Field based lower limb strength tests provide insight into sprint and change of direction ability in academy footballers

Conducting field-based strength assessments is embedded within football academy development processes. Yet, there is a limited understanding of how hip and groin strength assessments relate to vital game-based tasks such as sprinting and change of direction (COD) performance. Our aim was to explore field-based strength assessments and their relationships with both sprint and COD performance in male academy footballers. Participants (n = 146; age 14.2 ± 2.2 years; stature 166.3 ± 15.4 cm; body mass 55.6 ± 15.6 kg) performed maximal countermovement jump (CMJ), Nordic hamstring strength (NHS), isometric hip adductor (ADD)/abductor (ABD), 5m, 10m, 20m sprints and modified 505 agility test. All strength measures were allometrically scaled to account for body weight. Between limb differences were reported as imbalance scores. Principal component analysis reduced sprint and COD variables to a single 'running ability' component score. Scaled strength and imbalance, when controlled for age, were associated with 'running ability' (adjusted R2 = 0.78, P < 0.001). Significant effects on 'running ability' included: age, CMJ-impulse, NHS and hip-ADD. When the sprint and COD variables were explored independently, age and CMJ-impulse featured in all sprint and COD models. For 10m and 20m sprint distances, hip-ADD emerged as a significant effect. Mean 505 performance was explained by age, CMJ-impulse, hip-ADD, but also with the addition of NHS. Our findings suggest that insight into the underpinning strength qualities of 'running ability' of academy footballers can be obtained from a suite of field-based tests.