Physiological strain due to load carrying

SummaryIn an experimental study of load carrying the effects of mass (0, 5.4, 10.4 kg) and the type of support (on the shoulder or on waist) on parameters of physiological strain were quantified to determine the factor(s) which limit carrying time. Four categories of strain were investigated: metabolic (in terms of oxygen uptake), cardiovascular (in terms of heart rate), muscular (in terms of EMG activity) and skin pressure under the shoulder straps. Four young male subjects were tested on a treadmill using different combinations of load and speed. While standing, oxygen uptake was not influenced by the type or mass of the backpack, and averaged 10% maximal oxygen uptake. The heart rate increased significantly by 9 beats per min while standing wearing a backpack, independent of type of support or mass of backpack. While walking both the heart rate and the oxygen uptake were significantly influenced by the mass carried, but both types of strain remained below the tolerance limits for prolonged wear. Standing supporting a load did not significantly increase the root mean square value of the EMG signal of the trapezius pars descendens muscle. While walking, load carrying significantly increased the root mean square value, and, converted to force, the largest increase amounted to 2.7% of the maximal force for a load of 10.4 kg suspended from the shoulders. This was below levels of force producing fatigue, which was also indicated by an absence of changes in the median power frequency of the EMG signal. The pressure on the skin under the shoulder straps during load carrying on the shoulders was more than a factor of three times higher than the threshold value for skin and tissue irritation. Load transfer to the waist with a flexible frame reduced the pressures on the skin of the shoulder to far below the threshold value. On basis of these results it was concluded that even with relatively low loads the limiting factor was the pressure on the skin, if a waist belt did not relieve such pressure on the shoulders.

[1]  T. Husain,et al.  An experimental study of some pressure effects on tissues, with reference to the bed-sore problem. , 1953, The Journal of pathology and bacteriology.

[2]  W. Kubicek,et al.  Evaluation of pressure as a factor in the production of ischial ulcers. , 1958, Archives of physical medicine and rehabilitation.

[3]  S. Horvath,et al.  Cardiorespiratory responses during prolonged exercise. , 1961, Journal of applied physiology.

[4]  R. F. Goldman,et al.  Energy cost of load carriage. , 1962, Journal of applied physiology.

[5]  C. Davies.  Limitations to the prediction of maximum oxygen intake from cardiac frequency measurements. , 1968, Journal of applied physiology.

[6]  I Petersén,et al.  Dynamic spectrum analysis of myo-potentials and with special reference to muscle fatigue. , 1968, Electromyography.

[7]  P. Åstrand,et al.  Textbook of Work Physiology , 1970 .

[8]  Frank C. Scribano,et al.  DESIGN, DEVELOPMENT AND FABRICATION OF A PERSONNEL ARMOR LOAD PROFILE ANALYZER , 1970 .

[9]  S. R. Datta,et al.  Ergonomic comparison of seven modes of carrying loads on the horizontal plane. , 1971, Ergonomics.

[10]  B B Chatterjee,et al.  The relationship between energy expenditure and pulse rates with body weight and the load carried during load carrying on the level. , 1973, Ergonomics.

[11]  The Tolerance of Subjective Discomfort Induced by Pressure Applied to the Forearm , 1975 .

[12]  A Kilbon,et al.  Circulatory adaptation during static muscular contractions. A review. , 1976, Scandinavian journal of work, environment & health.

[13]  K B Pandolf,et al.  Metabolic energy expenditure and terrain coefficients for walking on snow. , 1976, Ergonomics.

[14]  G. Andersson,et al.  Quantitative electromyographic studies of back muscle activity relatated to posture and loading. , 1977, The Orthopedic clinics of North America.

[15]  R. F. Goldman,et al.  Predicting energy expenditure with loads while standing or walking very slowly. , 1977, Journal of applied physiology: respiratory, environmental and exercise physiology.

[16]  B Jonsson,et al.  Endurance limit of force in long-term intermittent static contractions. , 1977, Scandinavian journal of work, environment & health.

[17]  Y Shapiro,et al.  Maximal backpack load for long distance hiking. , 1977, The Journal of sports medicine and physical fitness.

