Effect of Work-To-Rest Cycles on Cardiovascular Drift and Maximal Oxygen Uptake During Heat Stress

dc.contributorRichardson, Mark T
dc.contributorWind, Stefanie A
dc.contributor.advisorWingo, Jonathan E.
dc.contributor.authorMulholland, Anne
dc.contributor.otherUniversity of Alabama Tuscaloosa
dc.date.accessioned2022-04-13T20:33:54Z
dc.date.available2022-04-13T20:33:54Z
dc.date.issued2020
dc.descriptionElectronic Thesis or Dissertationen_US
dc.description.abstractCardiovascular (CV) strain, indexed as CV drift—a progressive increase in heart rate (HR) and decrease in stroke volume (SV) during prolonged exercise—is exacerbated by environmental heat stress and is accompanied by a decrease in maximal work capacity (V?O2max). To attenuate CV strain, work:rest ratios have been recommended by the National Institute for Occupational Safety and Health (NIOSH). Whether these guidelines sufficiently mitigate CV drift and preserve V?O2max is unknown. PURPOSE: To test the hypothesis that during moderate work (201-300 kcal/h) in hot conditions [indoor wet-bulb globe temperature (WBGTin)=29 °C] utilizing the recommended 45:15 work:rest ratio, CV drift will ‘accumulate’ over time, and the magnitude of accumulated CV drift will be proportional to decrements in V?O2max after 120 min. METHODS: Eight subjects [5 women; (mean±SD) age=25±5 y; body mass=74.8±11.6 kg; V?O2max=42.9±5.6 mL/kg/min] completed 3 sessions on different days. The first visit involved measurement of V?O2max (WBGTin=18.1±1.2 °C). The following 2 experimental trials were counterbalanced (WBGTin=29.0±0.6 °C). Moderate work was achieved by 2.5 min of arm curls (4.5 kg at 20/min) and 20 min of walking (V?O2=1.0–1.1 L/min) on a treadmill, repeated once for a total of 45 min of work, and then followed by 15 min of seated rest. HR and SV were measured at 15 and 45 min of each work bout to evaluate CV drift. The 120-min trial consisted of 2 full work-rest cycles followed by measurement of V?O2max; the 15-min trial replicated the first 15 min of the 120-min visit followed by measurement of V?O2max and was necessary to measure V?O2max before CV drift occurred. RESULTS: CV drift accumulated between 15 and 105 min: HR increased 16.7% (18±9 bpm, P=0.004) and SV decreased 16.9% (-12.3±5.9 mL, P=0.003), but V?O2max was not affected after 2 full work-rest cycles (P=0.14). Core body temperature increased by 0.5±0.2 °C (P=0.006) over 2 h. CONCLUSION: Although CV drift occurred after two 45:15 work:rest cycles, V?O2max was unaffected. Work capacity is preserved during 2 hours of work in the heat with rest cycles patterned like those in this study, but CV and thermal strain persist unabated.en_US
dc.format.mediumelectronic
dc.format.mimetypeapplication/pdf
dc.identifier.otherhttp://purl.lib.ua.edu/182067
dc.identifier.otheru0015_0000001_0004220
dc.identifier.otherMulholland_alatus_0004M_14231
dc.identifier.urihttps://ir.ua.edu/handle/123456789/8399
dc.languageEnglish
dc.language.isoen_US
dc.publisherUniversity of Alabama Libraries
dc.relation.hasversionborn digital
dc.relation.ispartofThe University of Alabama Electronic Theses and Dissertations
dc.relation.ispartofThe University of Alabama Libraries Digital Collections
dc.rightsAll rights reserved by the author unless otherwise indicated.en_US
dc.subjectcardiovascular drift
dc.subjectheat stress
dc.subjectmaximal oxygen uptake
dc.subjectVO2max
dc.subjectwork rest ratios
dc.titleEffect of Work-To-Rest Cycles on Cardiovascular Drift and Maximal Oxygen Uptake During Heat Stressen_US
dc.typethesis
dc.typetext
etdms.degree.departmentUniversity of Alabama. Department of Kinesiology
etdms.degree.disciplineKinesiology
etdms.degree.grantorThe University of Alabama
etdms.degree.levelmaster's
etdms.degree.nameM.A.
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