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Int Arch Occup Environ Health (2016) 89:211–220
DOI 10.1007/s00420-015-1064-8
ORIGINAL ARTICLE
Measured by the oxygen uptake in the field, the work of refuse 
collectors is particularly hard work: Are the limit values 
for physical endurance workload too low?
Alexandra M. Preisser1 · Linfei Zhou1 · Marcial Velasco Garrido1 · Volker Harth1 
Received: 9 December 2014 / Accepted: 3 June 2015 / Published online: 19 June 2015 
© The Author(s) 2015. This article is published with open access at Springerlink.com
Conclusion HR as well as the measurement of VO2 can 
be valuable tools for investigating physiological workload, 
not only under laboratory conditions but also under normal 
working conditions in the field. Both in terms of absolute 
and relative HR and oxygen consumption, employment as 
a refuse collector should be classified in the upper range of 
defined heavy work. The limit of heavy work at about 33 % 
of the individual maximum load at continuous work should 
be reviewed.
Keywords Oxygen uptake · Physically heavy work · 
Mobile spiroergometry · Relative heart rate · Waste 
collectors · Endurance work
Introduction
The organized collecting of waste is essential for a func-
tioning community; however, there is no explicit job quali-
fication connected with, and the work of garbage collec-
tors receives little scientific attention. Collecting waste 
is described as physically demanding work and as being 
the cause of various physical disorders with respiratory, 
gastrointestinal, and musculoskeletal symptoms (Kuijer 
and Frings-Dresen 2004; Kuijer et al. 2010). This work is 
regarded as a benchmark for “particularly heavy” work. 
The definition of “heavy work” is based so far only on the 
assumption that the endurance limit is 30 % respectively 
33 % of the maximum load capacity, taking into account 
load peaks, manual work, and harmful temperatures 
(Ilmarinen et al. 1991; Rutenfranz et al. 1976). The deter-
mination of an “upper limit” is essential for defining the 
“reasonableness” of a work—in the sense of the absence of 
excessive risks to health. There are presently also no indi-
cations, showing how the physical performance is with this 
Abstract 
Purpose Collecting waste is regarded as a benchmark for 
“particularly heavy” work. This study aims to determine 
and compare the workload of refuse workers in the field. 
We examined heart rate (HR) and oxygen uptake as param-
eters of workload during their daily work.
Methods Sixty-five refuse collectors from three task-
specific groups (residual and organic waste collection, and 
street sweeping) of the municipal sanitation department 
in Hamburg, Germany, were included. Performance was 
determined by cardiopulmonary exercise testing (CPX) 
under laboratory conditions. Additionally, the oxygen 
uptake (VO2) and HR under field conditions (1-h morning 
shift) were recorded with a portable spiroergometry system 
and a pulse belt.
Results There was a substantial correlation of both abso-
lute HR and VO2 during CPX [HR/VO2 R 0.89 (SD 0.07)] 
as well as during field measurement [R 0.78 (0.19)]. Com-
pared to reference limits for heavy work, 44 % of the total 
sample had shift values above 30 % heart rate reserve 
(HRR); 34 % of the individuals had mean HR during work 
(HRsh) values that were above the HR corresponding to 
30 % of individual maximum oxygen uptake (VO2,max). All 
individuals had a mean oxygen uptake (VO2,1h) above 30 % 
of VO2,max.
Alexandra M. Preisser and Linfei Zhou are equally contributing 
first authors.
 * Alexandra M. Preisser 
 
a.preisser@uke.de
1 
Institute for Occupational and Maritime Medicine 
(ZfAM), University Medical Center Hamburg-Eppendorf, 
Seewartenstrasse 10, 20459 Hamburg, Germany
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1 3
heavy work with increasing age. An assessment is required 
in order to meet the challenges of demographic change in 
industrialized countries. Only few studies have investi-
gated in detail the refuse collectors in different countries 
with different tasks. Up to now, the heart rate (HR) is used 
as an indirect indicator of the physiological workload, for 
example in the Netherlands (Kemper et al. 1990), Japan 
(Tsujimura et al. 2012), and Brazil (Anjos et al. 2007). The 
oxygen uptake (VO2), as a direct measure of the metabolic 
processes, however, was mostly estimated via HR in these 
groups. So far, the VO2 of refuse collectors was determined 
only once by means of simulation in the laboratory (Kem-
per et al. 1990; Frings-Dresen et al. 1995). The relation 
between HR and VO2 has not yet been specified under field 
conditions. This may be due to the fact that the measure-
ment of oxygen uptake with a breathing mask for outdoor 
work in this occupation group is technically particularly 
challenging. In our view, however, the conclusion of HR 
on VO2,max requires a review. To our knowledge, there are 
no recent studies with refuse collectors, who were investi-
gated during their daily work with portable spiroergometry 
to determine the real oxygen uptake.
