Hébert-Losier, KimAnderson, Blake2025-09-152025-09-152025https://hdl.handle.net/10289/17653Sport has many mental and physical health benefits. However, with overall participation in sport increasing, sport-related issues and injuries are also increasing. Anterior cruciate ligament (ACL) injuries are common knee injuries in athletes and the general population, often occurring through non contact mechanisms. The Landing Error Scoring System (LESS) is a screening task used to identify athletes at higher risk of non-contact ACL and musculoskeletal injuries, where higher scores indicate poorer landing mechanics and greater risk of injury. Although the LESS is reliable, its predictive value is debated and it has been criticised for lacking validity in a sporting context. Previous studies have adapted LESS protocols in attempts to increase sport specificity, with changing head position or completing a dual task potentially suitable for this purpose as linked with ACL injury situations in sports. This thesis contains two experimental chapters. In the first experiment, 35 participants (22 males, 13 females) performed the LESS in two conditions allocated in a random order. In the control condition, participants jumped horizontally with both legs from a 30-cm high box to half their body height, landed with both feet, and jumped vertically as high as possible in one motion. In the head turned condition, participants performed the same double-leg jump landing movement while maintaining eye contact with an ‘X’ marked on a wall to their right, in line with the landing area. Participants performed three trials in each condition. Group mean LESS scores were significantly greater (P = 0.027) in the head turned (mean errors = 6.8 ± 1.5) than the control (mean errors = 6.4 ± 1.4) condition, with the mean difference of 0.4 errors being of small magnitude (Cohen’s d = 0.27 [0.51, 0.03]). No significant difference was found in the odds of being categorised at risk between conditions (P = 0.625, odds ratio = 3.00 [0.312, 28.8] based on a 5-error threshold. On an individual level, 28 participants were at risk in both conditions, although 13 had a meaningful increase in LESS score of one or more in the head turned condition. Average jump heights were significantly lower in the head turned condition, with the mean difference of 2.1 cm being of small magnitude (Cohen’s d = 0.20 [0.07,0.34]). Overall, performing the LESS with a head turned position appeared to increase the complexity and sport specificity of the task. Future research is required to determine the ability of the LESS to predict ACL injuries with a head turned condition as this aspect was not assessed. In the second experiment, an element of cognitive challenge was incorporated to the LESS in attempt to recreate the complex athlete-environment relationship of sports. In experiment two, 41 participants (20 males, 19 females, 2 others) performed the LESS in two conditions allocated in a random order. The control condition was the same as in the first experiment. In the tone counting condition, participants completed the same double-leg jump landing movement while mentally counting a random series of high-pitched and low-pitched tones, known as a tone counting task. Group mean LESS scores were not significantly different between tone counting (mean errors = 6.0 ± 1.3) and control (mean errors = 6.2 ± 1.5) conditions. Average jump heights were significantly lower in the tone counting than the control condition, with the mean difference of -4.2 cm being of small magnitude (Cohen’s d = 0.48 [0.30, 0.66]). No significant difference was found in the odds of being categorised at risk between conditions (P = 1.000, odds ratio = 1.00 [0.20, 4.95]) based on a 5-error threshold. Overall, performing the LESS with a secondary tone counting task significantly decreased jump heights with a small effect size, corroborating an increased cognitive load during testing that impaired jump performance. However, LESS scores were not meaningfully influenced. Overall, introducing a head turned position to the LESS task increased LESS errors significantly, and introducing a tone counting task or head turned position decreased jump heights. Although future research is required to determine the ability of the LESS to predict ACL injuries with these dual tasking conditions, this Thesis demonstrates that the complexity and sport specificity of the LESS task can be increased by introducing dual tasking requirements.enAll items in Research Commons are provided for private study and research purposes and are protected by copyright with all rights reserved unless otherwise indicated.sportACLanterior cruciate ligamentLESSlanding error scoring systemhead turnedcogntive loadThesis