FATIGUE IN INDUSTRY. Fatigue is a complex phenom enon that is difficult to define precisely. In a broad sense the term implies a diminished capacity for work which results not only from prolonged activity but also from a wide group of socio economic, psychological, and environmental factors affecting the mind and body of the worker which reflect on his capacity for work.
The loss of functional power is often, though not always, ac companied by a characteristic feeling of tiredness or weariness. Although this sensation is usually referred to the muscles them selves the seat of fatigue is mainly localized in the synapses of the central nervous system.
Although a moderate degree of fatigue is physiologically nor mal, after a day's work, cumulative fatigue may induce a vicious cycle in which fatigue becomes both the cause and effect of ill health.
Studies of industrial fatigue date back to 1893, when Sir Wil liam Mather, of the firm Mather and Pratt, Manchester, discov ered by trial that the output of his men increased materially by reducing the hours of work from S4 to 48 a week. These results were later verified by experiments in other countries, but the real impetus to fatigue studies came after the outbreak of the World War when an unprecedented demand was placed upon industry. As a result, the Health of Munition Workers Committee was established in 1915 and later (1918) superseded by the Industrial Fatigue (now Health) Research Board of the British Medical Re search Council.
In 1922 the activities of this board were supplemented by the National Institute of Industrial Psychology, a self-supporting institution for field and laboratory research.
In America, work on industrial fatigue has been undertaken by the U.S. Public Health Service, the Harvard Fatigue Laboratory, and various other interested agencies including laboratories of industrial physiology and The principal objects of fatigue studies are to determine whether the fatigue resulting from a given industrial operation affects the health of the worker; whether the worker is tired be cause he is ill, or ill because he is tired, and what causative fac tors must be controlled for the attainment of optimum conditions from the standpoint of both health and production.
Causes of industrial fatigue fall under two general classifica tions, (a) those pertaining to the general work environment and the work itself, and (b) those arising from extraneous conditions less directly associated with the industry itself. The latter may include personal constitutional factors, housing and living con ditions. financial status, nutrition, alcoholism, recreation, etc. Important as these factors might be in the production of fa tigue they are difficult to evaluate and little is known about them.
Most of the studies have been confined to direct industrial causes, but even here knowledge is limited.
Measurement of Fatigue.—Attempts to associate fatigue with measurable changes in body tissues, i.e., accumulation of specific fatigue substances in the blood or muscles, inadequate supply of oxygen, depletion of fuel reserves, and disturbance in the physico chemical equilibrium, have not proved entirely successful except in special instances. Physiological and psychological tests have likewise proved unreliable.
The most widely used tests are indirect, based on variations of quantity and quality of work, accident frequency, lost time, sick ness, and labour turnover. The output test is probably the most important where it can be applied satisfactorily and continued over a sufficient period to minimize the effects of psychic or other interfering factors.
A reduction of working hours from 12 to 8 hours a day in creased the total output and decreased the amount of lost time and incidence of illness in most studies. Such benefits may take weeks and even months to develop fully, as the workers must become adapted to the new conditions.
Suitable rest pauses both in the forenoon and afternoon are likewise accredited with a favourable effect on output and acci dent frequency, even in light work. The optimum duration and time of the pause must be determined by trial for each type of work.
Vernon has found that a mere change of position often affords a satisfactory form of rest and is also beneficial during the actual work spell, presumably by improving blood circulation to the active muscles.
Method of Work. Next to vocational fitness, the method of performing a given task with respect to exertion, speed, and pos ture, is an important factor in energy expenditure and output. Taylor was the first to study the methods of work in relation to output, but he took no account of the physiological cost of exer cise. His experiments were carried out in a yard of the Bethle hem Steel Co. where 500 men were employed in shovelling coal and ashes.
By suitable alterations in the design of shovels and in the amount of material shovelled in each lift he succeeded in increas ing the tonnage handled from 16 to S9 tons per man per day.
Industrial physiology is now doing much to organize industry on scientific bases by fitting the right man to the right job and by controlling the methods of work so as to obtain maximum output with minimum expenditure of energy and without exces sive fatigue.
Environmental conditions. The neuromuscular system works best within an optimum range of air conditions for any given type of work. Significant departures from the optimum temperature and humidity affect the inclination for work, reduce working ca pacity, and give rise to fatigue and other untoward symptoms. Such disinclination for work is believed to be a protective natural instinct.
Although the human energy expenditure in performing a nomi nal task is not appreciably affected by usual variations of tem perature, working capacity may be markedly affected. In experi ments of the American Society of Heating and Ventilating Engi neers, men working at a rate of 12,50o kgm. per hour, were able to carry on the work twice as long in temperatures between 4o° and 8o° F. than in one of Io5°, with 5o% relative hun idity in both instances.
