Figure 8. Behaviour of the deep compartment of tibialis anterior during normal standing.

For each 3 s interval of a whole trial the correlation between the deep compartment of tibialis anterior and CoG was calculated. The intervals were classified into negatively (white bars) and positively correlated intervals (black bars) and whole trial (grey bars). For these groups the following quantities are shown: A, correlation between the deep compartment of tibialis anterior change in muscle length and CoG; B, tibialis anterior standard deviation of EMG levels (modulation of activity); C, mean tibialis anterior EMG levels (tonic activity); D, percentage duration in each condition. The horizontal axis represents each subject tested (1–9); values are the mean for each subject and error bars show the standard error of the mean. The ‘Mean’ column is the average and s.e.m. for all the individuals. For all the subjects, the deep compartment of tibialis anterior is mainly negatively correlated with CoG (A and D) and its negative correlation portions are associated with a low modulation in the EMG activity (B) and in tonic activity (C).