A.A. Guchetl', postgraduate student
K.D. Chermit, professor, Dr.Biol.
A.B. Bguashev, professor, Ph.D.
Adyghe State University, Maikop

Keywords: functional system, afferent synthesis, area of sight, electromyography.

Introduction. Provision of useful adaptive results that meet the requirements is the key feature and the main force combining interacting components into a unified functional system. The original, key, supporting idea here is the one of N.A. Bernstein that the model of solution of a motor task is created to settle the problem, rather than to resolve it. Thus, there arises an idea of adjusting characteristics of movement and even its pattern to a great number of variable conditions of the external and internal environments. In addition to the external impact, human reaction and consequently its implementation program are determined by the response of the body associated with its current state. Visual control functions are optional in some of its components [1, 4].

The purpose of the study was to consider the effect of the method of sighting on the work of skeletal muscles when catching a falling object at the age of 5 years.

Materials and methods. Surface electromyogram (EMG) was recorded by a multifunction computer complex «Neuro-MEP». Processing of designated biopotentials results in making an interference curve, consisting of activity of a large number of motor units. Bipolar disc electrodes with electrode spacing of 2 cm were used to register EMG. They were placed along the direction of muscle fibers on the front surface of the deltoid muscle, in the middle of the biceps brachia and on the inner surface of the forearm. Muscle groups were selected using the visual analysis of catching a falling object.

The study involved 60 children aged 5 years. Each child was asked to catch a falling object while using binocular sight with the right eye and the left eye closed. Duration of the process of catching was assessed using the optical system of video analysis of movements.  

Results and discussion. Study of the parameters of the deltoid muscle electromyogram is an interference curve characterized by a sharp surge of bioelectric activity at the start of motor action (Figure 1). The maximum signal amplitude in the starting position is 180.7±20.1 mV, and during the motor action implementation it can increase up to 2,000 mV. The average value of the maximum signal amplitude during the time of execution of the motor action in the study group is 742±57.7 mV. The average frequency of the second signal realization in the starting position was 61.4 ± 15.6 times/s, and during the motor action realization process it can increase up to 170 times/s, its average value during the time of execution of the motor action in the examined group of children was 123.7±21.6 times/s.

5 years old

The maximum amplitude of the realization of the deltoid muscle signal during the time of catching a falling object increases by 4.1 times, and the average frequency increases by 2 times. Thus, changes in bioelectric activity are mainly due to an increase of the signal amplitude, indicating the high-speed nature of the motor units reductions in the given muscle group. 

 Figure 1. Electromyogram of the deltoid muscle while catching a falling object in 5-year-olds

Electromyogram of the biceps brachia is an interference curve with an intense increase and decrease of bioelectric activity. The maximum signal amplitude in the starting position is 35.3±12.1 mV, and in the process of catching a falling object it can increase up to 300 mV, and the average value of this indicator during the motor action execution is 106±26.5 mV. The average frequency of the second signal realization in the starting position is 15.3±3.5 times/s, and during the process of catching a falling object it can increase up to 70 mV, its average value during the time of motor action execution was 24.2±5.1 times/s (Figure 2). 

The maximum amplitude of the realization of the biceps brachia signal during the time of catching a falling object increases by 3 times, and the average frequency of signal realization - by 1.5 times. Changes in bioelectric activity are mainly due to an increase of the signal amplitude.

Figure 2. Electromyogram of the biceps brachia while catching a falling object in children of 5 years of age

Electromyogram of the forearm muscles is an interference curve with a smooth increase and a gradual decrease (Figure 3). The maximum signal amplitude in the starting position is 20.5 mV, and in the process of catching a falling object it can increase up to 200 mV, the average value of this indicator during the motor action execution is 70.8±18 mV. The average frequency of the second signal realization in the starting position was 14.5±3.5 mV, and it can increase up to 65 mV while catching a falling object, and the average value of this indicator during the motor action execution was 21.2±9 mV. 

The maximum amplitude of the realization of the forearm muscles signal while catching a falling object increases by 3.4 times, and the average frequency of its realization - by 1.4 times. Bioelectric activity changes mainly due to an increase of the maximum amplitude of the signal realization.

Figues 3. Electromyogram of the forearm muscles while catching a falling object in 5-year-olds

Analysis of bioelectrical activity of muscles and visual analysis of motor actions suggest that the outcome of catching a falling object is determined by the solution of two main motor tasks: moving an arm onto the fall trajectory of the object and capturing the falling object with a hand.

Fulfillment of the first task requires a high speed of moving the arm onto the fall trajectory of the object. Trajectory awareness is formed prior to the beginning of the fall and is a part of the afferent synthesis that determines the conditions of realization of future actions. The moment of falling of the object is the starting condition for the realization of the motor program.    

