# Lower Limb Joint Coordination and Coordination Variability During Landing: A Scoping Review
## 1 Introduction  
Landing from a jump is a high-impact task requiring precise coordination of the lower limb joints to safely dissipate forces [1]. During landing, the hip, knee, and ankle must move synchronously to control deceleration and maintain stability; how these joints coordinatetheir motions, and how consistent that coordination is across repeated landings, can influence both performance and injury risk [2]. In biomechanics, joint coordination refers to the timing and pattern of multi-joint movements (often quantified via coupling angles or phase relationships between joint motions), whereas **coordination variability** refers to the trial-to-trial fluctuations in joint coupling patterns, typically quantified using the standard deviation or angular dispersion of coupling angles over multiple trials [3]. Coordination variability is rooted in dynamic systems theory, which posits that healthy movement may exhibit a certain degree of flexibility or \"variability\" as the neuromuscular system explores different solutions for a task [4]. Sufficient variability can indicate adaptable motor control, while too little or too much variability might signify a less stable or less optimized coordination strategy [3]. Landing mechanics are often studied within this framework to understand why some individuals (or populations) are more injury-prone than others despite performing the same task [5]. Notably, non-contact injuries such as anterior cruciate ligament (ACL) ruptures frequently occur during landings; abnormal coordination pattern (for instance, poor hip-knee synchronization or excessive joint stiffness) is thought to elevate ligamentous loads and injury risk [6]. Therefore, examining how joints move together (coordination patterns) and how consistently they do so (coordination variability) provides insight beyond traditional discrete measures like peak angles or forces. Individual differences in coordination may arise from prior injuries, training background, sex, age, or the specific demands of the landing task [5]. Athletes recovering from ACL reconstruction or those with chronic ankle instability (CAI) often exhibit altered movement strategies during landing as part of protective or compensatory mechanisms, potentially leading to either unusually rigid couplings or excessive variability [7; 8]. Training interventions and fatigue can also modulate coordination; a well-conditioned athlete might display a refined, repeatable joint synergy, whereas fatigue may alter normal timing between joints and increase variability [9]. Sex differences have been documented as well; female athletes, who suffer higher rates of ACL injury, sometimes demonstrate different lower limb coordination strategies than males during landing and cutting manoeuvers [3]. Age and developmental stage are other factors: children and adolescents may not coordinate joints during landing with the same consistency or technique as adults due to neuromuscular maturation and skill learning [10]. Finally, the nature of the landing task itself (i.e., single-leg versus double-leg landings, expected versus unexpected landings, different directions or heights) strongly influences coordination patterns. A change in landing direction or the addition of a second landing in a sequence can alter how joints work together and how variable that coordination is. Given the multifactorial influences on landing coordination, this scoping review was conducted to map the literature on lower limb joint coordination and coordination variability during landing tasks. This review synthesizes findings from diverse populations and landing conditions, highlighting how injury status, training/fatigue, gender, age, and task demands affect inter-joint coordination. Understanding these patterns is crucial for biomechanics and clinicians aiming to identify at-risk movement profiles and to design interventions (training, rehabilitation, or technique modification) that promote safer and more effective landing mechanics.