Hip function and running mechanics in youth athletes
The identification and development of youth sporting talent is becoming increasingly important. However, injuries can disrupt training and hence the development of youth athletes. Although only a small proportion of youth athletes participate in pure running sports, many sports they do compete in involve a large proportion of running. During assessments of gait, clinicians typically evaluate dynamic lower extremity alignment. Poor frontal plane knee control during running is considered a risk factor for the development of injuries such as patellofemoral dysfunction in adults, however, there is minimal knowledge for youth athletes risk factors. This thesis has sought to gain knowledge of hip function and running mechanics in youth athletes; specifically, whether a lower limb functional exercise programme can reduce hip and knee frontal plane motion in this cohort. On the basis of the literature review on gait, strength and lower limb injuries in youth athletes, it was established that runners with lower limb overuse injuries were weaker on measures of hip abduction, extension and internal rotation muscle strength. In addition, these runners demonstrated increased hip internal rotation and hip adduction angles. No published studies focused on youth athletes and running mechanics. The discrepancy in literature regarding the relationship between hip muscle function and lower limb kinematics makes it difficult to assign absolute cause-effect relationships. There was some support for hip strengthening as prevention or rehabilitation for overuse injuries. Training studies with defined parameters, specific to appropriate age and development levels, are needed to optimise intervention strategies. The reliability and variability of within-day and between-day hip isometric strength measures and 3D frontal plane hip and knee range of motion during running was established in youth athletes as it has not been previously reported. Hip abductor, hip flexor, and hip internal and external rotator strength measures demonstrated sufficient within-day reliability to be used as a baseline classification tool for youth athletes. However, the between-day reliability of these measures was poor, and therefore it is not recommended that our technique be used to measure the change overtime in hip strength for youth athletes. Within-day and between-day reliability of hip and knee ab/adduction range of motion during the stance phase of running in a youth athlete population demonstrated average to good reliability. Hip and knee frontal plane range of motion could be useful as clinical screening tools. An intervention including lower limb functional exercises aimed at minimising knee valgus angle could potentially mediate the strength and alignment issues that lead to the development of lower limb overuse injuries in youth athletes. Although our 8-week lower limb functional exercise programme employed for this thesis study was minimal in changing frontal plane hip and knee motion when running, this study was the first to describe effects of such an intervention on running mechanics of youth athletes. Practical implications for future research as a result of this thesis include increasing volume for the lower limb functional exercise intervention to increase the likelihood of a effect on running mechanics, determining a series of lower limb functional exercises suitable for use with youth athletes, and determining more sensitive assessment measures to help classify youth athletes with variable movement patterns.