Anthropometric Characteristics of Feet of Soldiers in the New Zealand Army

Transcription

1 MILITARY MEDICINE, 176, 4:438, 2011 Anthropometric Characteristics of Feet of Soldiers in the New Zealand Army Marian L. Baxter, BPhsEd (Hons) * ; David G. Baxter, DPhil ABSTRACT Lower limb and lower back injuries are prevalent within the New Zealand (NZ) Army: independently collected data shows these to be most prevalent, with on average 10% of military personnel affected by such an injury at any time. To improve the quality and appropriateness of footwear, it is essential that normative foot anthropometric data is collected from NZ Army personnel. NZ Army personnel ( n = 807) were included in this study; data on foot length, circumference, width, and arch heights were collected. It was found that the NZ Army personnel had notable differences in feet anthropometry compared to an exemplary model for the NZ general population, specifically in terms of arch height. It was also found that a substantial proportion (approximately 50%) of personnel tested could not be provided with a boot that fit (mainly Maori and Pacific Island soldiers) because of a limited width range of the currently issued boot. INTRODUCTION The aim of this study was to develop a preliminary data set of the anthropometric characteristics of feet of soldiers within the New Zealand (NZ) Army. The purpose of this study is to allow better informed manufacture of footwear and, therefore, to reduce the incidence of related overuse injury. To do this, 807 military personnel were included in the study. Data were collected based on boot size, foot width, length, circumference, and arch height. Data were grouped and analyzed using available comparisons. Lower limb and lower back injuries are prevalent within the NZ Army. Data collected from the Accident Compensation Corporation (ACC) indicates that over a period of 5 years, 10% of the regular force was consistently affected by such injuries, which make these the most prevalent within the military population. Specific injuries of particular relevance here include stress fractures of the shin, stress fractures of the foot, knee injury or pain, hip injury or pain, and lower back injury or pain 1,2 (NZ Army ACC data). This is an important issue, as such injuries prevent the soldiers from attending the daily training; this is even more important during basic training as it has been reported that between a third 3 and a fifth 4 of recruits sustain such an injury during the first month of basic training, many of which require so many days off that the recruit then has to repeat the whole basic training course. 3,4 The biomechanical model of human movement suggests that kinetics and kinematics of movement follow a chain. The lower back and lower limb comprise a kinetic chain that starts with the foot. 5 7 It is, therefore, important to gather normative anthropometric data on feet within the NZ Army to better inform decisions on injury prevention, as it may be possible that those who are at risk are anthropometrically different to those at low risk. *School of Preventive and Social Medicine, University of Otago, PO Box 913, Dunedin 9054, New Zealand. School of Physiotherapy, 325 Great King Street, University of Otago, Dunedin 9054, Otago, New Zealand. This has been an area of developing research interest, with investigations focusing on foot structure and its relation to musculoskeletal overuse injury, 8 and in the past few years, targeted samples of the Australian military have been assigned specific interventions based on their foot anatomical characteristics.9 It has long been recognized in literature that fit of footwear has potential relevance in preventing injuries 10 ; therefore, knowledge of foot shape is imperative in producing well-fitting boots and consequently reducing injury. Despite this, there is currently no literature available on the anthropometric characteristics of the NZ population or the Army. Furthermore, no similar study has been published in other military populations. In the case of New Zealand, the population has such a unique ethnic diversity accompanied by anthropometric differences. wear designed overseas (as is currently the case) without reference to the characteristics of the NZ foot is always likely to be problematic. This study aimed to collect normative data of anthropometric foot characteristics from a representative sample of soldiers from the NZ Army and to describe differences with data for the general population. The ultimate goal of this work was to provide valid, accurate, and reliable data to allow comparison between at risk versus low risk groups and to inform production of appropriate and well-fitting footwear. SUBJECTS A randomly selected convenience sample (by walk past; the researchers positioned themselves at the Army mess buildings over 4 days and all soldiers who walked past were sampled) of 807 NZ Army personnel were included in this study. The single inclusion criterion was current membership of the NZ Army regular force; there was no filtering of participants based on anthropometric or anatomical characteristics. Participants were recruited from the 2 main military bases in NZ, and all measurements were completed on site. Approval for access was by verbal informed consent. Data were not collected for ethnicity, age, height, gender, or weight, as most of these 438 MILITARY MEDICINE, Vol. 176, April 2011

