Abstract
Evidence suggests that the primary motor cortex (M1) is involved in both voluntary, goal-directed movements and in postural control. Trunk muscles are involved in both tasks, however, the extent to which M1 controls these muscles in trunk flexion/extension (voluntary movement) and in rapid shoulder flexion (postural control) remains unclear. The purpose of this study was to investigate this question by examining excitability of corticospinal inputs to trunk muscles during voluntary and postural tasks. Twenty healthy adults participated. Transcranial magnetic stimulation was delivered to the M1 to examine motor evoked potentials (MEPs) in the trunk muscles (erector spinae (ES) and rectus abdominis (RA)) during dynamic shoulder flexion (DSF), static shoulder flexion (SSF), and static trunk extension (STE). The level of background muscle activity in the ES muscles was matched across tasks. MEP amplitudes in ES were significantly larger in DSF than in SSF or in STE; however, this was not observed for RA. Further, there were no differences in levels of muscle activity in RA between tasks. Our findings reveal that corticospinal excitability of the ES muscles appears greater during dynamic anticipatory posture-related adjustments than during static tasks requiring postural (SSF) and goal-directed voluntary (STE) activity. These results suggest that task-oriented rehabilitation of trunk muscles should be considered for optimal transfer of therapeutic effect to function.
Highlights
Trunk muscles play an essential role in the maintenance of upright posture and this has been extensively studied during limb movements, support surface translations and perturbations applied to the trunk [1,2,3,4]
Post-hoc tests showed that the motor evoked potentials (MEPs) amplitude in the dynamic shoulder flexion (DSF) task (0.59±0.33 mV) was greater than the static shoulder flexion (SSF) (0.32±0.27 mV; p
There was no effect of TASK (F1.45, 26.06 = 0.45, p = 0.58) on MEP latencies (DSF: 16.43±5.10 ms; SSF: 16.17±4.17 ms; STE: 17.24±1.64 ms; Fig 3b)
Summary
Trunk muscles play an essential role in the maintenance of upright posture and this has been extensively studied during limb movements, support surface translations and perturbations applied to the trunk [1,2,3,4] These muscles are activated for voluntary goal-directed movements such as simple movements of the trunk into flexion, extension and rotation [5,6,7]. Corticospinal Excitability of Trunk Muscles recorded over the motor cortex and electromyographic (EMG) activity is lower in postural than voluntary goal-directed tasks [12, 13]. This implies different neural mechanisms may mediate control of the two distinct classes of motor function
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