Julie R. Steele

Musculoskeletal disorders associated with obesity: a biomechanical perspective

Despite the multifactorial nature of musculoskeletal disease, obesity consistently emerges as a key and potentially modifiable risk factor in the onset and progression of musculoskeletal conditions of the hip, knee, ankle, foot and shoulder. To date, the majority of research has focused on the impact of obesity on bone and joint disorders, such as the risk of fracture and osteoarthritis. However, emerging evidence indicates that obesity may also have a profound effect on soft‐tissue structures, such as tendon, fascia and cartilage. Although the mechanism remains unclear, the functional and structural limitations imposed by the additional loading of the locomotor system in obesity have been almost universally accepted to produce aberrant mechanics during locomotor tasks, thereby unduly raising stress within connective‐tissue structures and the potential for musculoskeletal injury. While such mechanical theories abound, there is surprisingly little scientific evidence directly linking musculoskeletal injury to altered biomechanics in the obese. For the most part, even the biomechanical effects of obesity on the locomotor system remain unknown. Given the global increase in obesity and the rapid rise in musculoskeletal disorders, there is a need to determine the physical consequences of continued repetitive loading of major structures of the locomotor system in the obese and to establish how obesity may interact with other factors to potentially increase the risk of musculoskeletal disease.

The biomechanics of adiposity – structural and functional limitations of obesity and implications for movement

Obesity is a significant health problem and the incidence of the condition is increasing at an alarming rate worldwide. Despite significant advances in the knowledge and understanding of the multifactorial nature of the condition, many questions regarding the specific consequences of the disease remain unanswered. For example, there is a dearth of information pertaining to the structural and functional limitations imposed by overweight and obesity. A limited number of studies to date have considered plantar pressures under the feet of obese vs. non‐obese, the influence of foot structure on performance, gait characteristics of obese children and adults, and relationships between obesity and osteoarthritis. A better appreciation of the implications of increased levels of body weight and/or body fat on movement capabilities of the obese would provide an enhanced opportunity to offer more meaningful support in the prevention, treatment and management of the condition.

The biomechanics of restricted movement in adult obesity

In spite of significant advances in the knowledge and understanding of the multi‐factorial nature of obesity, many questions regarding the specific consequences of the disease remain unanswered. In particular, there is a relative dearth of information pertaining to the functional limitations imposed by overweight and obesity. The limited number of studies to date have mainly focused on the effect of obesity on the temporospatial characteristics of walking, plantar foot pressures, muscular strength and, to a lesser extent, postural balance. Collectively, these studies have implied that the functional limitations imposed by the additional loading of the locomotor system in obesity result in aberrant mechanics and the potential for musculoskeletal injury. Despite the greater prevalence of musculoskeletal disorders in the obese, there has been surprisingly little empirical investigation pertaining to the biomechanics of activities of daily living or into the mechanical and neuromuscular factors that may predispose the obese to injury. A better appreciation of the implications of increased levels of body adiposity on the movement capabilities of the obese would afford a greater opportunity to provide meaningful support in preventing, treating and managing the condition and its sequelae. Moreover, there is an urgent need to establish the physical consequences of continued repetitive loading of major structures of the body, particularly of the lower limbs in the obese, during the diverse range of activities of daily living.

Optimizing Footwear for Older People at Risk of Falls

Footwear influences balance and the subsequent risk of slips, trips, and falls by altering somatosensory feedback to the foot and ankle and modifying frictional conditions at the shoe/floor interface. Walking indoors barefoot or in socks and walking indoors or outdoors in high-heel shoes have been shown to increase the risk of falls in older people. Other footwear characteristics such as heel collar height, sole hardness, and tread and heel geometry also influence measures of balance and gait. Because many older people wear suboptimal shoes, maximizing safe shoe use may offer an effective fall prevention strategy. Based on findings of a systematic literature review, older people should wear shoes with low heels and firm slip-resistant soles both inside and outside the home. Future research should investigate the potential benefits of tread sole shoes for preventing slips and whether shoes with high collars or flared soles can enhance balance when challenging tasks are undertaken.

Does obesity influence foot structure in prepubescent children

OBJECTIVE: This study examines the relationship between obesity and foot structure in prepubescent children.DESIGN: Field-based, experimental data on BMI (body mass index) and foot structure were collected for 431 consenting children from 18 randomly selected primary schools.SUBJECTS: Of the 431 participants, 62 obese (BMI>95th percentile) and 62 non-obese (10th percentile<BMI>90th percentile) children (age=8.5±0.5 y) were selected.MEASUREMENTS: Height and weight were measured to calculate BMI. Static weight-bearing footprints for the right and left foot of each subject were then taken using a pedograph to calculate the Footprint Angle and the Chippaux-Smirak Index as representative measures of the surface area of the foot in contact with the ground.RESULTS: A significant difference was found between the Footprint Angle of the obese and non-obese subjects for both the left (t=3.663; P<0.001) and right (t=3.742; P<0.001) feet whereby obese subjects displayed a reduced angle. Chippaux–Smirak Index scores were also significantly different for both the left (t=−6.362; P<0.001) and right (t=−5.675; P<0.001) feet between the two subject groups where a greater score for the obese subjects was evident. A decreased footprint angle and an increased Chippaux–Smirak Index are characteristic of structural foot changes that have been associated with compromised foot function.CONCLUSIONS: Excess body mass appears to have a significant effect on the foot structure of prepubescent children whereby young obese children display structural foot characteristics which may develop into problematic symptoms if excessive weight gain continues. Further investigation into possible consequences, particularly any effects on foot function, is warranted.

