A stress-based examination of the impact of injury occurrence in elite youth football players
This thesis examined the impact of non-contact injury on the physical and psychological development of elite youth academy footballers (14.1 to 23.0 years old) and considered which physical and psychological measures might indicate risk of non-contact injury. Three studies, based on longitudinal observational designs, surveyed players during a critical stage in their football careers across separate seasons, comprising of a pre-season and competitive season. Most observed players were within the under 18 age group since this age range has been associated with high frequency and severity of injury. Study 1 assessed the impact of hamstring strain injuries (HSI) due to the known prevalence in elite football. Players not sustaining a HSI exhibited increased eccentric hamstring strength (mean difference (MD), 47 N 95%, confidence interval (CI) = 3 to 91 N; probability value(p) = 0.0378) and body mass (MD, 1.7 kg 95% CI, 0.1 to 3.3 kg; p= 0.0427) and were 2 years younger (MD, -2.1 years; 95% CI, -3.6 to 0.7 years; p= 0.0053) compared to those sustaining a HSI. Study 2 examined the impact of reduced training and match availability. Low availability alleviated pitch-based exposure, as players with high availability had superior accumulation of training and match stimuli (e.g., total PlayerLoad TM: MD, 12726 au; 95% CI, 4211 to 21242 au; p = 0.0053). Contrasting with low availability, high availability players had significantly lower sit and reach scores (MD, -9.8 cm; 95% CI, -16.9 to -2.8 cm; p= 0.0091) and counter movement jump(CMJ) peak landing force asymmetry (MD, -14.86%; 95% CI, -29.14 to 0.57%; p = 0.0422) at pre-season. This suggested potential hypermobile characteristics and less neuromuscular control when landing could influence availability for the upcoming season. Study 3 also assessed the impact of reduced training and match availability and incorporated additional psychological measures. Compared to high availability, players with low availability had greater development in CMJ eccentric mean force (p= 0.0307), and greater increases in CMJ take-off peak force vasymmetry (p= 0.0237). Reduced playing availability impacted psychological development. Players categorised with moderate availability, had reduced coping resources (e.g., active coping: p= 0.0043) compared to those with high availability. Players with low availability across the competitive season had higher fluctuations of stress and recovery compared to players with high availability (p= 0.0046). Across all three studies relationships were observed independent of non-contact injury. Numerous relationships were identified between measures of physical fitness. For instance, greater CMJ development suggested possible improved change of direction times (e.g., jump height: p= 0.0013). Multiple relationships were found between growth and physical fitness development and exposure variables. For example, training total PlayerLoad was associated with CMJ jump height (r = 0.62, large; p= 0.0043). Furthermore, multiple relationships were demonstrated between physical and psychological development. These findings denote how assessment techniques can be utilised to facilitate monitoring players for injury risk and/or their physical and psychological development, whether they are available to train and compete, or are rehabilitating.
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