Work-Related Effects of Heat, Activity, and Fat in Middle Aged Men
Condition: Obesity; Gender; Problem of Aging
Study type: Observational

Summary: 
      Obesity is associated with many undesirable health effects and disease, and middle age is
      associated with increased risk for disease. Unfortunately, while others have looked at the
      effects of obesity, gender, and middle age, the combined effects of obesity and middle age on
      men's ability to do work in hot industrial environments have not been satisfactorily
      investigated.

      This small study evaluates the heat tolerance of lean and obese middle aged men both while
      exercising and resting and the ways in which each compensate for and dissipate increasing
      environmental heat and heat generated by the body while exercising.

      As obesity is a worldwide public health crisis and as populations in many industrialized
      nations age, it is important to understand the combined effects of obesity and middle age for
      men on their ability to safely work in hot environments. Such information will permit
      establishing and revising of safe work standards and inform public health outreach to the
      target population, itself.
    

Detailed description: 
      The present study was initially approved by and conducted at The Pennsylvania State
      University in 1972 for the senior author's (Rodger J McCormick) D.Ed. thesis in Biological
      Sciences; funding support was provided by the US National Institute of Arthritis, Metabolism,
      and Digestive Diseases Grant AM-08311 and National Institutes of Health Grant 01748. Data
      re-analysis and representation of that study was first approved in 2011 by and conducted at
      the FSRG deGruyter-McKusick Institute of Health Sciences for partial fulfillment of an MS in
      Clinical and Applied Physiology being pursued by the junior author (Mikaela I Poling). No
      funding was received for this use of existing data.

      Importance of Present Study:

      Several heat tolerance studies, including Kenny, Gagnon, Dorman, Hardcastle, and Joy (2010),
      have indicated that middle-age men can perform hard work in hot environments nearly as well
      as younger men. Dufour and Candas (2007), in comparing passive heat responses and sudomotor
      function in young, middle aged, and older men, found only local, not global, decreases in
      sweat gland output in the two older groups, suggesting at least some significant preservation
      of sudomotor function. Since most studies employed subjects with lean normal body types,
      their results in terms of physiological reactions to heat stress may not be applicable to
      obese middle aged men. Other studies have demonstrated degraded heat stress exercise capacity
      in obese persons.

      Within high heat stress areas such as in the steel, fiberglass, aluminium, mining,
      professional sports, and defense industries, lean and obese middle aged men can readily be
      observed performing the same work task in the same hot environment. Little attention has been
      given to differences between the lean and obese middle aged men in their physiological
      responses to the combination of internal heat production from the work task performed and the
      heat load imposed from the external environment.

      In the present study, occupational heat stress endurance differences between lean and obese
      middle aged men and effect of obesity are investigated under laboratory simulated conditions
      to test the following hypotheses: (1) with greater baseline cardiovascular demands, it is
      expected that obese middle aged men will have reduced environmental heat tolerance and will
      gain and store more total heat; (2) poorer environmental heat tolerance of obese middle aged
      men will be greatly magnified by work (producing added metabolic heat); (3) lean middle aged
      men will thermoregulate well; (4) lean middle aged men will show few, if any, major signs of
      inability to compensate for added cardiovascular demands; (5) obese middle aged men will be
      functioning at a higher percentage of their maximal ventilation of expired oxygen; and (6)
      obese middle aged men will have poorer pulmonary fitness, as measured by maximal ventilation
      of expired oxygen, than lean middle aged men.
    

Intervention name(s): Cardiopulmonary Exercise Stress Test; Climatic-Controlled Cardiopulmonary Exercise Stress Test; Body Composition Evaluation; Pre-Exercise Risk Assessment
Intervention type(s): Procedure; Procedure; Procedure; Procedure
Intervention description(s): Test preceded by warm-up treadmill walking 5 min at 4.8 km/h, 5% grade with a 1 min sitting rest period. Test, then, begins at 4.8 km/h, 2.5% grade with incremental grade increases every 2 min until exhaustion. Ambient environment is maintained at neutral, with effective temperature of 19-21° C. Heart, lungs, temperature, and sweating is monitored during testing.; Test includes 30 min walking bouts on the treadmill, with two 5 min sitting rest periods between bouts (Rest I and Rest II) and 15 min sitting recovery period (Rest III), in effective temperatures of 21.1 (baseline), 26.7, 29.4, 32.2, and 35.0° C. Heart, lungs, temperature, and sweating is monitored during testing.; Multiple methods are used to accurately estimate percentage of body mass (weight) composed of fat, muscle, bone, and other connective tissues. Four different methods, including caliper and hydrostatic (underwater weighing) are used in this study to ensure an accurate estimation.; Includes non-invasive measurements of body functioning, a physical examination by a physician, and blood and urine testing to select subjects who can exercise with relative safety.
Other intervention name(s): Progressive Exercise Test; Graded Exercise Test; Stress Test; Environmental Chamber Exercise Test; Pre-Participation Examination
Observational model: Case-Control
Time perspective: Prospective
Sampling method: Non-Probability Sample
Study population: 
        Lean and obese middle aged men unaccustomed to working in hot industrial conditions
      
Keywords: heat stress response; cardiopulmonary exercise test; men; middle aged; heat-shock response