| Spinal cord injury is one of the most disabling health related problems that often results in paralysis and paresis of body musculature below the lesion site. Persons with incomplete-SCI typically exhibit impaired motor performance and varying degrees of functional limitations. Despite the obvious motor dysfunctions, physiological muscle adaptations following incomplete-SCI are relatively unstudied. An understanding of the muscular adaptations following an incomplete-SCI will help in the development of therapies aimed at reducing the secondary effects of paralysis and paresis. The overall objective of this dissertation was to investigate skeletal muscle adaptations following incomplete-SCI using combinations of non-invasive MRI and MRS techniques.;Findings from our human studies reveal that chronic incomplete-SCI is associated with significant muscle atrophy in the affected lower extremity that is uniform between limbs and somewhat influenced by mobility status. In addition, persons with incomplete-SCI demonstrate an increase in the total lipid, IMCL and extramyocellular EMCL content and enhancements in the T 2 relaxation properties of the lower leg muscles. Moreover, repetitive locomotor training with body weight support and a treadmill are associated with significant increases in the plantarflexor muscle size. Data from our animal experiments reveal that the paralyzed rat hindlimb muscle show faster rates of PCr depletion, thereby suggesting that, after SCI, there is either an increase in ATP requirement for similar demands in muscle contraction or the overall supply of ATP is compromised following the injury. In addition, a pronounced decrease in PCr recovery rates implies a less effective oxidative phosphorlyation and a reduction in the mitochondrial oxidative capacity of skeletal muscle. Collectively, findings from this dissertation work reveal that the paralyzed skeletal muscle shows drastic alterations in its morphological and metabolic properties after a SCI and that these adaptations can be successfully characterized by the use of non-invasive MR techniques.;The present work will provide a foundation from which the relationship between skeletal muscle adaptations and function in this population can be further explored. Moreover, the use of sophisticated MR techniques will enable characterizing the paralyzed muscle non-invasively and with high resolution; while also allowing longitudinal follow-ups---all of which are crucial in the assessment of injury mechanisms, disease progression and efficacy of therapeutic interventions. |
