Cardiorespiratory fitness in youth: relationship to insulin sensitivity and beta-cell function.
OBJECTIVE
We examined whether the relationship between cardiorespiratory fitness (CRF) and insulin sensitivity (IS)/secretion is independent of adiposity in healthy African-American (n = 65) and white (n = 57) youth.


METHODS
IS and beta-cell function were evaluated by a 3-hour hyperinsulinemic-euglycemic and a 2-hour hyperglycemic (12.5 mM) clamp, respectively. Total fat was measured by DXA and abdominal fat with computed tomography. CRF (peak volume of oxygen) was measured using a graded maximal treadmill test.


RESULTS
Independent of race, CRF was inversely (p < 0.05) related to total and abdominal fat, fasting insulin and first phase insulin secretion, and positively (p < 0.05) related to IS. When subjects were categorized into low (< or = 50th) and high (> 50th) CRF groups, IS was significantly (p < 0.05) higher in the high compared with the low CRF group independently of race. Furthermore, first and second phase insulin secretion were lower (p < 0.05) in the high CRF group in comparison with the low CRF group in both races. However, in multiple regression analyses CRF was not (p > 0.05) an independent predictor of IS and acute insulin secretion after accounting for total adiposity.


CONCLUSIONS
Our findings demonstrate that low CRF is associated with decreased IS compensated by higher insulin secretion in both African-American and white youth. However, this relationship disappears after adjusting for differences in adiposity, suggesting that the association between fitness and IS is mediated, at least in part, through fatness.
Lee
Sojung
S
Children's Hospital of Pittsburgh, Division of Pediatric Endocrinology, Metabolism, and Diabetes Mellitus, Weight Management and Wellness Center, University of Pittsburgh School of Medicine, Pittsburgh, PA 15213, USA.
Bacha
Fida
F
Gungor
Neslihan
N
Arslanian
Silva A
SA
D050153:Abdominal Fat / Q000378:metabolism; D000273:Adipose Tissue / Q000378:metabolism*; D050154:Adiposity / Q000502:physiology*; D000293:Adolescent; D001741:Black or African American; D001786:Blood Glucose / Q000378:metabolism*; D002648:Child; D005080:Exercise Test; D005260:Female; D015309:Glucose Clamp Technique; D006801:Humans; D007328:Insulin / Q000378:metabolism; D000078790:Insulin Secretion; D008297:Male; D010101:Oxygen Consumption / Q000502:physiology; D010809:Physical Fitness / Q000502:physiology*; D044465:White People
D001786:Blood Glucose; D007328:Insulin