Reviste 2003/32-10

ASSESSMENT OF THE PERSONAL BALANCE FREQUENCIES IN STANDING POSTURE AT THE SHOOTERS

GEORGE STIHI, EMIL POPA

National Institute of Sport Research, Bucharest

Key word: posture, equilibrium, spectral analysis, shooting

Key points:

1. The static postural capacity is tested with the informational feedback, using the computer assisted balance platform for a group of high ranked shooters.

2. It used for the data analysis the method of the "spectral and correlation analysis".

3. There are highlighted differences in the aspect of the group of major oscillating frequency between athletes with average concentration and at maximum concentration moments.

Introduction

Natural orthostatic position is the result of the interaction between an assembly of elementary reflex acts and the feedback information on the environment, info received via sensorial systems. This interaction ensures not only the vertical position of the body, but also the permanent and automatic correction of body's balance by adapting the neuro-muscular tonus to the needs of the moment.

It is common knowledge that the information on the body's balance comes from various internal sources, direct view being probably the most important one Schmidt, R.A.. Direct view gives the most complete set of information on the restrains of various movements and hazardous changes. Information issued by proprioceptors and vestibular apparatus may be of great significance too.

Objective

The essence of self-balance behavior consists in the correct evaluation and interpreting of the force relations between body's components and its ground support. Thus, one can postulate that stability is a natural characteristic of any system that responds by minimal output changes to relatively small input changes. In the specific case of the orthostatic position control system, the relatively small input changes consist of a summa of volitive (on purpose) Massion, J.] and random (postural balancing) movements [Blaszczyk, J.W..

Despite many years of research on body's balance and stability, the phenomenon is not fully understood yet. Scientists focus on more accurate description of movement control under various conditions as well as on the relation between balance and age or specific disease.

Methods

Postural balance capacity has a major influence on sport performance, especially where precise movement coordination is required. Since postural balance capacity and body stability are essential for high performance shooters, the paper shows an analysis based on high rank Romanian shooters tested during their training.

This paper is focused on applying specific analysis paths to parameters closely related to postural balance capacity in view of enhancing shooters' selection and controlling their evolution during training sessions.

A paper dated 1999 [Shea,-C.-H.] shows that subjects submited to a difficult balance task enhance their motor learning through external-focus instructions and feedback. Thus, enhancing several shooters' postural balance capacity through information feedback was tested by means of a computer controlled balance platform [Nistoroiu Gh.], [Hillerin, P. ].

The protocol established for testing shooters' postural balance capacity on the balance platform is part of a general set of tests [Stihi, G.] and the position on the platform was chosen according to the specific position for Bullseye Pistol Shooting. The subject remained steady and relaxed, with armed arm forward - fixing a target, eyes focused on the screen in order to track and control the evolution of the spot showing the projection of his own center of pressure.

The working hypothesis to be validated is the existence of one or several eigen-characteristics of vibration of the multi-joint system of shooter's body. In other word, is there a specific frequency tied to this sport? Does this frequency shifts from a test to another due to environmental or task changes?

The tool used for reaching this purpose was the spectral and correlation analysis [Popa, E.]. This technique was used before, on the same balance platform [Liu,S.H.] and showed a good correlation (R > 0,85) between the parameters generated through spectral analysis (mean spectral power, spectral area and maximal power) and the ones which describe the postural balance capacity. During the test, the evolution of the spot showing the projection of his own center of pressure was treated as a non-periodical signal. The maximal value (or values) in its frequency spectrum is (are) the frequency (frequencies) searched for.

Rezults

Figures 1, 2 and 4 show the test results for several shooters in the team. Those results characterise a general situation for average shooters or in a moment of average focusing. One can see several eigenfrequencies in the range of 0 to 1Hz, a result that is confirmed by other studies. Nevertheless, tests revealed exceptional situations in which high rank (olympic) shooters, in a moment of intense focusing, shown practically a single eigenfrequency in the same domain (figure 3 and 5) or a very reduced number of them..

We cannot tell if this aspect is a native or acquired quality, but its early discovery may prove useful either for selection or for training.

A particular case is the one of P.L., an average shooter, who's spectral analysis shows not only the "classical" frequencies in the 0 to 1Hz domain, but other significant frequencies in the 7 to 8Hz domain (see figure 6). Those frequencies appeared not only on multiple test the same day, but also the day after, when he was asked to reiterate the tests. The critical vibration period is of 140ms, which is approximately equivalent to the mean time of neuromuscular reaction of the human body and represent maybe a physiological problem.

Abstract

The current theories consider as correct the multiarticular muscular model, rather than the uniarticular one (of the reversed pendulum). The static postural capacity is tested with the informational feedback, using the computer assisted balance platform for a group of high ranked shooters. It was aimed to develop a modality to analyse the specific parameters necessary for the assessing of the postural balance capacity, by using the method of the "spectral and correlation analysis", having as declared purpose the increase of the selection and control possibilities of the sport preparation evolution. More oscillating frequencies were highlighted for athletes with average preparation or at a moment of average concentration, as well as in exceptional situations for top athletes at maximum concentration moments, when only one oscillating frequency was spotlighted.

Reference

Blaszczyk, J.W. & all., Age related differences in performance of stereotype arm movement: movement and posture interaction, Acta Neurobiol. Exp., 57, S.U.A.,1997

Hillerin, P.; Popa, E.: Schor, Vl.; Stihi, G.; Stupineanu, I.; Mihoci G., Utilizarea unei metode de evaluare a echilibrului in testarea sportivilor juniori din centrele olimpice. In: Stiinta Sportului, Bucuresti, nr. 5, 1997

Liu,-S.-H; Lawson,-D. - Power spectrum of the fast Fourier transform for measurement of standing balance. Australian-journal-of-science-and-medicine-in-sport, 27(3), Canberra, 1995

Massion, J.,Movement, posture and equilibrium: interaction and coordination. Prog. In: Neurobiol. S.U.A., 38, 1992.

Nistoroiu Gh.; Vladutu G., Metoda de evaluare a aptitudinilor de echilibru. In vol.: Simpozionul National "Perspective 2000", Bucuresti, C.C.P.S., 1996

Popa, E., Incercare de determinare a frecventei proprii intr-o proba de echilibru. In : Stiinta Sportului, Bucuresti, nr.6, 1997

Schmidt, R.A., Motor learning and performance. S.U.A., Human Kinetics Books, 1991.

Shea,-C.-H; Wulf,-G.,Enhancing motor learning through external-focus instructions and feedback. In: Human-movement-science, Amsterdam, 18(4), 1999

Stihi, G.; Stupineanu, I.; Popa, E.; Schor, Vl.; Enescu, M.,Analiza critica a bateriei de teste generale C.C.P.S. - C.O.R.. In: "Managementul viitorului in activitatile de educatie fizica si sport", Bucuresti, 1999