PhD, Associate Professor R.M. Gimazov¹
Yu.Yu. Starykh²
Dr.Biol., Professor S.I. Loginov^3
1Surgut State Pedagogical University, Surgut
²Surgut Clinical Trauma Hospital, Surgut
³Surgut State University, Surgut

Keywords: vertical stability, electroneuromyography, kinesthetic sensitivity, muscular synergy, athletes, Spearman's/ Kendall's correlations.

Introduction. The correlation of stabilometric vertical postural muscular coordination indicators with lower limb peripheral nerve electroneuromyographic indicators in man is the object of researchers’ deliberate attention [1, 10, 6]. At the same time, this type of correlation is still insufficiently studied in sport physiology and biomechanics [3, 4]. Since the ankle strategy is one of the main motor strategies of human postural stability [8, 9], it is to be expected that there also exists a correlation between the responses from the stimulated lower limb nerves and stabilometric indicators of the orthograde pose of man.

Objective of the study was to define the specifics of this correlation.

Research methods and structure. Subject to the study were 17 sport faculty students aged 18.7 ± 0.5 years, having the I category. Before the start of the experiment all the subjects were informed in detail on the ongoing research and gave a written consent to participate. The following tests were taken before and after physical load (30 squats in 1 min): stabilometry and Romberg’s test with eyes open and closed, "Dynamic balance" – straight body rocking back and forth during the Romberg’s test with eyes closed in the European posture. Each test lasted 51 seconds. The study was conducted using the software complex "MBN-Stabilo" (Moscow, 2003). The conductive function of the lower limb motor nerve fibers, namely n. Tibialis, n. Peroneus profundus and sensory fibers of n. Suralis, was studied using the electromyograph Neuro-MEP-4 ("Neurosoft" Ltd., Russia). The surveys were carried out at the premises of the department of functional and ultrasonic diagnostics at Surgut clinical trauma hospital. The statistical data processing was made using the STADIA_8 software for Windows (developed by SPA "Information science and computers" at Lomonosov Moscow State University, Moscow, Russia), which environment was used to analyze the correlation of electroneuromyographic indicators and stabilometric indicators of kinesthetic sensitivity and muscular synergy in athletes [5]. Based on the descriptive statistics data, we calculated Kendall's coefficient of concordance (t) and Spearman's rank correlation coefficient (r) with determination of the significance level (p≤0.05) [7].

Results and discussion. We detected statistically significant relations between the variables that characterize the conduction of excitation along the lower limb nerves and kinesthetic sensitivity indicators in the vertical posture, specifically between the sensory response (SR) and nerve conduction velocity (V) of n. Peroneus, SR and response amplitude (A) of n. Suralis in the Romberg’s test "Dynamic balance". These relations are expressed by the regression equations as follows: y = EXP (-6.04) 1.15x² (p=0.0074) for n. Peroneus and y = 0.1038+0.0111x (p=0.0066) for n. Suralis (Table 1). After physical load we detected the correlation relations between the motor response (MR) rate and latent time of n. Peroneus response, as well as between MR and conduction velocity of n. Tibialis in the Romberg’s test with eyes open. While taking the test with eyes closed, we detected the correlation between SR and response amplitude (A) of n. Suralis. The statistically significant relations between SR and V of n. Peroneus were detected during the "Dynamic balance" test. The dependence is expressed by the equation: y = -0.106 +0.0074x (p=0.0313). No other significant correlations were observed (Table 1).

Table 1. Correlation and regression relations between the indicators of conduction of excitation along the lower limb nerves and kinesthetic sensitivity indicators in the vertical posture

Note. МR – motor response NCV (nerve conduction velocity), SR – sensory response NCV; LT – latent time of response NCV in ms; А – response amplitude in mkV NCV; V – response rate in m/s NCV; t – Kendall's concordance coefficient; r – Spearman's rank correlation coefficient; NC – no correlation.

There are also statistically significant relations between the variables that characterize the conduction of excitation along the lower limb nerves and muscular synergy indicators in the vertical position, which change after standard physical load (Table. 2).

Тable 2. Correlation and regression relations between the indicators of conduction of excitation along the lower limb nerves and muscular synergy indicators in the vertical posture

Note. The legend is the same as in Table 1.

Before the physical load, the Romberg’s test (with eyes open) detected the relations between MR and V of n. Peroneus, the "Dynamic balance" test - the relation between SR and LT, CR and A of n. Suralis (the regression model is as follows: y = 264.23-8.64x) and SR and A, SR and V, MR and V of n. Tibialis (y = 733.8-11.61x) (see Table 2). Physical load caused relations between SR and V of n. Peroneus, SR and V of n. Suralis, MR and V, MR and A of n. Tibialis primarily in the Romberg’s test with eyes open. We obtained the regression model as follows: y = 545 -16.3x (p=0.0011). The "Dynamic balance" test revealed only one essential relation between SR and V of n. Tibialis (see Table 2).