Effects of walking surfaces and footwear on temporo-spatial gait parameters in young and older people

This study aimed to investigate the effects of walking surfaces and shoe features on gait variables associated with balance control and the risk of slips and trips in 10 young and 26 older adults. A systematic approach was adopted in which the features of a standard, Oxford-type shoe were individually modified. Subjects walked along a level (control), irregular, and wet walkway in eight randomised shoe conditions (standard, elevated heel, soft sole, hard sole, high-collar, flared sole, bevelled heel and tread sole). Walking velocity, step length, step width, cadence, double-support time, heel horizontal velocity and shoe-floor angle at heel contact, and toe clearance at mid-swing were measured. Older people exhibited a more conservative walking pattern, especially on the irregular and wet surfaces. Compared to the standard shoes, the elevated heel shoes elicited increased double-support time, heel horizontal velocity at heel strike and toe clearance. On the wet surface, the soft sole shoes led to shorter steps and a flatter foot landing, gait adaptations which are associated with perceptions of shoe/surface slipperiness. Increasing collar height led to greater double-support time and step width. The results indicate that shoes with elevated heels or soft soles impair walking stability in older people, especially on wet floors, and that high-collar shoes of medium sole hardness provide optimal stability on level dry, irregular and wet floors.

The Feet of Overweight and Obese Young Children: Are They Flat or Fat?

Objective: The purpose of this study was to determine whether the flat feet displayed by young obese and overweight children are attributable to the presence of a thicker midfoot plantar fat pad or a lowering of the longitudinal arch relative to that in non‐overweight children.

Changing Sidestep Cutting Technique Reduces Knee Valgus Loading

Background Common lower limb postures have been found when noncontact anterior cruciate ligament (ACL) injuries occur during sidestep cutting tasks. These same postures have been linked to knee loadings known to stress the ACL. Hypothesis Whole body technique modification would reduce knee loading. Study Design Controlled laboratory study. Methods Experienced team sport athletes were recruited for whole body sidestep cutting technique modification. Before and after a 6-week technique modification training, participants performed sidestep cutting tasks while ground-reaction force and motion data were collected. A kinematic and inverse dynamics model was used to calculate 3-dimensional knee loading during sidestep cutting. Results At initial foot contact, the participants placed their stance foot closer to the body’s midline and held their torso more upright, in line with the aims of the technique modification training. This was accompanied by significantly lower peak valgus moments in the weight acceptance phase of stance. Both postural changes were correlated with the change in peak valgus moment. Conclusion Whole body sidestep cutting technique modification resulted in reduced knee loading. Clinical Relevance Implementation of whole body technique modification may produce effective ACL injury prevention programs in sports involving sidestep cutting.

Biomechanics of the sprint start

SummaryMany variables have been studied pertaining to the block sprint start. Research suggests that the adoption of a medium block spacing is preferred, with front and rear knee angles in the set position approximating 90 and 130°, respectively, with the hips held moderately high. The sprinter must be capable of developing a high force rate combined with a high maximum force, especially in the horizontal direction. This ability to create high force underlies other important indicators of starting performance such as minimum block clearance time, maximum block leaving velocity and maximum block leaving acceleration. Once the sprinter has projected him/herself from the blocks at a low angle (40 to 45°) relative to the ground, the following 2 post-block steps should occur with the total body centre of gravity ahead of the contacting foot at foot strike to minimise potential horizontal braking forces.

What Are The Effects Of Obesity In Children On Plantar Pressure Distributions

OBJECTIVE: This study examined the effects of obesity on static and dynamic plantar pressure distributions displayed by children.DESIGN: Field-based experimental data on body mass index (BMI) and plantar pressures were collected for 10 obese children and 10 nonobese controls.SUBJECTS: In all, 10 obese (age 8.8±2.0 y, BMI 25.8±3.8 kg m−2) children matched to 10 nonobese children (age 8.9±2.1 y, BMI 16.8±2.0 kg m−2), for gender, age and height.MEASUREMENTS: Height and weight were measured to calculate BMI. Right and left foot plantar pressures were obtained using an AT-4 emed® pressure platform (Novelgmbh, Munich) to calculate the peak force and pressure experienced under areas of each childs feet during static and dynamic conditions.RESULTS: While standing, the obese children generated significantly higher forces over a larger foot area and experienced significantly higher plantar pressures compared to their nonobese counterparts (41.8±17.7; 30.1±12.0 N cm−2, respectively; P<0.022). Similarly, while walking, the obese children generated significantly higher forces over all areas of their feet, except the toes. Despite distributing these higher forces over a significantly larger foot area when walking, the obese children experienced significantly higher plantar pressures in the midfoot (P<0.003) and under the second to fifth metatarsal heads (P<0.006) compared to the nonobese children.CONCLUSIONS: It is postulated that obese children are at an increased risk of developing foot discomfort and/or foot pathologies due to increased plantar loads being borne by the small forefoot bones. Furthermore, continual bearing of excessive mass by children appears to flatten the medial midfoot region during walking. As the long-term consequences of these increased plantar loads are currently unknown, it is recommended that the effects of obesity on the structural and functional characteristics of obese childrens feet be further investigated.