Occupational Physiology
Hardianto Iridiastadi, Ph.D.
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
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
Aerobic Capacity
• NIOSH (1981)
– Male: 15 kcal/min (~3 l/min)
– Female: 10.5 kcal/min (~2.1 l/min)
Aerobic Capacity
Peneliti
Responden
10 orang
mahasiswa pria
(usia 17-23 tahun)
10 orang
Rakhmaniar
mahasiswa wanita
(2007)
(usia 19-22 tahun)
16 orang pekerja
Satriawan
industri pria
(2008)
(usia 20–25 tahun)
15 orang pekerja
Soleman
industri wanita
(2009)
(usia 20–25 tahun)
Widyasmara
(2007)
Yadi
(2009)
30 orang TNI AU,
AD, dan Polisi
(usia 19-25 tahun)
Nilai Konsumsi Oksigen
VO2max = 2,64 liter/menit (SD = 0,51)
VO2’ max = 42,42 ml/menit/kg (SD = 7,25)
VO2max = 1,89 liter/menit (SD=0,27)
VO2’ max = 33,63 ml/menit/kg (SD = 3,30)
VO2max = 3,7 liter/menit (SD = 0,55)
VO2’max = 65,11 ml/menit/kg (SD =
9,447)
VO2max = 2,5 liter/menit (SD = 0,69)
VO2’ max = 52,84 ml/menit/kg (SD =
15,58)
VO2max = 4,5 liter/menit (SD = 0,67)
VO2’ max = 71,4 ml/menit/kg (SD = 10,63)
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
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
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
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
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
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
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)
Workload Assessments
Should be based on
capacity!
Workload Assessment
• Direct measurement
– Calorimetric chamber
• Indirect measurement
– Rate of oxygen consumption (l/min)
(representative of metabolic process)
Workload Assessment
• Indirect measurement
– Heart rate (bpm)
(linearly related to oxygen consumption)
Note:
Use HR/VO2 as indicator for static component of
tasks
Workload Assessment – Early Study
• Recovery Heart Rate – Brouha Method
1. Measure HR 3 min after work
2. Measure HR at 30”, 90”, 150” (x 2)
3. Determine if recovery is sufficient, or if
workload is excessive
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
Workload Assessment
• Energy cost
Sleeping
1.3 kcal/min
Standing
2.3
Assembly
3.9
Welding
3.4
Stockroom
4.2
Chopping
wood
8.0
Athletic
10.0
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
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
Workload Assessments
Astuti
(1985)
Keytel
(2005)
Rakhmaniar
(2007)
Kamalakannan
et al.
(2007)
Persamaan
Y = 1,8041 – 0,229038 X + 4, 71733 . 10 -4 . X2
Y = energi (kkal/menit)
X = denyut jantung (denyut/menit)
EE = -20,4022 + (0,4472 HR) – (0,1263 w) + (0,074 A)
EE = pengeluaran energi, HR = denyut jantung (denyut/menit)
w = berat badan (kg), A = usia (tahun)
Y = 0,014 HR+ 0,017 w– 1,706
Y = konsumsi oksigen (liter/menit)
HR = denyut jantung (denyut/menit), w = berat badan (kg)
MWR = -1967 + 8.58 HR + 25.1 HT + 4.50 A – 7.47 RHR + 67.8
G
MWR = metabolic work rate (W)
HR = denyut jantung bekerja (denyut/menit)
HT = tinggi badan (inchi), A = usia (tahun)
RHR = denyut jantung istirahat (denyut/menit)
G = 1 untuk wanita, 0 untuk pria
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
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 ?
Workload Assessment
Workload*
Heart Rate (bpm)
Light
- 90
Moderate
90 – 110
Heavy
110 - 130
Very heavy
130 -150
Extremely heavy
150 - 170
*20 – 30 years old
%HRReserve (HRR) =
100% x (HRave – HR-rest)/(HRmax – HRrest)
Workload Assessments
Kategori Pekerjaan
Pengeluaran Energi
(kkal/menit)
Light
< 2.5
Moderate
2.5 – 5
Heavy
5 – 7.5
Very heavy
7.5 – 10
Extremely heavy
> 10
From: Wickens (2004)
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
Workload Assessment
• Borg’s Ratings of
Perceived Exertion
(RPE)
Ratings
6
7.5
9
11
13
15
17
19
20
Description
No exertion at all
Extremely light
Very light
Light
Somewhat hard
Hard (Heavy)
Very hard
Extremely hard
Maximal exertion
Workload Assessments
• Borg’s Category Ratio (CR) 10
0
0.5
1
3
5
7
10
-
Nothing at all
Extremely weak
Very weak
Moderate
Strong
Very strong
Extremely strong
Workload Assessments
• Example (1)
–
–
–
–
–
–
Female
30 years old
157 cm
55 kg
Working HR = 100 bpm
Resting HR = 65 bpm
Workload Assessments
• Example (2)
–
–
–
–
–
–
–
Male
Working for 5 years
58 years old
156 cm
51 kg
Working HR = 112 bpm
Resting HR = 65 bpm
Workload Assessments
• Example (3)
–
–
–
–
–
–
–
Male
Working for 15 years
60 years old
158 cm
55 kg
Working HR = 103 bpm
Resting HR = 62 bpm
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
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
Controls for Demanding Work
• Engineering
–
–
–
–
–
–
–
Decrease load weights
Elevate low-lying loads
Reduce walk/carry distances
Control heat
Decrease frequencies
Seated work
Lifting aids, ...
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
Controls for Demanding Work
• Rest period
R = (Ework – Erec)/(Ework – Erest)
E ~ Oxygen consumption
R: % of work time
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
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