ENHANCING MILITARY EFFICIENCY: A SOUTH AFRICAN PERSPECTIVE

ergonomics SA, 2001 (2)

ENHANCING MILITARY EFFICIENCY: A SOUTH AFRICAN PERSPECTIVE CJ Christie and AI Todd Department of Human Kinetics and Ergonomics, Rhodes University

ABSTRACT While extensive military research has been conducted in developed countries, very little work has been done on soldiers in industrially developing countries (IDCs). Although many aspects of marching are similar around the globe, the challenges facing soldiers in IDCs, and in particular South Africa, are unique. Since the 1990’s South Africa has seen a considerable shift in the morphological and cultural make-up of the South African National Defence Force (SANDF). The result is a mix of soldiers from a variety of ethnic backgrounds. Ethnic differences may ultimately impact performance particularly as research has postulated that Blacks and Whites may differ in body composition and body proportions. It is highly probable then that the universal recommendations of optimal marching speeds, load masses and gradients need to be modified to accommodate the diversity of soldiers which currently comprise the SANDF.

INTRODUCTION Substantial military research has been conducted on soldiers internationally. These studies date back to early research by Cathcart and co-workers in the 1920’s to recent military research contributions by Quesada et al. (2000) and Santee et al. (2001). Most of this research has focused on soldiers from developed countries with very little work being done on those from industrially developing countries (IDCs) such as South Africa. Furthermore, most of the international research has focused on Caucasian males yet most of the South African troops comprise a variety of ethnic groups. Consequently, in the SANDF, there is likely to be an extensive range of stature, leg length and body composition which in all likelihood will result in a wide range of mechanical and physiological responses to the same workloads (Christie, 2001; Todd, 2001). Because the make-up of the SANDF has changed considerably since the 1990’s, there is a need to investigate responses from the soldiers that reflect the demographics of the current national defence force.

Comparison Between South African and International Soldiers Over the past seven years the Human Kinetics and Ergonomics Department at Rhodes University has been involved in several projects investigating the efficiency of soldiers in the SANDF under varying conditions. These studies have been comprised of samples of predominantly Black Xhosa males. Comparison of anthropometric data and cardiovascular condition between South African soldiers and soldiers internationally, are shown in Table I.

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ergonomics SA, 2001 (2)

Table I: Comparison of anthropometric and VO2 max data from International and South African soldiers. Number Age Stature Mass Body BMI of fat subjects (yr) (mm) (kg) (%) (kg.m-2)

VO2 max (ml.kg-1.min-1)

International Studies Soule and Goldman(1969) Haisman and G o l d m a n (1974) Soule et al. (1978) Evans et al. (1980) Reynolds et al. (1990) Duggan and Haisman(1992) Legg et al. (1992) Jones et al. (1993) Jones et al. (1993) Quesada et al. (2000) Mean

10

21.6

173.6

69.9

23.2

8

20.9

177.2

75.3

10

21.5

177.8

75.4

6

22.8

171.1

66.7

15

21.1

173.9

77.1

18

26.5

173.0

68.7

11

24.0

174.1

73.2

14.2

24.1

303

20.2

175.4

75.5

16.9

24.6

186

20.2

175.2

73.6

16.9

24.3

12

22.4 22.1

179.1 175.0

78.6 73.4

16.2

24.5 24.0

15.7

48.6

24.0 23.9

45.1

16.2

22.8

50.3

17.4

25.5

58.5

23.0 55.7

58.3 52.8

South African Studies Clarke (1999) 32

28.0

170.6

67.6

23.2

42

29.6

170.1

68.0

16.8

23.5

30

29.2

171.1

68.2

17.4

23.8

40.0

32

26.5 28.3

171.4 170.8

67.0 67.7

14.8 16.3

22.6 23.3

38.6 39.4

James (2000) Christie (2001) Todd (2001) Mean

Most of the research reported in Table I has focussed on minimising energy expenditure during route marches to ensure that soldiers are not excessively strained and are “combat ready” post-march and able to perform critical operations demanding precision. Many factors have been shown to impact on the metabolic cost of marching, some of which include marching speed, load mass and gradient.

Impact of Anthropometric Differences on the Metabolic Cost of Marching Stature has an important effect when walking speed is altered particularly as the relationship between leg length and stride frequency is one of the main determinants of walking speed. Individuals use different stride frequencies which are dependent on leg length, which in turn plays an important role in determining the energy expenditure associated with a particular walking speed. Shorter soldiers will need to increase stride frequency and/or stride length to maintain the same speed as taller soldiers resulting in greater cost to the shorter individual. Charteris et al. (1982) reported that at the same absolute locomotor speeds, shorter individuals expend more energy per kilogram body mass than taller individuals.