[18]  Peter Zipp,et al.  ELEKTRISCHE UND BIOLOGISCHE EIGENSCHAFTEN VON ELEKTRODENPASTEN , 1977 .

[19]  R. F. Goldman,et al.  Energy expenditure of heavy load carriage. , 1978, Ergonomics.

[20]  R N Sen,et al.  Cardio-respiratory performance of porters carrying loads on a treadmill. , 1979, Ergonomics.

[21]  K B Pandolf,et al.  Energy expenditure while standing or walking slowly uphill or downhill with loads. , 1979, Ergonomics.

[22]  P. K. Nag,et al.  Occupational workload of Indian agricultural workers. , 1980 .

[23]  K B Pandolf,et al.  Self-paced hard work comparing men and women. , 1980, Ergonomics.

[24]  E. Piso,et al.  Fitting the task to the man: An ergonomic approach: E. Grandjean Taylor & Francis, London, 1980, x + 379 pages, £ 14.50, cloth, £9.50 paper, third edition , 1980 .

[25]  R W Norman,et al.  Metabolic measures to ascertain the optimal load to be carried by man. , 1981, Ergonomics.

[26]  M Hagberg,et al.  Work load and fatigue in repetitive arm elevations. , 1981, Ergonomics.

[27]  K B Pandolf,et al.  Comparison of uphill and downhill walking and concentric and eccentric cycling. , 1982, Ergonomics.

[28]  R W Norman,et al.  Use of the average electromyogram in design evaluation. Investigation of a whole-body task. , 1982, Ergonomics.

[29]  H Monod,et al.  Physiological responses to load holding and load carriage. , 1983, Ergonomics.

[30]  F. A. Gaffney,et al.  Electromechanical changes during electrically induced and maximal voluntary contractions: Surface and intramuscular EMG responses during sustained maximal voluntary contraction , 1985, Experimental Neurology.

[31]  Kurt Jø Rgensen.  Permissible loads based on energy expenditure measurements , 1985 .

[32]  J Rutenfranz,et al.  Energy expenditure constrained by sex and age. , 1985, Ergonomics.

[33]  K. Jørgensen,et al.  Permissible loads based on energy expenditure measurements. , 1985, Ergonomics.

[34]  R. C. Nelson,et al.  The effect of carried loads on the walking patterns of men and women. , 1986, Ergonomics.

[35]  S. Legg,et al.  Energy cost of backpacking in heavy boots. , 1986, Ergonomics.

[36]  G Sjøgaard,et al.  Intramuscular pressure, EMG and blood flow during low-level prolonged static contraction in man. , 1986, Acta physiologica Scandinavica.

[37]  T. Cook,et al.  The effects of load placement on the EMG activity of the low back muscles during load carrying by men and women. , 1987, Ergonomics.

[38]  Ann P. Woodhull-McNeal,et al.  Postural adjustments while standing with two types of loaded backpack , 1987 .

[39]  J. Czerniecki,et al.  Circulatory and mechanical response of skin to loading , 1989, Journal of orthopaedic research : official publication of the Orthopaedic Research Society.

[40]  V P Stokes,et al.  Rotational and translational movement features of the pelvis and thorax during adult human locomotion. , 1989, Journal of biomechanics.

[41]  M. N. Sawka,et al.  External load can alter the energy cost of prolonged exercise , 2004, European Journal of Applied Physiology and Occupational Physiology.

[42]  W. S. Myles,et al.  The physiological cost of carrying light and heavy loads , 1979, European Journal of Applied Physiology and Occupational Physiology.

[43]  W. Rohmert.  Ermittlung von Erholungspausen für statische Arbeit des Menschen , 1960, Internationale Zeitschrift für angewandte Physiologie einschließlich Arbeitsphysiologie.

[44]  B. Dietrich.  Textbook of Work Physiology: Physiological Bases of Exercise , 2004 .

[45]  A. P. Hollander,et al.  Influence of heavy weight carrying on the cardiorespiratory system during exercise , 2004, European Journal of Applied Physiology and Occupational Physiology.