# Lower Limb Joint Coordination and Coordination Variability During Landing: A Scoping Review
## 4 Discussion
(2) Novices, children, or those performing new/challenging tasks have higher variability as the system searches for stability. (3) Injuries or deficits can push variability to either end--some injuries cause a protective consistency (low var.) while others cause erratic movement (high var.). This U-shaped concept--that both too little and too much variability can be signs of trouble--is supported by multiple studies. Clinically, this suggests that simply \"reducing variability\" is not always the goal; rather, appropriate variability is the goal. A practical example is ACL injury prevention programs: some coaches initially tried to make athletes land the exact same \"perfect\" way every time (minimizing variability), but the research here indicates it may be beneficial for athletes to practice varying their landings (within safe technique bounds) to build resilience. Regarding symmetry, most healthy individuals land with symmetric coordination between limbs (especially in double-leg tasks), whereas injury can introduce asymmetry. No marked asymmetries were seen between dominant and non-dominant legs in standard tasks (dominant versus non-dominant differences only showed up under specific conditions like lateral landings). However, after an injury like ACLR, even if not explicitly measured in the reviewed studies, one can expect inter-limb asymmetry in coordination--for instance, the ACLR limb might show a different coupling strategy or variability than the intact limb. Rehabilitation should therefore aim not just to restore strength, but also to restore symmetric and normal coordination patterns between limbs. Some researchers have begun to use coordination variability as a return-to-sport metric, under the idea that an athlete who still shows aberrant variability or asymmetry in coordination is not fully rehabilitated, even if jump height or strength is back to normal. **Implications for Injury Prevention and Training:** Understanding these coordination differences can inform injury prevention. For ACL injuries, training might focus on increasing coordination variability in females (i.e., by teaching multiple landing strategies or increasing hip involvement to avoid a singular knee-dominant pattern). Conversely, for CAI, training focuses on decreasing excessive variability (i.e., through balance training to stabilize the ankle and produce a more reliable neuromuscular pattern). Coaches can incorporate drills that challenge coordination (like perturbation training: slight pushes during landing or landing on uneven surfaces) to enhance adaptability. Importantly, any intervention should be monitored to see if it moves the athlete's coordination metrics toward a healthier range (i.e., is variability decreasing or increasing as desired, are couplings becoming more in-phase when they should?). The review also highlights the importance of neuromuscular fatigue: late-game injuries might be explained in part by coordination breakdown. Strength and conditioning programs thus should also target muscular endurance and neurocognitive factors to maintain coordination quality under fatigue. **Youth Development:** For younger athletes and children, the findings underscore patience and proper progression. Children naturally have high variability; demanding perfect technique too early might hinder their self-optimization process. Instead, providing a variety of movement experiences and gradually increasing difficulty allows children to refine their coordination with age. The differences observed between sport-trained and non-trained children suggest that early engagement in jumping sports can accelerate coordination development--but those sports should ideally teach sound fundamentals (i.e., encourage the use of hip and knee flexion rather than landing stiff-legged). Injury risk in youth is lower for ACL (compared to teens/adults) partly because their landings are less forceful, but as they grow, if they carry forward a poor coordination habit (like always landing knee-straight due to lack of training), that becomes risky.