Frits J. Staudt* Centre for Agricultural Research in Surinam, Paramaribo, Surinam

Karel J. de Neeft Institute for Medical Science, Paramaribo, Su&am

Johan J. Schipperheyn Department of Cardiology, University Medical Center, Leiden, The Netherlands

Received 21 August 1978 and accepted 21 August 1978

Keywords : aerobic power, Bushnegroes, Surinam.

Physical Working Capacity of Male Inhabi- tants from Upper Surinam

Aerobic power tests were carried out on twenty male Bushnegroes, as part of a medical survey in two villages on the Upper Marowijn river in the interior of Surinam (South America).

The subjects were submitted to a discontinuous series of increasing submaximal loads by means of a bicycle ergometer. Heart rate and oxygen uptake were measured at each load. The maximum oxygen uptake was estimated according to Lange Andersen et al. (1971) and used as an index for the physical working capacity.

The mean aerobic power of the Bushnegroes was 35 ml Os/min/kg body weight or 2.2 I O,/min per individual. These values are low in comparison with results obtained from professional forest workers in Surinam or in other countries.

1. Introduction

In Surinam, as in most of the developing countries, there is a strong migration to urban

centres. People from the interior, for the greater part Bushnegroes, first try to get work in the districts around Paramaribo (Figure I), and finally, because of presumed better social possibilities, in the city itself.

The working capacity of migrated Bushnegroes working as forest labourers near

Paramaribo (Staudt, 1974, 1975) is rather low in comparison with European values. The

aerobic power of European forest labourers is the highest in comparison with the average value for the population without physical training (Astrand & Rodahl, 1970). It does not follow, however, that such a difference would also exist with respect to Bushnegroes living in the interior of Surinam. Their normal daily pattern of life contains much more physical work than that of the European reference group. However, it is of some practical interest

to be able to judge the working capacity of Bushnegroes, because the success of developing projects (e.g. in agriculture) in the interior, depends for an important part on the locally

available labour reserve. For this reason we studied the working capacity of the Bush- negroes, the main residents of the interior, as a part of a general medical survey.

2. Method

The survey was carried out in two Bushnegro villages on the Upper Marowijn and

Tapanahony river, viz Stoelmanseiland and Drietabbetje, about 200 km into the interior of Surinam (Figure 1). The population belongs to the Bushnegro tribe of the Aucaners. Estimation of the population of the two villages under study, carried out very carefully by local medical staff, resulted in 165 males and 162 females for Stoelmanseiland and 204

* Present address: Department of Forest Technique and Forest Products, State Agricultural University at Wageningen, The Nether- lands. t Present address: Organon International B.V., Oss, The Netherlands.

Journal of Human Evolution (1979) 8, 399-405

0047-2484/78/030399+07 $02.00/O 0 1978 Academic Press Inc. (London) Limited

400 F. J. STAUDT ET At.

Figure 1. Map of Surinam.

I ATLANTIC OCEAN

males and 261 females for Drietabbetje (Den Butter, 1974). The population pyramid of the Tapanahony area in which Drietabbetje is located shows a clear gap in the age range of 15-35 years, especially on the male side (see Figure 2). This is mainly due to the drift

of young men to the city.

Figure 2. Population pyramid of the Tapanahony area (including Drietabbetje).

UH

WORKING CAPACITY TESTS IN SURINAM 401

Twenty male subjects participated in this study, all of them were born and living-at least up to the moment of the study-in their parental area. They still live in a traditional way. The man is a woodcutter: he clears the woodland soil for the woman to grow food crops (shifting cultivation system), he builds the house and makes woodcarvings. Further- more he fishes, hunts and carries freight by canoe over the waterfalls. Bushnegroes are broadshouldered with strong muscles of the arms and thorax, but with less well developed musculature of pelvis and legs. Body weight and height are fairly low: on the average respectively 66 kg and 166 cm for males in the age classes varying from 20-39 years (Van der Kuyp, 1967).