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ergonomics SA, 2001 (2)

Ethnic differences in stature have recently been reported by Wagner and Heyward (2000). These authors showed that Blacks (who comprise a large portion of the SANDF) are, on average, shorter in stature than whites. This supports the comparisons made in Table I which shows that Caucasian soldiers internationally, on average, tend to be taller (1750 mm) than their Black South African counterparts, with an average stature of 1708 mm. These differences are further supported by the findings of Coetzer et al. (1993), reporting on South African distance runners, who show that Blacks are generally shorter and lighter than Whites. These differences are evident in varying body proportions as Blacks, on average, have shorter trunks and longer lower extremities than Whites (Wagner and Heyward, 2000). Most of the research papers reviewed, did not obtain a measure of extremity length and hence no comparison of this measure can be made. However, if leg length measures were shown to be similar, then the shorter stature may not result in a disadvantage particularly when faster walking speeds are employed.

In terms of morphological make-up, differences in body composition have been reported to impact upon load carriage (Buskirk and Taylor, 1957). Those individuals with more body fat are essentially carrying a large proportion of “dead weight” which in its self increases the metabolic cost of marching. Although Wagner and Heyward (2000) report that Blacks have a greater fat-free body density, in this review, there was little difference with a mean of 16.2% and 16.3% body fat predicted for Caucasian International and Black South African soldiers respectively.

To accommodate differences in body composition, it is generally accepted that relative load weights are ideal for marching. However, this is often impractical and hence most military operations use a standard absolute load depending on the circumstances. The US Army recommends maximum combat loads of 22kg and maximum approach loads of 33kg (Knapik, 1989). According to the database presented on South African soldiers this would equate to almost 50% of body mass (based on an averaged mean body mass of 68kg). In 1988, Epstein et al. proposed that 50% of body mass is the absolute maximum which soldiers should be required to carry and ideally it should be considerably less. In contrast, data from recent research shows that South African soldiers can cope with loads up to 73% of body mass at an appropriate marching speed (Christie, 2001).

Maloiy et al. (1986) and Charteris et al. (1989) have suggested that there is a “no cost” load, for loads from 20% to 30% of body mass. While these conclusions were based on the analysis of African female head-loaders, recently Quesada et al. (2000) investigating soldiers in the US military, showed that metabolic cost was not significantly altered with backpack loads up to 30% of body mass. According to the mean body mass of the South African soldier database this would equate to 20kg, considerably less than South African soldiers are required to carry.

Marching speed and gradient effects Recent South African research

investigating the responses of South African soldiers under 16 different

combinations of marching speeds and backpack loads found 13 different combinations of these two variables which can be selected depending on the particular military objective (Christie, 2001). These 13 speed and load combinations were subdivided into three categories of exertional strain, including “moderate”, “heavy” and “very heavy” stress marches. What is clear from this research is that speed and load should not be viewed in isolation but rather be investigated in combination. The three “moderate” stress marches were considered “ideal” for prolonged marches and included a range of speeds (3.5 km.h-1 to 5.5 km.h-1) and loads (20kg to 50kg). Thus a 12

ergonomics SA, 2001 (2)

speed of 5.5 km.h-1 can be tolerated but only if load is reduced to 20kg, and 50kg can be carried if speed is reduced to 3.5 km.h-1.

Although Christie (2001) found three “ideal” combinations of speed and load, these combinations were restricted to level marching. Subsequent studies in the same department found substantial changes in energy expenditure at various gradients when marching at these three speed/load combinations (Todd, 2001). Research has shown that positive gradients have a substantial impact on energy expenditure (Pandolf et al., 1977; Kirk and Schneider, 1992; Laursen et al., 2000). Laursen et al. (2000) found that carrying loads as light as 10kg at a positive gradient of only 8% increased energy expenditure by 70%, whilst a load of 20kg at the same gradient almost doubled the energy expenditure. These increases in energy expenditure are due to added work required to displace the centre of mass (body weight plus load carried) against gravity (Nagle et al., 1990).

