Postural control by cross country skiers grouped by skill levels

Фотографии: 

Applicant A.A. Kravchenko1
Associate Professor, PhD A.S. Bakhareva1
Professor, Dr.Biol. A.P. Isaev2
Associate Professor, PhD V.V. Erlikh1
1Institute of Sport, Tourism and Service, South Ural State University, Chelyabinsk
2Research Center of Sports Science, South Ural State University, Chelyabinsk

Keywords: stabilometrics, statokinetic stability, pressure centre, frontal plane, sagittal plane, stance, posture, balance.

Abstract

Objective of the study was to explore physiological aspects of the vertical posture control by cross-country skiers grouped by skill levels. Studies of postural control give the means to rate statokinetic stability in the cross-country skiers’ postural balancing process and other factors – from the race stances in their variation along the distance and to the integrated body postural performance data and analysis. More diverse frame conditions for research may provide a way to determine the body reserve capacities as verified by the general pressure centre positioning indices, dynamic equilibrium ratios, plane-specific energy indices etc. rated by the athletic skill groups. Formalized characteristics of the stabilometric elements make it possible to correct the statokinetic stablility control parameters on a timely basis.

Introduction

As things now stand in cross-country skiing sport, race speeds on distance have grown considerably for the last few years [1], and new research data emerge in this context that urges to study in more detail the cross-country skiers’ postural control mechanisms i.e. the posture variations and postural performance in dynamically changing race situations; with consideration for the relevant sensory-motor response (to the environmental impacts) generation patterns; and the voluntary motor actions (VMA). It has been found in the studies that the statokinetic stability (SKS) rates tend to grow with the growing motor activity rates; and the SKS rates are considered among the most informative criteria of the motor function control system performance conditions. This is the reason why we believe it is so important to have studied in more detail the vertical postural control mechanisms within the frame of locomotor patterns of cross-country skiers [6].

Objective of the study was to explore physiological aspects of vertical postural control by cross-country skiers grouped by skill levels.

Methods and structure of the study. The study was performed using MBN-Stabilo Computerized System for diagnostics of body equilibrium disorders and rehabilitation; the system includes a specialized stabilometer designed to register the athlete’s pressure centre projection on the test plate and its dynamical deviations in time within the coordinate system, with account of the feet position versus the standard (‘absolute’) position on the plate. Subjects to the tests were requested to perform 2 trials of 30 seconds each: one in the Main Stance with Open Eyes (MSOE); and the other in the Main Stance with Closed Eyes (MSCE). Subject to the study were 18 cross-country skiers qualified Masters of Sport (MS, 7 people) and Candidates for Master of Sport (CMS, 11 people).

Study results and discussion. Motor sequence performed in the main stance is viewed as the integrated actions of the athlete’s musculoskeletal system, vestibular apparatus, visual system and proprioceptive system with the relevant controls to secure the statokinetic stability in the process.

Table 1. Mean square deviations of the General Pressure Centre (GPC) in the frontal (x) and sagittal (y) planes, in mm, for the both test groups (M±m)

 

Test group

Open eyes

Closed eyes

Main stance

Head turned to the left

Head turned to the right

Main stance

Head turned to the left

Head turned to the right

Frontal plane

MS

12,6±2,9

21,2±2,7

44,3±0,9

31,2±2,5

33,8±4,0

53,7±11,1

CMS

6,38±0,76

20,59±2,15

11,22±2,04

5,4±1,12

12,11±1,76

7,15±1,45

p

< 0,01

> 0,05

< 0,001

< 0,001

< 0,01

< 0,001

Sagittal plane

MS

17,86±3,1

28,87±3,74

35,08±2,54

27,80±2,8

37,99±3,41

64,9±12,1

CMS

10,03±1,7

12,41±2,61

9,46±1,31

6,94±0,51

8,66±1,03

21,3±2,01

p

< 0,05

< 0,05

< 0,001

< 0,001

< 0,001

< 0,001

 
As demonstrated by the data given in Table 1, the mean square deviations of the General Pressure Centre in the frontal (x) and sagittal (y) planes show significantly higher deviations for the Masters of Sport (MS) group. Given in Table 2 hereunder are the Pressure Centre (PC) movement rates of the athletes that show that the MS group rates were higher than that of the CMS group. This fact may be indicative of the higher activity of motor neurons in the cervical spine segment of the higher-ranking athletes.

Table 2. Pressure Centre (PC) movement rates V (mm/ s), for both of the test groups (M±m)

 

Test group

Open eyes

Closed eyes

Main stance

Head turned to the left

Head turned to the right

Main stance

Head turned to the left

Head turned to the right

MS

13,90±0,50

16,66±0,73

18,89±0,89

20,98±1,12

23,5±1,41

30,0±1,7

CMS

11,96±0,54

15,21±0,49

13,44±0,50

13,56±0,50

13,49±0,5

16,4±0,6

p

< 0,05

< 0,05

< 0,05

< 0,05

< 0,01

< 0,01

The wide range of the GPC movement and the high movement rates may be characteristic of the high performance quality of the postural control system. We apply herein the so-called Dynamic Component of Equilibrium (DCE) rate that may be considered an integrated index as it permits to understand how effective the efforts to minimize the PC movement rate are; since the higher is the DCE, the better is the equilibrium control by the athlete [5] achieved by the precise nervous-system-driven control mechanisms that make sure that the due vertical balance of the body is maintained in the process [2] (see Table 3 hereunder).

Table 3. Dynamic Component of Equilibrium (DCE) rates for both of the groups (M±m)

Test group

Open eyes

Closed eyes

Main stance

Head turned to the left

Head turned to the right

Main stance

Head turned to the left

Head turned to the right

MS

71,23±1,49

75,98±1,27

78,82±1,67

80,93±2,01

82,97±2,1

86,7±2,9

CMS

66,56±1,32

73,71±1,49

70,25±1,02

70,5±1,02

70,35±1,0

75,6±1,5

p

< 0,05

< 0,05

< 0,05

< 0,05

< 0,01

< 0,01

For the vertical postural control being efficient, many muscular groups are involved with their actions being perfectly harmonized in the voluntary movement sequence [7].

Figure 1. Postural sway spectra for the frontal and sagittal planes of the main stance, for two test groups, (f60%, Hz)

As found by studies, athletes tested with better physical coordination qualities normally have more sophisticated voluntary motor action performance abilities. Given on Figure 1 are the data that show the average postural sways for the MS and CMS groups falling within the range of 0.5-1.5 Hz, albeit the absolute sway values are higher for the MS group (p <0.05). This may be indicative of the fact that the muscle contractions of higher-ranking athletes are less controlled by conscientious efforts [3]. Romberg ratios were found to make up 186.4±4.2% and 69.6±2.3%  for the MS and CMS groups, respectively. This fact may be due, on the one hand, to the visual control in the MS group prevailing over the proprioceptive system in the posture balancing process; and, on the other hand (as suggested by some study reports), it may be indicative of the higher-skilled Masters of Sport being more efficient in the vertical posture control with the growing muscular fatigue [4].

Conclusion. The integrated postural control and performance indicators obtained under the study provide the means to make judgements on the balance of neuro-physiological, sensory and energy abilities in the integrated performance profiles that secure high sport accomplishments for the skilled athletes. 

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