Activation of flexor and extensor trunk muscles in hemiparesis

Objective: The purpose of this work was to study the bilateral activity of trunk flexor and extensor muscles in post-stroke hemiparetic patients. Design: Criterion variables were degree of temporal synchronization and level of electromyographic activity in pertinent muscle pairs during two symmetrical tasks: (1) from reclined sitting, bringing the trunk forward; (2) during upright sitting, shrugging shoulders, and extending back. The recti abdomini and external oblique muscles were tested as prime movers of the first task, and the lumbar erector spinae and latissimus dorsi muscles were tested in the second task. Electromyographic recordings from these muscles during three repetitions of each exercise were used for analysis. Results: Cross-correlation analysis pointed to higher temporal synchronization between the abdominal muscles than between the back extensor muscles and in axial compared with para-axial muscles. Differences between patients and controls were found only for the erector spinae muscle pair, which indicates less synchronous activity between the two sides in the patients. The average electromyographic activity level was comparable for corresponding abdominal muscles, both in the patients and in the control subjects. Regarding the back extensor, side differences were detected for the latissimus dorsi muscles in both groups, with the paretic and right side less active in the patients and controls, respectively. Conclusions: Altogether, the findings do not support the claim of unilateral deficits in the function of trunk muscles in post- stroke hemiparetic patients. They emphasize the need for further characterization of the impairment of trunk extensor and flexor muscles in post-stroke patients.