Cerebral palsy (CP) is the largest single cause of childhood physical disability. While the brain lesion responsible for CP is static, there is a cascade of secondary musculoskeletal adaptations including reduced muscle size, reduced joint range of motion, increased joint stiffness, and muscle weakness. These secondary alterations progress with age and contribute to a gradual loss of functional capacity into adulthood. Strength training has been used to increase muscle strength in individuals with CP, however it may not be an effective intervention for improving gross mobility-related measures, such as walking performance. It is also unknown whether skeletal muscle in young adults with CP can undergo hypertrophy or architectural adaptations in response to different exercise modes. The general aim of this thesis was to examine the effect of combined functional anaerobic and strength training (FAST) on muscle properties, functional capacity, and gait in adolescents and young adults with CP.
A systematic review was undertaken (Chapter 2) to determine the effects of muscle strengthening interventions on skeletal muscle morphology and architecture in children and adolescents with CP. The analysis revealed preliminary evidence that strength training leads to increased muscle size in children and adolescents with CP, accompanied by an increase in muscle strength. Muscle hypertrophy findings may, however, be confounded by factors such as natural growth and concurrent therapies. The findings of this review informed the design of the FAST program and outcome measures used in the following studies to better understand the muscular responses to exercise training in this population. The full study protocol for the FAST intervention is described in Chapter 3. There have been no previous exercise trials conducted in young adults with CP using training parameters that meet established guidelines, that have measured muscle morphology and architecture outcomes. Details of the functional anaerobic and resistance training parameters and progressions according to established guidelines are set out, as well as establishing a-priori outcome measures and the data analysis plan for implementation of the intervention.
A cross-sectional study was undertaken (Chapter 4) to investigate the relationships between muscle strength, stiffness, and functional capacity in a larger sample of adults with CP. The results of this study demonstrated that maximum isometric plantar flexion strength independently explained 50 – 61% of variance in functional capacity outcome measures. Passive medial gastrocnemius muscle fascicle stiffness and ankle joint stiffness were not related to functional capacity measures. These findings suggest lower isometric muscle strength of the plantar flexor muscles contributes to the decline in functional capacity in adults with CP.
Chapter 5 investigated the impact of the FAST intervention on lower limb muscle volumes, joint and muscle stiffness, muscle strength, and functional capacity in a sample of 17 young adults with CP. Participants were randomised to 12 weeks, 3 sessions per week, of high intensity functional anaerobic and progressive resistance training of the lower limbs (n=8), or a waitlist control group (n=9). Pre- and post-training plantar flexor and tibialis anterior muscle volumes and composition, passive and active plantar flexor muscle properties, and functional capacity outcomes were assessed. The training group had higher values compared to the control group (adjusted mean difference) at 12-weeks for: more- and less-impaired total plantar flexor and tibialis anterior muscle volumes; maximum isometric plantar flexion strength; muscle power sprint test peak power; agility shuttle time; composite functional strength score; and six-minute walk test distance. The addition of anaerobic training to progressive resistance exercise likely contributed to the improved functional capacity.
The final experimental study (Chapter 6) reports on the gait outcomes following the FAST intervention. Participants walked at a preferred walking speed on a force instrumented, tandem treadmill, while three-dimensional kinematics, kinetics were simultaneously acquired. There were no changes between the training group and control group for maximum ankle DF angle at foot contact or during stance; gait profile score; and peak ankle power during late stance. Within-group analysis revealed an increase in ankle power generation during late stance after training in the intervention group, in part due to a compensatory reduction in hip power generation, indicating a potential trade-off between the two joints post-training. Overground functional capacity improvements reported in Chapter 5 occurred in the absence of treadmill gait kinematic changes.
The collection of studies in this thesis provides new information on the relationships between muscle structure and function in adults with CP, and the influence of a combined FAST intervention on muscle properties, functional capacity, and gait. Skeletal muscle in high functioning young adults appears to be capable of undergoing a hypertrophic response to FAST. Undertaking specific anaerobic exercises in addition to resistance exercise may be important for improving functional capacity in these individuals. Taken together, these findings have important implications for the prescription of exercise in high functioning young adults with CP as a means of addressing the muscle and functional deficits that progress with age in this population.