Browsing by Author "Kung, Stacey Mikayla"
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- ItemAge-related determinants of the walk-to-run transition in youth : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Sport and Exercise Science, Massey University, Wellington, New Zealand(Massey University, 2020) Kung, Stacey MikaylaThere is a lack of consensus regarding when mature or adult-like gait is achieved in youth. The ability to adjust gait during the walk-to-run transition (WRT) may be a good indicator of whether gait has matured. Specifically, age-related differences in the preferred transition speed (PTS) and determinants of WRT can provide insight into self-organising behaviours and how effectively gait patterns are regulated in youth. This thesis therefore assessed WRT in 49 youth (10-17-year-olds) and 13 young adults (19-29-year-olds) to: 1) investigate how effectively youth can adjust to increasing gait speed; and 2) explore age-related differences in determinants of PTS. Participants completed a WRT treadmill protocol that started at a self-selected walking speed and increased by 0.06 m∙s⁻¹ every 30 s to determine PTS. Participants also walked and ran on a treadmill at speeds near PTS (PTS, PTS±0.14 m·s⁻¹, PTS±0.28 m·s⁻¹). During these tests, muscle activity (rectus femoris, biceps femoris, tibialis anterior, medial gastrocnemius), oxygen consumption, heart rate and perceived exertion were assessed for their role in determining PTS. There were no age-related differences in PTS despite there being anthropometric differences. However, 10-12-year-olds exhibited more exploratory behaviour when determining PTS, while adults and 15-17-year-olds generally used a single transition to determine PTS. Age-related differences in PTS determinants were observed. Specifically, the biceps femoris and medial gastrocnemius were additional weak links among 10-12-year-olds and 10-17-year-olds, respectively, suggesting these muscles continue developing through childhood and adolescence. Because youth transition to minimise the demands of more muscles than adults, they may have more conflicting sources of feedback arising from the musculature when adjusting their gait. The 10-14-year-olds also exhibited greater difficulties distinguishing differences in perceived exertion between walking and running at speeds near PTS. The inability to anticipate increases in effort as gait speed increased could explain the indecisiveness in determining PTS among 10-12-year-olds. Overall, this thesis improves our understanding about rate-limiting factors of gait maturation. It seems that 10-12-year-olds have more conflicting sensory cues involved in regulating gait, which can cause difficulties determining how to optimise their gait. As the musculoskeletal system matures through adolescence, so does the ability to adapt gait effectively.
- ItemLower extremity kinematic and temporal changes in adolescent baseball pitchers during a simulated game : a thesis presented in partial fulfilment of the requirements for the degree of Master of Health Science in Sport and Exercise at Massey University, Wellington, New Zealand(Massey University, 2015) Kung, Stacey MikaylaAim: To investigate whether adolescent baseball pitchers change lower extremity kinematic and temporal parameters during a simulated game, which may affect performance outcomes. Method: Twelve male adolescent pitchers (14 – 16 years) threw 90 pitches (6 sets of 15 pitches) from an artificial mound towards a pitching net. Angular displacements, angular velocities and temporal parameters at the hip, knee and ankle of the trailing and leading legs were collected throughout the pitching cycle. Dependent variables were analysed from the balance position through to maximal internal rotation of the shoulder. Performance outcomes of ball velocity and pitching accuracy were also recorded. The last five pitches of the second and final sets were compared to determine whether changes in the pitching mechanics and performance outcomes had occurred by the end of the simulated game. Results: Pitchers assumed a less upright posture and the leading leg was not raised as high at the balance position in the final set. Throughout stride phase, pitchers decreased maximal hip extension and ankle plantarflexion displacements in the trailing leg. Additional decreases in the maximal angular velocities for hip abduction and knee extension were seen throughout the stride phase in the final set. Foot contact occurred earlier in the final set, resulting in decreased hip flexion and increased hip abduction in the leading leg. No kinematic differences were observed between sets at ball release. Ball velocity and pitching accuracy decreased in the final set. Conclusion: Kinematic differences in the lower extremities suggest that lower extremity musculature may have been affected by fatigue by the end of the simulated game. Consequently, pitchers may have produced less forward momentum during the final set of pitches, which could have contributed to the decreased ball velocity. The altered balance position seems to be the underlying factor for the subsequent changes in the lower extremity pitching mechanics. Therefore, the leading leg hip flexors and the trailing leg hip and knee extensors may require strengthening to maintain the balance position. Additional strengthening of the ankle plantarflexors would assist the hip and knee in producing consistent propulsive forces during the stride phase throughout a game.