Clinical Trial: Work-Related Effects of Heat, Activity, and Fat in Middle Aged Men

Study Status: Completed
Recruit Status: Completed
Study Type: Observational

Official Title: Relationship of Occupational Heat Stress Endurance, Work, and Percentage of Body Fat in Middle Aged Men

Brief 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 Summary:

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 th
Sponsor: Freeman-Sheldon Research Group, Inc.

Current Primary Outcome:

• Core (Rectal) Temperature Change with Exercise Level and Increased Heat Load [ Time Frame: Evaluated during each session at rest and while exercising, with sessions lasting approximately 165-170 min ]
  Failure to maintain rectal temperature within 0.15° C of subject baseline for interval from end of exercise Bout 2 to Bout 3.
• Oxygen Consumption Change with Exercise Level and Increased Heat Load [ Time Frame: Evaluated near the end of Exercise Bout 1 (2 min) and 3 (2 min) ]
  Oxygen consumption, measured by ventilation of expired oxygen, is used as a measure of physiological strain imposed by metabolic needs during exercise and exaggerated by obesity.
• Heart rate Change with Exercise Level and Increased Heat Load [ Time Frame: Evaluated during each session at rest and while exercising, with sessions lasting approximately 165-170 min ]
  Increased heart rate, measured electrocardiographically, is used as an index of cardiovascular strain imposed by needs during exercise and exaggerated by obesity.
• Difference in Routine and Maximal Ventilation of Expired Oxygen at Neutral Ambient Temperature [ Time Frame: Cardiopulmonary Stress Test, during the last 1 min of warm-up and at end of progressive portion as volitional exhaustion approached ]
  Warm-up approximates steady, normal work, while the progressive portion of the text places maximal metabolic burden on the subject in order to measure upper limit of heart and lung function

Original Primary Outcome: Same as current

Current Secondary Outcome:

• Perceived Exertion Change with Exercise Level and Increased Heat Load [ Time Frame: Evaluated during each session at rest and while exercising, with sessions lasting approximately 165-170 min ]
  Increased perceived exertion is used as an index of fatigue, an indirect indicator of physiological strain.
• Non-Invasive Arterial Blood Pressure Change with Exercise Level and Increased Heat Load [ Time Frame: Evaluated at rest before exercise (20-25 min) and at Rest I (5 min), II (5 min), and III (15 min) ]
  Increased non-invasive arterial blood pressure rate is used as an index of cardiovascular strain imposed by needs during exercise, is an important indicator of possible onset of shock, and exaggerated by obesity.
• Heart Rhythm Change with Exercise Level and Increased Heat Load [ Time Frame: Evaluated during each session at rest and while exercising, with sessions lasting approximately 165-170 min ]
  Heart rhythms, monitored by electrocardiograph, are used as an index of cardiovascular strain imposed by needs during exercise and could be exaggerated by obesity.
• Metabolic Rate Change with Exercise Level and Increased Heat Load [ Time Frame: Evaluated near the end of Exercise Bout 1 (2 min) and Bout 3 (2 min). ]
  Rate of energy usage of the body calculated from ventilation of expired oxygen values
• Heat Load Change with Exercise Level and Increased Environmental Temperature [ Time Frame: During Rest I (5 min), II (5 min), and III (15 min) ]
  Calculated metabolic and environmental heat gain minus heat loss

Original Secondary Outcome: Same as current

Information By: Freeman-Sheldon Research Group, Inc.

Dates:
Date Received: August 19, 2015
Date Started: June 1972
Date Completion:
Last Updated: August 23, 2015
Last Verified: August 2015