Patterned electromyographic activity in the sit-to-stand movement.

OBJECTIVES: Postural activity is an essential part of any voluntary movement. In movements involving all body parts such as in the sit-to-stand maneuver (STS), postural activity becomes intermingled with the activity required to perform the actual movement, and is usually difficult to recognize.
METHODS: In this paper, we have analyzed the electromyographic activity of muscles of the leg, thigh, trunk and neck in 20 healthy volunteers who performed the STS maneuver. In order to identify the postural and the executional EMG activity, subjects were requested to perform the movement according to 6 predefined experimental conditions. Our hypothesis was that changing the conditions or the strategies of the movement would modify the postural activity, without significantly altering the EMG pattern required for performing the movement itself.
RESULTS: Tibialis anterior (TA), abdominal (ABD) and sternocleidomastoid (SCM) were the muscles activated first in the most natural condition for the movement (reference), but their activity and that of the trapezius (TRA) was suppressed or greatly diminished in other conditions. Conversely, lumbar paraspinal (LPS), quadriceps (QUA), and hamstrings (HMS) were activated in a patterned sequence that was invariable in all conditions, and time locked to the moment of take-off from the seat. The soleus (SOL) was the last muscle activated and, together with QUA and HMS, remained active during standing.
CONCLUSIONS: We conclude that TA, SOL, ABD, SCM and TRA are involved in preparatory and accompanying postural movements, while LPS, QUA, and HMS are activated in a consistent patterned sequence and can be considered the executional muscles for the STS movement. Recognition of the role of each muscle in the STS movement can contribute to a better understanding of the movement deficits of certain patients, and help to devise adaptive motor strategies in neurorehabilitation.