2 TABLE I. Data Collected from the 807 Members of the Regular Force NZ Army Based on Width, Circumference,, Arch Height, and size (US) (cm) Width (cm) Circumference (cm) Range Mean (±SD) 9.80 (1.71) (1.71) (0.81) (1.68) Data given are size/measurement range and mean (±SD) for all measurements. variables have been identified previously as nonsignificant factors in terms of injury occurrence, prevention, and treatment for the injuries of interest. 11 Although it was not known at the time of data collection that there would be ethnicity differences (and was therefore considered to not be relevant), such differences became apparent as a result of the study. METHOD A total of 807 NZ Army personnel were included in this investigation. Feet were measured with boots and socks off, while in a weight-supported (standing) position. The aim of the study was to create a representative distribution of foot anthropometric data for soldiers in the NZ Army. MATERIALS This study included the use of a standard seamstress tape measure (1.5 m) to take measurements of the feet and a standardized visual scale of arch height as used within the NZ Army equipment issue stores and is defined as follows: For high arches: 30% or less ground contact just under the metatarsal phalangeal joint; For medium arches: >30% to <55% ground contact just under the metatarsal phalangeal joint; For low arches: 55% or more ground contact just under the metatarsal phalangeal joint; These measurements were taken with participants standing upright with both feet planted at hip width apart. TABLE II. Arch Height Distribution Counts and Percentages from the 807 Members of the NZ Army Who were Included in the Study: Possible Range from Very High to Low Arch Height Number of Participants (%) Very High 0 High 31 (3.84) High Medium 29 (3.59) Medium 103 (12.76) Medium Low 94 (11.65) Low 550 (68.15) PROCEDURE Data collection took place over 1 week at the NZ Army s 2 main bases; measurements took approximately 8 minutes per participant and all data collection was completed by the lead author (Marian L. Baxter). No other anthropometric or participant data were obtained for 2 reasons: most variables have been previously identified as nonconfounding (specifically height, weight, and gender 11 ), also it would have prolonged the measurement time unnecessarily, as only foot data was of interest in the study. characteristics were collected from each participant while they stood upright on 2 bare feet. This included boot size, foot length (measured from the rear of the talus where it makes contact with the ground to the tip of the second toe), foot width (measured as the distance between the widest part of the foot lateral medial), foot circumference (the circumference of the foot when standing around the metatarsal tarsal joint), and arch height (according to the NZ Army s standardized measurement system: percentage of ground contact when standing). Measurements were taken from the participant s longest foot, using a seamstress tape measure. Data Analysis Data recorded during measurement sessions were collated and entered into excel spreadsheets (Microsoft) for analysis using descriptive statistics. Values obtained were subsequently compared with data for the NZ general population. RESULTS Data are presented in Table I as means and SDs for arch height; frequency data are presented as appropriate in Table II ; Graphically represented percentages across arch heights are shown in Figure 1 ; and NZ population percentages are shown in Figure Distributions indicate that the NZ Army soldiers have feet that are different to that of the general population. It was also found that some soldiers (approximately 50%) were wearing boots that did not fit because of limited size and width availability (Table III ): this was an unexpected finding. DISCUSSION This study aimed to collect normative data of anthropometric foot characteristics from a representative sample of soldiers from the NZ Army and to describe differences with data for the general population. The ultimate goal was to provide valid, accurate, and reliable data to inform production of appropriate and well-fitting footwear. The principal findings were that NZ Army personnel had notable differences in feet anthropometry compared to the NZ general population, specifically related to arch height distribution ( Figures 1 and 2 ). This could have been due to the greater proportions of Maori and Pacific Islanders within the Army compared to the general population, which is somewhat speculative, and based on anecdotal evidence of a higher prevalence of a flatter arch. MILITARY MEDICINE, Vol. 176, April

