Postural control in obese adolescents assessed by limits of stability and gait initiation.

The biomechanical changes in postural control and in motor activities linked to obesity are still not fully understood. The aim of this study was to assess the adaptation in static and dynamic control of equilibrium when the body mass to be stabilized and moved is increased through obesity. Postural stability limits and gait initiation at slow and fast velocities were compared in a case control study that included a group of obese adolescents and a control group of adolescents with normal weight. The consequences of overweight are more clearly evident from the results on dynamic stability of the obese group than those on static equilibrium. Both the lower values of the biomechanical parameters characterizing the progression velocity of gait and the longer duration of the swing phase for the fast velocity condition suggest that obesity acts as a slowing factor. However, the reduction of the postural stability limits of the obese group, their inability to increase the anticipatory phase duration unlike the control group, the increase in the double support phase duration as well as some difficulty in controlling the fall of the centre of gravity suggest that, in these subjects, an adaptive strategy is adopted to preserve equilibrium by limiting progression velocity.

Muscular compensation and lesion of the anterior cruciate ligament: contribution of the soleus muscle during recovery from a forward fall.

BACKGROUND: Knee stability following an anterior cruciate ligament lesion has been widely studied. Only recent studies focused on the contribution of the soleus muscle. Our purpose was to characterize the dynamic and muscular activity of balance recovery in healthy subjects and patients with an anterior cruciate ligament rupture. The role of the soleus was investigated in the ipsilateral compensation developed to stabilize the knee and in the contralateral compensation to recover balance. METHODS: Twelve anterior cruciate ligament deficient patients, ten anterior cruciate ligament repaired patients and 14 control subjects were recorded during a forward fall involving stepping to recover balance. FINDINGS: The dynamic of the centre of gravity remained normal when compared to the control group regardless of the treatment, suggesting an adapted compensation to knee instability in this situation. A bilateral increase in soleus activity was related to an increased duration in the balance recovery process in all patients. Patients used one of two strategies to recover balance regardless of the treatment: reducing the step length, involving an early recruitment of the soleus before heel contact, or anticipating braking with a similar step length requiring a predominant activity of the hamstrings. INTERPRETATIONS: These results suggest that bilateral activity of the soleus is involved to compensate for instability and highlight the contribution of the soleus to rehabilitation after an anterior cruciate ligament lesion, not only as a compensatory muscle acting at the knee level but also at a higher level in the bilateral control of stance.