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Occupational Physiology

Occupational Physiology. Hardianto Iridiastadi, Ph.D. Aerobic Capacity. Definition Highest oxygen uptake an individual can attain (VO 2 max) Also known as maximal aerobic power Power = energy available / unit of time Measurement Douglas bag 1 liter O2 ~ 4.7 – 5.05 kcal

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Occupational Physiology

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  1. Occupational Physiology Hardianto Iridiastadi, Ph.D.

  2. Aerobic Capacity • Definition • Highest oxygen uptake an individual can attain (VO2 max) • Also known as maximal aerobic power • Power = energy available / unit of time • Measurement • Douglas bag • 1 liter O2 ~ 4.7 – 5.05 kcal • Metabolic analyzer

  3. Aerobic Capacity From National Institute for Occupational Safety and Health. (1981). A Work Practices Guide for Manual Lifting, Technical Report No. 81-122. Cincinnati, OH: U.S. Department of Health and Human Services (NIOSH) Fig 4.1

  4. Aerobic Capacity • NIOSH (1981) • Male: 15 kcal/min (~3 l/min) • Female: 10.5 kcal/min (~2.1 l/min)

  5. Aerobic Capacity

  6. Aerobic Capacity –Maximal Test • Max (direct) method • Begin at low level • Increase workload until VO2max is reached • Increase in workload does not increase VO2 • Occurs at max HR (~220-age) • Extreme dangers inherent to this method (push systems to their limit • Cannot perform on at risk persons

  7. Aerobic Capacity – Sub Maximal Test • Indirectly measure the maximum aerobic capacity – less fatiguing and less dangerous, but much less accurate • Method assumes a linear relationship between heart rate and oxygen consumption (dot indicates rates) • If VO2 = f(HR), then HRmax -> VO2 max - > Emax

  8. Aerobic Capacity – Sub Maximal Test • Max heart rate (HR) could be predicted by Max HR = 220 – age, or = 206 – (0.62 x age), or = 190 – (0.62 x (age – 25)) Note, Max HR prediction • No strong scientific backgroud • Has errors (up to 10 bpm) • Not suitable for children

  9. Measuring Aerobic Capacity • Methods • Treadmill • Cycle ergometer • Step test, nomogram • Need to involve large muscle groups • Treadmill test • Higher (5 – 11%) AC for inclined treadmill • 7% greater than ergocycle

  10. Aerobic Capacity vs Demographics • Gender effect • No differences before puberty • Female ~ 65 – 75% of male’s • Age effect • Peak at 18 – 20 years of age • AC at 65 yo ~ 75% at 25 yo • Jobs • Lower AC among white collar employees

  11. Aerobic Capacity vs. Performance • High AC not neccessary for high performance, due to other factors: • Training • Experience • Psychological state • Techniques • AC can be increased for another 10 year via training

  12. Maximum Heart Rate • Concept: • Indirect measure of energy • Increased heart rate ~ increased energy production (assumed) • Direct measurement • Indirect Measurement • MaxHR = 206 - (0.62 x age) • MaxHR = 220 – age • MaxHR = 190 – 0.62(age – 25)

  13. Workload Assessments Should be based on capacity!

  14. Workload Assessment • Direct measurement • Calorimetric chamber • Indirect measurement • Rate of oxygen consumption (l/min) (representative of metabolic process)

  15. Workload Assessment • Indirect measurement • Heart rate (bpm) (linearly related to oxygen consumption) Note: Use HR/VO2 as indicator for static component of tasks

  16. Workload Assessment – Early Study • Recovery Heart Rate – Brouha Method • Measure HR 3 min after work • Measure HR at 30”, 90”, 150” (x 2) 3. Determine if recovery is sufficient, or if workload is excessive

  17. Workload Assessment – Early Study • Recovery Heart Rate – Brouha Method • If HR1 – HR3 ≥ 10, or if HR1, HR2, and HR3 all below 90, recovery is normal • If the average of HR1 over a number of recordings is ≤ 110, and HR1 – HR3 ≥ 10, workload is not excessive • If HR1 – HR3 < 10, and if HR3 > 90, recovery is inadequate

  18. Workload Assessment • Energy cost

  19. Workload Assessment • Energy cost (Kamalakannan et al, 2007) E-cost = -1967 + 8.58HR + 25.1HT + 4.5A – 7.47RHR + 67.8G E-cost: Energy cost (Watt) HR: Working heart rate (bpm) HT: Height (inch) A: Age (yrs) RHR: Resting heart rate (bpm) G: Gender (m = 0; f = 1) 1 Watt ~ 0.0143 kcal/min

