We present our study of the influence of the head 30 degrees flexion position on the changes in the muscle strength of the upper extremities. This position is typical for a person working in front of a computer.The study involved 100 healthy volunteers and was performed at the Department of Morphology in Riga Stradiņš University, Riga, Latvia. For measurements we have used the MicroFET2 Hand Held Digital Muscle Tester to determine the strength of the muscles of the hand and the arm (M. deltoideus, M. biceps brachii, M. triceps brachii, M. abductor pollicis longus). The results of measurements were then used to analyze the difference in the strength of the muscles innervated by the spinal cord cervical region (C5-C8 nerves) for the same person sitting in the vertical position and sitting with the head flexed at 30°.The results of our study support the hypothesis that the changes in the strength of the measured muscles are related to the mechanical distension of the spinal cord, which leads to changes in spinal cord's blood supply. The kyphosis position of the cervical spine during head flexion at 30°extent shows Papers on Anthropology XXVI/1, 2017, pp. 115-125 116 | J. Vetra, V. Sklarevich, G. Anoufriev et al. that in the spinal cord segments C5, C6 and C7 are form mechanical distension, but the changes in segment C8 were not detectable.Using our statistical study, we can conclude that there is strong relationship in the strength change in most of the observed muscles between the vertical position and the flexion of head at 30 degrees.

We present our study of influence full cervical flexion position on the changes in muscle strength of the upper extremities. This position is typical for a person working on mobile phone or iPad. The purpose of the study was determination of the connection between change of the head flexed position and changes in upper extremity muscles strength. The present study involved 80 healthy volunteers and was performed at the Department of Morphology in Riga Stradins University, Riga, Latvia. For measurements we have used the MicroFET2 Hand Held Digital Muscle Tester to determine the strength of the muscles of the hand and arm (M. abductor pollicis longus, M. biceps brachii, M. triceps brachii, M. deltoideus). The results of measurements were then used to analyze the difference in the strength of the muscles innervated by the spinal cord cervical region (C5–C8 nerves) for the same person sitting in the vertical position and sitting with the head flexed maximally. The results of our study support the hypothesis that the changes in the strength of measured muscles are related to the mechanical distension of the spinal cord, which leads to changes in spinal cord's blood supply. The kyphotic position of the cervical spine during head flexion shows that in the spinal cord segments C5 and C7 are formed mechanical distension. Using our statistical study, we can conclude that there is strong relationship in the strength change in some of the observed muscles between vertical position and full flexion of head