Effects of exercise training on glucose homeostasis: the HERITAGE Family Study.
OBJECTIVE
To determine the effect of a 20-week endurance training program in healthy, previously sedentary participants on measures derived from an intravenous glucose tolerance test (i.v.GTT).


METHODS
An i.v.GTT was performed before and after a standardized training program in 316 women and 280 men (173 blacks and 423 whites). Participants exercised on cycle ergometers 3 days per week for 60 sessions. The exercise intensity was progressively increased from 55% VO2max for 30 min per session to 75% VO2max for 50 min per session.


RESULTS
Mean insulin sensitivity increased by 10% (P < 0.001) following the intervention, but the variability in the changes was high. Men had larger improvements than women (P = 0.02). Improvements in fasting insulin were transitory, disappearing 72 h after the last bout of exercise. There were also significant mean increases in the glucose disappearance index (3%, P = 0.02) and in glucose effectiveness (11%, P < 0.001), measures of glucose tolerance and of the capacity of glucose to mediate its own disposal, respectively. The acute insulin response to glucose, a measure of insulin secretion, increased by 7% in the quartile with the lowest baseline glucose tolerance and decreased by 14% in the quartile with the highest baseline glucose tolerance (P < 0.001). The glucose area below fasting levels during the i.v.GTT was reduced by 7% (P = 0.02).


CONCLUSIONS
Although the effects of structured regular exercise were highly variable, there were improvements in virtually all i.v.GTT-derived variables. In the absence of substantial weight loss, regular exercise is required for sustained improvements in glucose homeostasis.
Boulé
Normand G
NG
Division of Kinesiology, Laval University, Sainte-Foy, Québec, Canada.
Weisnagel
S John
SJ
Lakka
Timo A
TA
Tremblay
Angelo
A
Bergman
Richard N
RN
Rankinen
Tuomo
T
Leon
Arthur S
AS
Skinner
James S
JS
Wilmore
Jack H
JH
Rao
D C
DC
Bouchard
Claude
C
D000328:Adult; D044383:Black People; D001786:Blood Glucose / Q000378:metabolism*; D015444:Exercise; D005080:Exercise Test; D005215:Fasting; D005260:Female; D005951:Glucose Tolerance Test; D006801:Humans; D007328:Insulin / Q000097:blood; D008297:Male; D010809:Physical Fitness; D044465:White People
D001786:Blood Glucose; D007328:Insulin