Obesity and falls in older women: Mediating effects of muscle quality, foot loads and postural control

Background: Obesity is associated with an increased risk of falls in older women. However, it is not certain whether factors commonly associated with obesity and falls mediate this risk. Research question: Do lower-limb muscle quality, foot loads and postural control mediate the relationship between obesity and falls in women aged 60 years and older? Methods: At baseline, 246 female participants underwent obesity screening (BMI >= 30 kg/m(2)), and measurements of muscle quality (isokinetic dynamometer and dual-energy X-ray absorptiometry), foot loads (pressure platform) and postural balance (force platform). Incident falls were recorded at the end of the 18-month follow-up period via participant recall. To test whether, and to what extent, biomechanical factors mediated the relationship between obesity and falls, the Natural Indirect Effects (NIE), Natural Direct Effect (NDE) and proportion mediated were calculated using the counterfactual approach. Significance level was set at p < .05. Results: 204 participants (83 %) completed the follow-up. As expected, obesity was associated with a higher risk of being a faller (RR: 2.13, 95 % CI: 1.39-3.27). Using the counterfactual approach, only specific torque (NIE: 1.11, 95 % CI: 1.01-1.38) and flatfoot (NIE: 1.10, 95 % CI: 1.01-1.32) were significant mediators of the relationship between obesity and falls. Specific torque and flatfoot mediated 19 % and 21 % of the relationship, respectively. Significance: Lower-limb muscle quality (specific torque) and foot loads (flatfoot) mediate the relationship between obesity and falls in older women. The inclusion of muscle strengthening and podiatry interventions as part of a fall prevention program may benefit this population.