Balance Without Sight: A Surface Electromyography Study of Four Standing Yoga Postures Performed with and Without Visual Feedback

Abstract

Standing balance postures in yoga require continuous, moment-to-moment correction from the leg muscles and taking away vision is known to shift more of that correction onto the proprioceptive and vestibular systems. This study measured surface electromyography (EMG) from the gastrocnemius, soleus, vastus medialis, and vastus lateralis in 37 young adult male yoga practitioners while they held four standing balance asanas -- Natarajasana, Garudasana, Vrikshasana, and Virabhadrasana III -- first with the eyes open and then with the eyes closed. Root-mean-square (RMS) amplitude was compared across asanas and visual conditions using two-way repeated-measures ANOVA, with Greenhouse-Geisser correction when sphericity was violated. All four muscles trended higher without vision, and the pooled non-visual RMS ran 4.9 to 25.2 [mu]V above the visual condition in three of the four muscles. The interaction between asana and visual condition reached significance for the gastrocnemius, vastus medialis, and soleus (all p < .05). Vrikshasana produced by far the largest rise in gastrocnemius activity once the eyes closed (+59.7 [mu]V), while Virabhadrasana III produced the largest rise in soleus activity (+32.3

[mu]V). The two quadriceps muscles behaved differently in Natarajasana, where activity was actually higher with the eyes open, the only reversal found in the data set. These results indicate that the postural cost of closing the eyes is neither uniform across muscles nor constant across poses, and that the ankle muscles absorb more of that cost than the thigh muscles in most, though not all, of the asanas tested.