Slide 1Slide 2Intermittent Work (Work/Rest Cycles)Task/Work AnalysisENERGY COST OF WORKAcceptable Job Energy ExpenditureMonitoring Fatigue Heart Rate RecoverySubjective ratings of perceived exertion (RPE) (Borg, 1960)Ratings for WorkWork EfficiencyIE 5531IE 553 Engineering of Human WorkDr. Andris FreivaldsClass #27IE 5532IE 553 Engineering of Human WorkDr. Andris FreivaldsClass #27IE 5533Intermittent Work (Work/Rest Cycles)• Short, frequent W/R cycles are best• Self-paced work with spontaneous pauses• For prolonged work, VO2 should be at steady state412 WIE 5534Task/Work Analysis•Basic requirements for a job/task:–Energy exp < VO2max –Fatigue threshold (?)•Repeatable task–Eave = (Ew×Tw + Er×Tr)/(Tw+Tr)–Ew = [Eave(Tw+Tr) - Er×Tr]/TwIE 5535ENERGY COST OF WORKIE 5536Acceptable Job Energy Expenditure•Recommended physical work capacity: –ERPWC = VO2max/3 –uniform work best, –excursions make worse–static worse than dynamic–large muscles better than localized loading•For jobs exceeding RPWC:–Rest allocation or work/rest cycling–Tr = T(Ew - ERPWC) (Ew - Er)IE 5537Monitoring Fatigue Heart Rate Recovery•Brouha guidelines•Measure HR at:–0.5→1 min (HR1)–2.5→3 min (HR2)•Acceptable work if:–HR1 < 110/min –HR1 – HR2 ≥ 20/min•Work pulse < 40 /min •Avoid heart rate creep•Short, frequent work-rest cyclesIE 5538 Subjective ratings of perceived exertion (RPE) (Borg, 1960)IE 5539Ratings for WorkRating (AIHA)Energy (kcal/min)Heart Rate (/min)BorgLight < 2.5 < 90 < 9Moderate < 5.0 < 110 < 11Heavy < 7.5 < 130 < 13Very heavy < 10 < 150 < 15Extreme > 10 > 150 > 15IE 55310Work Efficiency•Gross efficiency (%) = WorkOut/E × 100•Net eff. (%) = WorkOut/(E-BMR) ×
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