CHAPTER VI.

A STUDY OF THE COMPARATIVE PHYSIOLOGICAL COSTS OF DIFFERENT METHODS OF WEIGHT CARRYING BY WOMEN.

By EILEEN M. HEWITT, M.D., H.M. Medical Inspector of Factories, and ELIZABETH M. BEDALE, working for the Industrial Fatigue Research Board of the Medical Research Council.

The investigation here reported was suggested by Dr. T. M. Legge, H.M. Senior Medical Inspector of Factories, and Professor E. P. Cathcart, of the Physiology Institute, University of Glasgow. It was carried out at the University of Glasgow under the kind direction of Professor Cathcart.

It is not generally appreciated that excessively heavy weights are carried, even in these days, in factories and other places. Employers, managers, foremen, etc., are often found bad judges of weights, and quite unaware of the strain being put on workers employed in carrying. For instance, one of the writers (H.) recently saw young women carrying loads which the manager stated, in quite good faith, were under 30 lb. On weighing, they were found to be close on 60 lb. Though many mechanical aids for the movement of heavy weights have been devised, their introduction and use depends altogether on the employer, for in this country there has been no legislation with reference to weight carrying by adults. In France maximum loads to be permitted for boys, girls, and women, have been fixed.* For carriage by hand it is as follows:-Males-under 14 years, 22 lb.; 14 or 15 years, 33 lb.; 16 to 18 years, 44 lb. Females-under 14 years, 11 lb.; 14 or 15 years, 18 lb.; 16 or 17 years, 22 lb.; 18 and over, 55 lb. This maximum load of 55 lb. was about the limit, in the experiments now recorded, which the two untrained subjects found it possible to reach.

Dame Adelaide Anderson's recent book† contains some interesting matter on the subject of weight carrying, some of which

* Bulletin de l'Inspection du Travail et de l'Hygiene Industrielle. Ministère du Travail et de la Prévoyance Sociale. Paris. 1908.

"Women in the Factory," Dame Adelaide Anderson. London. 1922.

has appeared from time to time in the Annual Reports of the Chief Inspector of Factories. One Inspector, in a special report stated: "In brick making, in tinplate works, in iron hollow-ware, and in warehouses in hardware trades, I have found girls aged 13 to 17 years carrying loads which weighed from 30 lb. to 111 lb. in the ordinary course of their employment." Other examples of a like nature are given in this book. Miss Taylor, H.M. Inspector of Factories, has very kindly written for us a detailed account of weight carrying by women in modern tinplate works, but unfortunately time has not allowed us to follow it up for this report. She saw one pile of tinplate weighing 130 lb. which had been carried by a woman. This was, however, quite exceptional, the usual weights varying from 50 to 90 lb.

Our attention has been drawn by women interested in the welfare of young persons in Glasgow to the fact that messenger girls frequently carry very heavy loads; this point, however, is outside the scope of the present inquiry.

*Method. The principles and technique of the DouglasHaldane method employed in these experiments are described by Professor Cathcart in his paper in the Journal of the Royal Army Medical Corps, December, 1918. In place of the usual mouthpiece and nose-clip, we have used a special rubber and metal facepiece arranged with Rosling valves. The expiratory valve leads through a flexible tube into a bag carried on the back. The expired air can thus be collected in bags at fixed intervals, while work is being carried on. After collection the air is measured and a sample analysed in duplicate. From the results the carbon dioxide output and oxygen consumption at different times can be determined and energy expenditure in Calories* can be calculated. The method has been used in a number of investigations made under the Metabolism Sub-Committee of the Royal Society Food (War) Committee. We have to thank Professor Cathcart for giving us access to an important unpublished paper on "Economic Loads for Marching," which has been of great assistance to us.

Present Work. The subjects of the present series of experiments were the two writers of this report. The average weight of E.M.H. (nude) was 56.5 kilograms, and her height 162.5 centimetres, giving a surface area of 1.60 square metres. The average weight of E.M.B. was 53.3 kilos, and her height 176 centimetres; her surface area, therefore, was 1.66 square metres. Neither was accustomed nor trained to weight carrying. Both subjects were in good health, and accustomed to walking considerable distances, but neither was athletic, and the muscles of the arms and shoulders were poorly developed in both. The experiments,

* For definitions of technical terms, see end of chapter.

