###### Abstract  
Landing on a single-leg without receiving direct visual information (e.g., not looking at the ground) may increase the risk of injury. We examined whether visual focus contributed to the changing lower-extremity dynamics and patellofemoral joint stress during a single-leg drop jump task. Twenty healthy volunteers visited the laboratory for three separate sessions. During each session, participants randomly performed either of two types of a single-leg drop jump task from a 30 cm high wooden box. Subsequently, participants looked at the landing spot (central vision condition) or kept their heads up (peripheral vision condition) when performing the task. Sagittal and frontal plane lower-extremity joint angles and joint moments (in the ankle, knee, and hip), including the vertical ground reaction force, and patellofemoral joint stress during the first landing phase (from initial contact to peak knee flexion) were compared. Greater ankle inversion and hip adduction were observed when landing with the peripheral vision condition. However, the magnitudes were negligeable (Cohen's d effect size <0.35). No statistical difference was observed in other comparisons. Landing on a single-leg from a 30 cm height without receiving full visual attention (peripheral vision condition) does not increase the risk of lower-extremity traumatic and overuse injuries. visual information; kinematics; kinetics; traumatic; overuse +
Footnote †: journal: Medical  
movement patterns for improving performance [16]. Hence, as the largest contributor to feedback control [17], the visual system gives us important information for processing images (e.g., spatial awareness, depth, and motion perception, light, and color), especially on multi-joint movements involving impact forces such as a single-leg landing. Moreover, unlike the vestibular and proprioceptive systems (e.g., autonomic nervous system), one can voluntarily control the number of visual inputs. For example, a deficit of direct visual information during landings (e.g., not looking at the landing spot by blocking vision or looking ahead) can alter their normal movement patterns in the lower-extremity [18]. Furthermore, these neuromechanical alterations, due to limited visual input, can be associated with factors that are proposed to increase the risk of injury [19]. Based on previous studies concerning visual blocking (e.g., being blindfolded) during double-leg landings, some researchers [19; 20] reported movement alterations while others [21; 22] did not. A study executing single-leg landing [23] also reported no difference in sagittal and frontal lower-extremity joint kinematics between landing conditions while receiving full (e.g., looking at the ground) and less (e.g., looking ahead) visual information. Therefore, while the relationship between injury risks and the level of visual input is inconclusive, the results of previous studies [18; 19; 20; 21; 22; 23] have revealed several practical limitations. First, a complete absence of visual information using a blindfold [19; 20; 21; 22] is extremely rare in real athletic situations. Hence, landing with peripheral vision (not looking at the ground with eyes-open) is more common due to the tendency to focus on other things, such as the ball or other individuals. Second, previous studies examining visual input observed double-leg landings [18; 19; 20; 21; 22], although single-leg landing was associated with a higher risk of injury than double-leg landing [24; 25; 26]. A study [23] also exists that reported single-leg landing; however, this study reported joint kinematics at time points of 100 ms before landing and at initial contact. Thus, the results of this study [23] have limitations because injuries occurred after landing [27; 28; 29]. Third, increased patellofemoral joint stress (PFJS) during functional activities was related to patellofemoral pain [30; 31], which accounted for approximately 7% of all musculoskeletal conditions [32].