Background: Intensive-Care-Unit Acquired Weakness (ICUAW) is a consequence of prolonged immobilisation in the ICU. Patients report perceived weakness, despite no demonstrable weakness in limb muscles. Research has focused on improving the strength of limb muscles through physical therapy. Patients with ICUAW are at high risk of falls and have poor balance, however the impact of ICUAW on the function of trunk muscles, which have a prominent role in the control of posture, has not been investigated. The tilt table is a medical device used in ICU rehabilitation to put patients into different angles of tilt, therefore reintroducing vertical position. Use of the tilt table has been used to improve upright stability, respiration, strength of limb muscles, and minimise the adverse effects of prolonged immobilisation. The extent to which combining post-ICU rehabilitation tasks with tilt table therapy might improve postural control remains unclear and is the basis for this healthy participant study.
Objectives: To assess the onsets and levels of activity in trunk muscles during a modified version of standard post-ICU rehabilitation task, rapid shoulder flexion, at different angles of tilt (0, 30, 60 and 90 degrees).
Methods: Electromyographic activity of trunk muscles (erector spinae, external obliques, rectus abdominis) was recorded bilaterally from 18 healthy volunteers (8 female, 10 male; mean±SD age 20.8±2.1 years). Participants undertook rapid shoulder flexion (5 times) in response to an auditory cue whilst secured on a tilt table, which was set at 4 different angles of tilt (0, 30, 60 and 90 degrees, with 90 degrees being vertical). Onsets of EMG activity (with respect to the prime mover muscle, anterior deltoid), mean EMG in the 100ms following onset and pre-stimulus (-100ms to 0ms) EMG were determined following averaging across the 5 trials and compared for differences across angles.
Results: There were no significant differences between dominant and nondominant sides, data were therefore collapsed across sides. There was a statistically significant effect of angle of tilt on the onset time of the erector spinae during the task. Post-hoc tests revealed differences between tilt angles 0° and 60° (p=0.03), and 0° and 90° (p=0.048). The mean (±SD) onset time at 0° was 3 (±31) ms, at 30° was 0 (±28) ms, at 60° was -21 (±35) ms and at 90° was -22 (±19) ms.
Discussion: Delayed onsets of trunk muscle activity associated with limb movements are observed in elderly people and in those with chronic low back pain and spinal cord injury. Exercise which advances delayed postural trunk muscle activity has been shown to improve functional trunk activity. We have shown that the angle of tilt influences the onset of trunk muscle activity during exercises that can be employed during rehabilitation. This suggests that combining rehabilitation tasks with tilt table therapy could be used to improve postural control in patients. This may have use in improving symptoms in patients such as those with ICUAW.