Objective Myoelectric activity of neck extensor muscles and head kinematic variables, when using a smartphone for one-handed browsing and two-handed texting while sitting, standing, and walking, were evaluated to compare the neck muscular load during these tasks and across the posture conditions. Background There has been limited research on the relation between head-down postures and the muscular load on the neck of smartphone users. Methods Twenty-one asymptomatic young users were asked to perform one-handed browsing and two-handed texting tasks in each of the posture conditions, and the myoelectric activities of the neck extensor muscles, head kinematic variables, and upper back posture were quantified. Results The muscle activation level when using a phone during walking was 21.2% and 41.7% higher than that of sitting and standing on average ( p < .01). Head vertical and angular accelerations were also significantly greater ( p < .01) for walking than for sitting and standing conditions. Between the two conducted tasks, participants flexed their heads more significantly ( p < .01) with higher activation of the neck extensor muscles ( p < .01) when texting as compared to when browsing. Conclusion Results indicate that two-handed texting while walking would be the most physically demanding scenario for neck musculature, and it might be attributable to the dynamics of the head while walking with the head facing downwards. Application These findings can be used to better understand the potential relation between smartphone use and the occurrence of neck musculoskeletal problems and to inform the users of the ergonomic risks of using smartphones while walking.

Within-subject design of an experimental study.Objective. The aim of this study was to determine the effects of smartphone use on the activity level of the lumbar erector spinae muscles and spine kinematics during walking. Summary of Background Data. Using a smartphone while walking makes the user hold the phone steady and look downward to interact with the phone. Walking with this nonnatural posture of the head and the arms may alter the spine kinematics and increase the muscular load on the low back extensor muscles. Methods. Twenty healthy young individuals participated in the laboratory experiment. Each participant walked on a treadmill in five different conditions: normal walking without using a phone, conducting one-handed browsing while walking, two-handed texting while walking, walking with one arm bound, and walking with both arms bound. Spine kinematics variables and the myoelectric activity levels of the lumbar erector spinae muscles were quantified and compared between the five walking conditions. Results. Participants walked with significantly (P < 0.05) more thoracic kyphosis and lumbar lordosis when using a phone compared to when walking without using the phone. The median level of muscle activity was also 16.5% (browsing) to 31.8% (texting) greater for the two smartphone use conditions than for the normal walking condition, and the differences were significant (P < .05). Between the normal walking and the two bound arm walking conditions, no significant difference in the muscle activity was found. Conclusion. Study results show that the concurrent use of a smartphone while walking could pose a larger muscular load to the lumbar erector spinae muscles than that of normal walking. Habitual use of a smartphone while walking could be a risk factor for low back musculoskeletal problems.

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Stiff-knee, which indicates reduced range of knee flexion, may decrease gait stability. Although it is closely related to an increase in fall risk, the effect of limited knee flexion on the balance capacity during walking has not been well studied. This study aimed at examining how walking with limited knee flexion would influence the center of pressure (COP) trajectory and spatiotemporal gait parameters. Sixteen healthy young participants conducted four different walking conditions: normal walking and walking with limited knee flexion of their left knee up to 40 and 20 degrees, respectively. Results show that the participants walked significantly (p<0.05) slower with shorter stride length, wider step width, less cadence, and decreased stance phase when walking with limited knee flexion, compared to normal walking. The increase in the asymmetry and variability of the COP was also observed. It indicates that limited knee flexion during walking might affect the dynamic balance.