This paper is based on a study about the physiological 
workload of 65 employees from three task-specific groups 
[residual waste collection (RWC), organic waste collection 
(OWC), and street cleaning (SC)] of a municipal sanita-
tion department in Germany. Our aim was to categorize the 
respective workload of these professions under real work-
ing conditions as a contribution to the development of a 
classification of workload in occupational health research. 
To evaluate the methods in the field of measurement, we 
also conducted comparisons of the methods of workload 
measurement. For this purpose, HR and oxygen uptake 
were determined in field measurements. For comparison, 
we measured the oxygen uptake by a stationary cycle car-
diopulmonary exercise test (CPX).
Methods
The study group consisted of 65 subjects (62 males and 
3 females), aged between 25 and 60, all employees in the 
municipal sanitation department in Hamburg, Germany. All 
participants volunteered and were granted compensatory 
time off by the employer. Before the start of the investiga-
tions, there was no selection of participants. The anthropo-
metric characteristics of the subjects (Table 1) are repre-
sentative in age and sex of the 1544 employees [46.5 (SD 
8.6) years; 98 % male) working in refuse collecting in this 
sanitation department. The examined employees were sub-
divided by their occupational tasks into three groups: RWC 
(n = 35), OWC (12), and SC (18). These jobs are mainly 
performed by male employees, although there are a few 
females in street sweeping in Hamburg. There were three 
women in the last group. The Declaration of Helsinki has 
been adequately addressed, and written informed consent 
was obtained from all participants. The study was approved 
by the Ethics Committee of the Hamburg Medical Associa-
tion (register number PV4524).
Elements of investigation were specific questioning and 
physical examination (regarding occupation, symptoms, 
and disorders according to body functions). Furthermore, 
spirometry, body plethysmography (MasterScreen™ Body 
by JAEGER™/CareFusion, Hoechberg, Germany), and 
CPX were performed with 61 subjects. Four persons were 
excluded due to cardiorespiratory risk factors.
Table 1  Characteristics of study participants
SD Standard deviation, BMI body mass index, RWC residual waste collectors, OWC organic waste collectors, SC street cleaners, Allfield subjects 
submitted to field measurement with portable spiroergometric system
Founded significant differences between a male/female; b RWC/SC; c OWC/SC, d OWCfield/allfield, and e SCfield/allfield. The first four differences 
can be explained by the inclusion of women in the SC group, the latter not
N
Female
Age (years)
Height (m)
Weight (kg)
BMI (kg/m2)
Mean
SD
Mean
SD
Mean
SD
Mean
SD
All
65
3
45.6
8.3
177.7
7.6
89.7
14.7
28.3
3.8
Male
62
45.5
8.4
177.0a
8.3
88.7a
15.3
28.2
3.9
Female
3
3
43.1
11.5
162.0
9.6
65.7
7.4
25.2
4.3
RWC
35
–
47.3b
7.0
179.1
7.4
92.5
15.5
28.8
4.0
OWC
12
–
46.7
8.3
177.8
5.3
94.3
12.8
30.0
4.0
SC
18
3
41.6
9.7
175.0
9.0
81.2b,c
11.1
26.5b,c
2.8
Allfield
13
2
49.7
6.7
174.8
9.3
87.1
15.9
28.3
4.0
RWCfield
5
–
51.1
4.0
178.6
11.5
88.6
12.5
27.6
1.2
OWCfield
3
–
50.4
6.3
175.7
3.8
103.0
14.5
33.4d
4.9
SCfield
5
2
47.8
9.6
170.6
9.0
76.0e
12.3
26.0
2.8
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Spirometry represents a measure of forced one-second 
capacity and vital capacity (FEV1, FVC) performed accord-
ing to the criteria of the American Thoracic Society (1995) 
with the calculation of FEV1/FVC. In addition, body ple-
thysmography determines the airways resistance as well as 
intrathoracic gas volume.
CPX was performed according to the recommendations 
of the German Society of Pneumology (Meyer et al. 2013) 
with 12-lead ECG monitoring on an electronically braked 
computer-controlled cycle ergometer (ergoselect 200p/
Ergoline Bitz, Germany) with a continuous increase in the 
load. This ramp-like protocol enables a precise determina-
tion of maximal aerobic and power output and the ventila-
tory threshold (VT) (Binder et al. 2008; Meyer et al. 2005). 
Performance and VO2 and carbon dioxide outputs (VCO2) 
were measured continuously (Oxycon Pro™ by JAE-
GER™/CareFusion, Hoechberg, Germany).
