# Lower Limb Joint Coordination and Coordination Variability During Landing: A Scoping Review
## 3 Results
### Healthy Individuals Under Different Landing Conditions  
The final category of studies focused on healthy individuals (typically young adult athletes or recreationally active people) and how their lower limb coordination varies with different landing task conditions. These works provide insight into the \"normal\" coordination strategies and how factors like task type, direction, and sequence can influence those strategies. **Double-Leg versus Single-Leg Landings:** Coordinating two limbs in a bilateral landing can be different from a unilateral landing. While none of the included studies directly compared single versus double in the same paper, we can draw from multiple sources. Generally, single-leg landings are more challenging, often leading to greater variability and different coordination emphasis than double-leg landings (because one limb must absorb all the load). For instance, in single-leg drop landings, [PERSON], [PERSON] [2] observed that even among trained female volleyball athletes, coordination quality could differ between the landing leg sides. They found that the non-dominant limb had better coordination (smoother knee-hip kinematic coupling) than the dominant limb when landing on one leg during multi-directional jumps. This somewhat counterintuitive result (the \"weaker\" or non-preferred leg coordinating more effectively) might be due to the dominant leg being used more forcefully and thus exhibiting more perturbations in motion. In any case, it suggests that symmetry is not a given: healthy individuals can have asymmetrical coordination patterns between limbs, with one leg showing a more stable intra-limb coordination than the other. In double-leg landings, on the other hand, studies like [PERSON] and [PERSON] [28] noted no major side-to-side coordination asymmetry, where both legs tend to move nearly simultaneously and symmetrically in healthy subjects during a normal drop landing. Thus, a normal healthy strategy in a bilateral landing is a symmetric one (each leg mirroring coordination), whereas unilateral landings highlight the unique coordination demands on each limb. **Landing Direction and Anticipation:** The direction of landing (or subsequent movement) can alter coordination. [PERSON], [PERSON] [2] had athletes perform single-leg landings in multiple directions: forward (0\({}^{\circ}\)), diagonal (30\({}^{\circ}\), 60\({}^{\circ}\)), and lateral (90\({}^{\circ}\)). They reported significant differences in knee coordination depending on direction. In particular, lateral landings (90\({}^{\circ}\) to the side) showed poorer knee joint coordination in the early phase of landing compared to forward or diagonal landings. \"Poorer coordination\" in their context was defined by a velocity-angle plot analysis, implying that the knee's angular velocity and angle did not follow the typical relationship seen in safer landings, likely indicating a timing mismatch between hip and knee or a more erratic knee motion when landing to the side. This makes intuitive sense: a pure lateral landing may impose more challenge on frontal-plane stability (hip abduction/adduction control, knee varus-valgus), disrupting the usual sagittal-plane flexion synergy. Diagonal and forward landings allowed more normal coordination (with the knee flexing in a controlled manner). The practical outcome is that as the landing direction deviates from straightforward, the coordination task becomes more complex and variability may increase. On a related note, whether a landing is anticipated or unanticipated can also influence coordination, though direct measures of coupling under these conditions are less common. Typically, unanticipated landings (when an athlete does not know which direction or when they will land) lead to stiffer, more cautious strategies, likely reducing variability in an attempt to stabilize, or sometimes causing atypical joint coupling because reflexes, rather than pre-planned muscle synergies, dominate the motion.