Bio-mechanical aspects of elite cyclists ’ motor system adaptation in process of competition activity

Purpose: to study the laws of motor structure adaptation of elite cyclists, specializing in 4 km individual pursuit racing

Introduction 1  Competition activity of elite athletes is regarded as important factor of pedagogic and physical influence.Competition is characterized by extreme conditions for manifestation of special fitness's different sides.
Competition is an effective mean of maximal realization of athletes' functional potentials [8].
Most specialists mark out conventionally start, distance and finish segments [19,27].Such division is a result of pedagogic observations.Recent years more detail division of competition distance has been offered [8,26].
Optimization of competition activity's structure implies searching of the most effective variants of qualitative and quantitative interconnections of athletes' special fitness different sides [28].For example in cyclists' 4 km pursuit racing on track it can be reduced to solution of the following tasks: rational fulfillment of start acceleration; transition to distance speed; finish acceleration [18].Effectiveness of the mentioned elements can influence on final sport result [9].Especially it is noticeable in competitions of athletes of approximately the same level [5].However, in elite athletes' training, work with the mentioned elements takes rather modest place.
In other works it was found: Influence of pedal's speed and crank length on pedaling mechanic in period of sub-maximal load.The authors found that distribution of joint torques and powers is mainly sustained in different conditions of pedaling [2]; For assessment of joint and segment movements working load of from 65 to 95% from maximal output power of separate cyclists can be used [3]; Dependences of power pedal's output and electromyography (EMG) of lower limb in different cyclic position.Besides, in this work the authors determined indicators of bilateral asymmetry of pedaling force and EMG.These results show that cyclists can "re-switch" between sitting and standing positions during competitions, for increasing race efficiency in different situations [6]; Professional cyclists increase pulling force in the phase of recreation for sustaining the same output power [12]; Effectiveness of cycling is influenced by profiles of foot angle.This factor is one of the most important and directly correlates with effective force, applied to bicycle [32].
Solution of the following problems is very important in athletes' training: Control of physical loads [17]; Optimization of physical loads [1,15]; Consideration of athletes' individual characteristics [10,11]; Determination of successfulness factor in sports [16,22,23]; Athlete's ability to distribute load being on distance.Such ability is required for prevention from too early fatigue [25].
In numerous studies there were found quantitative and qualitative changes of cyclists' motor actions' structure under influence of complex of factors.These factors determine external and internal conditions of realization of athletes' motor potential in the process of competition activity [13,27].Winners of elite competitions in kinds of sports for endurance do not reduce speed at the end of distance but increase it in state of rising fatigue [29].With it, technique of main sport movement changes [4,18].However it is still not cleared up: what factors influence on sustaining of high distance speed in the state of fatigue [7].Besides, working out of bio-mechanical pre-conditions for optimization of competition activity's structure is of great practical importance [21].This problem touches wide circle of questions.These questions are connected with searching of laws of individual adaptive reactions in motor system [24].Differentiated character of their manifestation depends on specificities of different physical qualities' development [30,31].
The purpose is to study the laws of motor structure adaptation of elite cyclists, specializing in 4 km individual pursuit racing on track.