CPX was preceded by 2 min of sitting at rest. After a 
warm-up period of 2 min with an external workload of 
25 W, the exercise followed with an increase of 15–25 W/
min (Meyer et al. 2013) depending on the individual fit-
ness level. Subjects were verbally encouraged until they 
could no longer sustain the required crank frequency of 
60–70 rpm. Maximum oxygen uptake (VO2,max) was calcu-
lated as the average of the highest eight consecutive breaths 
in the final minute of exercise. The standard equations 
by Hansen et al. (1984), Reiterer (1975), and Wasserman 
et al. (2004) for VO2,max and maximal wattage (Pmax) were 
used for assessment. The VT corresponds to the first VT; 
it was determined with a combination of VCO2/VO2 slope 
and increase in minute ventilation (VE) relative to oxygen 
consumption (VE/VO2), ventilatory equivalent named. This 
first VT is defined by the increase in VE/VO2 without a 
concurrent increase in VE/VCO2 (Binder et al. 2008; West-
hoff et al. 2013).
Forty-one subjects were studied while working with 
long-term HR measurements (T31 coded transmitter, 
Polar Electro, Buettelborn, Germany) during a work shift 
(mean 6.7 h). From this group, 20 subjects (18 males and 
2 females) were also connected to mobile CPX (Oxycon 
Mobile by JAEGER™/CareFusion, Hoechberg, Germany) 
and to the HR monitoring system for an average of 1.3 h 
to measure the correlation between HR and oxygen uptake 
under field conditions (HRfield, VO2,field) (Fig. 1). The field 
measurement was started before the truck left the depot and 
thus recorded approximately 30 min of driving plus 1 h of 
sustained work. The actual HR and oxygen uptake under 
task-specific work were recorded during the following 1 h 
of continuous work (HR1h, VO2,1h). Part of the work of the 
garbage collectors is transporting two-wheeled waste con-
tainers (120 l volume) of houses and cellars and the shift of 
large four-wheeled waste containers (240 l) of storerooms. 
The path length of an entire work day was estimated with 
a pedometer and was about 7–10 km. All waste containers 
were emptied machine-supported into the truck (Fig. 2a, b, 
photographs with waste worker, spiroergo mask, and gar-
bage cans). Occasional waste bags were towed. SC con-
sisted of sweeping waste and leaves, sometimes wet leaves, 
as well as picking up trash. Due to malfunction of the 
measuring instruments, refusal, and changes in the organi-
zation, valid data were obtained for only 13 of 20 subjects. 
Ahead of the gas exchange measurements in the field 
via face mask, the mobile CPX unit was volume and gas 
calibrated. HR and oxygen uptake were both depicted in 
absolute values and relative to individuals’ maximum val-
ues (%HRmax, %VO2,max) and individuals’ values at the 
VT (%HRVT,  %VO2,VT). The difference to maximum val-
ues as “reserve values” (%HRR,  %VO2,R) was defined 
as: (HRwork − HRrest)/(HRmax − HRrest) × 100 %, and 
(VO2,work − VO2,rest)/(VO2,max − VO2,rest) × 100 %, respec-
tively. The HR and VO2 at rest (HRrest,VO2,rest) were calcu-
lated from the mean values in the first 2 min of the exercise 
test and the previously measured resting value.
Statistics
Data are presented as means and standard deviations (SD). 
To assess the equivalence of linear regression, mean val-
ues for Pearson correlation (R), intercept, and slope were 
Fig. 1  Flowchart of the measurements
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Int Arch Occup Environ Health (2016) 89:211–220
1 3
determined for each individual. Student’s t test and Wilcoxon 
test were used to determine whether the mean intercepts and 
slopes differed from 0 to 1, respectively, and to verify dif-
ferences between sample characteristics and differences 
from reference limits. All calculations were performed using 
IBM SPSS Statistics 22. For all statistical analyses, the null 
hypothesis was rejected at a probability of p < 0.05.
Results
The 65 subjects of the study group showed only low differ-
ences in age and in body mass within the total sample for 
RWC, OWC, and SC, respectively (Table 1). All 61 subjects 
who could participate in the CPX had normal ECG readings 
and took no HR-affecting drugs. On the basis of spirometry 
and body plethysmography, obstructive lung disease (FEV1/
FVC < 70 %) was observed in 21.5 % of subjects. All work-
ers diagnosed with pulmonary disorders were active or for-
mer smokers (35.4 and 43.1 % of total sample, respectively).
The results from HR measurement at work (HRsh) of 41 
subjects with an average work shift time of 6.7 h are shown 
in Table 2. Mean values of the total sample were 100.2 b/
min and 27.9 % HRR, respectively. The HRsh values rela-
tive to individuals’ HRmax and to HRVT (%HRmax, %HRVT) 
determined in the laboratory CPX showed that the OWC 
had the highest strain compared with the three subgroups 
(data not shown in detail).
