***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: To eluci date the effects of endurance training on circulating irisin levels in young and middle-aged/older adults , and to determine the association between endurance training-induced alteration of irisin and reduction in body fat . Twenty-five healthy young ( age 21 ± 1 years ; 16 men , 9 women ) and 28 healthy middle-aged/older adults ( age 67 ± 8 years ; 12 men , 16 women ) participated in the study . Each age cohort was divided into two groups : the endurance-training group ( 14 young , 14 middle-aged/older ) and the control group . Subjects in the training groups completed an 8-week endurance-training program ( cycling at 60 - 70 % peak oxygen uptake [ V˙O2peak ] for 45 min , 3 days/week ) . Before and after the intervention , we evaluated serum irisin level , V˙O2peak , and body composition . The increase in V˙O2peak in the young and middle-aged/older training groups after the intervention period was significantly greater than those in the young and middle-aged/older control groups ( P < 0.05 ) . Serum irisin level was significantly increased in the middle-aged/older training group after the intervention period ( P < 0.01 ) , but not in the young training group . Furthermore , in the middle-aged/older training group , the endurance training-induced reduction in visceral adipose tissue area was negatively correlated with the change in serum irisin level ( r = −0.54 , P < 0.05 ) . These results suggest a possible role for secreted irisin in the exercise-induced alteration of abdominal visceral fat in middle-aged and older adults Aim /hypothesis Studies have suggested a link between insulin resistance and mitochondrial dysfunction in skeletal muscles . Our primary aim was to investigate the effect of aerobic training on mitochondrial respiration and mitochondrial reactive oxygen species ( ROS ) release in skeletal muscle of obese participants with and without type 2 diabetes . Methods Type 2 diabetic men ( n = 13 ) and control ( n = 14 ) participants matched for age , BMI and physical activity completed 10 weeks of aerobic training . Pre- and post-training muscle biopsies were obtained before a euglycaemic – hyperinsulinaemic clamp and used for measurement of respiratory function and ROS release in isolated mitochondria . Results Training significantly increased insulin sensitivity , maximal oxygen consumption and muscle mitochondrial respiration with no difference between groups . When expressed in relation to a marker of mitochondrial density ( intrinsic mitochondrial respiration ) , training result ed in increased mitochondrial ADP-stimulated respiration ( with NADH-generating substrates ) and decreased respiration without ADP . Intrinsic mitochondrial respiration was not different between groups despite lower insulin sensitivity in type 2 diabetic participants .  Mitochondrial ROS release tended to be higher in participants with type 2 diabetes . Conclusions /interpretationAerobic training improves muscle respiration and intrinsic mitochondrial respiration in untrained obese participants with and without type 2 diabetes . These adaptations demonstrate an increased metabolic fitness , but do not seem to be directly related to training-induced changes in insulin sensitivity OBJECTIVE Exercise twice every other day has been shown to lead to increasing peroxisome proliferator receptor γ coactivator-1α ( PGC-1α ) expression ( up-stream factor of irisin ) via lowered muscle glycogen level during second of exercise compared with exercise once daily . This study determined the influence of 4weeks of sprint training ( training once daily vs. twice every other day ) on the serum irisin concentration . MATERIAL S AND METHODS Twenty healthy males ( 20.9±1.3years ) were assigned r and omly to either the SINGLE or REPEATED group ( n=10 per group ) . The subjects in the SINGLE group participated in a sprint training session once daily ( 5days per week ) , whereas those in the REPEATED group performed two consecutive training sessions on the same day with a 1-h rest between sessions ( 2 - 3days per week ) . Both groups completed 20 training sessions over 4weeks . Each training session consisted of three consecutive 30-s maximal pedaling exercises with a 10-min rest between sets .  Blood sample s were collected before and after training period ( 48h after completing the last training session ) . RESULTS The serum irisin concentration decreased significantly after training in each group ( SINGLE , 338.5±77.8 to 207.6±64.6ng/mL ; REPEATED , 329.5±83.9 to 234.2±72.8ng/mL , p<0.05 ) . The plasma interleukin-6 ( IL-6 ) concentration tended to be lower after training in both groups ( main effect for period , p=0.054 ) . However , there was no significant difference in the serum irisin or plasma IL-6 concentration between groups after training . The serum high-molecular-weight adiponectin concentration did not change significantly after training in either group . CONCLUSION Sprint training for 4weeks significantly decreased the resting serum irisin concentration , despite different training programs ( training once daily vs. twice every other day ) CONTEXT The myokine irisin may increase energy expenditure and affect metabolism . OBJECTIVE The objective of the study was to eluci date predictors of irisin and study whether circulating irisin may have day-night rhythm in humans . DESIGN This was an observational , cross-sectional study with an additional 24-hour prospect i ve observational arm ( day-night rhythm sub study ) and two prospect i ve interventional arms ( mixed meal sub study and exercise sub study ) . SETTING The study was conducted at the Hellenic Military School of Medicine ( Thessaloniki , Greece ) . PATIENTS AND INTERVENTIONS One hundred twenty-two healthy , young individuals were subjected to anthropometric and body composition measurements , and their eating and exercise behavior profiles were assessed with vali date d question naires . Subgroups were subjected to day-night rhythm , st and ardized meal ingestion , and 30-minute aerobic exercise studies . MAIN OUTCOME MEASURES Circulating irisin levels were measured . RESULTS Ιrisin levels were lower in males than females ( P = .02 ) after adjustment for lean body mass , which was its major determinant . Irisin levels followed a day-night rhythm ( P < .001 ) with peak at 9:00 pm . Irisin levels were increased at the end of exercise ( 84.1 ± 10.0 vs 105.8 ± 14.3 ng/mL ; P < .001 ) . Irisin levels were not affected by intake of a st and ardized meal and were not associated with caloric intake or diet quality . CONCLUSIONS In healthy , young individuals , circulating irisin displays a day-night rhythm , is correlated with lean body mass , and increases acutely after exercise RATIONALE The newly discovered myokine irisin has been proposed to affect obesity and metabolism by promoting browning of white adipose tissue . However , clinical and functional studies on the association of irisin with obesity , muscle mass , and metabolic status remain controversial . Here we assessed the effect of 4 distinct exercise regimens on  serum irisin  levels in children and young adults and systematic ally evaluated the influence of diurnal rhythm , anthropometric and metabolic parameters , and exercise on irisin . RESULTS Serum irisin levels did not show diurnal variations , nor were they affected by meal intake or defined glucose load during oral glucose tolerance testing . Irisin levels decreased with age . In adults ,  irisin levels were higher in men than in women , and obese subjects had significantly higher levels than lean control subjects . Irisin levels were closely correlated with muscle-associated bioimpedance parameters such as fat-free mass and body cell mass . Of the 4 exercise regimens that differed in duration and intensity , we identified a clear and immediate increase in serum irisin levels after acute strenuous exercise ( cycling ergometry ) and a 30-minute bout of intensive exercise in children and young adults , whereas longer ( 6 weeks ) or chronic ( 1 year ) increases in physical activity did not affect irisin levels . SUMMARY We show that irisin levels are affected by age , sex , obesity , and particularly muscle mass , whereas diurnal rhythm and meals do not contribute to the variation in irisin levels . Short bouts of intensive exercise but not long-term elevations in physical activity , acutely and transiently increase serum irisin levels in children and adults 
    Output:
    
We found a contrast between st and ardised review methods and accuracy of the measurements used .