The purpose of this study was to determine the independent associations between physical activity (PA), cardiorespiratory fitness (CRF),
abdominal obesity and
insulin action in obese women. We studied 141 abdominally obese women (waist circumference (WC): 106.4 ± 10.2 cm). PA duration (min/day) and intensity (counts/min) were obtained by accelerometry. CRF was measured using a treadmill. WC was measured at the iliac crest; abdominal adiposity was measured by magnetic resonance imaging.
Glucose and
insulin measures were obtained during a 75-g, 2-h
glucose tolerance test. The homeostasis model of assessment iHOMA2-IS was used to estimate
insulin sensitivity. PA duration and intensity were not associated with
glucose or
insulin metabolism (p > 0.05). However, moderate-to-vigorous PA (MVPA) duration was associated with fasting
insulin and iHOMA2-IS (p < 0.01). CRF was associated with fasting
insulin and iHOMA2-IS (r = 0.27, p ≤ 0.01), whereas WC was associated with fasting
insulin (r = 0.50, p < 0.01) and iHOMA2-IS (r = -0.52, p ≤ 0.01). Following adjustment for CRF, MVPA, and age, WC remained associated with fasting
glucose,
insulin, 2-h
glucose and iHOMA2-IS (r = -0.44, p ≤ 0.01). CRF was associated with fasting
glucose as well as 1- and 2-h
glucose (r = 0.24, p < 0.01) after adjusting for WC, MVPA, and age. MVPA was not associated with
glucose or
insulin measures after control for CRF and WC (p > 0.05). Mediation analysis revealed that CRF and WC combined mediated the relationship between MVPA and both
glucose tolerance and
insulin resistance (p < 0.05). In conclusion, among abdominally obese women, WC and CRF are independently associated with measures of
glucose tolerance and
insulin resistance and mediate the association between MVPA and
insulin resistance.