Sport specialisation is defined as year-round, intentional participation in a single sport, to the exclusion of other sport, and it is a topic of ongoing debate in youth sport. While some believe specialising at a young age is important for future sporting success, there is little evidence to support this. Long-term outcomes for specialised young athletes are still unknown, but there has been some suggestion it may limit movement development, and this may be associated with increased risk of injury. Anecdotally, youth football in New Zealand (NZ) has a high prevalence of specialisation, and an increase in youth sport injuries in NZ has been reported. Therefore, the aim of this research was to investigate the association between sport specialisation and movement competency in youth football players in NZ.

A review of the literature was completed (Chapter 2), to investigate the evidence for an association between sport specialisation and movement competency in youth sport. Results suggested that jump landing strategies may differ in specialised youth compared to their non-specialised counterparts. However, inconsistencies in the definitions and methods used to define and measure both specialisation and movement competency were highlighted, as was the need for sport specific research.

A nationwide survey of youth football players was then conducted to determine the prevalence of specialisation in NZ, and whether there were associations between the level of specialisation and 12-month injury history (Chapter 3). Forty-three percent of 10–15-year-old football players were classified as highly specialised and a high proportion (84%) of participants reported injuries in the past 12 months. While no difference was observed in the odds of reporting an acute injury, highly specialised players were four times more likely to report a gradual onset injury than low and moderately specialised players, when the volume of sport participation was controlled for.

Three cross-sectional studies were subsequently conducted (Chapters 4, 5 and 6). First, an investigation of early specialisation and its association with movement competency in pre peak height velocity (PHV) football players, categorised into high, moderate, or low specialisation groups (Chapter 4). Drop jump landings were compared using the landing error scoring system and dynamic balance was analysed using the Y-balance test. Highly specialised players demonstrated superior landing mechanics (less technique errors) and better relative reach distances in the Y-balance test.

The association between football development pathway and movement competency in a cohort of post-PHV players was investigated in Chapter 5. Movement competency was assessed using a single-leg countermovement jump, drop jump and Y-balance test. Players were grouped based on their history of participation as having undertaken a specialised or diverse (i.e., not specialised) pathway. Results were analysed based on group (specialised or diverse) and the number of years players had been specialised. No differences between specialised and diverse groups were found; however, small improvements in reactive strength index, jump height, and the number of landing errors were seen with an increase in the time specialised.

The final cross-sectional study investigated the association between sprint and change of direction (COD) performance and development pathway in post-PHV footballers (Chapter 6). Specialised players exhibited greater COD asymmetries and sprint kinetic outcomes, and COD kinematic strategies associated with faster, but more risky task completion strategies than diverse players.

Cumulatively, the results from this thesis suggest a high prevalence of specialisation in youth football in NZ, and that specialisation is associated with a history of overuse injury. Some strategies displayed by specialised players suggested improved movement competency and increased efficiency; however, some of these strategies are associated with increased injury risk. While there may be some improvement in movement outcomes in specialised players, the strategies used to achieve these outcomes need further investigation, including longitudinal research.