HR recorded during one representative work hour 
(Table 3) showed a slightly higher mean HR1h of 109.2 b/
min and 45.1 % HRR, respectively, for the 13 subjects (for 
whom also the oxygen uptake was measured) than in the 
measurement over the whole work shift of the total sam-
ple. There were no significant differences between the 
groups OWC, RWC, and SC for 1 h of measurement. Mean 
HR values during 1 h as well as during a work shift were 
close to the HR at VT. Between HR1h and HRsh of these 
13 subjects, there was a mean correlation coefficient of R 
0.64. The regression of HR1h was slightly but significantly 
(p < 0.05) higher than HRsh by 10.6 b/min. During the one 
representative working hour (Table 3), the group mean 
achieved an oxygen uptake (VO2,1h) of 1103 ml/min. Here 
too, mean VO2 was close to VO2,VT. The groups did not dif-
fer significantly.
Fig. 2  a, b Refuse collector with spiroergo mask, equipment, and garbage cans
Table 2  Mean heart rate during a work shift (HRsh) of 6.7 h of n = 41, percentage of maximal heart rate (%HRmax), and heart rate at the ventila-
tory threshold (%HRVT) from CPX (values relative to heart rate reserve (%HRR))
RWC Residual waste collectors, OWC organic waste collectors, SC street cleaners
a Significant difference RWC/OWC
b Significant difference RWC/SC
N
Female
Mean HRsh (b/min)
HRsh,max (b/min)
%HRmax
%HRVT
%HRR,sh
Mean
SD
Mean
SD
Mean
SD
Mean
SD
Mean
SD
All
41
3
100.2
11.9
153.7
28.2
63.1
9.2
79.4
12.9
27.9
14.2
RWC
18
–
93.4a,b
11.8
150.6
30.5
58.3a,b
8.6
75.8
16.2
25.3
13.7
OWC
9
–
107.8
7.5
152.8
22.4
68.8
8.9
85.2
8.9
26.1
14.8
SC
14
3
103.9
9.9
158.2
29.8
65.7
7.4
80.1
9.1
32.5
14.2
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The results of CPX with measurement of VO2 of all 61 
participants and of the 13 subjects with field measured data 
are depicted in Tables 4 and 5. The three subgroups RWC, 
OWC, and SC do not differ significantly in this test with 
respect to Pmax, VO2,max, and HRmax (data not shown). The 
spiroergometric field measurements’ sample of 13 sub-
jects did not differ significantly from the whole group. A 
relationship between the maximal values from Pmax and 
VO2,max could be observed with mean correlation coeffi-
cient (R) of 0.88; HRmax was weakly correlated with age (R 
0.45). Therefore, older participants showed surprisingly a 
slight increase in HRmax with age (data not shown in detail). 
The individuals reached values close to age-predicted val-
ues with 95.6 % (SD 18.2) VO2,max/VO2,pred, and 90.8 % 
(SD 7.4) HRmax/HRpred, (Hansen et al. 1984; Reiterer 1975; 
Wasserman et al. 2004).
The linear regression analysis was accomplished to study 
the relationship between HR and VO2 for CPX and field meas-
urement. Data of HR and oxygen uptake during CPX create 
an individual linear heart/oxygen uptake relationship and a 
substantial correlation (mean R 0.89, p < 0.001). There was 
also a linear regression, with a mean correlation coefficient of 
Table 3  Average of heart rate (HR1h) and oxygen uptake (VO2,1h) during 1 h of work
HR1h and VO2,1h relative to maximal heart rate and maximal oxygen uptake during CPX (%HRmax; %VO2,max). HR1h and VO2,1h relative to heart 
rate and oxygen uptake at the ventilatory threshold (%HRVT; %VO2,VT). And values relative to heart rate reserve (%HRR)
RWC Residual waste collection, OWC organic waste collection, SC street cleaning, Allfield subjects submitted to field measurement with portable 
spiroergometric system
N
HR1h (b/min)
%HRR,1h
% HRmax
%HRVT
VO2,1h (ml)
%VO2,max
%VO2,VT
Mean
SD
Mean
SD
Mean
SD
Mean
SD
Mean
SD
Mean
SD
Mean
SD
Alla
field
13
109.2
12.5
45.1
18.9
71.1
11.5
86.7
17.2
1103
237.3
45.7
9.3
60.0
14.3
RWCfield
5
106.4
15.0
38.3
20.3
66.6
9.8
84.5
22.1
1160
137.0
42.9
5.8
57.8
15.1
OWCfield
3
106.5
9.1
32.7
12.7
67.2
13.5
82.4
14.3
1286
80.2
50.8
7.2
69.1
13.3
SCa
field
5
113.7
12.7
59.3
12.6
78.0
10.7
91.6
15.8
935
287.1
45.2
13.0
56.7
14.5
Table 4  Results of CPX tests
a The difference to Table 1 can be explained by the exclusion of four people due to cardiac disease or 
medication
N
Female
Pmax  
(W)
Pmax  
(W/kg)
VO2,max  
(ml)
VO2,max  
(ml/kg)
HRmax  
(b/min)
RERmax
Mean
SD
Mean
SD
Mean
SD
Mean
SD
Mean
SD
Mean
SD
All
61a
3
192.1
39.2
2.1
0.5
2623
