Dominant and non-dominant single-leg landings at different heights: which one is safer among females? Implications for ACL injuries

INTRODUCTION: Landing is a common manoeuvre in sporting activities that can often lead to anterior cruciate ligament (ACL) injury with greater risk found in females [1]. Single-leg landing increases the risk of injury compared to double-leg landing because it is performed with less knee flexion and provides less stability. Although there has shown to be significant differences in maximum valgus angle between landing with the dominant and non-dominant leg [2], there is a dearth of information with regards to muscle forces at high risk instances such as when peak GRF occurs during landing. A lack of muscle coordination or delay in their activation due to for example, fatigue at the time of peak ground reaction force (GRF), is believed to be a possible cause of ACL injury. The quadriceps (Q) and hamstring (H) muscles are the main lower body decelerator and knee joint stabilizer during landing, respectively. At peak GRF, the Q/H force ratio, unlike the Q/H strength ratio measured isokinetically, can provide insight into the loading condition at the knee joint during landing. Greater Q/H ratios represent higher anterior knee muscle force and thus increase the risk of the ACL injury. The aim of this study was to compare dominant versus non-dominant single-leg landings at two heights in females to better understand the effects of muscle coordination with respect to GRFs on ACL injury. Because we propose that dominant leg landing will be better coordinated than non-dominant leg landings, we hypothesized that the Q/H ratio peak will be lower during dominant leg landings compared to nondominant leg landings. We also hypothesized that the peak Q/H ratio will occur closer to peak GRF at higher landing tasks as well as during non-dominant landing since, we assume that such landing manoeuvres need quicker muscle coordination response (i.e. peak Q/H) to peak GRF to avoid ACL injury.