Patterned electromyographic activity in the sit-to-stand movement

Objectives: Postural activity is an essential part of any voluntary movemen t. In movements involving all body parts such as in the sit-to-stand maneuv er (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 elechomyographic activity of m uscles of the leg, thigh, trunk and neck in 20 healthy volunteers who perfo rmed the STS maneuver. In order to identify the postural and the executiona l EMG activity, subjects were requested to perform. the movement according to 6 predefined experimental conditions. Our hypothesis was that changing t he conditions or the strategies of the movement would modify the postural a ctivity, without significantly altering the EMG pattern required for perfor ming the movement itself. Results: Tibialis anterior (TA), abdominal (ABD) and sternocleidomastoid (S CM) were the muscles activated first in the most natural condition for the movement (reference), but their activity and that of the trapezius (TRA) wa s 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 lake-off from the seat. The soleus (SOL) was the last mus cle activated and, together with QUA and HMS, remained active during standi ng. Conclusions: We conclude that TA, SOL, ABD, SCM and TRA are involved in pre paratory and accompanying postural movements, while LPS, QUA, and HMS are a ctivated in a consistent patterned sequence and can be considered the execu tional muscles for the STS movement. Recognition of the role of each muscle in the STS movement can contribute to a better understanding of the moveme nt deficits of certain patients, and help to devise adaptive motor strategi es in neurorehabilitation. (C) 1999 Elsevier Science Ireland Ltd. All right s reserved.