Evidence suggests that a flexible, task-dependent neuronal coupling of the upper and lower limbs exists, and this allows for coordinated rhythmic movement (e.g., locomotion). To further understand this coupling, muscle activity and reflex patterns can be examined by stimulating peripheral nerves during various tasks. In particular, cutaneous reflexes demonstrate task- and phase-dependent modulation, making them highly sensitive probes into neural activity during rhythmic movement. The purpose of this research was to use reflex modulation to probe the neuronal coupling between the arms and legs. This was done using a cycling paradigm that allowed for the separation of arm and leg movement, which is difficult to do in most forms of locomotion (i.e., walking). Participants (N=14) performed three cycling tasks: 1)arm cycling with stationary legs (ARM); 2)leg cycling with stationary arms (LEG); and 3)combined arm and leg cycling (ARM&LEG). The relative contributions from the arms and legs to reflex modulation in the legs were then determined throughout the movement cycle. It was hypothesized that the individual contributions from arm and leg movement to reflex amplitudes in the legs would summate during the combined arm and leg task. This hypothesis was tested explicitly by comparing the reflex amplitudes expressed during the combined arm and leg task to the algebraic summation of the reflex amplitudes expressed during the arm cycling and leg cycling tasks alone. Static trials were also collected at 4 positions within each task. Tasks were performed under two different cycling conditions: 1) Focused tibialis anterior (TA) contraction (FCC) (N=14); and 2) normal cycling (NC) (n=8). During all trials, stimulation was delivered pseudorandomly throughout the movement cycle to the superficial peroneal nerve at the ankle. EMG was recorded bilaterally from muscles in the arms and legs, and kinematic data were obtained from the elbow and knee joints. Results focused on the middle latency reflex amplitudes in TA (ipsilateral to the site of stimulation) during the FCC condition because the focused contraction did not significantly alter EMG or reflex activity in the other leg muscles studied. This also allowed for comparisons among tasks at comparable EMG levels. The main finding from this study was that reflex amplitudes expressed during the ARM&LEG task agreed with the predicted algebraic summation of reflex amplitudes expressed during the ARM and LEG tasks separately. Examination of the relative contributions from the arms and legs to the reflexes expressed during the combined task revealed that across all movement phases the legs accounted for 33% (p < .05) of the variance observed during the ARM&LEG task, while the arms accounted for an additional 5% (p < .05). The relative contributions from the arms and legs were also found to be phase dependent. That is, the relative contribution from the arms was dominant during the power phase of leg cycling while the leg contribution was dominant during the recovery phase. More specifically, the greatest contribution from the arms accounted for 57% of the variance in the ARM&LEG task when the leg was at 11 o'clock (p < .05) and the greatest contribution from the legs was 71% of the variance accounted for when the legs were at 9 o'clock (p < .05). Additionally, characteristic patterns of reflex amplitude modulation (i.e., phase- and task-dependent modulation) were observed during most of the cycling tasks. In conclusion, these findings suggest evidence for a neuronal coupling between the rhythm generators responsible for arm and leg movement which is functionally gated throughout the movement cycle of a combined arm and leg task.
| Identifer | oai:union.ndltd.org:uvic.ca/oai:dspace.library.uvic.ca:1828/1841 |
| Date | 13 November 2009 |
| Creators | Balter, Jaclyn Elise |
| Contributors | Zehr, E. Paul |
| Source Sets | University of Victoria |
| Language | English, English |
| Detected Language | English |
| Type | Thesis |
| Rights | Available to the World Wide Web |
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