571
29.2
6.4
158.9
14.3
1.27
0.12
Allfield
13
2
184.5
46.9
2.1
0.5
2458
562
28.4
5.5
155.2
14.1
1.26
0.13
RWCfield
5
–
200.0
17.0
2.3
0.2
2739
398
31.0
2.2
160.0
4.8
1.25
0.15
OWCfield
3
–
180.0
56.3
1.8
0.6
2562
372
25.2
4.6
162.0
27.2
1.22
0.28
SCfield
5
2
171.6
64.8
2.2
0.7
2113
682
27.7
7.8
146.2
6.4
1.28
0.06
Table 5  Heart rate (HRVT), power output (PVT), and oxygen uptake (VO2,VT) at ventilatory threshold (VT) from CPX tests [relative to maximal 
values from CPX (%Pmax, % VO2,max, %HRmax)]
RWC Residual waste collectors, OWC organic waste collectors, SC street cleaners, Allfield subjects submitted to field measurement with portable 
spiroergometric system
N
Female
P at VT (W)
VO2 at VT (ml)
HR at VT (b/min) %Pmax
%VO2,max
%HRmax
Mean
SD
Mean
SD
Mean
SD
Mean
SD
Mean
SD
Mean
SD
All
61
3
129.7
43.6
1843
498
125.1
15.3
66.9
16.3
70.3
11.8
79.0
9.3
Allfield
13
2
130.0
49.5
1914
549
128.4
15.8
69.2
12.6
77.1
8.0
82.9
8.4
RWCfield
5
–
143.0
43.1
2109
514
129.6
20.1
70.5
17.0
76.0
9.3
81.0
12.7
OWCfield
3
–
115.0
43.6
1908
400
131.3
19.3
63.1
4.4
74.0
4.5
81.3
2.4
SCfield
5
2
126.0
64.5
1723
684
125.4
11.7
71.6
12.0
80.0
8.6
85.7
5.9
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R 0.78 (p < 0.001) between HRfield and VO2,field. The equations 
obtained here were nearly the same; both regressions for CPX 
and field measurement are shown in Fig. 3a, b. The correlation 
between %HRR and %VO2,R during CPX was high (R 0.96). 
The correlation during field measurement was similar, albeit 
lower, (R 0.78, both p < 0.001) (Fig. 4a, b).
During the field measurement of continuous HRfield and 
VO2,field, a simultaneous increase and decrease in HR and 
oxygen uptake could be observed in each individual. In 
Fig. 5, a typical example is given of one subject.
Discussion
Relationship of HR to VO2 to determine the validity 
of measuring methods in the field
Heart rate increases linearly as a function of workload 
intensity and is closely related to oxygen uptake (Arts and 
Kuipers 1994; Gastinger et al. 2010). Nevertheless, the 
value of the HR/VO2 relationship can vary between indi-
viduals due to metabolic stress or physical training level 
and therefore should be ascertained individually (Skin-
ner et al. 2003). Similarly, interindividual differences are 
observed when CPX and field measurements during work 
are compared. To determine the physiological workload of 
physically demanding work, we investigated the relation 
between HR and oxygen uptake under field conditions. We 
could demonstrate that the HR/VO2 relationship was linear 
not just during the incremental cycle exercise test (CPX) 
but also in their usual working environment with climatic 
and other factors. Nevertheless, the range of the correla-
tion coefficients shows that HR is more strongly correlated 
to VO2 during CPX (R 0.89, p < 0.001) than during field 
measurement (R 0.78, p < 0.001) (Fig. 3a, b). Yet, there is 
0
20
40
60
80
100
120
140
160
180
200
220
0
500
1000
1500
2000
2500
3000
HR  [b/min]
VO2 [ml/min]
0
20
40
60
80
100
120
140
160
180
200
220
0
500
1000
1500
2000
2500
3000
HR [b/min]
VO2 [ml/min]
(a)
(b)
Fig. 3  Heart rate (HR) and oxygen uptake (VO2) during CPX with 
increasing workload by 15–25 W/min (a) and during spiroergo-
metric field measurement at work (b), for 13 subjects. a HR (b/
min) = 0.03 × VO2 (ml/min) + 70.95 (drawn trendline); R2 = 0.80; 
n = 426; p < 0.001. b. HR (b/min) = 0.03 × VO2 (ml/min) + 76.2 
(drawn trendline); R2 = 0.65; n = 2191; p < 0.001
-20%
0%
20%
40%
60%
80%
100%
120%
140%
-20%
0%
20%
40%
60%
80%
100%
%HRR
%VO2,R
-20%
0%
20%
40%
60%
80%
100%
120%
140%
-20%
0%
20%
40%
60%
80%
100%
%HRR
%VO2,R
(a)
(b)
Fig. 4  Heart rate as a percentage of heart rate reserve (%HRR) in 
relation to oxygen uptake as a percentage of oxygen uptake reserve 
(%VO2,R), determined during CPX (a) and field measurement (b), 
for 13 subjects. a %HRR = 0.925 × %VO2,R (ml/min) − 0.017; 
R2 = 0.93; n = 325; p < 0.001. b %HRR = 0.783 × %VO2,R (ml/
min) + 0.130; R2 = 0.68; n = 2146; p < 0.001
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a significant correlation between HR and VO2 in the field 
measurement, and furthermore, a congruent increasing and 
decreasing profile could be demonstrated (Fig. 5).