  20. Workload Assessment • Energy cost (Keytel, 2005) E-cost = -55.0959 + (HR x 0.6309) + (W x 0.1988) + (A x 0.2017) E-cost: Energy cost (kJoule/min) HR: Working heart rate (bpm) W: Weight (kg) A: Age (yrs) 1 KJoule/min ~ 0.239 kcal/min

  21. Workload Assessments

  22. Workload Assessment • Energy cost (Indonesian, male) VO2 = -1.169 + 0.02HR – 0.035A + 0.019W (Adj.R2 = 78.1%) • VO2 = oxygen consumption (l/min) • HR = heart rate (bpm) • W = weight (kg) • A = age (20 – 40 yrs) • VO2max = 3.4± 0.55 l/min

  23. Workload Assessment • Energy cost (Indonesian, female) VO2 = -1.991 + 0.013HR + 0.024W (Adj.R2 = 63.6%) • VO2 = oxygen consumption (l/min) • HR = heart rate (bpm) • W = weight (kg) • A = age (20 – 40 yrs) • VO2max = 2.3 ± 0. 6/min ?

  24. Workload Assessment *20 – 30 years old %HRReserve (HRR) = 100% x (HRave – HR-rest)/(HRmax – HRrest)

  25. Workload Assessments From: Wickens (2004)

  26. Workload Assessments • Physical Activity Ratio (PAR) • Light – Less than 3 x resting energy • Heavy – About 6 to 8 x resting energy • Maximal – More than 9 x resting energy

  27. Workload Assessment • Borg’s Ratings of Perceived Exertion (RPE)

  28. Workload Assessments • Borg’s Category Ratio (CR) 10 0 - Nothing at all 0.5 - Extremely weak • - Very weak 3 - Moderate 5 - Strong 7 - Very strong 10 - Extremely strong

  29. Workload Assessments • Example (1) • Female • 30 years old • 157 cm • 55 kg • Working HR = 100 bpm • Resting HR = 65 bpm

  30. Workload Assessments • Example (2) • Male • Working for 5 years • 58 years old • 156 cm • 51 kg • Working HR = 112 bpm • Resting HR = 65 bpm

  31. Workload Assessments • Example (3) • Male • Working for 15 years • 60 years old • 158 cm • 55 kg • Working HR = 103 bpm • Resting HR = 62 bpm

  32. Fatigue • Concept • Workload > 30 – 40% of work capacity • Likely experienced at end of shift • Associated with • Tiredness, exhaustion, etc. • Impaired performance • Increased lactic acid; lower blood glucose • Lower job satisfaction and increased health risks • Could be due to other factors (motivation, poor health, etc.) • Experienced also due to static work • HR > 110 after 30 – 60 min of rest

  33. Fatigue • Short term • VO2 max • Long term • 33% max (8 hours); 25% max (conservative) • 60% max (1 hr/shift) • NIOSH • 1981: 3.5 kcal/min for 8 hrs acceptable by 99% of M, 50% of F, 75% of total • 1991: 3.1kcal/min if lifting from <30"; 2.2 kcal/min if lifting from >30" to ‘protect’ 50% of F and 99% of M

  34. Controls for Demanding Work • Engineering • Decrease load weights • Elevate low-lying loads • Reduce walk/carry distances • Control heat • Decrease frequencies • Seated work • Lifting aids, ...

  35. Controls for Demanding Work • Administrative • Work-rest schedules • productivity • acceptability • feasibility • length of rest breaks (many small better than few long breaks) • Team work • Fatigue Monitoring • productivity, discomfort surveys, HR monitoring • Worker Selection • compare capacity with job energy demands

  36. Controls for Demanding Work • Rest period R = (Ework – Erec)/(Ework – Erest) E ~ Oxygen consumption R: % of work time

  37. Controls for Demanding Work • Rest period = (PWC - Ejob) / (Erest – Ejob) Example PWC = 5 kcal/min Ejob = 6.5 kcal/min Erest = 1.5 kcal/min Rest = 30% of work duration

  38. Controls for Demanding Work • Adequate supply of water and sugar • Training (strength vs. endurance) • Max improvement 10 – 20% • Changes to training and work pace often not possible; rest is more feasible

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