Fulfillment of the second task requires precision of movements, correction of one’s own actions, assessment of the speed of falling of the object for capturing it at a selected point of the trajectory of falling. Formation of binocular vision largely determines the development of the child’s motor function. Expansion of the area of sight due to binocular vision helps address motor tasks that arise quickly, accurately and appropriately. This is confirmed by a significant increase of time of catching a falling object with the sighting eye closed at the age of 5. Besides the increase of the time of catching it was found that over 40% of the children are not able to perform the set task at the first attempt. The study of bioelectric activity of the main muscles suggests that in the group of children of 5 years of age with the right eye as the sighting one in the event of closing it while catching a falling object a significant reduction was found in the maximum amplitude of the realization of the electromyogram signal of the deltoid muscle from 772±87.7 to 402.1±48.2 mV. The same pattern was observed in the group of children with the left eye as the sighting one, where the maximum amplitude of the electromyogram signal of the deltoid muscle decreased from 802±91.2 to 511.6 mV. In addition, there was a change in the pattern form of the electromyogram that was expressed in smoothing the surge of bioelectrical activity at the starting time of the movement.  

No significant changes of the maximum amplitude of the signal in the biceps brachia and forearm muscles have been detected. Activity of these muscles determines the possibility of the timely capture of a falling object. In this case, detection of the exact moment of capture depends not only on the visual, but also on the tactile sensitivity of the hand of the child; most probably it becomes the leading one, which explains the absence of changes in the bioelectrical activity of these muscles during narrowing of the area of sight.     

The average frequency of signal realization has not changed. Change of this parameter of the electromyogram helps assess the changes in the number of motor units involved in the operation and characterizes the exhibited power that remains stable in the conditions of narrowing the area of sight. 

Decrease of the maximum signal amplitude of the electromyogram, the deltoid muscle, with the sighting eye closed suggests a decrease of the contraction rate of motor units, which leads to time wasting while moving the arm onto the fall trajectory of the object. The speed of solving this issue other than the ability to manifest speed is determined by formation of an accurate understanding of the location of the fall trajectory in the spatial area of the subject. However, it is time consuming to realize this function at the age of 5 in the conditions of narrowing the area of sight.

Increase of time of moving the arm onto the fall trajectory of the object leads to a change in the pose of the child at the time of catching. It is difficult to determine the average angular kinematic characteristics of these poses and positions of the parts of the biomechanical apparatus due to their diversity. However, visual analysis of records of the catching makes it possible to state that the main changes of the pose while catching relate to angles of the hip, knee, shoulder and elbow joints.

Another important feature of the movements control mechanism when closing the sighting eye is the change in the starting position, where over 73% of children throw back their heads in order to have visual control of the falling object, while 63% try to move their arms onto the fall trajectory of the object before it starts falling. 

It is known that efficiency of a locomotor act is largely determined by a properly chosen position [2, 3]. Changing the starting position, a child adapts it for carrying out the motor task set for him in the conditions of narrowing the area of sight, where it turns out to be impossible for him to simultaneously realize the functions of imagining the fall trajectory of the object and controlling it. A child can control either the object, or its fall trajectory. Therefore, to accomplish the motor task at hand the subject first forms his understanding of the fall trajectory, then moves his arm in its direction, and after that leaves the fall trajectory without visual control as he shifts it onto the falling object by throwing back his head. However, for the sake of standardization of the study conditions, we did not allow the children to move their arms onto the fall trajectory of the object in advance, that resulting in 40% of the subjects being unable to accomplish the task at first attempt.

When the sighting eye is closed, the area of action exceeds the area of sight. In such conditions it is impossible to solve motor tasks quickly and accurately at the same time. Therefore, for accurate catch of the falling object a child sacrifices its speed, which results in more time spent for catching while reducing the maximum amplitude of the realization of the deltoid muscle electromyogram signal. In addition, the child has to change the position while catching the falling object, since catching is carried out at a lower point in space.       

Programming of results of future actions based on two types of thinking - visual and virtual - causes appearance of two types of action programs: a visual action program created by means of visual thinking in the conditions of the area of sight exceeding the area of action and a virtual action program created by means of virtual thinking in the conditions of decreasing the area of sight as compared to the area of action.  Realization of these programs under the overall direction of the performed actions and targeting one result is characterized by different time, spatial and bioelectrical characteristics of the subject’s movements.

Conclusion.  Narrowing of the area of sight leads to a change in the content of the components of the functional system of catching falling objects: the formation of virtual situational afferentation, manifestation of virtual-creative thinking in the phase of decision-making and construction of a virtual action program.

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Corresponding author: zabolotniy-tol1@yandex.ru