Central Activation of the Upper Limb Muscles in Humans Related to Creation of an Isometric Effort: Dependence on the Position of the Point of Force Application within the Operational Space

Abstract

We examined the peculiarities of central coordination of motor commands coming to the muscles of the shoulder belt and shoulder in the course of generation of targeted isometric efforts by the arm. The dependence of these commands on changes in the effort direction and position of the forearm within the working space were analyzed. The intensity of the central commands was estimated according to the amplitudes of rectified and averaged EMGs recorded from the corresponding muscles. Sector diagrams of EMG activity of the above muscles depending on the direction of the effort vector, EV, were plotted [1]. Preferential sectors of activity where the efforts were formed due to activation of definite functional muscle groups were identified. As was found, the direction of these sectors depends significantly on the EV orientation. Differences between the patterns of coactivation of the examined muscles were demonstrated. Organization of the motor commands under conditions of creation of extensor efforts is distinguished by a more complex pattern than that related to flexor efforts. In the former case, the activity of extensor muscles is accompanied by more significant activation of the flexors.

Hysteresis Properties of EMG Activity of the Shoulder Belt and Shoulder Muscles at the Development of Isometric Efforts by the Human Arm

“…As was mentioned above, the level of EMG activity of all muscles significantly depended on the direction of the developed effort; this statement completely agrees with the results of our earlier studies [10][11][12][13]. Findings made in the above-described tests supported, in general, conclusions formulated in our earlier studies on animals.…”

Activation of the Shoulder Belt and Shoulder Muscles in Humans Providing Generation of “Two-Joint” Isometric Efforts

“…The synergic correspondence of the moments of forces generated by muscles of separate fingers providing a total force applied to the object can serve as an example [3,8,11,12,14,[82][83][84][85][86]. In particular, dependences of the characteristics of motor commands that arrive at these muscles in an isometric regime on change in the direction of effort and position of the arm in the horizontal plane were studied to understand the phenomenology and mechanisms of synergic interaction of the shoulder belt and shoulder muscles [87].…”

Untitled

“…Такі ЕМГ розглядалися як відображення суперпозиції центральних моторних команд (ЦМК) у ряді робіт [5][6][7]. Показано, що формування повільних ізоме-тричних зусиль, які розвивають м›язи плеча та плечового пояса людини, зумовлено насамперед м'язами, які є агоністами віднос-но певного рухового патерна [8][9][10][11][12][13]. Вивчали також моторні команди при двосуглобних ізометричних рухових актах, що надходили до м'язів плеча та передпліччя.…”