The participants were selected out of the larger male population from the medical survey (n = 97) on registration sequence (first come, first served) and good health. This appeared from the physical examination with special attention to blood pressure (lying, measured at the end of the physical examination), ECG and lung function as measured by means of a Vitalograph (reported values are maximum of 3 measurements, done after an initial opportunity to familiarize with the apparatus). Their age ranged from 18-50 years, with a mean of 33. Body weight averaged 63 kg (Table 1). In case of a successful test each participant received a djogo (1 liter bottle of beer). The tests were carried out in the shade, there was little or no wind. Temperature and relative humidity of the air during the tests varied respectively from 2933°C and 61-74%.

Table 1 Aerobic power and other anthropometric and physiological

data from the twenty tested individuals

Age Height Subject (years) (cm)

I-sec. Aerobic power Blood Vital value r-----l

Weight pressure capa.city (Oh vital (I O,/min (ml O,/min/kg

(kg) (mm Hg) (1 BTPS) capacity) STPD) STPD)

8 9

10 11 I2 13 14 23 15 24 16 17 18 19 20

Mean SEM

34 38 38 27 50 18 23 39 34 29 33 39 35

42 26 39 30 48 -

33 1.9

160 56 120185 164 59 1 IO/70 168 72 130/80 180 73 130/80 155 56 1 oo/so 165 59 120180 178 63 135j85 170 87 130180 174 71 171 61 149 50 171 56 167 67 165 58 167 60 150 58 158 56 165 59 162 64 164 66

-- -

165 63 1.9 1.9

13oj90 130/85 125/80 130/80 130/90

-

130!70 130/85 130/80 120170 1 IO/70 120/80

3.61 82 1.98 35 3.73 78 1.87 32 4.17 85 1.73 24 5.72 87 2.32 32 3.67 82 2.16 39 4.26 81 2.48 42 3.62 93 1.55 25 4.11 85 3.04 35 4.44 84 2.73 38 4.48 88 2.15 35 2.49 91 1.35 27 3.54 72 1.95 35 4.75 91 4.20 63 - - 2.96 51

3.69 83 1.90 32 2.58 85 1.80 31 4.01 90 1.71 31 4.16 90 2.05 35 4.46 93 2.08 33 3.72 81 2,06 31

- -

3.96 85 2.20 35 0.170 1.3 0.147 2.0

As a measure for the physical working capacity the aerobic power, i.e. the maximum oxygen consumption was used. To determine the aerobic power the participants were submitted to a discontinuous series of four to five tests, using a portable bicycle ergometer

402 F. J. STAUDT ET AL.

(make Puch Tunturi, type TP 197 1, mechanical brake, total weight 34 kg). Calibration of the load (at the flywheel) was carried out daily on the spot. Because some of the subjects were not used to cycling, running shoes were mounted on the pedals to prevent their feet from slipping from the pedals. The participants were allowed to familiarize themselves with their task by looking at their predecessor and by a period of freewheeling cycling before the test started. The load was increased after every test, starting at almost 0 and mostly ending up at about 150 Watts. Only the last three tests, with registrated heart rates between 100 and 180 beats per minute, were processed. The effort periods lasted 6 min, long enough to reach a steady heart rate; the intermittent rest periods lasted 10 min.

Throughout the experiment the ECG was recorded for about 10 set at the end of every minute, using a cardiograph type 531, Philips. The average heart rate of the (end of the) fifth and the sixth minute of each load was considered to be representative for the load chosen.

Expiratory air was collected in a Douglas bag during the complete sixth minute of each load. The subjects were connected with the bag by a mouth piece held by the teeth, a

valve, a corrugated tube, and a tap. Subject’s nose was shut with a nose clip or simply closed between thumb and forefinger. The volume of expired air was measured with a wet gas-meter (make Dordrecht, type 1); oxygen content was measured with a para- magnetic oxygen-analyser (make Servomex, type OA 272). As standard gases nitrogen and fresh air were used. The oxygen-analyser was calibrated before and after every measurement. The CO,-content of the expiratory gas mixture was not measured. The respiratory quotient was assumed to be 1.0. Oxygen consumption was expressed in liters (STPD) per minute.

