human
***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 objective was to investigate the effects of iron depletion on adaptation to aerobic exercise , assessed by time to complete a 15-km cycle ergometer test . Forty-two iron-depleted ( serum ferritin < 16 microg/l ) , nonanemic ( Hb > 12 g/dl ) women ( 18 - 33 yr old ) received 100 mg of ferrous sulfate ( S ) or placebo ( P ) per day for 6 wk in a r and omized , double-blind trial . Subjects trained for 30 min/day , 5 days/wk at 75 - 85 % of maximum heart rate for the final 4 wk of the study . There were no group differences in baseline iron status or in 15-km time . Iron supplementation increased serum ferritin and decreased transferrin receptors in the S compared with the P group . The S and P groups decreased 15-km time and respiratory exchange ratio and increased work rate during the 15-km time trial after training . The decrease in 15-km time was greater in the S than in the P group ( P = 0.04 ) and could be partially attributed to increases in serum ferritin and Hb . These results indicate that iron deficiency without anemia impairs favorable adaptation to aerobic exercise BACKGROUND Iron deficiency without anemia has been shown to reduce both muscle-tissue oxidative capacity and endurance in animals . However , the consequences of iron deficiency in humans remain unclear . OBJECTIVE We investigated the effects of iron supplementation on adaptation to aerobic training among marginally iron-depleted women . We hypothesized that iron supplementation for 6 wk would significantly improve iron status and maximal oxygen uptake ( VO(2)max ) after 4 wk of concurrent aerobic training . DESIGN Forty-one untrained , iron-depleted , nonanemic women were r and omly assigned to receive either 50 mg FeSO(4 ) or a placebo twice daily for 6 wk in a double-blind trial . All subjects trained on cycle ergometers 5 d/wk for 4 wk , beginning on week 3 of the study . RESULTS Six weeks of iron supplementation significantly improved serum ferritin and serum transferrin receptor ( sTfR ) concentrations and transferrin saturation without affecting hemoglobin concentrations or hematocrit . Average VO(2)max and maximal respiratory exchange ratio improved in both the placebo and iron groups after training ; however , the iron group experienced significantly greater improvements in VO(2)max . Both iron-status and fitness outcomes were analyzed after stratifying by baseline sTfR concentration ( > and < or = 8.0 mg/L ) , which showed that the previously observed treatment effects were due to iron-status and fitness improvements among subjects with poor baseline iron status . CONCLUSIONS Our findings strongly suggest that iron deficiency without anemia but with elevated sTfR status impairs aerobic adaptation among previously untrained women and that this can be corrected with iron supplementation BACKGROUND We previously showed that iron supplementation significantly improves iron status and maximal work capacity in previously untrained , marginally iron-deficient women with a baseline serum transferrin receptor concentration > 8.0 mg/L. However , the effect of transferrin receptor status on adaptation in endurance capacity after aerobic training in these subjects has not been fully explored . OBJECTIVE Our objective was to examine the effect of baseline serum transferrin receptor status on adaptations in endurance capacity . DESIGN Forty-one untrained , iron-depleted , nonanemic women were r and omly assigned to receive either 100 mg FeSO(4 ) or a placebo for 6 wk in a double-blind trial . All subjects trained on cycle ergometers 5 d/wk for the last 4 wk of the study . Endurance capacity was assessed at baseline and after treatment by using a 15-km time trial conducted on a cycle ergometer . RESULTS Significant treatment effects were observed for time to complete the 15-km time trial , work rate , and percentage of maximal oxygen uptake in subjects with a baseline serum transferrin receptor concentration > 8.0 mg/L. No significant treatment effects were observed in subjects with a normal baseline transferrin receptor concentration . CONCLUSIONS Our findings suggest that , in the presence of overt tissue iron deficiency , iron deficiency without anemia impairs adaptation in endurance capacity after aerobic training in previously untrained women . This impairment can be corrected with iron supplementation Eighty iron-deficient , nonpregnant female