The nature of the effects of stroke on trunk flexor and extensor muscles during work and at rest

PURPOSE: To investigate the nature of stroke induced functional disturbances of rectus abdominis and erector spinae in their postural and dynamic roles and compare the performances of stroke and neurologically unimpaired groups. METHODS: EMG activity was recorded from rectus abdominis and erector spinae during five rest/work cycles in forward and backward of vertical positions and during reaching and shoe donning. Repeated measures ANOVA was used to compare within and between group EMG activity to determine the significance of differences between paretic and non-paretic muscles of the stroke group and matched muscles of the control group in the two postures and dynamic tasks. RESULTS: In the stroke group rectus abdominis responded normally in most instances, demonstrating weakness only during shoe donning. This weakness was particularly noticeable on the paretic side. Erector spinae activity of the stroke group was significantly higher than the controls during all postural and dynamic work and at rest after most tasks particularly on the paretic side. CONCLUSION: Findings indicated that stroke appears to induce increased activity in erector spinae on both sides during postural and dynamic roles and at subsequent rest. By contrast, rectus abdominis performed reasonably normally after stroke with weakness noted only during dynamic postural support of shoe donning. Explanations for these differences might depend on the extent to which cortical influences to muscles are disrupted by stroke. Generous contributions from the intact hemisphere might enable more normal activity in rectus abdominis, whereas, the abnormal responses of erector spinae might reflect a more severe disruption of cortical influences on motor unit activity.