The relationship between insulin sensitivity and maximal oxygen uptake is confounded by method of adjustment for body composition.

ABSTRACT

BACKGROUND: The use of ratios for analyzing physiologic variables often creates spurious associations. METHODS: Results of a euglycaemic clamp, a graded exercise test to measure maximal oxygen uptake (VO2max) and underwater weighing in 358 nondiabetic adults (166 women and 192 men) were used to compare the effects of weight standardization by division or by partial Spearman correlations on the association between VO2max and insulin sensitivity. RESULTS: VO2max and insulin sensitivity were negatively correlated when VO2max was divided by weight. When partial Spearman correlations were used to adjust VO2max for body composition, the correlation between VO2max and insulin sensitivity was greatly diminished. CONCLUSIONS: Division of VO2max by weight does not adjust for weight, but it creates spurious associations between VO2max and insulin sensitivity.