A total of 3,354 workers >18 years from the continuous 1999–2004 NHANES was used for analysis in this study, representing an approximate annual average of 51 million United States residents, based on the number of participants with a completed VO₂max test. Table 1 shows the sociodemographic characteristics of the sample, including gender, age, ethnicity/race, education, BMI, marital status, daily level of physical activity, and activity level in previous month. Males comprised approximately 57% of the sample, 48% were younger than 30 years of age, 45% were white, non-Hispanic, and 49% had completed more than high school. Overweight or obese (according to BMI) participants made up over 56% of the sample, only 32% reported taking the stairs and/or lifting light or heavy loads on a daily basis, and 30% had not engaged in vigorous or moderate activity in the previous month.

Table 2 shows the survey-adjusted means and SE for estimated VO₂max by occupation for the total sample and by gender. For all occupations, the mean estimated VO₂max levels for the total sample, males, and females were 40.4 ml/kg/min (SE = 0.3), 43.8 ml/kg/min (SE = 0.3), and 35.9 ml/kg/min (SE = 0.3), respectively. The lowest average estimated VO₂max value was found for Farm operators, managers, and supervisors in both males (M = 37.7 ml/kg/min, SE = 1.8) and females (M = 27.4 ml/kg/min, SE = 0.9). The highest average estimated VO₂max value for males was found for Construction laborers (M = 49.5 ml/kg/min, SE = 2.2). In females the highest average estimated VO₂max value was found for Construction trades (M = 44.9 ml/kg/min, SE = 6.4).

Table 3 shows the survey-adjusted percentages and SE for the low, moderate, and high CVF groups by occupation. Overall, all occupations had 16.1% (SE = 0.9), 35.5% (SE = 1.2), and 48.4% (SE = 1.5) of workers in the low, moderate, and high CVF categories, respectively. Approximately 7% of Farm and nursery workers, Related agricultural, forestry, and fishing occupations, and Health diagnosing, assessing, and treating occupations had low CVF. Miscellaneous food preparation and service occupations, Secretaries, stenographers, and typists, Sales workers, retail, and personal services, Farm operators, managers, and supervisors, and Fabricators, assemblers, inspectors, and samplers had at least 25% of their workers with low CVF levels.

Farm operators, managers, and supervisors, Secretaries, stenographers, and typists, Vehicle and mobile equipment mechanics and repairers, and Protective service occupations had the lowest prevalence (<32%) of high CVF. At least 59% of workers of Engineers, architects, and scientists, Private household occupations, Construction laborers, and Related agricultural, forestry, and fishing occupations had high CVF.

Following adjustment for age, gender, and survey design, Executive, administrators, and managers (Wald χ² [1] = 7.2, p = 0.008; odds ratio [OR] = 0.55, 95% confidence interval [CI] = 0.35, 0.86), Health diagnosing, assessment, and treating occupations (Wald χ² [1] = 4.4, p = 0.04; OR = 0.42, 95% CI = 0.18, 0.97), Waiters and waitresses (Wald χ² [1] = 4.9, p = 0.03; OR = 0.44, 95% CI = 0.21, 0.93), Personal service occupations (Wald χ² [1] = 6.1, p = 0.01; OR = 0.42, 95% CI = 0.21, 0.85), and Related agricultural, forestry, and fishing occupations (Wald χ² [1] = 4.2, p = 0.04; OR = 0.36, 95% CI = 0.13, 0.98) had a smaller percentage of workers with low CVF compared to all other occupations. Sales workers, retail, and personal services (Wald χ² [1] = 7.3, p = 0.007; OR = 1.89, 95% CI = 1.18, 3.02), Miscellaneous administrative support occupations (Wald χ² [1] = 4.8, p = 0.03; OR = 1.54, 95% CI = 1.03, 2.30), and Miscellaneous food preparation and service occupations (Wald χ² [1] = 3.9, p = 0.05; OR = 1.96, 95% CI = 0.98, 3.92) had a higher percentage of workers with low CVF compared to all other occupations.

To our knowledge, this population-based study of American workers is the first to examine CVF, as measured by estimated VO₂max, across 40 different occupation categories. Approximately 16% of all workers had low CVF. For men, the lowest level of mean estimated VO₂max was for Farm operators, managers, and supervisors, and the highest levels were for Cooks and Construction laborers. For women, the lowest average estimated VO₂max value was for Farm operators, managers, and supervisors, and the highest values were for Textile, apparel, and furnishings machine operators and Construction trades. Several occupations had particularly unfit workers according to percentages adjusted by age and gender, including Sales workers, retail, and personal services, Miscellaneous administrative support occupations, and Miscellaneous food preparation and service occupations. Moreover, Executive, administrators, and managers, Health diagnosing, assessment, and treating occupations, Waiters and waitresses, Personal service occupations, and Related agricultural, forestry, and fishing occupations had the lowest levels of low CVF compared to all other occupations. These findings are consistent with the limited research available for occupation-based studies of CVF, which show a range of estimated VO₂max values from the low 20s ml/kg/min for service and white collar personnel²¹ to a higher average VO₂max of 46.6 ml/kg/min in workers engaging in greater on-the-job activity, such as firefighters.²²

