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Weakness and subjective fatigue are common features of rheumatoid arthritis (RA). However, whether there is a true increase in the fatigability of rheumatoid skeletal muscle, in which fibre atrophy has been frequently reported, is unclear. Such factors may influence the ability to respond to exercise programmes. In this work, a reliable and sensitive technique for the objective measurement of forearm muscle fatigue during sustained grip was developed, using power spectral analysis of the surface myoelectric signal (SMES).The inter-relationships between grip force (hand function) and the activity and severity of the rheumatoid disease process with muscle fatigue (defined as the decline in the median frequency of the SMES with work, (MDFG)) and the initial median frequency of the SMES (IMF) were examined. It has been previously suggested that the IMF of the SMES may reflect the fibre type of the underlying muscle. The response to a 12-week progressive right hand grip strengthening programme in healthy females and those with RA was also evaluated. Potential predictors of outcome and the mechanisms of strength gain were examined. Forearm muscle fatigue in RA was not significantly greater than in healthy controls. However, higher levels of fatigue were associated with greater systemic disease activity and greater disease severity. The IMF of the SMES was shown to be stable over a wide range of grip forces for a given individual. It was significantly elevated in rheumatoid subjects, and showed a direct association with greater disease severity. Handgrip exercise was highly effective in improving hand function in females with RA. Strength gains were also demonstrated in healthy controls. Subjects with more severe disease and greater IMF of the SMES showed the greatest improvement in hand function. Greater systemic and local disease activity during the 12-week programme were limiting factors to improvement in grip. Local (right hand) disease activity remained stable or improved in the RA group overall, in spite of a trend towards deteriorating systemic and left handed disease activity. The two main potential mechanisms of strength gain (neural adaptation and gains in muscle mass) were assessed in both rheumatoid and healthy groups. The former was assessed by evaluation of the neuromuscular efficiency, derived from the relationship of the root mean square of the SMES at a given grip force. Gains in muscle mass were also assessed using this technique and by volumetric analysis of forearm musculature using magnetic resonance imaging. Although significant gains in muscle mass were demonstrated in the control group, no such gains were seen in the rheumatoid subjects. This indicates that neural adaptation was an effective method of strength gain in the rheumatoid group.

Osteoporosis is a disease characterized by bone loss affecting 10% of the US population over 50 years old. The spine is one critical area affected by the disease. The effectiveness of experimental treatments can be tested on an ovariectomized rat osteoporosis model. As a result, lumbar vertebral bodies are often mechanically tested in uniaxial compression in order to determine whether or not the mechanical properties of the bone in ovariectomized rats improve with treatment. The irregular shape of rat vertebral bodies requires some specimen preparation to create two parallel loading surfaces for uniaxial compression testing. Two specimen preparation methods are reported in the current body of literature. One cuts the cranial and caudal surfaces to make them parallel to each other. The other cuts the caudal surface and uses bone cement to create a flat loading surface at the cranial end. In this thesis a total of twenty rat vertebral bodies were tested. Ten were prepared with a cut specimen preparation method and ten with an embedding method. Each specimen was tested in uniaxial compression and was microCT scanned before and after testing. Eleven parameters were calculated from the mechanical testing data and compared between the two groups using Student’s t-tests. The specimens were also categorized into six failure modes and locations observed in the microCT images. The embedded specimens showed a lower stiffness (p = 0.026), greater yield displacement (p = 0.007) and apparent strain at failure (p = 0.050). These differences were largely attributed to the embedded specimens being 1 mm taller than the cut specimens. The shorter size of the cut specimens affected the mechanical parameters. The cut specimens were easier to prepare and were less sensitive to end effect failures. The embedded specimens kept the endplate, which distributes the load from the intervertebral disk through the vertebral body, intact. In addition, the embedded specimens exhibited two failure modes, endplate failure and failure at the center of the vertebral body, observed in ex vivo human lumbar vertebral body testing, which suggests the interaction of the vertebral body with the endplate is an important factor in vertebral body failure in uniaxial compression testing. In conclusion, neither preparation method showed an overwhelming advantage over the other, and experimental parameters should be considered when choosing a loading surface preparation method. / Thesis (Master, Mechanical and Materials Engineering) -- Queen's University, 2013-09-30 11:58:32.794

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