workers were r and omly assigned to ferrous sulphate ( 60 or 120 mg Fe/d ) or placebo treatment for 12 wk . Energy expenditure was estimated during 3 d by heart rate ( HR ) recording . Production efficiency ( PE ) was calculated as the ratio of productivity to energy expenditure . In the iron-treated group mean hemoglobin ( Hb ) increased from 114 to 127 g/L ( P < 0.001 ) , mean serum ferritin increased from 9.7 to 30.0 micrograms/L ( P < 0.001 ) , and mean free erythrocyte protoporphyrin decreased from 1.01 to 0.49 mumol/L ( P < 0.001 ) . Mean HR at work decreased from 95.5 to 91.1 beats/min ( P < 0.001 ) , which was inversely correlated with the change in Hb ( r = -0.60 , P < 0.001 ) . PE increased significantly in the iron-treated group ( P < 0.001 ) and its change paralleled the change in Hb ( r = 0.58 , P < 0.001 ) . The results show that iron supplementation enabled these women to do the same work at a lower energy cost Studies in laboratory animals found that iron deficiency without anemia decreased oxidative capacity and increased reliance on carbohydrate as the substrate for energy , thereby causing impaired endurance . The purpose of this cross-sectional study was to investigate the relation between iron deficiency without anemia and physical performance in healthy active women aged 19 - 36 y. Iron-status assessment included determination of hemoglobin , hematocrit , transferrin saturation , and serum ferritin values . Dietary iron intake was assessed by frequency question naires and physical activity level was estimated by frequency question naires and 2-wk records . Fifteen women with normal iron status and 15 women with iron depletion ( serum ferritin < 12 micrograms/L ) were chosen r and omly from a group of 69 nonanemic women and given physical-performance tests , including determinations of maximum oxygen consumption ( VO2max ) , ventilatory threshold , and delta-efficiency . There were no significant differences between the two groups in body size , body composition , physical activity level , dietary iron intake , delta-efficiency , or ventilatory threshold . Compared with the iron-depleted group , the iron-sufficient group had significantly higher hemoglobin , transferrin saturation , and serum ferritin values and a significantly greater tendency to use iron supplements . When physical activity level and fat-free mass were controlled for , the iron-depleted group had a significantly lower VO2max . The difference in VO2max was significantly associated with serum ferritin concentration ; hemoglobin value was not a significant confounder . Therefore , reduction of VO2max in nonanemic women with iron depletion was likely caused by factors related to reduced body iron storage but was unrelated to decreased oxygen-transport capacity of the blood BACKGROUND Tissue iron depletion may negatively affect endurance performance and muscle fatigability . OBJECTIVE We investigated tissue-level iron depletion and progressive fatigue of the quadriceps during dynamic knee-extension exercise in young women . DESIGN Twenty iron-depleted ( serum ferritin < 20 micro g/L ) , nonanemic ( hemoglobin > 110 g/L ) women ( macro x + /- SEM age : 29.1 + /- 1.2 y ) received iron ( iron group ) or placebo ( placebo group ) for 6 wk in a r and omized , double-blind trial ( n = 10 per group ) . A protocol integrating 2 - 3-s maximal voluntary static contractions ( MVCs ) with dynamic knee extensions was used to assess fatigue . RESULTS No significant differences between the groups in baseline iron status , MVC at rest , or MVC at the end of the protocol were observed . After treatment , serum iron and transferrin saturation increased significantly in the iron group ( P = 0.02 and P = 0.03 , respectively ) . Serum transferrin receptor concentrations increased significantly in the placebo group ( P < 0.01 ) but not in the iron group . After treatment , the rate of decrease in MVC was attenuated in the iron group but not in the placebo group ( P = 0.01 ) . In the iron group , MVC at the sixth minute of the fatigue protocol and MVC at the end of the protocol were approximately 15 % ( P = 0.04 ) and approximately 27 % higher ( P < 0.01 ) , respectively , after treatment . These improvements were not related to changes in iron-status indexes or tissue iron stores , although power was low ( < 0.50 ) to detect these relations . CONCLUSIONS Iron supplementation was associated with a significant