Biofeedback allows the individual to gain awareness and directly control a biomechanical or biological variable of interest. The biofeedback of postural performance has aroused a great interest of Rehabilitation Sciences due to its potential impact on the control of postural stability. While it is well established that biofeedback seems to limit body movements in orthostatism, it is not clear whether such a postural strategy occurs at the cost of increasing the level of muscle activity and whether it differs between different biofeedback techniques applied to postural control.

This study is aimed at investigating the effect of different types of biofeedback techniques on the level of muscle activity postural sway during standing.

Three adults were tested in three standing conditions: (1) eyes open (EO); (2) biofeedback of acceleration (BFac), consisting of reducing the linear acceleration of the trunk in the anteroposterior (AP) direction; (3) biofeedback of laser (BFlaser), consisting of pointing a laser as close as possible to a target from the right wrist. The acceleration components were collected through a triaxial accelerometer (TrignoTM Wireless EMG System Overview, Delsys, USA; ±2g), positioned roughly at L5 level, and the variability (standard deviation) calculated in the AP direction. Surface electromyograms (EMG) were collected from the medial gastrocnemius (MG) and tibialis anterior (TA) muscles bilaterally from the Trigno system (1.926Hz). The EMG's RMS amplitude was obtained to evaluate the degree of muscle excitation. Due to the small sample size, the statistical analysis involves data description by means of median (minimum – maximum).

In relation to EO (8.41, 7.56 – 8.98 gx10-3), the standard deviation of ACAP reduced with BFac (median, min-max: 7.82, 4.32 – 11.45 gx10-3) and increased with BFlaser (9.83, 6.50 – 11.01 gx10-3). For the right body side, the RMS of TA increased with the biofeedback (BFac: 6.33, 2.99 – 9.67rms; BFlaser: 6.11, 2.31 – 8.32rms) when compared to EO (5.07, 2.11 – 7.16 rms). For the MG, while RMS was smaller with BFac (5.53, 2.95 – 17.84 rms), the RMS was higher with BFlaser (7.35, 2.93 – 16.95 rms) in relation to EO (6.63, 2.51 – 23.92 rms). For the left side, both ankle muscles showed a smaller RMS with BFac (TA: 4.29, 3,70 – 7.07rms; MG: 6.22, 2.53 – 10.93rms) and with BFlaser (TA: 3.59, 2,32 – 3.59rms; MG: 6.90, 2.38 – 15.44rms) do que EO (TA: 5.18, 4.50 – 6.70rms; MG: 8.31, 2.01 – 23.29rms).

These qualitative considerations indicate BFac seems to reduce the size of postural sway, while BFlaser increases it during standing balance, when compared to EO. Furthermore, an asymmetric postural activation was revealed regardless of biofeedback. TA and MG seem to reduce the level of muscle excitation at left, while they are more active at right.

Findings suggest that EMGs may provide different estimates of muscle arousal if collected unilaterally during upright posture with biofeedback. Ongoing study with more individuals to advance knowledge about the potential of biofeedback in improving postural control and reducing the risk of falling.