The Physiological Cost of Carrying Loads in Temperate and Hot Environments

• Published in: Human factors 1971-04, Vol.13 (2), p.153-161
• Main Authors: Kamon, Eliezer, Belding, Harwood S.
• Format: Article
• Language: English
• Subjects: Air temperature; Ambient temperature; Body weight; Cartons; Fatigue; Heart diseases; Heart rate; Load; Load distribution; Metabolism; Packages; Walking
• ISSN: 0018-7208; 1547-8181
• DOI: 10.1177/001872087101300207

Cartons weighing 10, 15, and 20 kg. were carried by the hands in front of the body at speeds of 4 and 5 km/hr on level and at 4% grade at dry ambient temperatures of 20, 35 and 45°C. Three pretrained subjects were used. Each test involved three 5-min. periods of carrying the load, walking without the load and sitting, repeated three times. At each speed, step rate increased with increase in the weight of the load, although the increase (but not total cost) was less when carrying uphill. Metabolic cost per total weight of body and load also increased with increase in the load; thus work efficiency decreased. The metabolic cost for each kilogram of load carried was 1.3 to 2.3 times greater than the cost per kilogram of body weight without load. No significant differences in metabolic cost were observed under the three thermal conditions, but heart rate increased about 7 to 10 beats/min for each 10°C-rise in air temperature. Heart rate increased progressively from first to third cycle when 20 kg. were carried at 20° and 35° C; this was more obvious for uphill carrying. Such progressive rise in heart rate was most conspicuous when the subject was carrying 15 and 20 kg. at 45° C. Based on considerations of metabolic and cardiac cost, fatigue and need for rest pauses, 15-kg. packages were determined to be preferable to 10- and 20-kg. packages when large amounts of material must be moved by hand.