improvement in muscle fatigability . Interpretation regarding the direct role of tissue iron status is limited by the study 's low power to detect relations between tissue iron improvement and decreased muscle fatigue Forty-seven previously sedentary women participating in a 12-wk moderate aerobic-exercise program were r and omly assigned to one of four dietary groups : 50-mg/d iron supplement and a low food-iron diet ( 50 FE + EX ) , 10-mg/d iron supplement and a low food-iron diet ( 10 FE + EX ) , placebo and unrestricted diet ( P + EX ) , and meat supplement and high food-iron diet ( M + EX ) . A sedentary control group ( n = 13 ) received no dietary interventions . Hematocrit , total iron-binding capacity , and hemoglobin , serum iron , serum ferritin , and serum albumin concentrations were measured every 4 wk . Hemoglobin values decreased at the end of 4 wk in all exercising groups compared with the control group . Iron status in the 50 FE + EX and M + EX groups improved after week 4 as indicated by an increase in serum ferritin , serum iron , and hemoglobin concentrations , and a decline in total iron-binding capacity . Thus , short-term , moderate aerobic exercise result ed in compromised iron status that was offset to varying degrees by ingesting iron or meat supplements . However , meat supplements were more effective in protecting hemoglobin and ferritin status than were iron supplements Background Iron deficiency without anemia is related to adverse symptoms that can be relieved by supplementation . Since a blood donation can induce such an iron deficiency , we investigated the clinical impact of iron treatment after a blood donation . Methods One week after donation , we r and omly assigned 154 female donors with iron deficiency without anemia , aged below 50 years , to a four-week oral treatment of ferrous sulfate versus a placebo . The main outcome was the change in the level of fatigue before and after the intervention . Aerobic capacity , mood disorder , quality of life , compliance and adverse events were also evaluated . Hemoglobin and ferritin were used as biological markers . Results The effect of the treatment from baseline to four weeks of iron treatment was an increase in hemoglobin and ferritin levels to 5.2 g/L ( P < 0.01 ) and 14.8 ng/mL ( P < 0.01 ) , respectively . No significant clinical effect was observed for fatigue ( -0.15 points , 95 % confidence interval -0.9 points to 0.6 points , P = 0.697 ) or for other outcomes . Compliance and interruption for side effects was similar in both groups . Additionally , blood donation did not induce overt symptoms of fatigue in spite of the significant biological changes it produces . Conclusions These data are valuable as they enable us to conclude that donors with iron deficiency without anemia after a blood donation would not clinical ly benefit from iron supplementation . Trial Registration Clinical Trials.gov : PURPOSE The purpose of this study was to find out whether iron repletion leads to an increase in red blood cell volume ( RBV ) and performance capacity in iron-deficient nonanemic athletes . METHODS 40 young elite athletes ( 13 - 25 yr ) with low serum ferritin ( < 20 microg . L-1 ) and normal hemoglobin ( males > 13.5 g.dL-1 , females > 11.7 g.dL-1 ) were r and omly assigned to 12-wk treatment with either twice a day ferrous iron ( equivalent to 2 x 100 mg elemental iron ) or with placebo using a double blind method . Before and after treatment , hematological measures and parameters of iron status were determined in venous blood . RBV , blood volume ( BV ) , and plasma volume ( PV ) were measured by CO rebreathing . For determination of the aerobic and anaerobic capacity ( maximal accumulated oxygen deficit , MAOD ) , the athletes performed an incremental as well as a highly intensive treadmill test . RESULTS After 12 wk , ferritin levels were within the normal range in the iron-treated group ( IG ) with a significant ( P < 0.001 ) mean increase by 20 microg . L-1 opposed to a slight nonsignificant decrease in the placebo group ( PG ) . RBV did not change significantly in either group nor did any of the hematological measures . However , only in IG there were significant increases in VO2max and 
    Output:
    
agent
Daily iron supplementation significantly improves maximal and submaximal exercise performance in WRA , providing a rationale to prevent and treat iron deficiency in this group .
