High-gain visual feedback exacerbates ankle movement variability in children

The purpose was to compare the effect of low- and high-gain visual feedback on ankle movement variability and muscle activation in children and young adults. Six young adults (19.8 +/- A 0.6 years) and nine children (9.4 +/- A 1.6 years) traced a sinusoidal target by performing ankle plantar/dorsiflexion movements. The targeted range of motion was 10A degrees, and the frequency of the sinusoidal target was 0.4 Hz for 35 s. Low-gain visual feedback was 0.66A degrees, and high-gain visual feedback was 4.68A degrees. Surface EMG was recorded from the tibialis anterior (TA) muscle. Movement variability amplitude was quantified as the standard deviation of the position fluctuations after the task frequency was removed with a notch filter (second-order; 0.3-0.5 Hz). We quantified the oscillations in movement variability and TA EMG burst using the following frequency bands: 0-0.3, 0.3-0.6, 0.6-0.9, 0.9-1.2, and 1.2-1.5 Hz. Children exhibited greater movement variability than young adults, which was exacerbated during the high-gain visual feedback condition (P < 0.05). The greater ankle movement variability in children at the high-gain visual feedback condition was predicted by greater power within the 0-0.3 Hz of their movement variability (R (2) = 0.51, P < 0.001). The greater power in movement variability from 0 to 0.3 Hz in children was predicted by greater power within the 0-0.3 Hz in their TA EMG burst activity (R (2) = 0.6, P < 0.001). The observed deficiency in movement control with amplified visual feedback in children may be related to an ineffective use of visual feedback and the immaturity of the cortico-motor systems.