The aerobic power of the individuals was calculated graphically according to Lange Andersen et al. (1971). The decrease of maximum heart rate with age was corrected for by

an age factor.

3. Results

Some anthropometric- and physiological data are presented together with the aerobic power in Table 1. Hemoglobin concentration (not tabled) was 8.73 + 0.13 mmol/l (range 7-7-9.6; n = 18; drop out nrs. 7 and 14). Data on blood pressure and lung func- tion show that no obvious disturbances in cardiovascular and pulmonary functions were present in the sample studied. The calculated mean aerbobic power of the group was 2.20 1 O,/min or 35 ml O,/min/kg body weight.

b. Discussion

The bushnegroes of Surinam are characterised by low body weight and length in com- parison with North European standards. The values from this study were on the average 63 kg and 165 cm respectively; corresponding European values are 70 kg and 175 cm. Height and body weight compare well with values produced by van der Kuyp (1967) studying a similar population. The weight/length-ratio according to WHO-standards (Jelliffe, 1966) was normal for 80% of the tested population whereas 10% scored under- weight and 10% overweight. The vital capacity was low in comparison with European values corrected for age and height, but normal to high in comparison with values from other negroid populations (Huizinga & Glanville, 1968). The hemoglobin concentration was above the lower limit of normal and similar to that of the male population under study

WORKING CAPACITY TESTS IN SURINAM 403

(S-50 f 0.08 mmol/ 1; range : 6.0-l 0.6; n = 97). Between hemoglobin concentration and aerobic power there existed no clear relation.

The mean aerobic power of the population under study, being 35 ml O,/min/kg body weight was less (P < O-05) than that of professional forest workers in Surinam of the same origin and much lower than available data from other countries (Table 2). However, a comparison on the basis of body weight does not show a significant difference between both Surinam-groups. This may be due to differences in body composition, but no data are available to elucidate this point.

Table 2 Aerobic power values from forest labourers collected from various developed and developing countries in sequence of relative aerobic power

Country (author)

Mean Mean Mean Number of weight height age

subjects (kg) (cm) (years)

Mean aerobic power

1 O,/min ml Os/min/kg

Surinam* (Staudt, 1975)

India (Hansson, 1966)

Norway (Hansson, 1966)

Sweden (Hansson, 1966)

Venezuela (Mueller-

Darss & Staudt, 1974)

16 58 165 24

58 48 161 31

14 65 172 43

50 73 174 38

86 60 165 27

2.4 f 0.1 42 ‘r 2

2.2 f 0.05 44 i: 1

3.1 f 0.2 48 + 1

3.5 * 0.1 49 + 1

3.0 50

* Bushnegroes from the interior, working in the districts around Paramaribo.

The question could be raised whether the low aerobic power values resulting from this study might be due to the inaccuracy of the method used. It is clear that field circum- stances in a tropical forest make quite different demands on standard laboratory equip- ment. This has to be taken into account during the following discussion.

Essential parameters for the method used were the heart rate and the oxygen consump- tion during the efforts. A reason for the heart rate turning out too high in relation to the work load could be unfamiliarity with test operations or cycling, which could cause a psychological stress. As resting rate on the bicycle did not differ from heart rate during previous ECG recording this is minimal. However, in testing unexperienced subjects some uneasiness is inevitable. Everything was done to reduce this factor: the bicycle test was planned at the end of the medical survey, full attention was given to a free-wheeling test of five minutes to familiarize the subject with the procedure, followed by a ten minutes rest period before the actual measurements started. Furthermore from the actual tests only the last three out of a total of four to five tests were taken into account.