In deep mines where temperatures may range between 85° and 100° F., with humidities close to saturation, the miners work only one-half to one-third of the time, spending the remaining hours in cooling off (Sayers and Harrington).
In such hot environments, fatigue and loss of working capacity appear to be associated largely with circulatory insufficiency as shown by abnormal rise of pulse rate approaching the limit of endurance of the heart muscle itself. Heat cramps, heat stroke, or heat exhaustion may occur under extreme conditions, and their incidence in hot industries is still quite high although in some instances it has been greatly reduced by preventive medical and engineering methods, such as administration of chlorides (in the drinking water) to replace those lost in the sweat, improved ventilation, etc.
Abnormal air conditions in industry affect also accident lia bility and incidence of illness. The frequency of minor accidents among men and women in British munition plants was found to reach a minimum at temperatures between 67° and 7o° F., in creasing above and below this temperature range.
Although there are mental and psychological elements in acci dent proneness, discomfort and fatigue exert a definite influence on the essential nervous processes involved in muscle co-ordination, integration, and inhibition, and hence on accidents and output.
Respiratory diseases and rheumatism are the chief chronic af fections associated with exposure to heat or cold and temperature changes.
Inadequate lighting and excessive noise affect not only the specific sense organs but the entire body by increasing the strain on the nervous system.
Reduction of objectionable noise, even when brought about by the use of ear defenders, has a beneficial effect on output and labour turnover.
Toxic dusts, fumes, and gases in certain industries may affect fatigue and output indirectly by undermining the health of the workers.
Among other industrial factors conducive to fatigue are lack of skill, lack of incentive or boredom, worry, insecurity of employ ment, irritation, discontent, and last but not least the social rela tions between management and workers and between the workers themselves. Their adverse effects result from inhibition which can be distinguished from fatigue by observing the effect on output, accidents, or labour turnover after removing the cause. The boredom and discontent in mechanized industry or in repetitive work may be reduced by careful selection of workers. Intelligent persons are as unsuitable for monotonous work as are persons of inferior capacity for creative work. As a rule dull workers prefer repetitive work, and compensate for the monot ony by talking, singing, or "day-dreaming." Music alleviates boredom and stimulates the output and pleasure in work (Wyatt and Langdon) .
Social behaviour in industry, whether rational or irrational, may sometimes dominate even the economic interest of the work ers. In carefully conducted experiments by Henderson and Mayo on telephone relay winding and bank-wiring work, the speed of work and output varied markedly with changes in the sentiments among the employees themselves and toward their supervisors. Individual performance was related to the individual's position in the group, rather than to actual ability or earnings. Although these facts apply specifically to the groups under observation, they deserve serious consideration because they contradict tradi tional methods of social organization in industry.
For further reading see Josephine Goldmark, et al., "Comparison of an Eight-hour Plant and a Ten-hour Plant." U.S. Public Health Service Bulletin No. ro6 (192o) ; H. M. Vernon, Industrial Fa tigue and Efficiency (19 2 I) ; A Review of general literature on industrial accidents, factory management, hours of work, fatigue and rest periods, lighting, etc., Library of National Bureau of Casualty and Surety Underwriters, New York (1928) ; Bibliogra phy on Industrial Fatigue and Allied Subjects, Am. Pub. Health Assn., New York (1929) and Supplement (193o) ; International Labor Office, Geneva, Occupation and Health, Vol. I (193o), Vol. 2 (1934), Industrial Accident Prevention Work in the U.S. (1936), Industrial Medicine (1937); E. Simonson, "Der heutige Stand der Theorie der Ermudung," Ergeb. Physiol., 37 : ) D. B. Dill, et al., "Industrial Fatigue," Jour. Ind. Hyg., 18:417 (1936); L. J. Henderson and E. Mayo, "The Effects of Social Environment," Ibid. 18:401 (1936); National Safety Council Inc., Accident Facts (1936) ; H. M. Vernon, Accidents and Their Prevention (1936); C. P. Yaglou. "Abnormal Air Conditions in Industry and Methods of Control," 1 our. Ind. Hyg., 19 :12 7 ) C. P. McCord, et al., "Noise and Its Effects on Human Beings," Jour. Am. bled. Assn., I Io ; Fourth Report of the Dept. Committee on Lighting at Factories, Home Office, London (1938) ; S. Wyatt and J. N. Langdon, "Fatigue and Boredom in Repetitive Work" Medical Research Council, Industrial Health Research Board, Rep. No. 77 (London, (C. P. Y.)