Foot dimensions and morphology in healthy weight, overweight and obese males
Introduction
The prevalence of adults who are overweight or obese is increasing and figures suggest these adults represent 10–30% of the global population (World Health Organisation, WHO, 2014). It is important that these populations are physically active as part of weight management programmes and to improve cardiovascular health (WHO, 2014), which demands appropriate and comfortable footwear. A high prevalence of disabling foot pain and perceptions of poor foot health have been reported in adults who are overweight or obese (Mickle and Steele, 2015, Mølgaard et al., 2010). A systematic review has also identified relationships between increased body mass index (BMI) and tendonitis and flat foot (Butterworth et al., 2012). Furthermore, obese adults also report reduced satisfaction with retail footwear and that it becomes increasingly difficult to find comfortable and appropriate footwear as BMI increases (Jelinek and Fox, 2009, Park, 2012). This may be attributable to morphological and dimensional discrepancies between the obese foot and the standard and wide-fit retail footwear designed to accommodate it (Price and Nester, 2015).
The foot of an adult who is obese may differ in structure and function compared with the foot of a healthy weight individual due to alterations in morphology, soft tissue properties and functional capability (Dowling et al., 2001, Hills et al., 2002, Riddiford-Harland et al., 2011). Specifically, lower longitudinal arch heights (Gilmour and Burns, 2001, Gravante et al., 2003, Mickle et al., 2006) and greater foot lengths and girths (Mickle and Steele, 2015, Mickle et al., 2006, Park, 2012) are evident in the feet of adults and children who are obese compared with healthy controls. The morphology and function of the feet of adults who are overweight are yet to be widely and thoroughly investigated independently from obese populations as some work does not differentiate overweight and obese individuals (Mauch et al., 2008). Existing research identifies that the ball of the foot is wider, taller and of a larger girth, but this may have also been a function of gender as these were mixed groups with inconsistent proportions of males and females (Mickle and Steele, 2015). Within-gender differences between obese, overweight and healthy weight groups have not been considered in isolation, but are particularly important because footwear is gender specific.
In order to provide (through retail) or prescribe (via clinic) appropriate footwear to these populations, accurately quantifying the dimensions and morphology of the foot is key. In both retail and clinical contexts measures of foot size and shape are traditionally undertaken with a Brannock device and a tape, which provides simple length, width and girth measures, but may be influenced by human error. Alternatively, measures taken using a 3D scanner have high validity and repeatability and automatically quantify standard measurements required for last manufacture and the definition of footwear (Mits et al., 2009, Telfer and Woodburn, 2010). These methods have been utilised to define feet of specific populations e.g. older adults (Menz et al., 2014, Mickle et al., 2010). However the appropriateness of these automated measures to fully define the anthropometry of specific population's feet has yet to be explored. These measures utilise bony landmarks to define measures, which may not be identifiable in the feet of obese/overweight adults, due to smoothing from additional adipose tissue. The automated measures also, if defined, may not represent the largest dimensions of the foot. Therefore, it is not clear whether manual or 3D scanner measures capture enough data to fully define the dimensions and morphology of the obese foot and therefore the requirements for footwear to meet. Higher resolution foot measures which provide more detailed morphology are more likely to adequately capture differences between groups. This is key for podiatry, footwear design and related researchers to fully define populations.
The current study was undertaken to compare foot dimensions and morphology between healthy, overweight and obese adults. The measurements for comparisons included standard anatomical measures in addition to cross-sections along the length of the foot.
Section snippets
Participants
The mean measures from 69 male participants formed three groups of 23 participants categorised by BMI and these defined the healthy weight, overweight and obese feet samples (Table 1). Healthy weight, overweight and obesity are defined by adults having a BMI of 18.5–24.9, 25–29.9 and ≥ 30 kg.m− 2 respectively. Groups were drawn from an existing data set and matched for age (P = 0.058), height (P = 0.943) and shoe size (P = 0.196) (tested via non-parametric comparisons). The sample size was consistent
Anatomical measures
Measures of absolute foot length did not differ between the groups (healthy weight mean 266.2, SD 10.9 mm; overweight mean 267.6, SD 9.0 mm; obese mean 265.4, SD 10.8 mm, P = 0.751). The anatomical measures of foot, ball and heel width increased with each increase in group BMI however significant differences were only evident between the healthy weight and obese groups (P = 0.001–0.006; Fig. 3). The height and circumference of the ball of the foot followed the same pattern. For heel circumference the
Discussion
The data collected within this study demonstrates that the feet of obese adults significantly differ from those of adults who are overweight and a healthy weight. The feet of the obese adults in this study had larger dimensions for ball height, and widths (heel, ball and foot) and circumferences (heel and ball) of the foot. It is proposed that with increases in mass, the foot structure spreads and increases its dimensions with increases in weight bearing (Tsung et al., 2003, Xiong et al., 2008
Conclusions
It is evident that the morphology of the feet of obese adults differs significantly from those of overweight and healthy weight adults. The reliance on anatomical landmarks to describe foot shape may not be sensitive enough to fully quantify the foot affected by obesity; however additional cross-sectional measures are able to define differences between these populations in foot regions. Researchers, clinicians and footwear designers should consider the foot holistically as a complex volume as
Acknowledgements
With thanks to Dr Jonathon Chapman, Dr Ana Martinez Santos for contribution to data collection and Dr Daniel Parker for assistance with the use of Rhinoceros 5 software.
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