The battery powered EGG-recorder was calibrated before and after the survey; no variations were observed. During the measurements no irregularity or disturbance in the ECG’s (e.g. in the QRS- or ST-duration) due to irregular paper transport were observed. Errors in calculating heart rate are therefore improbable. The oxygen-analyser was, as mentioned before, calibrated before and after every measurement. The breathing gas was

404 F. J. STAUDT ET AL.

collected through a tubing system, the nose was closed by a clip, or simply by hand. No anaesthesia masks were used. Loss of breathing gas is therefore highly improbable, Collection of the gas-mixture and reading off the oxygen content, volume, temperature, atmospheric pressure and humidity was done very precisely and where possible checked by a second observer.

Finally there is the inaccuracy of the estimation of the maximum oxygen consumption according to Lange Andersen et al. (1971). A simple linear relation between O,-consump- tion and heart rate is supposed. Individual exceptions in the linearity may happen and will cause inevitable variations in the calculated aerobic power, which however is inherent to the method of estimation by submaximal tests.

The decrease of the maximum heart rate as a function of age in Bushnegroes from Surinam appeared in other unpublished investigations to be similar to that of Lange Andersen et al. in Northern European man. From the foregoing it is clear that the experi- ments were carefully controlled to minimize external disturbances.

If one intends to carry out working capacity tests in a developing country it is still a point of discussion whether one will use a step or a bicycle test. Unfamiliarity with cycling could create technical cycling problems. This problem was solved by an extra 15 min unloaded exercise on the ergometer, with running shoes mounted on the pedals. However, a step test can also cause technical problems, e.g. when a subject can’t keep up with the metronome rhythm (Staudt, 1975). A bicycle test is preferable to a step test for two reasons. Firstly, the more or less stable body position during a bicycle test makes it easier to do observations than on a moving body as during a step test; secondly, because of the more general application of bicycle tests the results are comparable with the outcome of similar studies in other populations and climates.

For practical reasons the estimation of the aerobic power was done using a submaximal effort test instead of a maximal test. Subjects who participate in a population survey will never show a high motivation, as e.g. students of gymnastics will do; there is a big chance that the former group will not cycle through to their maximum but finish the test when they lose interest. Also, checking whether a subject has reached its maximum or not, as can be done by a closed oxygen-circuit or by measuring the final blood lactate content is highly impracticle under tropical field circumstances.

The question could be raised, whether the Surinam aerobic power values were influ- enced by the high temperature and humidity of the not air-conditioned test location. Wyndham (1970) found a reduction in work output of O-15 o/o at an “effective” tempera- ture level between 26 and 29”ET, being the climatical conditions as observed during the present study. Also our own investigations (not published) show lower heart rate values at 15”ET than at 28”ET during the same load on a bicycle. It is therefore most likely that under tropical circumstances both aerobic power and work output are influenced in a negative way by a high “effective” temperature. Using the aerobic power as an index for the working capacity under tropical outdoor working conditions one is particularly inter- ested in values including heat stress, to avoid getting a too favourable impression about the actual working capacity. The lower aerobic power values one sometimes finds in tropical countries (Table 2) might partly be explained by this heat effect.

The low aerobic power values of the population under study will have consequences for the “eight-hour allowable work load”. In the literature different limits are described; they vary from 50% (Shephard, 1971) to 30% (Bonjer, 1968) of the aerobic power. Taking the average of the limits cited the “eight-hour allowable work load” for the popula-

WORKING CAPACITY TESTS IN SURINAM 405

tion under study will be O-9 1 O,/min (40% of 2.2 1 O,/min). In terms of a specific task

this means oxygen consumption was measured in Surinam during pruning pine trees with

a machete up to a height of 2 m (Staudt, 1974) or walking through the woods with little

or no equipment (Mueller-Darss & Staudt, 1974) : both activities are considered to be

light to moderately heavy work. During heavier work resting periods have to be taken

into account. It is evident that based on an aerobic power of 2.2 1 O,/min one cannot

expect too much productivity from the population under study. Together with the gap in

the population-pyramid, this low power is important when considering work-intensive

projects in the interior of Surinam.

The technical assistance of L. Tjon A. Meeuw is gratefully acknowledged. We are most

grateful to Dr H. den Butter who introduced us to the local inhabitants.

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