This research team previously explored three other factors related to CAD/CVD by occupation: (1) obesity, (2) self-reported physical activity level, and (3) cardiometabolic syndrome.^27–29 From 1986 to 2002, male workers in the following occupations had the highest rates of obesity: Motor vehicle operators, Material-moving equipment operators, Police and firefighters, Other transportation except motor vehicle moving operators, and Other protective services employees. For female workers, the highest rates of obesity were among Motor vehicle operators, Other protective service workers, Health services workers, Material-moving equipment operators, and Cleaning and building services workers.²⁷ None of these similar occupation groups had noteworthy levels of CVF in the current study (neither low nor high). Thus, the theorized relationship between high levels of obesity and low levels of CVF may require further investigation, as few reports have addressed this area in the general population, particularly by occupation category.³⁰ Also, measuring BMI, compared to actual body fat, introduces error into the relationship, given that BMI does not account for a high level of muscle (or fat free) mass.^31;32

Using the National Health Interview Surveys from 1997–2004, a previous study by this team found only one-third of male and female workers met recommended leisure-time physical activity levels.²⁸ Additionally, mixed results were found, when leisure-time physical activity levels were measured by occupation groups. The lowest rates of leisure-time physical activity were found in blue-collar occupations (16–55%). Thus, the current findings of high prevalence of low CVF in some blue collar occupations are not surprising, given the modest relationship between physical activity and CVF.

Utilizing the 1999–2004 NHANES, this group found that 20% of all workers met criteria for cardiometabolic syndrome, with Miscellaneous food preparation and food service workers and Farm operators, managers, and supervisors having the highest prevalence (30%).²⁹ These results are consistent with the current study, given that 16% of all workers had a low level of CVF, and Miscellaneous food preparation and food service workers and Farm operators, managers, and supervisors had a particularly high prevalence of low CVF. Several cross-sectional and longitudinal studies show that CVF is inversely associated with cardiometabolic syndrome.^33–36

Because we used a nationally-representative sample of adults in the United States population, the results of this study provide useful information for decision makers and employers who are conducting and/or planning wellness programs, specifically with the goal of improving CVF. Focusing on improving CVF will not only result in a healthier labor force by preventing many people from developing chronic disease, but also can work to reverse disease symptoms for those already diagnosed.^13;14;33 Additionally, investing in the fitness and general health of employees saves money in terms of enhanced productivity and lower health care costs.^37;38

The primary limitation of this study is the inability to ascertain causality, given its cross-sectional nature. It cannot be determined if simply working as a farm operator, secretary, or a retail sales worker contributes to low levels of CVF because of the lack of physical demands on the job and/or if people choosing these types of occupations do not typically engage in enough exercise to demonstrate higher levels of CVF at the time of the assessment.²⁸ Likewise, it is unknown if scientists, health-related occupations, teachers, or construction laborers have a greater prevalence of high CVF because their positions are more physically oriented (e.g., health technicians spend a good deal of time on their feet) or if these positions afford these workers the time and/or access to exercise compared to other occupation groups (e.g., teachers have access to the school gym). Nonetheless, others have found that workers with job-characterizing demands (including shift work and physical strain) are more sedentary compared to workers who are more autonomous.³⁹ Blue collar workers report low levels of physical activity,²⁸ which do not directly relate to the amount of time spent working.⁴⁰ In addition, blue collar occupations may be more difficult to target for physical activity intervention due to intra-individual, interpersonal, and bureaucratic norms.^41–43 For example, a farm operator may work alone in an isolated rural location that lacks access to convenient exercise facilities. Secretaries may not feel empowered to leave their work place during the day to exercise without an environment that fosters health and wellness.

Given the beneficial effect that CVF, possibly independent of obesity,^30;44;45 has on reducing the risk of CAD/CVD, diabetes, cardiometabolic syndrome, and all-cause mortality,^46–50 employer awareness of this population-based assessment by occupation is of paramount importance to foster improved worksite wellness and health promotion activities.³ Increasing CVF, and the expected concomitant weight loss, may also augment the quantity of work performed, reduce the amount of extra effort required to perform the job, and improve indicators of presenteeism, although this area of investigation has been relatively unstudied.⁵¹ In addition, obese workers have been shown to be at greater risk for worksite traumatic injuries,⁵² hence improved CVF could indirectly counter this problem as well. Having a moderate to high level of CVF, while it may not directly translate into lower levels of absenteeism, would reduce the incidence and prevalence of many chronic diseases, and therefore any worksite wellness program should contain elements focused on improving CVF levels related to the known health benefits.⁵³ Additionally, modifiable risk factors, such as depression, hyperglycemia, obesity, hypertension, and a sedentary lifestyle, are related to higher employer health care expenditures,⁵⁴ and these factors are directly counteracted by improving CVF levels. Therefore, continued efforts at increasing the levels of CVF in the American workforce are critically important to curtail the effects of the various epidemics of chronic disease in the United States.

In summary, these data suggest that levels of CVF are varied among the United States working population. Some occupation categories require strategies to improve CVF levels more than others, while taking into account the type of job and the demands and constraints related to the organization. Additional studies that look at the combined effects of CVF, measures of body composition, and increasingly prevalent morbid conditions, including cardiometabolic syndrome, may provide employers with better approaches to reduce the risk of CAD/CVD, diabetes, and other related complications that are known to be counteracted by increasing CVF. Future work can examine whether longitudinal changes in CVF mediate the risk of these diseases within occupation groups.