Effects of different unstable supports on EMG activity and balance.

This study analysed the equilibrium strategies and EMG activity during postural equilibrium in four different unstable surfaces. Thirteen team sport males were tested on a FLAT surface and on three different wobble boards (JAKOBS(®) with easy multidirectional displacements, FREEMAN with strong multidirectional displacements and LATERAL with unidirectional lateral displacements). They had to maintain single-limb stance during 5s for each condition. The right foot centre of pressure (COP) position and its variability with concomitant EMG activity of soleus (SOL), tibialis anterior (TA), peroneus longus (PL) and extensor digitorum longus (EXD) muscles were recorded. Subjects maintained balance by making seesaw rotations. LATERAL and FREEMAN boards demonstrated significantly greater COP variability than JAKOBS(®) and FLAT in both anteroposterior and mediolateral directions. Similarly, PL, EXD, and TA muscles EMG activity were significantly greater using the LATERAL board, and in some cases using FREEMAN as compared with JAKOBS(®) and FLAT. These results highlighted new knowledge about central nervous system organisation while keeping equilibrium with a predominant anteroposterior control.