Effect of Work-to-Rest Cycles on Cardiovascular Strain and Maximal Oxygen Uptake During Heat Stress

Details

• Personal Author:
  Mulholland AM ; Wingo JE ; Yoder HA
• Description:
  Cardiovascular drift-a progressive increase in heart rate (HR) and decrease in stroke volume (SV) during prolonged exercise-is exacerbated by heat stress and thermal strain, and often accompanied by a decrease in work capacity (indexed as maximal oxygen uptake [V.O2max]). To attenuate physiological strain during work in the heat, use of work:rest ratios is recommended by the National Institute for Occupational Safety and Health. The purpose of this study was to test the hypothesis that during moderate work in hot conditions, utilizing the recommended 45:15 min work:rest ratio would result in cardiovascular drift 'accumulating' over consecutive work:rest cycles and accompanying decrements in V.O2max. Eight people (5 women; (mean +/- SD) age = 25 +/- 5 y; body mass = 74.8 +/- 11.6 kg; V.O2max = 42.9 +/- 5.6 mL·kg-1·min-1) performed 120 min of simulated moderate work (201-300 kcal·h-1) in hot conditions (indoor wet-bulb globe temperature = 29.0 +/- 0.6 degrees C). Participants completed two 45:15 min work:rest cycles. Cardiovascular drift was evaluated at 15 and 45 min of each work bout; V.O2max was measured after 120 min. On a separate day, V.O2max was measured after 15 min under identical conditions for comparison before and after cardiovascular drift occurred. HR increased 16.7% (18 +/- 9 beats·min-1, p = 0.004) and SV decreased 16.9% (-12.3 +/- 5.9 mL, p = 0.003) between 15 and 105 min, but V.O2max was unaffected after 120 min (p = 0.14). Core body temperature increased 0.5 +/- 0.2 degrees C (p = 0.006) over 2 h. Recommended work:rest ratios preserved work capacity but did not prevent the accumulation of cardiovascular and thermal strain. [Description provided by NIOSH]
• Subjects:
  Cardiovascular System Heat Stress Disorders Hot Temperature Occupational Health Oxygen Safety Temperature Workload
• Keywords:
  Author Keywords: Cardiovascular Drift BMI Body Mass Index Cardiovascular Function Heart Rate Heat Stress Hot Environments Occupational Health And Safety Physical Exercise Temperature Effects Thermal Effects Work:rest Ratios Work Capacity

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• ISSN:
  1660-4601
• Document Type:
  Text
• Funding:
  Grant
• Genre:
  Journal Article
• Place as Subject:
  Alabama ; New Mexico ; OSHA Region 4 ; OSHA Region 6
• CIO:
  National Institute for Occupational Safety and Health (NIOSH)
• Topic:
  Workplace Safety & Health
• Location:
  North America
• Volume:
  20
• Issue:
  5
• NIOSHTIC Number:
  nn:20067093
• Citation:
  Int J Environ Res Public Health 2023 Mar; 20(5):4580
• Contact Point Address:
  Anne M. Mulholland, Department of Kinesiology, The University of Alabama, Tuscaloosa, AL 35487
• Email:
  ammulholland@crimson.ua.edu
• Federal Fiscal Year:
  2023
• Performing Organization:
  University of Alabama at Birmingham
• Peer Reviewed:
  True
• Start Date:
  20050701
• Source Full Name:
  International Journal of Environmental Research and Public Health
• End Date:
  20270630
• Collection(s):
  National Institute for Occupational Safety and Health
• Main Document Checksum:
  urn:sha-512:794a7d31440f56744dc6a9ce46a4faeef288e66e8eea9655977b51b2ba5fa75f0f2a1a338b6778f7d5dfdec28427f7bfc357de0553afae5728334e6fa6484abc
• Download URL:
  https://stacks.cdc.gov/view/cdc/231286/cdc_231286_DS1.pdf
• File Type:
  [PDF - 1.78 MB ]