274 



TEMPERATURE AND HUMIDITY 



the heat addition to closed spaces resulting 

 from human occupancy to be compared with 

 inputs from heater units, incandescent lights, 

 and electronic apparatus. 



The figures quoted in Table I make no 

 reference to duration of activity. In esti- 

 mating the heat stress to which the human 

 body may be subject, or the heat which 

 human activity may add to a closed space, 

 it must be clear that increasing rates are 

 associated with decreasing durations in some 

 manner. A very condensed statement of 

 this relationship can be given. 



TABLE I 



Heat Production Associated with Various 



Activities 



(from Sherman, 36) 



Occupation 



Sleeping 



Sitting at rest 



Tj^pewriting rapidly 



Walking at 2.6 miles per 



hour 



Walking at 3.75 miles per 



hour 



Stone working 



Swimming 



Walking up a flight of 



stairs 



Mets* 



.76 

 1.2 

 1.7 



2.4 



3.5 



4.7 

 5.9 



12.9 



* Multiples of 85.0 kg. cal./hr./1.7 m.^ equiva- 

 lent to met unit of 50 kg. cal./m.Vhr. 



Benedict and Cathcart (5) observed a 

 professional bicycle rider working to the 

 point of exhaustion on a bicycle ergometer. 

 He was unable to continue after 4 hours and 

 22 minutes; and during this period he worked 

 at a rate of 111.6 kg. cal. per hour. The 

 metabolism of the subject was not actually 

 observed; but the excess over the basal 

 metabolism was computed from the work 

 performed, assuming an efficiency of 25 per- 

 cent. During the period of activity, the 

 subject accomplished work at the rate of 112 

 Calories per hour, giving a computed total 

 metabolism of 526 Calories per hour, ap- 

 proximately Sherman's estimate for swim- 

 ming. Henderson and Haggard (25) 



recorded the work performed in a crew race 

 in which exhaustion occurred after 22 min- 

 utes. Here, the work performed was at the 

 rate of 288 Calories per hour. Assuming a 

 25 percent efficiency, this indicates a work- 

 metabolism rate of 1152 Calories per hour, 

 plus an estimated basal metabolism of 80, a 

 total of 1230 Calories per hour. 



Finally, Nielsen (31) actually recorded 

 the metabohsm of a subject working on an 



TABLE II 



Approximate Time to Exhaustion at Various 

 Levels of Work 



Benedict . . 

 Henderson 

 Neilsen 



Period of Ex- 

 haustion, hours 



4.367 

 0.367 

 0.006 



Metabolism, kg. 

 cal. per hour 



526 

 1230 

 3930 



ergometer under such extreme conditions 

 that the subject was completely exhausted in 

 22 seconds. (The presence of the number 

 22 in these three studies is coincidental.) 

 Nielsen's subject showed a metabolic rate 

 during his 22 seconds of 3930 Calories per 

 hour. 



From these three studies we derive the 

 relationships of Table II. 



Comparing Benedict and Henderson, an 

 approximate doubling of metabolic rate 

 decreased the time limit to about one-twelfth 

 of its Benedict value. Comparing Hender- 

 son and Nielsen, a further tripling of meta- 

 bolic rate decreased the period of endurance 

 to one-sixtieth of the Henderson figure. 



Thus we see that enormous rates of 

 metabohsm can be maintained for brief 

 periods of time. Computations on an hourly 

 basis are, however, obviously artificial. 

 Only some figure between 500 and 1000 

 Calories could actually be maintained for as 

 long as one hour. On a 24-hour basis, it 

 has been estimated that trained partici- 

 pants in a six-day bicycle race might main- 

 tain a rate of some 10,000 Calories per day. 

 Under ordinary circumstances, the metab- 

 olism of a 24-hour period with average 

 muscular work has been computed by 

 Sherman as given in Table III. 