***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 objective was to investigate the effects of iron depletion on adaptation to aerobic exercise , assessed by time to complete a 15-km cycle ergometer test . Forty-two iron-depleted ( serum ferritin < 16 microg/l ) , nonanemic ( Hb > 12 g/dl ) women ( 18 - 33 yr old ) received 100 mg of ferrous sulfate ( S ) or placebo ( P ) per day for 6 wk in a r and omized , double-blind trial . Subjects trained for 30 min/day , 5 days/wk at 75 - 85 % of maximum heart rate for the final 4 wk of the study . There were no group differences in baseline iron status or in 15-km time . Iron supplementation increased serum ferritin and decreased transferrin receptors in the S compared with the P group . The S and P groups decreased 15-km time and respiratory exchange ratio and increased work rate during the 15-km time trial after training . The decrease in 15-km time was greater in the S than in the P group ( P = 0.04 ) and could be partially attributed to increases in serum ferritin and Hb . These results indicate that iron deficiency without anemia impairs favorable adaptation to aerobic exercise BACKGROUND Iron deficiency without anemia has been shown to reduce both muscle-tissue oxidative capacity and endurance in animals . However , the consequences of iron deficiency in humans remain unclear . OBJECTIVE We investigated the effects of iron supplementation on adaptation to aerobic training among marginally iron-depleted women . We hypothesized that iron supplementation for 6 wk would significantly improve iron status and maximal oxygen uptake ( VO(2)max ) after 4 wk of concurrent aerobic training . DESIGN Forty-one untrained , iron-depleted , nonanemic women were r and omly assigned to receive either 50 mg FeSO(4 ) or a placebo twice daily for 6 wk in a double-blind trial . All subjects trained on cycle ergometers 5 d/wk for 4 wk , beginning on week 3 of the study . RESULTS Six weeks of iron supplementation significantly improved serum ferritin and serum transferrin receptor ( sTfR ) concentrations and transferrin saturation without affecting hemoglobin concentrations or hematocrit . Average VO(2)max and maximal respiratory exchange ratio improved in both the placebo and iron groups after training ; however , the iron group experienced significantly greater improvements in VO(2)max . Both iron-status and fitness outcomes were analyzed after stratifying by baseline sTfR concentration ( > and < or = 8.0 mg/L ) , which showed that the previously observed treatment effects were due to iron-status and fitness improvements among subjects with poor baseline iron status . CONCLUSIONS Our findings strongly suggest that iron deficiency without anemia but with elevated sTfR status impairs aerobic adaptation among previously untrained women and that this can be corrected with iron supplementation BACKGROUND We previously showed that iron supplementation significantly improves iron status and maximal work capacity in previously untrained , marginally iron-deficient women with a baseline serum transferrin receptor concentration > 8.0 mg/L. However , the effect of transferrin receptor status on adaptation in endurance capacity after aerobic training in these subjects has not been fully explored . OBJECTIVE Our objective was to examine the effect of baseline serum transferrin receptor status on adaptations in endurance capacity . DESIGN Forty-one untrained , iron-depleted , nonanemic women were r and omly assigned to receive either 100 mg FeSO(4 ) or a placebo for 6 wk in a double-blind trial . All subjects trained on cycle ergometers 5 d/wk for the last 4 wk of the study . Endurance capacity was assessed at baseline and after treatment by using a 15-km time trial conducted on a cycle ergometer . RESULTS Significant treatment effects were observed for time to complete the 15-km time trial , work rate , and percentage of maximal oxygen uptake in subjects with a baseline serum transferrin receptor concentration > 8.0 mg/L. No significant treatment effects were observed in subjects with a normal baseline transferrin receptor concentration . CONCLUSIONS Our findings suggest that , in the presence of overt tissue iron deficiency , iron deficiency without anemia impairs adaptation in endurance capacity after aerobic training in previously untrained women . This impairment can be corrected with iron