Work and leisure time sitting and inactivity: Effects on cardiorespiratory and metabolic health.

BACKGROUND Prospective relationships between sedentary behaviour and cardiorespiratory and metabolic markers need to be better delineated in adults with different physical activity levels. We examined the separate and combined relationships of work and leisure time sitting and moderate to vigorous physical activity (MVPA) with cardiorespiratory fitness and cardiometabolic risk factors. METHODS A total of 2308 adults from the Health2006 cohort were followed for five years. Work sitting, leisure time sitting and MVPA were self-reported and cardiorespiratory fitness (Vo2max) was estimated by a submaximal step test. Cardiometabolic risk factors included body mass index, waist circumference, systolic and diastolic blood pressure, triglycerides, high-density lipoprotein cholesterol and insulin levels. Prospective associations with each sitting domain alone and in combination with MVPA level were investigated by multiple linear regression analyses, as were the reverse associations with weight status (body mass index and waist circumference). RESULTS Baseline leisure time sitting predicted increased insulin (p < 0.05) and decreased estimated Vo2max (p < 0.05), whereas work sitting predicted decreased waist circumference (p < 0.05) and increased estimated Vo2max (p < 0.01) over the five-year study. Low baseline leisure time sitting, but not work sitting, predicted increased estimated Vo2max regardless of the MVPA level. Weight status predicted increased leisure time sitting (p < 0.01), but leisure time sitting did not predict weight. CONCLUSIONS These findings emphasize sedentary behaviour during leisure time, rather than at work, as a risk behaviour in relation to cardiorespiratory and metabolic health. For cardiorespiratory fitness, it may be important not only to promote MVPA, but also to discourage sedentary behaviour during leisure time.