3 (cm) of s Included in the Study ( n = 807) FIGURE 1. Histogram showing extrapolated arch height distribution of soldiers in the NZ army ( n = 807). FIGURE 2. Histogram showing extrapolated arch height distribution of the NZ general population. 12 Because of the limited research within NZ on anthropometric foot data, it is impossible to make further comparisons besides that of arch height distribution. It was also found that a proportion of the personnel tested (approximately 1 soldier in 6) could not be provided with a boot that fitted properly, apparently because of a limited width range of the current boot (see Table III ). The current issue boot () 440 MILITARY MEDICINE, Vol. 176, April 2011

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6 Those who were not wearing the correct boots are shown in italics is made and designed for soldiers who are of European descendent, who are anecdotally considered to have a characteristically thinner foot than the Maori or Pacific Island peoples. If this were indeed the case, a boot specifically designed with the unique characteristics found in the NZ Army soldier population could address some of the current problems with injuries. As seen in Table I, the range of foot sizes were US size 4 to 14, with mean and standard deviation of US size 9.8 and 1.7, respectively. This was expected, as information from army supply stores indicates that foot wear is ordered from US size 4 to US size 16, the most common size being a US size The mean and standard deviation suggest that foot sizes tend to be towards the larger end of the scale. As the investigation was primarily to collect anthropometric data, boot size may seem to hold little relevance here. However, it is of particular relevance within the NZ Army as MILITARY MEDICINE, Vol. 176, April

7 there is anecdotal evidence of limited width availability for army boots; collection of boot size data was to allow comparison with data for foot length to assess whether soldiers were wearing correct footwear based upon the measured lengths. It was found that an average of 1 in 7 soldiers was wearing a boot that was larger than required (in some cases up to 3 sizes too big) apparently to have a boot that was wide enough. This finding suggests that the current footwear supplied by the army is inappropriate for some soldiers. length ranged from 18.2 to 32 cm, with means and standard deviations of 26.3 cm and 1.7, respectively; these data are comparable to the data on boot size. However, the average length is slightly shorter than that required for the average boot size, which might be expected given that a proportion of the boots the soldiers are wearing is too big compared to their foot length. width ranged from 8.3 to 19.0 cm; corresponding values for mean and standard deviation were 10.3 cm and 0.8, respectively. No relevant data were available in current literature for comparison. circumferences ranged from 10.5 to 31.0 cm, with mean of cm and standard deviation of Arch height range ( Table II ) was compared to members of the NZ general public ( Figures 1 and 3 ). A visual comparison suggested that army personnel tended to have lower arches than the NZ general public. The apparent reason for this was the relative difference in the proportion of population accounted for by Maori and Pacific Islanders; the general population includes just over 15% Maori and Pacific Islanders, although comparative data for the NZ Army includes 30% (Dunn, personal communication). It is widely accepted that anthropometric differences between Europeans and Maori/ Pacific Islanders includes a tendency for lower arches, although there are no published data to confirm this. Practical Implications The current findings on foot anthropometric characteristics of NZ Army soldiers suggest that some of the prevalence of lower limb and lower back injury may be attributable to issue related to footwear. These data should also inform production of more suitable footwear; knowledge of the tendency of lower arch height and need for a wider fit are especially important. Perhaps the most important finding was that a proportion of soldiers were wearing boots too big to have a suitable width ( n = 463, Table III ). Wearing boots that are too big has been proven to increase the risk of overuse injury. 13 Given that the most common injury within the NZ Army is overuse injury of the lower limb and lower back and the relation to inappropriate footwear, 13 it is clear that this issue needs to be addressed. More research is needed in this area to confirm and extend the findings of this study. It is suggested that more research would enable the NZ Army to better improve the currently issued equipment. FIGURE 3. Measurements taken from the foot; Top: foot length and width were measured, along with arch height (while standing). Arch height was measured as the percent ground contact under the arch. Bottom: the circumference of the metatarsal phalangeal joint was measured. Future Directions A major issue faced in this study was the lack of comparative data, which did not allow firm conclusions to be made on the findings. More research is necessary to provide comparative and baseline data sets. A similar study completed across a larger sample size is warranted. Future research should focus on the soldiers who were seen to have most problems (apparently Maori and Pacific Islanders). In addition, a matched sample of the population (matched by ethnicity) should be undertaken. This will add further support to the findings of this study and clarify whether particular demands of being in the NZ Army has an effect on foot anthropometry. It has been strongly recommended that boots should be made available in sufficient width and length ranges to provide a boot that fits to all soldiers. To achieve this, further investigation is warranted as to the specific range of widths and lengths required within the soldier population, and boot manufacturers need to be provided with these demographics to ensure that availability needs are met. 444 MILITARY MEDICINE, Vol. 176, April 2011

