Cardiorespiratory Fitness, Physical Activity, and Insulin Resistance in Children

Abstract

Purpose: Few studies have investigated the independent and joint associations of cardiorespiratory fitness (CRF) and body fat percentage (BF%) with insulin resistance in children. We investigated the independent and combined associations of CRF and BF% with fasting glycemia and insulin resistance and their interactions with physical activity (PA) and sedentary time among 452 children age 6 to 8 yr. Methods: We assessed CRF with a maximal cycle ergometer exercise test and used allometrically scaled maximal power output (Wmax) for lean body mass (LM1.13) and body mass (BM1) as measures of CRF. The BF% and LM were measured by dual-energy X-ray absorptiometry, fasting glycemia by fasting plasma glucose, and insulin resistance by fasting serum insulin and Homeostatic Model Assessment for Insulin Resistance (HOMA-IR). The PA energy expenditure, moderate-to-vigorous PA (MVPA), and sedentary time were assessed by combined movement and heart rate sensor. Results: Wmax/LM1.13 was not associated with glucose (β = 0.065, 95% confidence interval [CI] = −0.031 to 0.161), insulin (β = −0.079, 95% CI = −0.172 to 0.015), or HOMA-IR (β = −0.065, 95% CI = −0.161 to 0.030). Wmax/BM1 was inversely associated with insulin (β = −0.289, 95% CI = −0.377 to −0.200) and HOMA-IR (β = −0.269, 95% CI = −0.359 to −0.180). The BF% was directly associated with insulin (β = 0.409, 95% CI = 0.325 to 0.494) and HOMA-IR (β = 0.390, 95% CI = 0.304 to 0.475). Higher Wmax/BM1, but not Wmax/LM1.13, was associated with lower insulin and HOMA-IR in children with higher BF%. Children with higher BF% and who had lower levels of MVPA or higher levels of sedentary time had the highest insulin and HOMA-IR. Conclusions: Children with higher BF% together with less MVPA or higher levels of sedentary time had the highest insulin and HOMA-IR. Cardiorespiratory fitness appropriately controlled for body size and composition using LM was not related to insulin resistance among children.