Gender differences in neck muscle activity during near-maximum forward head flexion while using smartphones with varied postures.

Women frequently express heightened neck discomfort even though they exhibit smaller neck flexion (NF) during smartphone use. Differences in natural posture while using smartphones may result in varying muscle activation patterns between genders. However, no study focused on this issue. This study investigated the influence of gender on neck muscle activity and NF when using smartphones, ranging from slight (20°) to nearly maximal forward head flexion, across different postures. We analyzed smartphone usage patterns in 16 men and 16 women and examined these behaviors across different scenarios: standing, supported sitting, and unsupported sitting, at 20°, 30°, 40°, and the maximum head angles. During data collection, muscle activity was measured, expressed as a percentage of the maximum voluntary contraction (%MVC), in the cervical erector spinae (CES) and upper trapezius (UTZ), along with NF. Results show significant influences of gender, head angle, and posture on all measures, with notable interactions among these variables. Women displayed higher muscle activities in CES and UTZ, yet exhibited lesser NF, while using smartphones in both standing (12.3%MVC, 10.7% MVC, and 69.0°, respectively) and unsupported sitting (10.8%MVC, 12.3%MVC, and 71.8°, respectively) compared to men (standing: 9.5%MVC, 8.8%MVC, and 76.1°; unsupported sitting: 9.7%MVC, 10.8%MVC, and 76.1°). This study provides a potential rationale for gender-related disparities in injury outcomes, emphasizing that women experience higher neck and shoulder discomfort level, despite their smaller NF during smartphone use, as found in previous research. Additionally, the cervical flexion-relaxation phenomenon may occur when the head angle exceeded 40°. The near-maximum head angle during smartphone use might induce the cervical flexion-relaxation phenomenon, potentially aggravating neck issues. We recommend limiting smartphone usage postures that exceed the near-maximum head angle, as they are commonly adopted by individuals in the daily smartphone activities.

Neck and shoulder strains under various head flexing positions while standing and sitting with and without back support for male and female smartphone users.

This study recruited 30 young participants (15 men and 15 women) to examine the smartphone usage patterns in three postures (standing, supported sitting, and unsupported sitting) and at five head angle (HA) positions (0°-40°). Cervical erector spinae (CES) and upper trapezius (UTZ) muscle activity, neck flexion (NF), gaze angle (GA), viewing distance (VD), and discomfort scores were collected. Results showed that HA and posture almost affected all responses, while CES muscle activity, NF, and VD differed between sexes. Strain in the neck and shoulder region increased with HA increase. Particularly, when the HA exceeded 20°, the discomfort scores considerably increased. Unsupported sitting should be avoided during smartphone use because of relatively poor responses in all variables. However, both standing and supported sitting have their respective benefits. Sex-related differences were typically observed in the standing position, with women tending to have lower NF but higher CES muscle activity compared with men.Practitioner summary: Although smartphones have become daily necessities, the overall quantitative neck and shoulder strain of using smartphones in different postures is rarely evaluated. We suggest that maintaining the HA within 20° is recommended because of relatively low load on the neck and shoulders. An unsupported sitting should be avoided during smartphone use.

Postural Variabilities Associated with the Most Comfortable Sitting Postures: A Preliminary Study.

This study examined postural variabilities based on the self-perceived most comfortable postures of 12 participants (six men and six women) when sitting on three commonly used types of chairs (a stool, computer chair, and gaming chair). Participants' global joint angles were recorded and analyzed. Of the chairs studied, the stool was not adjustable, but the computer and gaming chairs were moderately and highly adjustable, respectively. During the test, participants were encouraged to adjust the chairs until they perceived that the most comfortable posture had been reached. The results demonstrated that in a sitting position perceived to be comfortable, the participants' postural variabilities with respect to global joint angle, calculated from five repetitions, were unexpectedly high for all three chair types, at approximately 9.4, 10.2, and 11.1° for head inclination, trunk angle, and knee angle, respectively. The average differences in range for each joint angle among the three chair types were relatively low, with all values within 3°. The result also showed that gender (p < 0.01) and chair type (p < 0.001) significantly affected trunk angle, whereas these variables did not affect head inclination or knee angle (p > 0.05). The preliminary results observed unexpectedly high variabilities in sitting posture when the participants sat at a posture that they perceived to be the most comfortable. The findings also indicated an inherent difference in comfortable sitting posture between genders; women tend to extend their trunk backward more than men. For permanent use with only an initial adjustment and memory-aided seat design, designers should minimize the loads that are borne by body parts over a prolonged period due to an unchanging sitting posture.