# For Patients with Stroke, Balance Ability Affects the Leg Extension Angle on the Affected Side
###### Abstract  
In stroke patients, the impact of lower limb physical functions on the leg extension angle remains unclear. We set out to reveal the physical impairments of the affected side in such patients that were associated with leg extension angle during gait. Twenty-six stroke patients walked for 16 m at a spontaneous speed. During walking, the leg extension angle and the increment of velocity during late stance, as an indicator of propulsion, were measured by inertial measurement units. The Berg balance scale (BBS), Fugl-Meyer assessment-lower limb, and motricity index-lower limb (MI-LL) were also evaluated. Stepwise multiple regression analysis was employed to reveal functions associated with the leg extension angle on the affected side. A path analysis was also used to confirm the relationship between the extracted factors, leg extension angle, and gait speed. Multiple regression analysis showed that the BBS was significantly related to the leg extension angle on the affected side (\(p<0.001\)). Path analysis revealed that the leg extension angle was also indirectly affected by the MI-LL and that it affected gait speed via propulsion on the affected side. These findings could guide the prescription of effective gait training for improving gait performance during stroke rehabilitation.  
Stroke; leg extension angle; balance; inertial measurement units; gait analysis +
Footnote †: journal: Medical  
affected side compared with the non-affected side in the post-stroke gait [5]. An increase in the propulsion force on the affected side after gait training results in an increased gait speed in stroke patients [15]. Furthermore, the leg extension angle is associated with the 6-minute walk distance [16] and knee flexion angle during the swing phase [17]. Therefore, the leg extension angle on the affected side is a beneficial indicator of gait quality and the main target for gait training during stroke rehabilitation. The previous literature reports that the leg extension angle can be altered by gait training using bio-feedback, functional electrical stimulation, and treadmill exercises in post-stroke patients [18; 19; 20; 21]. However, it remains unclear whether the physical function of the lower limb influences the leg extension angle.  
Previous researchers have identified multiple factors that influence the ability of stroke patients to walk, such as the severity of paralysis, muscle strength, and cognitive impairment [22; 23; 24]. Importantly, the strongest predictor of walking ability, such as that required for community ambulation in stroke patients, is their ability to balance [24; 25; 26; 27; 28; 29]. The Berg balance scale (BBS) is widely used to measure balancing ability in clinical practice [30]. The BBS is commonly used during inpatient rehabilitation and can predict the duration of hospitalization in stroke patients [31]. Thus, the ability to balance could be considered one of the most important factors in post-stroke gait, and it likely affects the leg extension angle during gait. Balancing ability may contribute to gait speed via its effects on the leg extension angle.  
Understanding the relationship between the leg extension angle on the affected side, physical functions, such as balancing ability, and the severity of paralysis is critical for planning effective gait training programs that increase the leg extension angle and improve gait velocity in post-stroke gait. This study set out to clarify the physical impairments associated with the leg extension angle on the affected side during walking. We hypothesized that the balancing ability assessed by the BBS could predict the leg extension angle on the affected side during gait in stroke patients, and that the ability to balance influenced gait speed through its effects on the leg extension angle.