External load can alter the energy cost of prolonged exercise

  • Y. Epstein
  • J. Rosenblum
  • R. Burstein
  • M. N. Sawka


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.

Key words

Backpack Energy cost Work intensity External load Prolonged exercise 


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  1. Astrand I (1960) Aerobic work capacity in men and women. Acta Physiol Scand [Suppl] 49:69Google Scholar
  2. Astrand P-O, Rodhal K (1977) Textbook of work physiology. McGraw Hill, New YorkGoogle Scholar
  3. Cathcart EP, Richardson DT, Campbell W (1923) On the maximum load to be carried by the soldier. J Roy Army Med Corps 40:435–443; 41:12–24, 87–89, 161–178Google Scholar
  4. Cobb LA, Johnson WP (1963) Hemodynamic relationship of anaerobic metabolism and plasma free fatty acids during prolonged, strenous exercise in trained and untrained subjects. J Clin Invest 42:800–810Google Scholar
  5. Consolazio CF, Johnson RE, Pecora LJ (1963) Metabolic statistics. In: Physiological measurements of metabolic functions in man. McGraw Hill, New York, pp 437–452Google Scholar
  6. Costill DL, Sparks K, Gregor R, Turner C (1971) Muscle glycogen utilization during exhaustive running. J Appl Physiol 31:353–356Google Scholar
  7. Daniels FJ Jr, Vanderbic JH, Bommarito CL (1952) Energy cost of load carrying on a treadmill. Fed Proc 11:30Google Scholar
  8. Ekelund LG (1966) Circulatory and respiratory adaptation during prolonged exercise in the supine position. Acta Physiol Scand 68:382–396Google Scholar
  9. Ekelund LG (1967) Circulatory and respiratory adaptation during prolonged exercise of moderate intensity in the sitting position. Acta Physiol Scand 69:327–340Google Scholar
  10. Givoni B, Goldman RF (1971) Predicting metabolic energy cost. J Appl Physiol 30:429–433Google Scholar
  11. Goldman RF (1965) Energy expenditure of soldiers performing combat type activities. Ergonomics 8:321–327Google Scholar
  12. Gollnick PD, Armstrong RB, Sanbert IV CW, Sembrowich WL, Shepherd RE, Saltin B (1973) Glycogen depletion patterns in human skeletal muscle fibers during prolonged work. Pflügers Arch 344:1–12Google Scholar
  13. Grimby G, Nilsson NJ, Sanne H (1966) Repeated serial determination of cardiac output during 30 min exercise. J Appl Physiol 21:1750–1756Google Scholar
  14. Hughes AL, Goldman RF (1970) Energy cost of “hard work”. J Appl Physiol 20:570–572Google Scholar
  15. Karlsson J, Nordesjo L-O, Saltin B (1974) Muscle glycogen utilization during exercise after physical training. Acta Physiol Scand 90:210–217Google Scholar
  16. Keren G, Epstein Y, Magazanik A, Sohar E (1981) The energy cost of walking and running with and without a backpack load. Eur J Appl Physiol 46:317–324Google Scholar
  17. Martin PE, Nelson RC (1986) The effect of carried loads on the walking pattern of man and woman. Ergonomics 29:1191–1202Google Scholar
  18. Michael ED, Hutton KE, Horvath SM (1961) Cardiorespiratory responses during prolonged exercise. J Appl Physiol 16:997–1000Google Scholar
  19. Pandolf KB, Givoni B, Goldman RF (1977) Predicting energy expenditure with loads while standing or walking very slowly. J Appl Physiol 43:577–581Google Scholar
  20. Rowell LB (1971) Cardiovascular limitations to work capacity. In: Simonson E (ed) Physiology of work capacity and fatigue, Charles C. Thomas Publ, Springfield Ill, pp 132Google Scholar
  21. Rowell LB, Kraning KK, Evans TO, Kennedy JW, Blackman JR, Kusumi F (1966) Splanchnic removal of lactate and pyrovate during prolonged exercise in man. J Appl Physiol 21:1773–1783Google Scholar
  22. Saltin B, Stenberg J (1964) Circulatory response to prolonged severe exercise. J Appl Physiol 19:833–838Google Scholar
  23. Sawka MN, Knowlton RG, Critz JB (1979) Thermal and circulatory responses to repeated bouts of prolonged running. Med Sci Sport 11:177–180Google Scholar
  24. Soule RG, Pandolf KB, Goldman RF (1978) Energy expenditure of heavy load carriage. Ergonomics 21:373–381Google Scholar
  25. Taylor HL, Buskirk ER, Henschel A (1955) Maximal oxygen intake as an objective measure of cardio-respiratory performance. J Appl Physiol 8:73–80Google Scholar

Copyright information

© Springer-Verlag 1988

Authors and Affiliations

  • Y. Epstein
    • 1
  • J. Rosenblum
    • 1
  • R. Burstein
    • 1
  • M. N. Sawka
    • 2
  1. 1.Heller Institute of Medical ResearchChaim Sheba Medical CenterTel-HashomerIsrael
  2. 2.Military Ergonomics DivisionUS Array Research Institute of Environmental MedicineNatickUSA

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