The effect of visual cues on muscular activation in the lower limbs of Parkinson's disease patients with freezing of gait: a preliminary study

Freezing of gait (FOG) is a disabling symptom of Parkinson's disease (PD) patients, especially in advanced stages. Visual cues, such as the laser, have been confirmed to improve kinematic performance and alleviate FOG incidences. However, the muscular effect is unknown. In this study, we aim to investigate the effect of visual cues on muscular activity in the lower limbs of PD patients with FOG. Surface EMG signals of the tibialis anterior (TA), lateral gastrocnemius (GL), rectus femoris (RF), and biceps femoris (BF) muscles were collected from eight patients (FOGer) and eight healthy elderly (HC) in both normal walking and walking with laser cues. Results showed that visual cues improved FOGer's muscular activation pattern towards normal. The RMS of TA was significantly increased in the loading response phase (p=0.02) and decreased in the pre-swing phase for FOGer (p=0.005) under visual cue. The RMS of GL in FOGer was considerably reduced in the loading response phase (p<0.001) and increased in the pre-swing phase (p=0.008) of their gait cycle. A significant strong correlation was also observed between the decrement in GL RMS during the loading response phase and the increment in GL RMS during the pre-swing phase (R=-0.952, p<0.001) incurred by visual cue in FOGer. These results indicate that the visual cues can help FOGer to modulate their muscular activation of ankle muscles, especially to normalize GL's activation distribution during stance. For clinical purposes, future rehabilitative strategies aimed at the modulation of ankle muscles are suggested.