8 ACKNOWLEDGMENTS ACC Data were obtained with thanks from the NZ Defence Force Medical Database, Burnham Military Camp. Authors thank NZ Army for approval for access and accommodation and travel to and from the Army bases. Funding for travel involved in this study was provided by Marian Baxter. Road transport from airports to Military bases, accommodation, and food was provided by the NZ Army. REFERENCES 1. Larsen K, Weidich F, Leboeuf-Yde C : Can custom-made biomechanic shoe orthoses prevent problems in the back and lower extremities? A randomized, controlled intervention trial of 146 military conscripts. J Manipulative Physiol Ther 2002 ; 25 (5) : Davidson PL, Wilson SJ, Chalmers DJ, Wilson BD, McBride D : Examination of interventions to prevent common lower-limb injuries in the New Zealand Defense Force. Mil Med 2009 ; 174 (11) : Sormaala MJ, Niva MH, Kiuru MJ, Mattila VM, Pihlajamaki HK : Bone stress injuries of the talus in military recruits. Bone 2006 ; 39 (1) : Ross J, Woodward A : Risk factors for injury during basic military training: is there a social element to injury pathogenesis? J Occ Env Med 1994 ; 36 (10) : Sormaala MJ, Niva MH, Kiuru MJ, Mattila VM, Pihlajamaki HK : Bone stress injuries of the talus in military recruits. Bone 2006 ; 39 (1) : Larsen K, Weidich F, Leboeuf-Yde C : Can custom-made biomechanic shoe orthoses prevent problems in the back and lower extremities? A randomized, controlled intervention trial of 146 military conscripts. J Manipulative Physiol Ther 2002 ; 25 (5) : Withnall R, Eastaugh J, Freemantle N : Do shock absorbing insoles in recruits undertaking high levels of physical activity reduce lower limb injury? A randomized controlled trial. J R Soc Med 2006 ; 99 (9) : Kaufman KR, Brodine SK, Shaffer RA, Johnson CW, Cullison TR : The effect of foot structure and range of motion on musculoskeletal overuse injuries. Am J Sports Med 1999 ; 27: Esterman A, Pilotto L : shape and its effect on functioning in Royal Australian Air Force Recruits. Mil Med 2005 ; 170 (7) : Bensel CK : Lower extremity disorders amoung men and women in army basic training and effects of two types of boot. US Army Research and Developmental Laboratories Available at ; accessed 28 October Wen DY : Risk factors for overuse injuries in runners. Curr Sports Med Rep 2007 ; 6 (5) : Redmond AC, Crane YZ, Menz HB : Normative values for the Posture Index. J Ankle Res 2008 ; 1 (6) : Bergman BP, Miller SA : Equal opportuniteis, equal risk? Overuse injuries in female military recruits. Journal of Public Health Medicine 2001 ; 23 (1) : MILITARY MEDICINE, Vol. 176, April