Differences in lower extremity muscular coactivation during postural control between healthy and obese adults

Introduction: It is well established that obesity is associated with deterioration in postural control that may reduce obese adults' autonomy and increase risks of falls. However, neuromuscular mechanisms through which postural control alterations occur in obese adults remain unclear. Objective: To investigate the effects of obesity on muscle coactivation at the ankle joint during static and dynamic postural control. Materials and methods: A control group (CG; n = 20; age = 32.5 +/- 7.6 years; BMI = 22.4 +/- 2.2 Kg/m(2)) and an obese group (OG; n = 20; age = 34.2 +/- 5.6 years; BMI = 38.6 ++/- 4.1 Kg/m(2)) participated in this study. Static postural control was evaluated by center of pressure (CoP) displacements during quiet standing. Dynamic postural control was assessed by the maximal distance traveled by the CoP during a forward lean test. Electromyography activity data for the gastrocnemius medialis (GM), soleus (SOL) and tibialis anterior (TA) were collected during both quiet standing and forward lean tests. Muscle activities were used to calculate two separate coactivation indexes (CI) between ankle plantar and dorsal flexors (GM/TA and SOL/TA, respectively). Results: CoP displacements were higher in the OG than in the CG for quiet standing (p < 0.05). When leaning forward, the maximal distance of the CoP was higher in the CG than in the OG (p < 0.05). Only the CI value calculated for SOL/TA was higher in the OG than in the CG for both static and dynamic tasks (p < 0.05). The SOL/TA CI value in the OG was positively correlated with CoP displacements during quiet standing (r = 0.79; p < 0.05). Conclusion: Obesity increases muscle coactivation of the soleus and tibialis anterior muscles at the ankle joint during both static and dynamic postural control. This adaptive neuromuscular response may represent a joint stiffening strategy for enhancing stability. Consequently, increased ankle muscle coactivation could not be considered as a good adaptation in obese adults.