DISCUSSION
The objective of this study was to provide material that could be used to help prevent musculoskeletal disorders caused or exacerbated by smartphone use. The average height of the 20 year old female participants was 161.5 cm and their average weight was 52.8 kg. these participants, 51% used a smartphone with an LCD screen that was greater than 5 inches, and 49% used a smartphone with an LCD screen that was less than 5 inches. Therefore, it appeared that the majority of subjects preferred a large LCD screen. According to the results relating to smartphone use, 42.5% used smartphones for chatting, 38.2% used them for searching the Internet, 12.5% used them for playing games, 3.8% used them for other activities, and 3.0% used them for writing documents. Chatting and searching the Internet accounted for 80.7% of use, which indicates that most students use their smartphones for these activities. The majority of the students used their smartphone at home (58.4%) and most preferred sitting (40.0%) or lying on their back (34.9%) when using a smartphone. As shown earlier, many of the subjects used smartphones in poor working environments, as indicated by their sitting and lying positions. Therefore, there is a high likelihood that they will suffer from musculoskeletal disorders10). Regarding the average daily use, 42.1% used smartphones for more than 4 hours, and 21.6% use them for between 3 and 4 hours. In short, 80% of the students used smartphones for more than 2 hours every day11). When smartphones are constantly used at home without any rest, and a poor posture is maintained over a long period of time, musculoskeletal pain can occur. Repeated motions whilst in a static posture can result in a variety of problems, such as shoulder and neck pain12, 13). According to studies by Bendix et al.14), Lee et al.11), and by Mekhora et al.15), the longer that display terminals are used, the more the bending
angles of the neck bone and the waist bone are increased. According to studies by Burnett et al.16) and O’Sullivan et al.17), adopting an incorrect posture for a long period of time can lead to a lowering in the function of waist muscles, triggering pain in the waist. Therefore, it is evident that using smartphones whilst in a sitting posture for a long time can trigger musculoskeletal disorders. In this study, it was observed that neck pain and shoulder pain were the most commonly experience kinds of pain. The studies by Straker et al.18) and Szeto and Lee5) also revealed that the bending angles of the neck and back bones increased significantly. As mentioned earlier, in this study, it was found that pain in the waist had a positive correlation with the size of an LCD screen. Pain in the legs and feet were negatively correlated with the period of smartphone use, while there was no statistically significant correlation between the size of the LCD screen and pain in the eyes, neck, shoulders, arms, hands, wrists, fingers, or waist. This indicates that since larger LCD screens are more comfortable and convenient, their use will lead to a reduction in the complaint rate of musculoskeletal symptoms. Lee8) also reported that as display terminal screens became smaller, the bending angles of the neck and back bones significantly increased. In other words, the larger the terminal display screens, the lower the complaint rate of musculoskeletal symptoms. The results of this study are important in a number of areas: First, they provide university students with fundamental information and advice on their use of smartphones. Second, the data shows that the size of the LCD screen is closely correlated with pains in specific body regions. Third, the amount of time that a smartphone is used is also correlated with pain. This study has limitations in that it is not representative of the whole population, as it specifically focused on university students. Additionally, it should be noted that a self-administered questionnaire does increase the risk of response bias.