Due to different proportions between HR and VO2, 
a method based on heart rate reserve (%HRR) and VO2 
reserve (%VO2,R) is widely used for the comparison of rel-
ative values. Swain and Leutholtz (1997) and recent stud-
ies by Lounana et al. (2007) have shown that %HRR data 
at group level are consistent with %VO2,R. We aimed to 
find out whether this correlation can also be validated for 
our group in CPX and especially in spiroergometric field 
measurement under working conditions. For the incremen-
tal exercise testing, we can confirm a substantial correla-
tion of %HRR and %VO2,R with R 0.96 (p < 0.01) (Fig. 4a). 
For spiroergometric field measurement, we found a lower 
correlation of R 0.78 (p < 0.001). Both regressions show 
that %HRR does not overestimate %VO2,R as their inter-
cepts are close to 0 (Fig. 4b). Possible reasons for lower 
field correlations between HR and VO2 could be malfunc-
tioning in gathering the individual values, different load 
shapes, and the varyingly high intensity of physical strain 
of muscle groups with differing efficiency. During work as 
a refuse collector, especially arm work is performed, while 
the incremental cycle exercise consists mostly of legwork. 
A better equivalence between %HRR and %VO2,R for leg-
work than for arm work has been described by (Rotstein 
and Meckel 2000). Additionally, HR can be impaired by 
further factors, such as temperature, emotion, and physical 
fitness status (Achten and Jeukendrup 2003). We neverthe-
less could demonstrate an equivalence between absolute 
values of HR and VO2, and equally in relative calculations 
to HRR and VO2,R in dynamic work, even if it was meas-
ured in the field.
Fitness and workload capacity evaluated by various 
thresholds and aspects
Because the VT reflects the workload threshold beyond 
which endurance exercise will not lead to anaerobic 
metabolism, it can therefore be regarded as the upper limit 
of intensity during the endurance performance (Binder 
et al. 2008). The present study showed a high endurance 
performance for the entire sample during 1 h of work and 
also during the whole work shift, depending on the HR 
measurement with a mean of 86.7 % HRVT and 79.4 % 
HRVT, respectively. The percentage of VO2 during 1 h of 
work in percentage of VO2,VT was likewise, but lower, with 
a mean of 60 % VO2,VT. In Fig. 5, which shows a repre-
sentative measurement from the field tests, the subject’s 
HR well exceeded most of the time the individual HRVT. 
Similarly, VO2,VT was exceeded several times. For individ-
ual values relative to the VT (%HRVT, %VO2,VT), our data 
show that %HRVT may overestimate the real workload; 
%VO2,VT seems to be more realistic (see Table 5). Fur-
thermore, VT not only differs between individuals but also 
varies depending on the state of training and the type of 
exercise protocol (Faude et al. 2009). Therefore, the ques-
tion arises whether %HRVT is comparable to %VO2,VT. 
We would recommend to determine VT and likewise the 
HRVT and VO2,VT, by CPX in the laboratory. This will 
enable an accurate estimate of %VO2,VT during the field 
measurement.
Fig. 5  Case report: heart rate 
and oxygen uptake during field 
measurement (HRfield,VO2,field) 
of one subject. Individual maxi-
mal heart rate, maximal oxygen 
uptake (HRmax, VO2,max), 
and the values at ventilatory 
threshold (HRVT, VO2,VT) are 
also shown
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1 3
In our sample, the CPX results are close to the individual 
predicted and age-dependent values (Table 2). Kroidl et al. 
