Regular readers may recall previous posts on the finding that obese individuals tend to spend less time on their feet than lean people – a trait that is apparently not corrected by weight loss.
In a study from the Laboratoire TIMC-IMAG in La Tronche, France, just published in PLoS, Jean-Baptiste Mignardot and colleagues show that obese individuals need more attentional resources to control postural stability while standing than non-obese indivdiuals.
These results were based on observations in 10 non-obese (BMI = 22 age = 42) and 10 obese (BMI=35, age=46) adults, who were asked to maintain postural stability on a force platform in while seated or while standing on one leg.
While there were no differences in postural stability while seated, obese participants showed far greater postural instability (measured as centre of foot pressure oscillations) standing on one leg than their lean counterparts.
Additionally, when challenged with an acoustic reaction time test, there were no differences between the groups while seated but, when standing on one leg, obese individuals had substantially slower reaction times, suggesting that they were exerting far more attentional resources on maintaining their stance than the lean participants.
Thus, it appears that to reduce the risk of falling over, obese individuals must dedicate a substantial part of their attentional resources to postural control, to the detriment of non-postural events.
This may well be one reason why obese individuals would prefer to sit down while performing tasks that require their full attention. Thus, standing may not only be physically exhausting for obese individuals (from holding up that extra weight) but also mentally exhausting from the increased mental demand required to maintain their balance.
What the study does not tell us is whether or not this increased attention cost of standing in obese individuals is simply due to lack of training or perhaps a reflection of some innate neurological problem with balance control.
Indeed, the authors propose that the greater problem with balance experienced by obese individuals may be related to changes in their body schema resulting from altered inputs from cutaneous and proprioceptive receptors to their somato-sensory cortical area responsible for balance and coordination.
The study certainly helps me better understand the almost pathological fear of falling expressed by so many of my overweight and obese patients.
Let us not forget that balance and coordination can be made even worse by some medications (e.g. antidepressants) as well as complications of obesity such as arthritis or diabetic neuropathy.
This is certainly a problem that clinicians should be aware of to help prevent falls and injuries in their obese clients.
Mignardot JB, Olivier I, Promayon E, & Nougier V (2010). Obesity impact on the attentional cost for controlling posture. PloS one, 5 (12) PMID: 21187914