While rocking the straight body back and forth during the Romberg’s test with eyes closed in the European posture we observed the largest number (61.9%) of statistically significant correlation coefficients and regression equations for the functional correlations between the indicators of conduction of excitation along the lower limb nerves and stabilometric vertical postural muscular coordination indicators in man.

We assume, this is due to the fact that ENMG is an active method of stimulation of human nerves. Body rocking back and forth with eyes closed is also more active compared to the maintenance of usual posture in a nominal static position. A meaningful result of this analysis is the detection of a large number of correlation coefficients and regression equations for the functional correlations (28.8%) in the Romberg’s test with eyes open after standard physical load of 30 squats in 1 min. The data presented in the tables indicate that the group of the surveyed young people have the highest number of statistically significant correlation coefficients and regression equations for the functional correlations between the indicators of conduction of excitation along the lower limb nerves and stabilometric vertical postural muscular coordination indicators obtained during the tests, where the human body is forced to activate its functional capacities to maintain the vertical position in a complex environment. In order to conduct an in-depth analysis of the detected relations, let us turn our attention to the foot movement nervous control model (see Fig.).

Figure 1. Foot movement nervous control model

It is believed that regulatory impact when performing various foot movements is organized according to the following pattern: n. Peroneus innervates the skeletal muscles, muscle and ligament receptors of the dorsum of the foot; n. Tibialis innervates the skeletal muscles, muscle and ligament receptors of the planta of the foot, and finally, the main function of n. Suralis is to control the changes in the interarticular corners of the foot bones. This kind of organization of foot movements is fully justified from a biomechanics perspective.

Kinesthetic sensitivity (KS), defined by the stabilometric study as the average value of the first three maxima of the cross-amplitude characteristics of the vertical component ((kg*Hz)^1/2), represents the motor (proprioceptive) sensitivity threshold of man. The lower this value, the higher the human sensitivity to the subtle analysis of the body position, skeletal muscle sizes, and the higher the efficiency of the efforts made during movements when solving various motor tasks. Positive values ​​of the coefficients of correlation and regression models suggest that the lower the values ​​of the electrical potentials of n. Suralis of the foot, the lower the KS threshold values and the higher level of development of individual sensitivity to the subtle analysis of the body position. The lower the values of sensory and motor nerve responses of n. Peroneus, the higher the level of development of man’s ability to control the muscle tension in the dorsum of the foot. The statistical significance of the stabilometric test results varied from p=0.0021 to p=0.0462.

The muscle synergy level, defined by the stabilometric tests as a ratio of the equilibrium function quality (EFQ, c.u.) and the average values of the first three maxima of the cross-amplitude characteristics of the vertical component ((kg*Hz)^1/2), can be treated as an indicator of intermuscular coordination. The higher EFQ, which reflects the fluctuations of CCP on the horizontal plane of the stabilometric platform in the frontal and sagittal planes, and the less efforts on the support in the vertical component, the higher the consistency in the tension and relaxation processes in the muscle system while maintaining the vertical body position. Negative values ​​​​of the coefficients of correlation and regression models indicate that the lower the value of the electrical responses of n. Tibialis and n. Suralis of the foot, the higher the values ​​of inermuscular coordination, and the higher the level of muscular synergy in human movements. This reaffirms the important role of n. Suralis in the foot movements of man. According to the foot movement nervous control model we propose, information from this nerve serves as a guide for the motor nerve centers of n. Tibialis when organizing plantar flexion and muscle tensions. It can be concluded that the level of muscular synergy when controlling the vertical posture of man is more likely to reflect the velocity and amplitude values of the sensory and motor responses of the stimulated n. Tibialis (based on the stabilometric tests, the statistical significance varied from p=0.0011 to p=0.0469).

Conclusion. Through the postural stability control conditions being made more complicated, we found the maximum number of significant correlation ratios and regression equations for the functional correlations of the indicators of conduction of excitation along the lower limb nerves and stabilometric vertical postural muscular coordination indicators in man.

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Corresponding author: logsi@list.ru

Abstract
The study revealed a correlation of the stabilometric postural muscular coordination indicators with the lower-limb peripheral nerves stimulation electroneuromyographic (ENMG) indicators in the post- and pre-physical workload tests of 17 university athletes aged 18.7 ± 0.5 years, with the Kendall’s concordance ratios and Spearman’s range correlation ratios being applied in the calculations. The study found signifi-cant correlations of the kinesthetic sensitivity rates and the n. Peroneus excitation variables, and offered three regression models. The statistical data difference significance rates varied from р=0.0021 to р=0.0462. The muscle synergy levels in the vertical posture control process were found to correlate with the n. Tibialis sensor-motor response rates and amplitudes (with the correlation significance rates varying from р=0.0011 to р=0.0469). The article presents a foot movement nervous control model considering the contributions of n. Suralis, n. Tibialis and n. Peroneus. Through the postural stability control conditions being made more complicated, we found the maximum number of the significant correlation ratios and regression equations – for the functional correlations of the stabilometric vertical postural muscular coor-dination indicators with the lower-limb peripheral nerves stimulation electroneuromyographic (ENMG) indicators.