The aim of this work was to investigate physiological, perceptive and neurological responses to exercise intensity in people with multiple sclerosis (PwMS). The thesis begins with reviews of Multiple Sclerosis (MS) and exercise followed by three main studies.
The first study explores the within session and test-retest reliability of motor evoked potentials (MEPs) elicited by transcranial magnetic stimulation (TMS) from the resting tibialis anterior (TA) muscle of people with multiple sclerosis (PwMS). MEPs were recorded from 10 PwMS (2male, 8female) in 5 blocks of 5 trials using stimulators configured to fire a single pulse. MEP peak amplitudes (mV) and MEP areas (mV.mS) were measured at 2 durations MEPshort (30ms) and MEPlong (mean 50ms). The size of the first MEP (T1) from each block (mean 5.1) was significantly different to subsequent trials (T2 -T5) for MEPlong (mean 4.5 p <0.05). After T1 was discarded, repeated measures ANOVAs of blocks (averages of 4 trials) revealed no significant differences within-subjects for amplitudes (MEPpeak) and areas (MEParea) for both MEPshort and MEPlong. A repeat session 7-14 days later revealed no significant differences between sessions (p>0.05). The testretest
intraclass coefficients of correlation (ICC) and their 95% confidence intervals
indicated high (>0.80) reliability for both MEParea and MEPpeak. The results
showed that consistent, repeatable TMS measures were obtained from the resting TA of PwMS.
The second study compared physiological and perceptive measures of PwMS to a group of healthy individuals while performing a symptom-limited graded exercise test (GXT), and through the post-exercise time-course to recovery. 54 PwMS (MSG, mean age 52.8years ± 9.0) and 17 healthy, age-matched controls (CG,mean age 48.9 years ± 5.7) performed a symptom-limited graded exercise test (GXT). Expired air (VO2), heart rate (HR), and differential ratings of perceived exertion (RPE breathing and RPE legs) were recorded during exercise, and HR and RPE (breathing and legs) during the recovery period. There were no significant differences in any baseline measure except RPEleg (MSG mean1.1±1.2; CG 0.2 ±0.4 p <0.05). During the GXT MS group means (±SD) failed to reach any criterion measure considered to represent peak performance. The control group mean exercise measures reached recognised criteria for peak testing on two measures; mean heart rate of within ± 10 beats of age predicted HRmax, mean RER value greater than 1.10. Significant differences existed between groups in all peak measures (mean MSG VO2 peak 20.1±6.4, mean CG VO2 peak 27.8 ±6.8; mean
MSG HRpeak 140.1±24.8, mean CG HRpeak 167.7± 9.4; mean MSG RPE
breathing 5.1±1.7, mean CG RPE breathing 6.8± 2.3; mean MS watts 97.4±35.2, mean CG watts 161.8 ± 43.4 p <0.05) except for RPEleg (mean MSG 6.2 ±1.7, mean CG 7.0±1.8p>0.05). There were no significant effects on the peak measures of variables when weighted by MS classification (RR-MS, SP-MS and PP- MS). There were differences between group recovery values for RPEleg at 10 mins (mean MSG 1.8 ±1.2, mean CG 1.0±1.1 p<0.05) and Temp°C at 3mins (mean MSG 36.5± 0.5, mean CG 36.9± 0.6 p<0.05) and 10mins (mean MSG 36.4±0.4, mean CG 37.0±0.3p<0.05) post-exercise. MS HR remained marginally above preexercise HR values at 10 minutes post-exercise. Differential measures of RPE for both groups recovered to pre-exercise values at 5 mins (±SD). During maximal exertion, it was observed that PwMS irrespective of disease classification, or years from onset were neither limited by their heart rate, nor their breathing, but that leg fatigue or lack of central drive to the lower limb was the reason for their inability to
In the third study, the physiological perceptive and central responses of PwMS were explored during exercise at low and high intensity, and through the timecourse to recovery. Participants performed 2 exercise training (ET) sessions where they performed 20 minutes of exercise on a cycle ergometer at 45% (ET45) and 60% (ET60) relative to peak watts determined during a GXT. 12 MSG and 9 CG completed the 2 exercise sessions. Repeated measures ANOVA revealed no significant differences in groups’baseline measures of HR, Temp°C, RPEbr, RPEleg or TMS measures between-groups or between-sessions. When comparing groups during ET45, measures of all variables were similar, except for RPE leg at 14mins,(mean MSG 3.3 ±1.1, CG 2.1±1.2 p<0.05). During ET60 MSG HR was higher from 14mins (mean 107.8bpm ±12.6 bpm, CG 136.8 bpm ±13.8 p<0.05).
When comparing the results of MSG ET45 and ET60, during the 35 minute postexercise phase MSG HR recovered to pre-exercise values at 10 mins (mean HR 71.4bpm ±12.7, baseline 63.8 bpm ±9.8 p>0.05) after ET45, while post-ET60 HR failed to recover before session-end (mean HR 83 bpm ±11.3, baseline 64.6 bpm ±8.2, p<0.05). TMS measures were significantly depressed after both training sessions. Mean MEP size were 71% ±38% of pre-exercise levels at 30 secs post-ET45 (p<0.05) and 52% ±17.8% post ET60 at 2 minutes (p<0.05). Post-ET45 MEPs recovered to pre-exercise values at 10mins while post-ET-60 MEPs recovered at 20 mins. MEP
latency and MEPρeriph were unchanged. Following ET60 we observed a strong negative relationship between Temp°C and MEPs (r=-.65, p=0.023).
The investigation revealed significant, intensity-dependent, physiological and
perceptive differences, during exercise and through the time-course to recovery. Analysis of responses to post-exercise TMS revealed a significant depression in corticospinal excitability, with a clear intensity-dependent difference in the depth and duration of MEP depression. In addition, an inverse relationship was found between internal body temperature and corticospinal excitability. The results may offer further guidance to clinicians for the provision of safe, appropriate and effective exercise prescription to PwMS.
Faculty of Health and Life SciencesDepartment of Biological and Medical Sciences
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