<P>To examine the effects of purported fiber-type transformation following spinal cord injury (SCI), twitch contractile properties of the soleus, tibialis anterior (TA) and thenar muscles were examined in individuals with chronic (> 4 years) SCI. Furthermore, the force-frequency relationship, fatigue and posttetanic potentiation (PTP) of the paralyzed TA muscle were also evaluated. Nine adults with SCI (22-59 yrs; lesion level C3-T2) and 9 age-and gender-matched able-bodied controls (AB) participated in this study.</P><P>On the first visit to the laboratory, the maximum twitch response for all three muscles was determined by delivering a series of single stimuli with gradually increasing intensity. For evaluation of PTP, tetanic stimulation (100Hz) was applied to the TA for 5 seconds followed by single twitches delivered at 5 seconds after tetanus and then at 30-second intervals for 4 minutes posttetanus. On a second visit, the force-frequency relationship (FFR) and 15Hz fatigue of the TA was evaluated. One second bursts ranging from 1-1OOHz were delivered randomly with 2 minutes of rest in between each frequency for assessment of FFR. Following a 1 0-minute rest period, the first fatigue protocol was given, consisting of 1-minute of tetanic stimulation at 15Hz. At the third session, the 30Hz fatigue of the TA was performed, consisting of 1-minute of tetanic stimulation at 30Hz.</P><P>In the soleus muscle, the AB had a higher peak twitch torque (PT) and M-wave amplitude compared to.the SCI group (14.2 ± 3.9Nm vs. 8.9 ± 6.1Nm; p = 0.058, and
13.5 ± 5.3mV and 5.5 ± 4.0mV; p < 0.05, respectively). Contractile speed was not significantly different between groups. Time to peak torque (TPT) was longer in AB
(111.5 ± 15.4ms) compared to the SCI (76.7 ± 25.0ms; p<0.05) due to the larger twitches; however, the rates of torque development (RTD) were similar between groups. In the TA muscle, AB and SCI had similar PT (2.8 ± 0.5Nm and 3.2 ± 1.2Nm, respectively). TA contractile properties were faster in SCI, as seen by significantly shorter TPT and faster RTD (p<0.05). M-wave amplitude of AB was significantly greater than the SCI group,
8.3 ± 2.6mV versus 4.2 ± 1.7mV, respectively (p<0.05). Finally, in the thenar muscle, PT appeared to be smaller in AB compared to SCI, 1.7 ± 0.8Nm versus 2.9 ± 1.3Nm, respectively (p = 0.094). The RTD was faster in the SCI group compared to AB (p<0.05).</P><P>Evaluation of FFR revealed that the curve of the SCI was shifted to the left of that of AB. The F50 (frequency required to elicit 50% of maximum peak torque) was significantly lower in the SCI compared to AB, 6.7 ± 3.4Hz and 16.7 ± 4.1Hz, respectively (p<0.05). Following the fatigue protocols, SCI group tended to fatigue more rapidly and to a greater extent than AB at both frequencies, however this was only significant at 15Hz. The M-wave declined with fatigue (30Hz) in both groups, but this decline tended to be more rapid in SCI.</P><P>For the assessment of PTP, both groups started off with similar baseline twitches in their TA muscle (2.7 ± 0.3Nm and 2.9 ± 0.8Nm, respectively). At 5 seconds following tetanus, PT was significantly greater in both groups, but the amount of potentiation was greater in SCI versus AB (p = 0.058). Over the 4-min recovery period, PT declined in both groups until it was no longer significantly greater than baseline by 3 minutes 30 seconds. The potentiated twitch of both groups was faster than at baseline. RTD increased significantly by an average of 56% in the AB group and 91% in the SCI group and was significantly greater in SCI compared with AB at 30-150 seconds post-tetanus (p<0.05). At 5 seconds post-tetanus, RTR was significantly faster in both groups and had increased by 77% and 53% in the AB and SCI groups, respectively. The recovery ofRTD and R TR over the 4 minutes occurred more rapidly in AB versus SCI.</P><P>In conclusion, changes in contractile properties following SCI differ between muscle groups; faster contractile properties indicative of fiber type transformation are more evident in TA and thenar muscle groups, compared with the soleus. The smaller M-waves seen in the lower extremities support the significant muscle atrophy following SCI. Furthermore, the predicted transformation towards a higher proportion of fast-twitch fibers following paralysis was supported by a trend for decreased fatigue resistance and significantly greater PTP in the SCI group. The FFR data, however, did not support this predicted fiber type transformation, shifting to the left instead of the right. This leftward shift of FFR has been reported in other paralyzed human muscle presenting with faster contractile speeds; the mechanisms behind this warrant further investigation.</P> / Thesis / Master of Science (MSc)
| Identifer | oai:union.ndltd.org:mcmaster.ca/oai:macsphere.mcmaster.ca:11375/21785 |
| Date | 07 1900 |
| Creators | Rodrigues, Lisa |
| Contributors | Hicks, Audrey, Kinesiology |
| Source Sets | McMaster University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis |
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