We investigated fatigue in the erector spinae, upper trapezius muscles and changes in the cervical flexion-extension angle when individuals watched 360° videos, general videos using virtual reality (VR), and smartphones. The subjects included 34 young, healthy, South Korean college students. The systems VR Gear3, the Galaxy S8, and “STAR WARS 360 VR” made by the manufacturer Cube CZ were utilized. The subject test conditions were: 1) watching 360° video with VR (V360), 2) watching 360° video on a smartphone (S360), 3) watching general video with VR (VG), 4) and watching general video on a smartphone (SG). The subjects watched a video for 10 min under each condition, where median frequencies of the erector spinae and upper trapezius muscles were measured using electromyography, while changes in the cervical flexionextension angle were measured with an electrogoniometer. The results noted that the erector spinae and upper trapezius muscles were significantly fatigued over time in all conditions, with significant differences relating to time and conditional effect. Watching 360° videos was less fatiguing than watching general videos and neck muscles moved the most when watching V360, and least watching general videos. These results suggest that neck muscles are less fatigued when watching 360° videos.

It is generally accepted that mechanical properties of sandwich composite are affected by curing pressure variation. For the present study, the effects of curing pressure variation on the compressive properties of balsa wood sandwich composite were investigated. For this purpose, a compressive test was conducted using balsa wood and honeycomb core sandwich composite, applying 40 psi and 60 psi curing pressure conditions. The results showed that compressive load of balsa wood sandwich composite applying 60 psi curing pressure condition is higher than applying a 40-psi curing condition. This phenomenon is due to an increase in the adhesive strength of the balsa wood sandwich composite as the curing pressure increases, thereby improving the compressive strength. Deboning and local buckling were observed on fracture surfaces of all balsa wood sandwich composite, but only global buckling was observed at honeycomb core sandwich composite.