Previous Page Table of Contents Next Page

Physiology of manual work in forestry

by H. GLASER, Lecturer, Forestry Faculty, University of Göttingen, Hannover - Münden

Few kinds of employment entail such heavy work as forestry. Logging, in fact, is one of the types of human effort that require the highest calorie consumption, and the old-fashioned, back-breaking labor that it involves has no doubt been the principal reason why so many young country workers have rejected work in the woods and turned instead to the lighter and machine-aided tasks available in the towns.

In the forests of Europe the use of machines is still exceptional: felling and conversion, and in many cases also the hauling of wood, has to be carried out by manual labor. It is for this reason that physiological methods of research have been developed in forest work science in Germany over the past twenty-five years. Over this period very close co-operation has been maintained between the Max-Planck-Institut fur Arbeits-physiologie in Dortmund and the centers concerned with purely forest work science, a line of investigation started 30 years ago by Professor Hilf, now at Reinbek, University of Hamburg.

Research was first concentrated on the most efficient forms of cross-cut saws and the techniques of hand sawing. E. G. Strehlke reported on this early research work in his book Die Methodik des Sägeversuchs. The present writer continued Strehlke's work and published some further results, from which the most interesting points to emerge were:

1. An optimum radius of curvature of the teeth line is 2.5 meters for triangular-toothed saws for sawing pine wood.

2. A minimum length of saw is 1.4 meters for sawing logs of 30 centimeters diameter.

3. Sawing with higher pressure improves the work efficiency; therefore sawing with two hands is more economic than with one hand, and crosscutting of logs lying on the ground is better performed by workers in a kneeling position than when standing.

In the years before the war, E. Stentzel continued this research and found that the optimum rhythm for sawing was rather slow and that sawing slowly but with pressure was more efficient than sawing quickly and without pressure. In the case of raked-toothed saws, those results have lately been confirmed by Grandjean, Egli and Steinlein in Switzerland. In the writer's laboratory at Hannover-Münden, University of Göttingen, physiological research on one-man sawing was started again last year, but results are not yet available.

Another extraction operation entailing physiological strain is the hauling of billets by wheeled cart or by carrying to the nearest forest road. This work was examined before the war, by K. Plouda, who published his findings in respect to fuelwood. He found that on uneven ground where extraction by cart was impossible, carrying of billets on the shoulder and below the arms was most efficient. Generally, transport by vehicle is always more efficient, even for short distances of 15 meters.

In mountain areas, where wood is normally transported by sledge, carrying or drawing empty sledges uphill is very heavy work. G. Kaminsky of the Institut für forstliche Arbeitswissenschaft, Reinbek, used respiration test methods to check this and at the same time an instrument for measuring the pulse rate developed by E. A. Müller. The results showed very high figures of calorie consumption, exceeding all other known values for forest work. The practical implications are that only young and very strong workers are able to perform this kind of work, the very type that are becoming more and more difficult to find.

After the war, research on physiology of human work in forestry was begun at the Abteilung für Waldarbeit und Forstmaschinenkunde in Hannover-Münden University of Göttingen. There were at first many difficulties to be overcome, but helpful assistance was given by the Max-Planck-Institut at Dortmund and by Professors Lehmann and Müller. We now have a small laboratory with three pieces of Haldane apparatus for analyzing gas-samples, and we are working with Douglas bags and also portable gas-meters.

Respiration test with a Douglas bag in making the undercut.

The first forestry tool on which intensive research was made was the axe. In order to ascertain the rate of efficiency, we had to measure not only the human energy in calories by respiration tests but also the result of one axe stroke in kilograms. Without going into technical details of the methods used for this purpose, which involved the use of test harness to measure force of stroke, the results may be summarized as follows:

1. The optimum weight of a hammer used both for vertical and horizontal strokes is about 2.5 kilograms.

2. For striking a point near the soil a more efficient performance is given by a worker in a standing than in a kneeling position.

3. The optimum working rhythm with a hammer or an axe is about 25 to 35 strokes per minute;

4. A stroke with full power consumes less calories per kilogram than a stroke with half the force.

5. An optimum for length of handle is about 70 to 80 centimeters and this optimum is valid for all weights of hammers (between 1 and 4 kilograms) and also for both vertical and horizontal direction of stroke.

In comparing the results of these investigations to work with real axes, we always used the same axe, loading it with additional weights, the shape and sharpness of the cutting edge did not therefore have any influence on the results. We found that for making the undercut for felling (that is for horizontally directed strokes) and for making a notch in a lying log (that is for vertically directed strokes), both for softwood and hardwood, efficiency of work increased with the weight of axe up to an optimum of about 1.8 kilograms. This optimum is less than that for the experimental tests with hammers since heavy axes tend to remain fixed in the wood requiring additional time and energy for drawing them out again.

Calorie expenditure per minute of some items in logging work.

Laboratory research has also been carried out on a number of other operations in forestry work. H. Leyendecker investigated the operations of whole working day according to the "Arbeitsschauuhr" of Poppelreuter. He found that the calorie consumption of all the workers he had under observation in all parts of Germany varied only between the narrow limits of about 300 to 350 calories per hour. This was true for all types of logging work investigated, from felling small spruce to large beech.

Later on we found the same applied to logging work on steep hill sites. Although climbing and walking on steep slopes is the kind of work which shows the highest calorie expenditure per minute, we found that the total calorie consumption for a whole day's work was not higher than for logging work on level sites which amounted also to only 300 to 350 calories per hour. From this it may be deduced that in logging work, men adjust themselves to a limit of human effort represented by a calorie consumption not exceeding about 300 to 350 calories per hour. Research at the Max-Planck Institut has also shown that there exists an upper limit of human energy turnover for a day's work at a figure of about 2,000 to 2,500 calories per day, corresponding to the 300 to 350 calories per hour for a working day of seven hours as was generally observed in our forest work. Experiments in Sweden some years before by Zotterman and Lundgren yielded higher figures than those which we obtained, but these tests dealt with one-man work, a method of operation usual in the Scandinavian countries whereas two-man team work is commonly practiced in Germany. The high calorie consumption for work in Sweden is perhaps due to the fact that workers there usually live in logging camps for only part of the year and are keen on making as high earnings as possible during the short time away from their families, so that they perhaps exceed the upper limits of calorie turnover observed among German workers.

Human work in forestry still presents many interesting problems for research. Since the use of machines in forestry has definite limitations, the improvement of the productivity of forest work may often lie largely in research on hand tools and working techniques by physiological methods. Research at present seems to be restricted to Germany, Switzerland, Finland and Sweden. Doubtless, it will soon be extended elsewhere.

Previous Page Top of Page Next Page