External load can alter the energy cost of prolonged exercise

Y. Epstein*, J. Rosenblum, R. Burstein, M. N. Sawka

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review


The present study was undertaken to examine the energy cost of prolonged walking while carrying a backpack load. Six trained subjects were tested while walking for 120 min on a treadmill at a speed of 1.25 m · s-1 and 5% elevation with a well fitted backpack load of 25 and 40 kg alternately. Carrying 40 kg elicited a significantly higher (p<0.01) enery cost than 25 kg. Furthermore, whereas carrying 25 kg resulted in a constant energy cost, 40 kg yielded a highly significant (p<0.05) increase in energy cost over time. The study implies that increase in load causes physical fatigue, once work intensity is higher than 50% maximal work capacity. This is probably due to altered locomotion biomechanics which in turn lead to the increase in energy cost. Finally, the prediction model which estimates energy cost while carrying loads should be used with some caution when applied to heavy loads and long duration of exercise, since it might underestimate the acutal enery cost.

Original languageEnglish
Pages (from-to)243-247
Number of pages5
JournalEuropean Journal of Applied Physiology and Occupational Physiology
Issue number2
StatePublished - Mar 1988
Externally publishedYes


  • Backpack
  • Energy cost
  • External load
  • Prolonged exercise
  • Work intensity


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