supplementation Eighty iron-deficient , nonpregnant female workers were r and omly assigned to ferrous sulphate ( 60 or 120 mg Fe/d ) or placebo treatment for 12 wk . Energy expenditure was estimated during 3 d by heart rate ( HR ) recording . Production efficiency ( PE ) was calculated as the ratio of productivity to energy expenditure . In the iron-treated group mean hemoglobin ( Hb ) increased from 114 to 127 g/L ( P < 0.001 ) , mean serum ferritin increased from 9.7 to 30.0 micrograms/L ( P < 0.001 ) , and mean free erythrocyte protoporphyrin decreased from 1.01 to 0.49 mumol/L ( P < 0.001 ) . Mean HR at work decreased from 95.5 to 91.1 beats/min ( P < 0.001 ) , which was inversely correlated with the change in Hb ( r = -0.60 , P < 0.001 ) . PE increased significantly in the iron-treated group ( P < 0.001 ) and its change paralleled the change in Hb ( r = 0.58 , P < 0.001 ) . The results show that iron supplementation enabled these women to do the same work at a lower energy cost Studies in laboratory animals found that iron deficiency without anemia decreased oxidative capacity and increased reliance on carbohydrate as the substrate for energy , thereby causing impaired endurance . The purpose of this cross-sectional study was to investigate the relation between iron deficiency without anemia and physical performance in healthy active women aged 19 - 36 y. Iron-status assessment included determination of hemoglobin , hematocrit , transferrin saturation , and serum ferritin values . Dietary iron intake was assessed by frequency question naires and physical activity level was estimated by frequency question naires and 2-wk records . Fifteen women with normal iron status and 15 women with iron depletion ( serum ferritin < 12 micrograms/L ) were chosen r and omly from a group of 69 nonanemic women and given physical-performance tests , including determinations of maximum oxygen consumption ( VO2max ) , ventilatory threshold , and delta-efficiency . There were no significant differences between the two groups in body size , body composition , physical activity level , dietary iron intake , delta-efficiency , or ventilatory threshold . Compared with the iron-depleted group , the iron-sufficient group had significantly higher hemoglobin , transferrin saturation , and serum ferritin values and a significantly greater tendency to use iron supplements . When physical activity level and fat-free mass were controlled for , the iron-depleted group had a significantly lower VO2max . The difference in VO2max was significantly associated with serum ferritin concentration ; hemoglobin value was not a significant confounder . Therefore , reduction of VO2max in nonanemic women with iron depletion was likely caused by factors related to reduced body iron storage but was unrelated to decreased oxygen-transport capacity of the blood BACKGROUND Tissue iron depletion may negatively affect endurance performance and muscle fatigability . OBJECTIVE We investigated tissue-level iron depletion and progressive fatigue of the quadriceps during dynamic knee-extension exercise in young women . DESIGN Twenty iron-depleted ( serum ferritin < 20 micro g/L ) , nonanemic ( hemoglobin > 110 g/L ) women ( macro x + /- SEM age : 29.1 + /- 1.2 y ) received iron ( iron group ) or placebo ( placebo group ) for 6 wk in a r and omized , double-blind trial ( n = 10 per group ) . A protocol integrating 2 - 3-s maximal voluntary static contractions ( MVCs ) with dynamic knee extensions was used to assess fatigue . RESULTS No significant differences between the groups in baseline iron status , MVC at rest , or MVC at the end of the protocol were observed . After treatment , serum iron and transferrin saturation increased significantly in the iron group ( P = 0.02 and P = 0.03 , respectively ) . Serum transferrin receptor concentrations increased significantly in the placebo group ( P < 0.01 ) but not in the iron group . After treatment , the rate of decrease in MVC was attenuated in the iron group but not in the placebo group ( P = 0.01 ) . In the iron group , MVC at the sixth minute of the fatigue protocol and MVC at the end of the protocol were approximately 15 % ( P = 0.04 ) and approximately 27 % higher ( P < 0.01 ) , respectively , after treatment . These improvements were not related to changes in iron-status indexes or tissue iron stores , although