Biomechanical investigations of coordination during initial acceleration in highly trained to world class sprinters

Abstract

Initial sprint acceleration is a complex and dynamic skill, requiring the application of large forces to propel the body forwards. Effective force application is achieved through the use of joint and segment rotations in an organised and inter-related manner. While many of the isolated angular kinematic features associated with effective external force profiles are established, little is currently known about the relationships that exist between the key segments during the first steps of acceleration, i.e., the coordination of movement between functionally related elements. Through a series of three studies, this thesis explores inter- and intra-limb coordination during initial acceleration in sprinters ranging from highly trained to world class level, to enhance the understanding of sprint acceleration technique and performance.

The first study provided a detailed description and quantification of inter-limb thigh-thigh, intra-limb shank-foot, and trunk-shank coordination during the first four steps of acceleration, and investigated changes in coordination between steps. Specific coordination features were identified and between-individual variation in coordination patterns in preparation for, or response to, the major transitions in the step cycle, i.e., touchdown and toe-off, were observed. Additionally, step-to-step changes in coordination and angular kinematics were identified, showing clearly differentiated coordination in step 1 compared to later steps.

The second study utilised a novel application of hierarchical cluster analysis to vector coding data in order to identify and characterise sub-groups of sprinters with similar thigh-thigh and shank-foot coordination patterns, and subsequently explored discrete kinematic and performance differences between sub-groups. Three sub-groups were identified in step 1 and two sub-groups over steps 2-4. Sub-groups tended to be differentiated by differences in thigh-thigh coordination at the beginning and end of the step, and shank-foot coordination during flight as well as during ankle dorsiflexion in early stance. Combining sub-groups from step 1 and steps 2-4 to describe entire initial acceleration strategies, cluster combinations identified coordination approaches more likely to be associated with higher level sprinters and better performance.

In the final investigation, relationships between coordination and lower body strength were evaluated in the context of dynamical systems theory, and the interaction of these two factors with regard to acceleration performance was explored. Several correlations existed between measures of lower body strength and features of thigh-thigh and shank-foot coordination, while multiple regression analysis suggested the presence of interaction effects between coordination and tests associated with lower body power in relation to performance. Thus, lower body power appeared to influence the relationships between coordination features and performance, such that the effectiveness of particular coordination patterns varied depending the lower body power of the athlete.

The work included in this thesis provides a basis for understanding coordination during initial sprint acceleration, and includes several novel and exploratory approaches to investigating these questions which provides relevant information for practitioners and coaches interested in exploring the organisation of the body and coordination of segments during initial acceleration. Moreover, this work facilitate the generation of new hypotheses and encourages new directions in future research.