Physical activity (PA) is defined as any bodily movement produced by the skeletal muscles, resulting in increased energy expenditure . Regular PA is associated with a lower risk of cardiovascular and overall morbidity and mortality . Indeed, physical inactivity was recently ranked as the fourth most important risk factor of mortality worldwide, by the World Health Organization (WHO) . The recommended level of medium intensity aerobic activity being 150 minutes/week, only half of the adult population in the USA reach this level of PA according to self-reported data , while the Eurobarometer study estimated that only 23 % of the Swedish population were sufficiently physically active .
Both cardiorespiratory fitness (CRF), defined as the maximum oxygen uptake on treadmill or by bicycle ergometer , and the level of physical activity have been found to be independently associated with cardiovascular risk factors, such as blood lipids, body mass index (BMI), blood pressure and insulin resistance [6, 7], as well as predicting morbidity and mortality [8, 9]. In addition, sedentary behaviour and few breaks in sitting time, is also independently associated to cardiovascular risk factors . In addition to the direct effects on the cardiovascular system, physical inactivity also increases future risk of developing mental disorders and stress .
The definitions of sedentary behaviour has varied in the literature, initially including a low physical activity level in addition to being still, making comparisons between studies difficult . The health risk related to sedentary behaviour seems to be independent of the time spent performing light and moderate to vigorous PA [13, 14]. In these studies, sedentary behaviour was defined as an accelerometer count of <100/min, but has also been defined as all activities that consume not over 1.0-1.5 metabolic equivalent units (METs; equivalent to energy expenditure from oxygen uptake of 3.5 ml·kg-1·min-1) . Recently the Sedentary Behaviour Research Network has suggested a standardized description , defining inactive individuals are those not meeting recommended level of PA, while sedentary behaviour is defined as any awake activities while sitting or reclining posture with an energy expenditure <1.5 METs. Moreover the actual sitting time has recently also been independently related to increased risk for all-cause and cardiovascular disease (CVD) mortality [17, 18].
Indeed, the greatest net-effect for health may be gained by any positive change from sedentary behavior . As a result, identifying and targeting physically inactive, including sedentary, or insufficiently active individuals, is one of the major tasks in primary and secondary prevention in everyday health care.
The Framingham Risk Score and the European Society of Cardiology’s SCORE, based on cholesterol, gender, age, blood pressure and smoking, are used to identify individuals with increased risk of cardiovascular events [20, 21]. However, both risk score charts lack information about the physical activity level, which would be a valuable contribution to identify patients at risk, as both physical activity levels and CRF are important independent risk factors for CVD [9, 22]. While direct measurement of the individual CRF level, using e.g. bicycle ergometers or treadmill tests may not be feasible in everyday health care, a simple assessment of the physical activity level, identifying patients at potentially increased cardiovascular risk, by being physically inactive, would be useful.
In a previous longitudinal study, we used a four level scale to assess the self-reported physical activity level in a working population, showing an association with both perceived stress and self-reported mental disorders . This scale was originally developed by Saltin and Grimby (here termed Saltin-Grimby Physical Activity Level Scale, SGPALS) .
In the present study, we thus aimed to study the relationship between the self-reported level of PA according to the modernized version of SGPALS and other traditional cardiovascular risk factors in a large Swedish population. We also wanted to characterise the subjects having the lowest level of PA, according to SGPALS, with regard to their risk of having pre-defined abnormal levels of the classical risk factors.