A study published in the Journal of Electromyography and Kinesiology aimed to determine the effect of medial/lateral prosthetic alignment shifts on muscle activity and to compare muscle activity between people with and without transtibial amputations during sit-to-stand. The study’s authors concluded that their results suggested that lateral alignment shifts may reduce muscle activity during sit-to-stand for people with transtibial amputations, and they emphasize the importance of analyzing sit-to-stand in three dimensions.
The researchers quantified ground reaction forces and three-dimensional center-of-mass position to interpret muscle activity results, measured by integrated electromyography (iEMG). Compared to the prescribed alignment, the bilateral knee extensors had greater activity in the medial alignment and the amputated side gluteus medius and less activity in the lateral alignment, which may be a result of altered muscular requirements for postural control, according to the study. In people with transtibial amputations, smaller intact side gluteus medius activity was associated with frontal plane motion of the center-of-mass, which was not observed in participants without amputations.
Compared to individuals without amputations, people with transtibial amputations had greater iEMG in the intact side tibialis anterior and amputated side rectus femoris. The study’s authors wrote that that may be required to brake the body center-of-mass in the absence of the amputated side tibialis anterior.