Report to Army Hygiene Advisory Committee (will appear in R.A.M.C. Journal).

with the exception of a few preliminary ones, which are not included in the main tables, were carried out in a wide, well-lit, well-ventilated corridor, 50 yards in length, with a granolithic floor. The lack of spring in the floor was an undesirable feature even with light loads. The cooling power, as estimated by the dry kata thermometer, rarely exceeded 9 or fell below 7.

The plan of the experiments was arranged to determine the comparative cost of carrying loads from 20 lb. upwards by different methods :

(1) The load was carried in a tray held in both hands.

(2) The load was carried in a tray as in Series (1), but the weight was taken off the arms by means of a webbing strap slung round the shoulders.

(3) The load was divided evenly and carried, tied up in suitable form, in the two hands.

(4) The load was distributed on a board and carried on the left shoulder.

Such carrying in a factory would not be continuous, but generally the worker, having deposited the load, would return to the starting place with empty tray or board. In order that factory conditions might be reproduced as closely as possible, circuits were alternately "loaded" and "unloaded." In Series (1), (2) and (4) an empty tray or board was carried during the unloaded circuit. Work was done in each experiment for one hour, save in a few cases where the load was so heavy and the method so unsatisfactory that the subject could only carry on with considerable distress. Samples of expired air were taken every twenty minutes for measurement and analysis, and each consisted of the air expired during one loaded and one unloaded circuit, together with that expired during the few seconds taken to lay down the load and pick up the empty tray or board. This method of sampling should give the expenditure of energy for the composite work, which really consists of carrying load, carrying empty, and laying down and picking up. In two series, intermittent samples were taken, i.e., each was taken during two loaded rounds only. This intermittent sampling was, however, given up. In the first place it was not representative of the working hour. In the second place it was impossible to isolate the cost of the loaded from the unloaded circuits because, as is well known, the heightened output of carbon dioxide, and the increased consumption of oxygen, do not cease simultaneously with the cessation of work. Weights of 20, 30, 40, 50 and 60 lb. were carried. These weights, together with clothes and apparatus, were equivalent to the following percentages of body weight :

The subjects were unable to carry greater weights without local fatigue or such dyspnoea as would vitiate the results. The pace chosen was the one found most satisfactory to both subjects for carrying medium loads the 100 yards' circuit was covered in 73 seconds, a pace of 75.2 metres per minute. This, of course, was much below the normal walking rate of either subject, but was judged to be about as great as could be maintained by a woman working all day. Theoretically, this means that the external work performed for a given load should be approximately the same for both subjects by any method of carrying. With successive loads the increments of work expressed in horizontal kilogrammetres per minute should graph in a straight line. Actually this was not so. The regulation of the rate of work presented the one technical difficulty in the investigation. The rate of walking with and without the load was kept approximately accurate with the aid of a metronome, but even here, though the beat was kept with ease, there was some difficulty in keeping the strides equal. This was due partly to the frequent interruption of the walking rhythm by loading and unloading, and partly to hampering of the gait by heavier loads, especially in Series (1) and to a less extent in Series (2), where the centre of gravity was much displaced. But a more important factor influencing the deviation of actual work performed from its theoretical value lies in the unavoidable difference of time taken in loading and unloading. At the end of every circuit the subject stood for a few seconds, performing no external work in horizontal kilogrammetres. Each sample taken, as already explained, represents one loaded and one unloaded circuit, together with the pause between the two in which the load is laid down and the "empty" picked up. The subjects being primarily interested in attaining experimental accuracy, there was no question of voluntary slacking off in the pauses. This operation, therefore, was kept down to the minimum time possible without such hurry as would have led to increased physiological cost and sense of strain. It is clear that a personal, perhaps a psychological, factor is here involved; in these two subjects, unlike in build and in temperament, there was a marked difference in the natural working rhythm. With H. the pause was always considerably shorter, being 2.3 per cent. of the total time sampled, whereas with B. it was 4.4 per cent. H. showed throughout a tendency to hurry over work, and frequently performed work in excess of the estimate; but she was more distressed by the greater loads than B. whose working output was almost always below the theoretical curve. Apart from the personal difference, the curves of work performed tend in both subjects to be regressive with the higher loads and in the less satisfactory methods of carrying. This may be regarded as a real fatigue symptom of obvious practical bearing on the question of general efficiency of method, and of loads.

Basal Metabolism.* The majority of our experiments were preceded by a determination of the basal metabolism by the

See definition at end of chapter.