power was low ( < 0.50 ) to detect these relations . CONCLUSIONS Iron supplementation was associated with a significant improvement in muscle fatigability . Interpretation regarding the direct role of tissue iron status is limited by the study 's low power to detect relations between tissue iron improvement and decreased muscle fatigue Forty-seven previously sedentary women participating in a 12-wk moderate aerobic-exercise program were r and omly assigned to one of four dietary groups : 50-mg/d iron supplement and a low food-iron diet ( 50 FE + EX ) , 10-mg/d iron supplement and a low food-iron diet ( 10 FE + EX ) , placebo and unrestricted diet ( P + EX ) , and meat supplement and high food-iron diet ( M + EX ) . A sedentary control group ( n = 13 ) received no dietary interventions . Hematocrit , total iron-binding capacity , and hemoglobin , serum iron , serum ferritin , and serum albumin concentrations were measured every 4 wk . Hemoglobin values decreased at the end of 4 wk in all exercising groups compared with the control group . Iron status in the 50 FE + EX and M + EX groups improved after week 4 as indicated by an increase in serum ferritin , serum iron , and hemoglobin concentrations , and a decline in total iron-binding capacity . Thus , short-term , moderate aerobic exercise result ed in compromised iron status that was offset to varying degrees by ingesting iron or meat supplements . However , meat supplements were more effective in protecting hemoglobin and ferritin status than were iron supplements Background Iron deficiency without anemia is related to adverse symptoms that can be relieved by supplementation . Since a blood donation can induce such an iron deficiency , we investigated the clinical impact of iron treatment after a blood donation . Methods One week after donation , we r and omly assigned 154 female donors with iron deficiency without anemia , aged below 50 years , to a four-week oral treatment of ferrous sulfate versus a placebo . The main outcome was the change in the level of fatigue before and after the intervention . Aerobic capacity , mood disorder , quality of life , compliance and adverse events were also evaluated . Hemoglobin and ferritin were used as biological markers . Results The effect of the treatment from baseline to four weeks of iron treatment was an increase in hemoglobin and ferritin levels to 5.2 g/L ( P < 0.01 ) and 14.8 ng/mL ( P < 0.01 ) , respectively . No significant clinical effect was observed for fatigue ( -0.15 points , 95 % confidence interval -0.9 points to 0.6 points , P = 0.697 ) or for other outcomes . Compliance and interruption for side effects was similar in both groups . Additionally , blood donation did not induce overt symptoms of fatigue in spite of the significant biological changes it produces . Conclusions These data are valuable as they enable us to conclude that donors with iron deficiency without anemia after a blood donation would not clinical ly benefit from iron supplementation . Trial Registration Clinical Trials.gov : PURPOSE The purpose of this study was to find out whether iron repletion leads to an increase in red blood cell volume ( RBV ) and performance capacity in iron-deficient nonanemic athletes . METHODS 40 young elite athletes ( 13 - 25 yr ) with low serum ferritin ( < 20 microg . L-1 ) and normal hemoglobin ( males > 13.5 g.dL-1 , females > 11.7 g.dL-1 ) were r and omly assigned to 12-wk treatment with either twice a day ferrous iron ( equivalent to 2 x 100 mg elemental iron ) or with placebo using a double blind method . Before and after treatment , hematological measures and parameters of iron status were determined in venous blood . RBV , blood volume ( BV ) , and plasma volume ( PV ) were measured by CO rebreathing . For determination of the aerobic and anaerobic capacity ( maximal accumulated oxygen deficit , MAOD ) , the athletes performed an incremental as well as a highly intensive treadmill test . RESULTS After 12 wk , ferritin levels were within the normal range in the iron-treated group ( IG ) with a significant ( P < 0.001 ) mean increase by 20 microg . L-1 opposed to a slight nonsignificant decrease in the placebo group ( PG ) . RBV did not change significantly in either group nor did any of the hematological measures . However , only in IG there were significant increases in VO2max and 
    Output:
    