The literature is less conclusive with regards to energy expenditure responses to negative gradients. Some authors (Margaria, 1968; Pimental et al., 1982; Nagle et al., 1990) argue that there will be a decrease in energy expenditure, since gravity helps to move the load in a downward direction thereby requiring the recruitment of fewer muscle fibres reducing energy requirements. However, this may be altered when soldiers are either required to walk at an enforced pace, or when heavy loads are imposed. Wanta et al. (1993) argue that there is a U-shaped relationship between energy expenditure and negative gradients with optimal gradients between –6 to –5%, depending on individual gait characteristics, walking speed and load carried.

Todd’s research found that a 10% uphill gradient resulted in substantial increases in the demands placed on soldiers, to as high as 106% of predicted VO2max (Todd, 2001). A 10% downhill gradient did not result in a reduction in energy expenditure in some circumstances (Todd, 2001). It was established that under heavy load carriage (50kg) South African soldiers found downhill marching to be metabolically equivalent or more taxing than level marching while carrying the same load.

Cardiovascular Status A major concern is that South African soldiers have lower maximal oxygen consumption (VO2 max) values than those reported by international authors (39.4 ml.kg-1.min-1 compared to 52.8 ml.kg-1.min-1 respectively - see Table I). It is acknowledged that only two South African studies have provided estimations of VO2 max of South African soldiers and that these were both submaximal protocols which tend to underestimate cardiovascular condition. However, these values are still lower than expected and difficult to explain.

The maximum oxygen consumption values of South African soldiers are 10% lower than benchmark normative data provided over 50 years ago by Wyndham and co-workers who studied several hundred miners from around South Africa. According to the American College of Sports Medicine (1986) healthy, sedentary individuals have VO2 max values of between 40-45 ml.kg-1.min-1. It is expected however that soldiers, who have a number of years military experience, would have higher values than the equivalent sedentary person.

A possible explanation can be drawn from relevant sports science research. Recently a considerable amount of research has focussed on the dominance of Black African runners in distance running events and yet explanation for this disproportionate success is unclear. Interestingly some investigations have confirmed that VO2 max is not

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unduly high in Black runners and therefore factors other than VO2 max must contribute to their success (Bosch et al., 1990; Coetzer et al., 1993; Weston et al., 2000). The Black runners in these studies had VO2 max values of 55 ml.kg.-1.min-1, considerably higher than those recorded on SANDF soldiers, but often lower than expected for elite runners. These studies have indicated that Black African distance runners race at a higher percentage of VO2 max inferring that fractional utilisation of VO2 max is greater in Black African runners. Weston et al. (2000) found that when comparing Caucasian runners to Black runners, the Blacks raced the 10 km event at a higher percentage of VO2 peak while accumulating similar concentrations of plasma lactate as the Caucasian runners. These authors suggest that this may explain the success of this ethnic group. Noteworthy is that the predominantly Black soldiers in the South African research, did not exhibit impaired performance despite lower VO2

max

values

compared to their international counterparts (see Table I). A partial explanation may be that most of the subjects had been in the military for a number of years and thus subsequent adaptations, relative to military demands, may have taken place. Alternatively, there may be a need to consider other performance assessment criteria other than the traditional VO2 max test in order to obtain a more defining measure of performance in the military.

CONCLUSION These comparisons emphasise the need to consider each soldier as a unique individual and acknowledge that due to the diverse morphology of the South African military personnel, responses to the same workloads will exhibit substantial variability. It is therefore evident that there is still a considerable amount of research needed within the South African military in order to better understand the demographics of South African troops and the impact these differences may have on determining “ideal” marching conditions.

REFERENCES Note:

Asterisked citations ∗ are secondary sources. These were not directly consulted and are referenced as fully as primary sources, indicated in brackets, permit.

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Charteris J, Scott PA and Nottrodt JW (1989). Metabolic and kinematic responses of African women headload carriers under controlled conditions of load and speed. Ergonomics, 32 (12): 1539-1550.

Christie CJ (2001). Physiological and perceptual responses of SANDF personnel to varying combinations of marching speed and backpack load. Unpublished MSc Thesis, Department of Human Kinetics and Ergonomics, Rhodes University, Grahamstown, South Africa.

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Clark L (1999). Physiological, perceptual and other performance decrements in combat related tasks following prolonged heavy-load marching. MSc Thesis, Department of Human Kinetics and Ergonomics, Rhodes University, Grahamstown, South Africa.

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* Margaria R (1968). Positive and negative work performances and their efficiencies in human locomotion. Internationale Zeitschrift Angewandte Physiologie, 25: 339-351. (see Knapik et al., 1996).

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Wanta DM, Nagle FJ and Webb P (1993). Metabolic response to graded downhill walking. Medicine and Science in Sports and Exercise, 25: 159-162.

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