Coronary heart disease takes a large toll of middle-aged males thereby reducing the overall occupational fitness and potential of the workforce. Most of the risk factors for CHD (and other diseases) are self-determined and/or the result of preventable behaviour or alterable environment. The Multiple Risk Factor Hypothesis and the CHD risk factors are reviewed in detail in Chapter 2. It is more the interaction among risk factors within supposedly "normal" limits, rather than abnormally high levels of one or a few factors which results in the development of CHD, a phenomenon which obscures the issue of causation. It is hypothesized that the imbalance between the collective pathogenic effects of risk factors and the ability of the body to resist and/or repair such effects cause CHD. States such as sedentariness and obesity in which most of the risk factors tend to be clustered are important risk indicators. Moreover, since the overall risk profile is improved with reversal of these two states through regular aerobic activity and weight loss, the latter two are key interventions in CHD prevention. Risk factor screening to identify those at risk and subsequent modification of the risk status are useful manoeuvers for the prevention of CHD. As well as being secondary to the ravages of such diseases as CHD, occupational productivity is also reduced by poor levels of employee physical fitness. The recognition by employers of the potential success of CHD prevention programs and the increased productivity of the fit employee has led to the emergence of employer-sponsored occupational fitness programs. Such programs are based on a wholistic health-enhancement approach with regular aerobic physical activity as the core. The operative principles, contents (including the what and how of the all important assessment component) and benefits of such programs are reviewed in Chapter 3. A review of the state of health and fitness in the Canadian Forces and the experimental portion of the thesis make up Chapter 4. In spite of policies, orders and programs to ensure the health and fitness of Canadian Forces' personnel, the CF remains a fairly high-risk population. The cross-sectional study on the health and fitness of 2 83 CF personnel at National Defence Headquarters shows that Other Ranks constitute a higher-risk rank grouping than Officers, as do lower ranks in both of these two major rank groupings. Volunteers appear to be a self-selected sub-population which is healthier and fitter than average. Aerobic fitness (VO₂ max), obesity and resting heart rate emerge as the three key indicators of health and CHD risk status. Chapter 5 summarizes the thesis and contains conclusions and recommendations to the CF for future actions which are also applicable to most occupational settings. / Medicine, Faculty of / Population and Public Health (SPPH), School of / Graduate