 0.12 ) g/cm2 respectively . A backward elimination regression analysis showed that age , body mass , body fat , distance run , magnesium , and zinc intake were the variables significantly associated with BMD . Lumbar spine BMD ( g/cm2 ) = −1.90 + ( 0.0486 × age ( years ) ) + ( 0.342 × log mass ( kg ) ) − ( 0.000861 × age2 ( years ) ) − ( 0.00128 × distance ( km/week ) ) , with an R2 = 30.1 % ( SEE = 0.089 ( 95 % confidence interval ( CI ) 0.05 to 0.23 ) ; p<0.001 ) . Femoral neck BMD ( g/cm2 ) = −2.51 − ( 0.00989 × age ( years ) ) + ( 0.720 × log mass ( kg ) ) + ( 0.000951 × magnesium ( mg/day ) ) −(0.0289 × zinc ( mg/day ) ) − ( 0.00821 × body fat ( % ) ) − ( 0.00226 × distance ( km/week ) ) , with an R2 = 50.2 % ( SEE = 0.100 ( 95 % CI 0.06 to 0.22 ) ; p<0.001 ) . The negative association between skeletal BMD and distance run suggested that participants who ran longer distances had a lower BMD of the lumbar spine and femoral neck . Further , the results indicated a positive association between body mass and BMD , and a negative association between body fat and BMD . Conclusions : The results suggest a negative association between endurance running distance and lumbar spine and femoral neck BMD , with a positive association between body mass and femoral neck and lumbar spine BMD . However , longitudinal studies are required to assess directly the effect of endurance running and body mass on BMD , and to see if the addition of alternative exercise that would increase lean body mass would have a positive effect on BMD and therefore help to prevent osteoporosis The purpose of this investigation was to examine the effects of 7 - 10 days of inactivity ( IA ) on glucose tolerance ( GT ) , resting metabolic rate ( RMR ) , thermic effect of a meal ( TEM ) , and limb blood flow in endurance-trained men . Eight highly trained ( peak O2 consumption 64 + /- 2 ml . kg-1 . min-1 ) endurance athletes participated in this study involving two identical test days , one approximately 24 h after a normal training bout ( Tr ) and the second after 7 - 10 days of IA . The following tests were conducted at each visit : 75-g oral glucose tolerance test ( OGTT ) , RMR , and TEM and measurements of calf and forearm blood flow ( BF ) by using venous occlusive plethysmography . Body weight remained unchanged during this short period of IA ( Tr , 78.5 + /- 1 kg ; IA , 78.7 + /- 1 kg ) . The area under the glucose and insulin curves increased 65 % ( Tr , 3,375 + /- 877 vs. IA , 5,559.4 + /- 621 mg . dl-1 . 180 min-1 ) and 73 % ( Tr , 2,182.5 + /- 270 vs. IA , 3,793.1 + /- 739 microU . ml-1 . 180 min-1 ) after IA , respectively ( P < 0.01 ) . RMR decreased significantly ( 4 % ; 1.5 + /- 0 . 02 vs. 1.44 + /- 0.02 kcal/min ; P < 0.05 ) and respiratory exchange ratio during the OGTT increased ( 4 % , 0.812 + /- 0.011 vs. 0.842 + /- 0 . 009 ; P < 0.05 ) after IA , whereas TEM increased similarly in the Tr and IA states . In the Tr state , mean calf BF increased by 22 % ( 3.17 + /- 0.22 vs. 3.87 + /- 0.38 ml . 100 ml-1 . min-1 ; P < 0.05 ) during the OGTT but remained unchanged after IA , whereas no differences at rest or during OGTTs existed between the two conditions for forearm BF . Incremental insulin area above fasting during the OGTT was correlated with mean calf BF in the Tr ( r = 0.76 , P < 0.05 ) and I 
    Output:
    
During the competition phase , both body mass and fat-free mass were significantly higher compared to other seasonal training phases ( p < 0.05 ) .
Male and female endurance athletes show important training seasonal fluctuations in TEE , energy intake , and body composition .