###### Abstract  
Background: While cross-legged-sitting (CLS) posture is widely practised in some communities, its biomechanical effect on the lower limbs is not clear. This study aimed to investigate whether CLS would affect biomechanical parameters in lower limbs during gait. Methods: Thirty healthy volunteers participated in this study and performed CLS on ground for 20 min. Their modes of gait were compared before and after CLS regarding to temporospatial parameters and the kinetic and kinematic parameters in the lower limb joints. Results: CLS significantly increased walking cadence and speed. In kinematics, the ranges of motion for almost all lower limb joints were increased after CLS except the knee in sagittal plane. In kinetics, the medial and lateral forces increased significantly after CLS in the lower limb joints, e.g., the hip posterior force was increased more than 14% on both sides. Furthermore, all hip, knee, and ankle powers were increased significantly after CLS. Conclusion: CLS has a positive impact on the biomechanical parameters of almost all lower limb joints except the knee flexion/extension angle and internal/external joint moments. Therefore, CLS can be used in the daily routine and in any rehabilitation programme to improve the biomechanical parameters of the lower extremities. cross-legged-sitting gait; joint kinematics; joint kinetics; posture +
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The appropriate and suitable sitting posture performs a significant role in maintaining the proper general posture during all activities of daily living. This is because sitting behaviour can influence the discomfort level, pressure distribution, and muscular status of the back and lower limbs, which might be responsible for balanced and coordinated walking [10; 15]. According to the activity level, prolonged sitting or standing might lead to some lower limb problems, such as plantar fascitis, knee flexors, and ankles plantar flexor muscles, particularly gastrocnemius and soleus, e.g., increasing pressure at the medial and lateral arch, hallux, mid-foot, hind-foot, and forefoot. Thus, the gait biomechanical parameters will be affected negatively because of the long-time of sitting without any activities or locomotion [16]. For this reason, [PERSON] and [PERSON] (2014) and [PERSON] et al. (2015) discussed that the excessive activation of the gluteus Medius muscle during prolonged static postures, such as sitting, can alter not only the spinal alignment, but also the biomechanical parameters of the lower limb during the dynamic posture, such as walking, by increasing the abduction range of motion at the hip joint and causing the muscular fatigue or walking with the pronated foot to compensate for the excessive pain [17; 18]. An example of the influences of sitting posture on the body biomechanics is that after 20 min of forward-leaning sitting, the body shifted the centre of gravity anteriorly, causing equilibrium disturbance and increasing level of discomfort at the hip joint during the walking [5]. Although the 7-10 min of backward-leaning sitting can the hip and knee kinematics, especially if the knee is at the same level as the hip, it can also increase the hip and knee muscular spasm [19]. However, the 10 min of upright cross-legged sitting (sitting on a chair with one leg over another) can cause many adverse side effects that might occur during changing the position from sitting to standing or during locomotion, such as disturbance in the Gluteus Maximus, Medius and minimums pressure, or incoordination in the angle between the horizontal and inlet planes of the pelvis [10]. Although the cross-legged-sitting (CLS) posture has been widely practised as a part of daily routine in some communities, little research has focused on the effects of CLS on the lower limbs in terms of biomechanics. As CLS usually takes long duration, e.g., hours, some people have the doubts that CLS would cause negative effects on the lower limbs or joints, especially on the knee.