(2014) have described the requirements for high, normal, 
and pathological endurance performance, based on values 
at VT > 80 %, around 60 %, and <40 % of maximal val-
ues, respectively. In comparison, our subjects also reached 
performance levels in the upper range of normal endurance 
(Table 2). In the present study, workers show normal ranges 
of individual fitness. Long work periods with a high level 
of physical activity did not lead to an increase in maximal 
oxygen uptake, and only slightly better endurance perfor-
mance was observed in them. This seems to be compat-
ible with results from previous studies which also investi-
gated workers with heavy workload (Ilmarinen et al. 1991; 
Søgaard et al. 1996).
It is commonly suggested that 33–40 % of the indi-
vidual’s VO2,max should be the capable workload for 8 h 
of physical work (Åstrand et al. 2003; Ilmarinen 1992). 
But %VO2,max depends on the type of exercise performed. 
According to Kemper et al. (1990), the acceptable limit for 
refuse collecting work in particular, which mainly consists 
of arm work combined with legwork, should be at 30 % 
VO2,max for an 8-h shift. To describe the exercise intensity 
in our sample, we took HRsh at a given %VO2,max. This 
method is according to Skinner et al. (2003); they have 
demonstrated that once VO2,max and the relationship among 
HR and VO2 are known, the corresponding HR is a good 
estimate for relative workload. Taking the mean HR values 
of the 41 subjects in our study who had undergone HRsh 
measurement, there was a slight exceedance (mean HR 
100.2 b/min) of the standards of calculated mean HR value 
at 30 % VO2,max (96.6 b/min); ns). Here, 66 % of the indi-
viduals had mean HRsh values above 30 % VO2max. Frings-
Dresen and Kemper 1995, under laboratory conditions, 
showed that 33–59 % of the subjects, depending on the 
waste collector activity (bags, different container volumes), 
exceeded the 30 % of VO2max.
Comparing these results with the oxygen uptake of the 
13 individuals from the 1-h VO2 measurement, the means 
even exceeded the reference of 30 % VO2,max significantly 
(mean VO2,1h 1103 ml/min vs. calculated VO2 at 30 % 
VO2,max of 737.3 ml/min, p < 0.05). All subjects achieved 
a mean VO2, which was above the reference limit of 30 % 
VO2,max, with a total range of 35–69 % VO2,max. These 
results are consistent with the relation between HR1h and 
HRsh as the 1-h values were slightly but significantly higher 
than HRsh. Nevertheless, in both specifications (HR and 
VO2), very high values have been found, which reflects the 
high continuous work load of refuse collectors.
In general, exercises that are performed with a 
HRR > 30 % for an 8-h shift are assumed to be at high car-
diovascular load (Ilmarinen et al. 1991; Shimaoka et al. 
1998). With long-term HR measurement for a work shift of 
6.7 h, 39 % of residual waste collectors, 33 % of organic 
waste collectors, and 39 % of the street cleaners had 
%HRR,sh values that were higher than 30 % HRR. These 
findings are consistent with Kuijer et al. (1999), who found 
36.4 %HRR for refuse collectors and 22.6 %HRR for street 
sweepers. Therefore, we can conclude that refuse collectors 
and street cleaners have high endurance performance and 
high cardiovascular load during work.
Åstrand et al. (2003) specified easy, moderate, and 
heavy work during an 8-h work shift on the basis of oxy-
gen consumption at <600, 600–1000, and >1000 ml/min 
VO2, respectively, and required a maximum VO2 for work 
at 40 %VO2,max at <1500, <1500–2500, and >2500 ml/
min, respectively. When compared to Åstrand’s require-
ments of workload, the refuse collectors in our study had a 
mean VO2,1h of 1103 ml/min during work corresponding to 
46 % VO2,max (Table 4) and a mean VO2,max of 2623 ml/min 
during CPX corresponding to oxygen uptake under heavy 
physical work. This confirms Åstrand’s findings; the work-
load of refuse collectors can be classified in the upper field 
of heavy work. Whether the relatively high physical endur-
ance is a health risk for the refuse collectors remains open. 
In our initial cross-sectional study, we found no evidence 
to this.
Comparison with other occupations
Compared to jobs which are commonly referred to as phys-
ically heavy, the relative workload found in this study was 
rather high. The means for HRsh and %HRmax (Table 3) 
during one work shift are consistent with Wultsch et al. 
(2012) findings for workers from waste processing (activi-
ties were not differentiated). They found mean HRsh 100 b/
min for male and 120 for female, 59 and 65 % HRmax, 
respectively. Compared to the other investigated profes-
sions (workers in metal industry, slaughterhouse work, or 
healthcare business) referred in this study (Wultsch et al. 
