Subjective references are often made to the physical limitations, including movement difficulties, of the obese. Problems commonly cited include general discomfort in simple activities of daily living such as walking and stair-climbing, pain in the joints of the lower extremity, poor circulation including oedema, and soreness or numbness in the feet, particularly following periods of standing.
In a normal weight individual, the major joints of the lower extremity are exposed to reaction forces of approximately three to six times body weight during locomotion (single leg stance phase).1,2 It may be reasonable to hypothesise that obese individuals experience greater absolute loads at these joints than individuals of normal weight.3
Persistent loading of the musculoskeletal system of the obese has been implicated in predisposition to pathological gait patterns, loss of mobility and subsequent progression of disability,3 to a range of orthopaedic conditions that include knee osteoarthritis4,5,6,7,8 and diabetic foot pathology.9Relatively few studies have considered issues related to biomechanics3,10,11 and joints other than the knee.
A small number of studies have addressed the gait characteristics of the obese. These include studies of children during walking at different speeds using temporal, kinematic and electromyographic analyses.12,13,14,15 Compared with normal weight children, obese subjects in these studies displayed asymmetry in temporal characteristics, particularly at the slow speed of walking, and a wider stance width. Flatfootedness and sub-talar pronation that contributed to a degree of out-toeing, particularly during the swing phase of gait, was also prevalent in the obese.
A gait analysis of obese middle-aged adults16 reported similar temporal and kinematic differences between obese and normal weight individuals to those found for children. The slower walking velocity and greater stride width are suggestive of a more tentative gait in the obese and adjustments in the base of the support due to both the size of the thighs and an attempt to maintain balance. The work of Messier et al17 also identified features that adversely affect gait in obese subjects. Independent of other co-morbid diseases, rear-foot movement variables and mean dynamic foot angles were significantly altered in a severely obese group (mean body mass index (BMI) of approximately 41.14 kg/m2).
In summary, relatively little research has addressed the movement capabilities and effects of loading on the musculoskeletal system during common weight-bearing tasks.9,11,18 The present study is the first to present data on the peak pressures under the feet of obese adults who completed a protocol that utilised the basic locomotor tasks of standing and walking. The results provide an objective summary of the foot mechanics of this population compared with normal weight individuals. Potential physical consequences of increased or decreased pressures under the feet, including the prevention of pain and disability in the major structures of the lower extremity, are discussed.
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