16. Sedentary occupation—the effect of posture. Crowden (1932)5classify muscular work in industry into three general types:
)i) Heavy muscular work that is too strenuous for a steady, continues rate of work to be maintained. Examples of this type of work are loading trucks, building roads and possibly mining coal.
(ii) Moderate heavy work that is continuous and which the rate of expenditure of effort is much lower than in the first type and is somewhat balanced by the rate of recovery. Examples of this type of work include machines tending and many other kinds of factory work.
(iii) In this type muscular work in the industry is light, speed work which involves a relatively small expenditure of energy but which often require a postural stain that cause unnecessary fatigue.
Example is office work.
Crowden found that in a 50 yard borrow run the worker expends approximately 8% of his energy in raising and lowering the handles, 22% in attaining a wheeling speed and in stopping, and the remaining 70% in the run itself. This study shows the tremendous inefficiencies that would result from interfering with the run once it is stared. While studying the
energy cost of moderately heavy work, Bedale (1924) found that carrying a load with a yoke as a milk-maid does is the most economical method from the point of view of expenditure of bodily energy. Any method of carrying weights which requires postural strain and displacement of the body when
walking is more costly.
Crowden holds the view that light speed work involves little expenditure of energy, but that there may be considerable fatigue because of the cramped or uncomfortable position maintained by the worker.
According to Blum & Naylor, the men who had been driving prior to being tested performed less efficiently on the average than those who had not driven on tests of the functions like (i) aiming, (ii) resistance to glare and (iii) speed of eye movement.
The data on these tests, however, do not differentiate consistently between drivers who worked from 1 to 10 hours and those who worked over 10hours. In items 1–7 this difference does occur. The heart rate decreased slightly with hours of driving. The average white cell count was higher in
men who had driven since sleeping than in men who had not drivers since sleeping. No relationship was found between hours of driving and ability to estimate the size of known objects, differentiate white cell counts, hemoglobin content of the blood, acidity of the urine, specific gravity of urine, visual
acuity and the total base and potassium concentration of blood serum.