2012), our findings on the physical demand of refuse col-
lectors were higher. Compared to a study with housekeep-
ers which also used a portable spiroergometric system for 
field measurements (MJ Fröhlich, personal communica-
tion), we found similar values at HR1h and VO2,1h to those 
they determined with 112 b/min and 1.06 l/min, respec-
tively. However, compared to portable spiroergometric 
measurements with lumberjacks (Hagen et al. 1993)—their 
job is considered to be the hardest form of physical work 
(with 49 % VO2,max for the younger, 53 % VO2,max for the 
older, and a HRsh of 138 and 126 b/min, respectively)—our 
measurement results were rather low.
Other studies with refuse collectors have also reported 
similar HR values to those found in our study. Kemper et al. 
(1990) have found a mean HRsh of 99.5 b/min in Dutch 
refuse collectors during one work shift, and—compared to 
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1 3
the threshold value of 30 % VO2,max calculated over HRsh—
30 % of their participants had exceeded that limit. Further-
more, they also established a linear relationship between 
HR and VO2 during work, but they did not describe this 
correlation further. In a recent study with Brazilian refuse 
collectors, Anjos et al. (2007) outlined a mean HR for 
the total working time at 97.6 b/min, 53.4 % HRmax, and 
32.8 % HRR; nevertheless, their results were partially lower 
than those found in the present study. In addition, they 
identified HR values during the actual working time which 
can be compared with our values for 1 h of continuous 
work. A recent Japanese study by Tsujimura et al. (2012) 
found mean HR values for garbage collectors of 97.5 b/
min, which were similar to the Brazilians but lower than 
our findings. These studies of refuse collectors, however, 
determined the workload only by the HR without VO2 field 
measurements.
Conclusion
The present study demonstrates that HR and oxygen con-
sumption are strongly correlated even during field measure-
ments of the heavy dynamic work of the refuse collectors. 
Therefore, HR measurement is a valuable tool for evaluat-
ing the parameters of physiological workload during work. 
But the correlation between HR and VO2 was stronger 
under steady conditions in the laboratory, while HR can also 
be influenced by several external circumstances. In addition, 
we included only persons without heart disease or medi-
cation. In persons with cardiac disease or HR influencing 
medication, the sole determination of HR cannot replace the 
measurement of VO2. Therefore, if possible, the determina-
tion of VO2 should be aimed in the field measurement.
Refuse collectors exceed the upper limits set for physical 
work stress in the literature (Åstrand et al. 2003; Ilmarinen 
et al. 1991; Shimaoka et al. 1998). But all investigated 
employees were in our study within their individual refer-
ence limits of physical capacity and aerobic fitness, both 
in terms of absolute and relative HR as well as in oxygen 
consumption. The three task-specific groups (RWC, OWC, 
SC) did not differ in workload. The results of the present 
study can finally confirm the high workload of refuse col-
lectors with the determination of VO2 at work. In addition, 
the endurance workload of refuse collectors is well above the 
hitherto recommended limits. The currently applicable limits 
for an 8-h shift with a maximum of 33–40 % of the individu-
al’s VO2 max or HRR > 30 % should be reviewed. Other field 
measurements with determination of oxygen uptake with 
other physically hardworking professionals are necessary.
Acknowledgments The authors would like to thank L. Herrmann, 
Stadtreinigung, Hamburg, for his support in recruiting the volunteers, 
and H.-J. Krankenhagen and A. Frosch for preparing heart rate data 
in the field measurements. We would like to thank Sabine Bößler 
and Anne Winkelmann for their excellent support with the technical 
patient examinations. We are indebted to Cordula Bittner, MD, and 
Thomas von Münster, MD, who implemented clinical examinations. 
The study is a part of the investigation: “Ergonomic study of waste 
collectors in the system garbage collection and street cleaning of the 
municipal sanitation department in Hamburg” and was funded by a 
grant from Stadtreinigung, Hamburg.
Conflict of interest The authors declare that they have no conflict 
of interest.
Ethical standard All procedures performed in studies involving 
human participants were in accordance with the ethical standards 
of the institutional and/or national research committee and with the 
Declaration of Helsinki 1964 and its later amendments or comparable 
ethical standards.
Open Access This article is distributed under the terms of the 
Creative Commons Attribution 4.0 International License (http://crea-
tivecommons.org/licenses/by/4.0/), which permits unrestricted use, 
distribution, and reproduction in any medium, provided you give 
appropriate credit to the original author(s) and the source, provide a 
link to the Creative Commons license, and indicate if changes were 
made.
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Measured by the oxygen uptake in the field, the work of refuse collectors is particularly hard work: Are the limit values for physical endurance workload too low?
Preisser, Alexandra M,Zhou, Linfei,Velasco Garrido, Marcial,Harth, Volker