Cardiorespiratory Fitness Mediates the Associations between Sedentary Behavior and Markers of Cardiometabolic Health in Women

Background: Sedentary behavior has been shown to be inversely associated with markers of insulin sensitivity and cardiometabolic health in middle-aged and older adults, independent of moderate-to-vigorous physical activity (MVPA). Low cardiorespiratory fitness (CRF) is an independent risk factor for cardiovascular disease (CVD) mortality, yet it is unknown whether CRF influences the associations between sedentary behavior and cardiometabolic health.

Purpose: To investigate whether the associations between sedentary behavior and markers of cardiometabolic health were independent of CRF in young women.

Methods: Blood pressure, waist circumference, and fasting glucose, triglycerides and high-density lipoprotein were measured in 50 women (Mean±SD: age 24.0±4.8 y; BMI 27.0±4.8 kg/m2; body fat 33.5±7.0%; CRF 2.8±0.5 L/min). Body composition was estimated by BodPod, CRF was measured by an incremental treadmill test to exhaustion, and lipid accumulation product (LAP) was calculated. Accelerometers were worn over 7 d to assess sedentary time (<150 counts/min) and MVPA (≥2690 counts/min). Multiple regression analyses examined the associations between sedentary behavior and markers of cardiometabolic health, with MVPA, CRF and body mass as covariates.

Results: On average participants spent 8.4 hours (57%) of their waking day being sedentary and 1 hour (7%) in MVPA. Sedentary behavior was independently associated with triglycerides after adjusting for MVPA (R2=0.10, β=0.31, p=0.03). This association was attenuated when CRF and body mass were entered into the model (R2=0.26, β=0.27, p=0.05). Sedentary behavior was independently associated with LAP after adjusting for MVPA (R2 =0.11, β =0.32, p=0.02) but this association was no longer signifi cant with the addition of CRF and body mass into the model (R2=0.46, β =0.21, p=0.07). CRF and body weight were the strongest contributors to triglycerides and LAP in these models (p<0.01).

Conclusions: We are the first to show sedentary behavior was associated with markers of cardiometabolic health independent of MVPA but not CRF. These findings suggest that CRF may be an important predictor and mediator of cardiometabolic risk in young women. Thus, increasing CRF may be more advantageous than increasing daily MVPA for maintaining cardiometabolic health in young women.