California Longshoremen Study
The California Longshoremen study began in 1951 as a population-based examination of coronary heart disease (CHD) in men who performed strenuous, moderate, and light tasks working as longshoremen.
The 6,351 subjects were longshoremen aged 35 to 74 years, enrolled on the basis of their job classification. Health screenings were completed in 1951 and 1961. 
Subjects were followed by which interval occurred first: 22 years of follow-up, their 75th birthday, or death.
After 22 years of follow-up, longshoremen in tasks requiring strenuous work experienced fewer coronary events than those in light or moderate classes of work.  The relative risks of CHD for those who completed moderate or light work were 1.7 and 1.8, respectively.
Relative risk of sudden or delayed death from CHD among those in moderate work classes versus heavy was 3.5 for sudden death and 1.4 for delayed death. Longshoremen engaged in light work had a relative risk of 2.8 for sudden death and 1.5 for delayed death.  Bias from job change was reduced by analyses using work classifications of the decedents six months prior to death.
The California Longshoremen study affirmed the results of other population-based work activity studies suggesting that repeated bursts of high energy output activity was protective of CHD. It found this particularly for sudden coronary death and discussed plausible potential mechanisms. Strengths of the study included the large population and limited loss to follow-up. Weaknesses relate to the vagaries of job classifications as a true measure of habitual energy expenditure and bias from change to lighter jobs.
 Paffenbarger RS, Hale WE (1975). Work activity and coronary heart mortality. New England Journal of Medicine, 292 (11), 545-550.