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 (LM) and body mass (BM) 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/LM 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/BM 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/BM, but not Wmax/LM, 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.

Figure 1

Differences in HOMA-IR among children with different levels of body fat percentage (BF%) and cardiorespiratory fitness scaled by lean body mass (LM) or body mass (BM). N in W_max/LM^-1.13 or W_max/LM¹ = Lower BF%/higher CRF=121; Lower BF%/lower CRF=105; Higher CRF/higher BF%=121; Higher BF%/lower CRF=120. N in W_max/BM^0.48 or W_max/LM¹ = Lower BF%/higher CRF=158; Lower BF%/lower CRF=68; Higher CRF/higher BF%=68; Higher BF%/lower CRF=158. Lines between groups denotes a statistically significant difference between groups at p<0.05.

Figure 2

Differences in physical activity energy expenditure (PAEE), moderate to vigorous physical activity (MVPA), and sedentary time (ST) among children with different levels of body fat percentage and cardiorespiratory fitness normalised for lean mass (LM^1.13). N = Lower BF%/higher CRF=121; Lower BF%/lower CRF=105; Higher CRF/higher BF%=121; Higher BF%/lower CRF=120. Lines between groups denotes a statistically significant difference between groups at p<0.05.

Figure 3

Differences in HOMA-IR among children with different levels of body fat percentage (BF%), allometrically scaled cardiorespiratory fitness for lean mass (LM^1.13), and physical activity energy expenditure (PAEE), moderate to vigorous physical activity (MVPA), or sedentary time (ST). N=lower BF%/higher CRF/lower PA or higher ST = 32; lower BF%/higher CRF/higher PA or lower ST = 75; lower BF%/lower CRF/lower PA or higher ST = 37; lower BF%/lower CRF/higher PA or lower ST = 52; higher BF%/higher CRF/lower PA or higher ST = 47; higher BF%/higher CRF/higher PA or lower ST = 45; higher BF%/lower CRF/lower PA or higher ST = 79; higher BF%/higher CRF/higher PA or lower ST = 45. Lines between groups denotes a statistically significant difference between groups at p<0.05.