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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.

The Body composition is related to higher physical performance and a lower risk of health problems, it connects to external and internal factors. Military activitiesf are characterized with a high physical load and a psychological load, physical fitness and the body composition have an adverse effect on military performance. The primary purpose of the body composition and physical fitness is related to the selection of individuals the best suited to the demands of military service [2,10]. The proper body mass supports good health capacity [11,13]. The maintenance of body composition and appropriate physical fitness standards by the military personnel is affected by the intrinsic factors such as the individual's genetic factors, development history, social background, and extrinsic factors, environmental changes and institutional, systemic changes. The effects of the excess body mass are widespread, raise the variety of concerns relevant to the health and performance of the military personnel [1,3,4,5]. The diabetes mellitus, hyperlipidemia, hypertension and heart disease increased with the obesity [6,7,9,12]. The individuals with overweight have more medical complication than the individuals with the standard body mass. The higher body mass index was associated with higher morbidity and mortality [8]. We have classified individuals according to the age into subgroups and provided the evaluation of the body composition on the basis of the main anthropometric characteristics as well the analysis of the standard physical fitness tests results. The analysis of the average value of the body mass and the Body Mass Index have shown large individual changes inside the subgroups and between the subgroups. The assessment of the results of physical fitness tests is provided differentially according to the individual corresponding age subgroup. The analysis of the respondent data http://dx.doi.org/10.12697/poa.2016.25.1.03Papers on Anthropology XXV/1, 2016, pp. 27-36 28 | L. Pļaviņa, S. Umbraško reveals the overweight and obesity problem that became actual with the increasing the age of individuals. Physical fitness tests results have shown that the excellent physical fitness evaluation is received by about 33-44% of the military personnel that reflects a high unit of operational readiness.