Physical work demands and physical fitness in low social classes
研究低社会阶层男性中，体力工作需求与体能对缺血性心脏病死亡率的影响，发现高体力工作需求仅增加低体能者的死亡风险。
<h3>Objectives</h3> Social class and physical work demands are strongly correlated and by implication much more prevalent among manual workers, that is, lower social classes. To challenge physical work demands as a risk factor for ischaemic heart disease (IHD) mortality, we analysed the interplay of physical work demands, physical fitness and mortality exclusively among the lower social classes. <h3>Methods</h3> 30-year follow-up in the Copenhagen Male Study of 5249 gainfully employed men aged 40–59 years. 274 men with cardiovascular disease were excluded from the follow-up. Physical fitness (maximal oxygen consumption, VO<sub>2</sub>Max) was estimated using the Åstrand cycling test, and participants divided into low (VO<sub>2</sub>Max 15–26 ml/kg/min) or high (VO<sub>2</sub>Max 39–78 ml/kg/min) physical fitness. Physical work demands were determined by two self-reported questions. <h3>Results</h3> Overall, 583 men (11.9%) died due to IHD and 2648 (54.0%) from all cause mortality (ACM). Among the higher social classes (I–III), only 3.5% had high physical work demands versus 30% among classes IV and V. Among 2707 belonging to social classes IV and V, multiple-adjusted Cox proportional hazard ratios (HR) with 95% CI showed a substantial increased risk of IHD mortality from high physical work demands among men with low physical fitness (HR:2.90, 95% CI: 1.21 to 6.96), but not among men with high physical fitness (HR:0.60, 95% CI: 0.24 to 1.47), referencing men with low physical work demands. Similar, but weaker associations were found for ACM. <h3>Conclusions</h3> These findings among low social class men support that high physical work demands increases the risk of IHD mortality among those with low physical fitness.