Background: Several factors contribute to shoulder pain, including abnormal neck posture, repeated use of the upper limbs, work involving raising the upper limbs above the head, and the effects of vibration. However, previous study has reported that constant vibration exposure could impact improvement of the stability on joints related with muscle recruitment and activation. For this difference reason, we need to verify for the complex study of relationship with repetitive upper limb movements, poor head posture, and constant vibration exposure. Objects: Our study was made to investigate the influence of vibration exposure on the shoulder muscle activity during forward-head and over-head tasks with isometric shoulder flexion. Methods: In a total of 22 healthy subjects, surface electromyography (EMG) data were collected from shoulder muscles (upper/lower trapezius, serratus anterior, and lumbar erector spinae) on tasks (neutral-head task [NHT], forward-head task [FHT], and over-head task [OHT]) with and without vibration exposure. Results: In all tasks, the EMG data of the upper trapezius and serratus anterior significantly increased with vibration exposure (p < 0.05). Furthermore, the EMG data of the lumbar erector spinae significantly increased with vibration exposure in the NHT and FHT (p < 0.05). Conclusion: We suggest that continuous vibration exposure during the use of hand-held tools in the tasks could be associated with harmful effects in the workplace. Lastly, we clinically need to examine the guidelines regarding the optimal posture and vibration exposure.

Background: A backpack is available equipment for moving some objects. Most studies have found that the appropriate weight limit of backpack for students is between 10% to 15% of their body weight (BW). However, Some students should carry a backpack heavier than 15% of BW. Therefore, It is associated with abnormal shoulder and neck posture on students. Objects: This study tested the effects that various amounts of weight carried by university students in their backpacks had on their cervical posture and electromyography of neck muscle. Methods: The subjects consisted of 12 students (6 male, 6 female) in university. There were three loading conditions tested: no backpack, a backpack that weighed 10% and 15% of the student’s BW. The dependent variables were the craniovertebral angle (tragus to C7) and the neck muscle activities (sternocleidomastoid, upper trapezius). All 12 subjects were asked to walk while wearing a backpack for 5 minutes and were then instructed to rest for 2 minutes. Results: When assessing the craniovertebral angle, the results of this study were significantly decreased in the order of 0%, 10%, and 15%. And then, there were significantly increased electromyography of neck muscles that comparison of the weight of 10% and 15% on 0%. It was found that as the weight of the backpack increased, the craniovertebral angle decreased (p < 0.05) and the muscle activities increased (upper trapezius p = 0.012, sternocleidomastoid p = 0.013). Conclusion: Our study recommended that some students shouldn’t carry on over the 15% backpack of own weight, and also they should distribute backpack load to equal on body for optimal posture.