Material and methods
Participants: in the research 18 elite athletes participated.(12 international masters of sports and 6 honored masters of sports).
Organization of the research: we applied complex method to bio-mechanical researches.The athletes were tested in laboratory and natural conditions (4 km individual pursuit racing).We studied dynamic of kinematic and dynamic characteristics of horizontal and vertical components of forces, applied by cyclist.Besides, we studied bio-electrical activity of the following muscles: quadriceps and biceps of thigh; shin and frontal tibialis of right leg.We registered amplitude and frequency of biopotentials; rhythm structure of electric activity; integrated bio-electrical activity of muscles.Besides, we calculated indicators of effectiveness and efficiency of motor functioning and determined variability of the studied motor characteristics [20].
Statistical analysis: in statistical processing we found mean values of indicators and their errors (X±m), difference between mean values and confidence of differences (t, p), correlation between the studied indicators (r); and the value of dispersion (variant around mean value (σ, CV)).
In our complex pedagogic, bio-mechanical and biological athletes' examinations we observed legislation of Ukraine about health protection; Helsinki declaration 2000 and directive №86/609 of European community about human participation in medical-biological researches.
Integral indicators of pedaling technique (effectiveness, efficiency and symmetry of cyclist's legs' work) are highly stable (see fig. 1).
Realization moments of forces maximums are in constant definite zones of pedaling cycle (see table 1).It is interpreted as specific characteristic of elite cyclists.The constancy is achieved owing to many years' process of special training.The moments of beginning and end of vertical forces are highly stable.Space characteristics of horizontal forces gradually increase from the beginning to the end of distance.
Characteristic feature of distance's finish segment is significant increase of zone of application of both legs' forces' horizontal components.It should be regarded as a method of sustaining high speed on finish segment in conditions of rising fatigue.
Time indicators of vertical forces are also highly stable (see table 2).Time characteristics of pushing increase with approaching finish.Increase of pushing forces duration (by left and right legs) is connected with increase of duration of force's reduction phase.Duration of forces' increase up to maximal value is constant on all distance segments.Time indicators of right leg's moving reduce by 32% by the middle of the distance.In the second half of the distance time indicators of right and left legs' moving also increase.On finish segment time indicators of right and left legs' moving exceed average level on distance by 40%.Duration of left leg's moving has opposite direction.
Maximal forces of both legs' pressing and left leg's pulling up are highly stable (see table 3).Maximal forces of right leg are pulling up increase by 41% by the end of distance.Forces of both legs' pushing and moving reduce by 15% by the end of distance.
The character of pedaling technique's adaptive reconstructions changes, depending on athletes' individual characteristics (see Fig. 1).
Reconstructions in pedaling technique depend on the following: -share participation of many factors in pedaling technique's structure; -Compensation of insufficient level of one movement's characteristics by hypertrophied level of other; -Variability of motor system's adaptive reconstructions, which appear under influence of fatigue.
Speed at different segments of distance is conditioned by the structure and quantitative characteristic of interconnection with pedaling technique.Multiple correlation analysis determined the influence of more than 120 indicators of cyclists' pedaling technique on competition distance.On some distance segments oneside influence of certain indicators' groups is observed.It permits to unite separate segments of distance.Conventionally we marked out the groups of indicators, which condition pedaling speed on different distance segments.High speed on start segment depends on effectiveness of right leg's pulling up and pressing/ moving of left leg.On initial part of distance segment high efficiency and effectiveness of pedaling technique is ensured by legs' pressing and pulling up.On middle part effectiveness of left leg's pushing is important.With rising of fatigue, importance of horizontal components of forces increases.On final part of distance segment high workability depends on the following: right leg's moving; left leg's pressing, pulling up and pushing.Finish segment requires great mobilization of athlete's

05
functions for sustaining high speed.Passing this segment is characterized by fatigue's rising.Significant reconstructions in motor structure take place on finish segment.Speed on this segment is determined by right leg's pressing, pulling up and moving; as well as by left leg's pressing and pulling up.

Discussion
Changes of pedaling technique's time characteristics shall be regarded as adaptive reconstructions of cyclists' motor structures.It witnesses about gradual transition of cyclists' technique to qualitatively new coordination level by the end of distance [5].With fatigue's emersion correction of external motor characteristics occurs.With fatigue, significance of horizontal elements of pedaling technique increases.At finish effectiveness of cyclists resulting forces increases [27].Our results concord well with other data and are confirmed by them [2,3,6].
Increase of pedaling power is conditioned by change of applied forces.Choice of biomechanically the most reasonable zone of maximal force application in pedaling cycle is a decisive condition, determining pedaling technique's effectiveness [31].Horizontal components of forces are of special significance.Duration of horizontal components of forces is less than in vertical components.It is confirmed by other researches [2,32].
Sustaining of pedaling high speed on distance is determined by possibilities and purposefulness of motor system's adaptive reconstructions.The mentioned reconstructions are pre-conditioned by changes of motor activity's regime.It is connected with involvement of additional muscular motor units in work.On finish

Fig. 1 .
Fig. 1.Dynamic of integral indicators of elite cyclists' pedaling technique on model distance of pursuit racing: Vspeed, km/hr; F -spent forces, N; K -coefficient of force efficiency, %; I -total impulse of force, N•s; Ks -symmetry indicator by coefficient of force efficiency, %; Fs -symmetry indicator by spent forces, %; L -length of distance, %.

Table 1 .
Dynamic of space characteristics (moments of maximal forces) in pedaling cycle of elite cyclists on model pursuit racing, degrees

Table 2 .
Dynamic of time characteristics (moments of maximal forces) in pedaling cycle of elite cyclists on model pursuit racing, sec.

Table 3 .
Dynamic of maximal forces in pedaling cycle of elite cyclists on model pursuit racing, H