Relationship between aerobic fitness and adipose tissue insulin resistance.

Aerobic fitness correlated negatively with the adipose tissue insulin resistance index of palmitate (ADIPO-IRpalmitate).

• ADIPO-IRpalmitate data were available for 340 volunteers across six previously published and two unpublished protocols.
• Fitness was measured as peak oxygen consumption (V̇o2peak) in mL·kg FFM-1·min-1.
• Pearson's correlation analysis was used to assess the relationship between fitness and ADIPO-IRpalmitate.
• Stepwise regression showed fitness independently predicted ADIPO-IRpalmitate after adjusting for other significant factors.

Aerobic fitness correlated negatively with the insulin concentration resulting in 50% suppression of palmitate rate of appearance (FFApalmitate IC50).

• FFApalmitate IC50 data were available for 108 volunteers.
• FFApalmitate IC50 was measured using the insulin clamp technique.
• Stepwise regression showed fitness independently predicted FFApalmitate IC50 after adjusting for other significant factors.
• This measure reflects the sensitivity of adipose tissue lipolysis to insulin suppression.

BMI, percent body fat, total body fat, and visceral adipose tissue (VAT) were the factors most strongly associated with both ADIPO-IRpalmitate and FFApalmitate IC50.

• These factors were univariately correlated with both ADIPO-IRpalmitate and FFApalmitate IC50 at P < 0.001.
• These variables were included alongside fitness, age, and sex in multiple linear regression analyses.
• Body composition variables were stronger univariate predictors than fitness.

Aerobic fitness independently predicted adipose tissue insulin resistance after adjusting for age, sex, BMI, VAT, body fat, percent body fat, and adipocyte size.

• Stepwise multiple linear regression analysis was used to identify independent predictors.
• Fitness remained a significant independent predictor of both ADIPO-IRpalmitate and FFApalmitate IC50 in multivariable models.
• This independence from body composition variables suggests a direct association between fitness and adipose tissue insulin responsiveness.

The study collated data from eight protocols, including six previously published and two unpublished datasets.

• A total of 340 volunteers had ADIPO-IRpalmitate data available, and 108 volunteers had FFApalmitate IC50 data available.
• One protocol was registered as a clinical trial (NCT00254371); the others were not considered clinical trials at the time they were conducted.
• Pearson's correlation and multiple linear regression analysis were the primary statistical methods used.

The findings suggest that aerobic fitness may promote metabolic health through positive effects on adipose tissue lipolysis regulation.

• The authors state these findings suggest 'aerobic fitness may promote metabolic health through positive effects on adipose tissue.'
• The authors propose that 'exercise, if it improves fitness, may improve both adipose tissue and muscle function.'
• Prior literature established fitness associations with skeletal muscle insulin sensitivity; this study extends that to adipose tissue.