# Lower Limb Joint Coordination and Coordination Variability During Landing: A Scoping Review
## 3 Results
### Healthy Individuals Under Different Landing Conditions
While none of the 18 studies explicitly gave an unanticipated versus anticipated landing comparison focusing on coordination, the general biomechanics literature suggests only modest changes in landing mechanics with unanticipated conditions. Those changes (i.e., slightly increased knee valgus or different muscle timing) could correspond to slight shifts in coordination pattern (perhaps a bit more out-of-phase motion due to surprise). In summary, healthy individuals adapt their inter-joint coordination depending on what the landing task demands: straightforward tasks yield consistent in-phase joint motions, whereas unusual directions or uncertain landings can perturb that coordination. **Sequential Landings and Task Complexity:** The DVJ task, which includes a drop landing followed by an immediate jump and then a second landing, provides a scenario to study how coordination might change from one landing to the next. [PERSON] and [PERSON] [28] showed that the second landing (after the jump) elicited different coordination outcomes than the first. They found reductions in the proportion of in-phase coordination for certain joint couplings (hip sagittal-knee sagittal, knee frontal-ankle frontal, knee sagittal-ankle sagittal) in the second landing, with corresponding increases in joint-dominant or anti-phase patterns. Essentially, the joints were less synchronized in their movements the second time around, possibly because the intervening jump altered landing mechanics (the athlete might land more upright or with different muscle pre-activation). As noted earlier, coordination variability was higher in that second landing. This demonstrates that even in the same individual, performing a landing under a slightly altered context (here, a rebound jump in between) can change coordination. Another example of task complexity is height: a higher drop likely means greater impact, which could influence coordination. Although not directly measured as coupling variability in the included studies, one can hypothesize that at higher drop heights, some individuals might shift to a more synchronous, rigid pattern to resist the large impact (reducing variability as they brace), or conversely, others might buckle differently each time (increasing variability). The interplay is not fully clear without direct data, but task difficulty (height, single versus double leg, one landing versus repeated landings) definitely modulates how joints coordinate. **Coordination and \"Normal\" Variability:** It is important to highlight what a normal coordination pattern looks like in healthy young adults during a standard landing. Generally, during the initial impact phase of a drop landing, an in-phase pattern of hip and knee flexion is expected, where both hip and knee flex (and ankle dorsiflexes) together to cushion the landing. Vector coding analyses often find this in-phase (synchronized flexion) occupies a large percentage of the stance phase in healthy athletes. As the motion continues, some joint dominance may occur; for example, later in the eccentric phase, the knee might slow its flexion while the hip continues to flex (a proximal dominance phase), or the ankle may plantarflex while the knee is still flexing (distal dominance), depending on the task. These subtle shifts are part of a normal pattern to redistribute loads. Coordination variability in healthy individuals is typically moderate: not zero (because no two landings are identical, and some adaptability is present) but not extremely high either (because skilled individuals have a practiced strategy). One study found coordination variability (standard deviation of coupling angle) on the order of a few degrees for experienced athletes in controlled landings, whereas novices or perturbed conditions yielded much larger values. Healthy individuals also demonstrate symmetric coordination between limbs in bilateral tasks. If significant asymmetry is observed (one limb uses a different coordination strategy than the other), it could indicate a hidden deficit or limb dominance issue.