V.I. Frolov, associate professor, Ph.D.
P.V. Frolov, postgraduate
Russian state university of physical culture, sport, youth and tourism (SCOLIPhC), Moscow
I.V. Chistyakov
Moscow mining university, Moscow

Key words: bobsleigh, starting stride, acceleration, flyover, track, explosive muscle strength, bobsledders.

Relevance. In bobsleigh when other conditions are equal the winner is the crew with the highest speed output after the starting stride of the bob. It has been determined in the 80s of the last century [2-4] that the result in the starting stride mainly depends on the muscle explosive force of bobsledders and on their ability to quickly reproduce the recurring in cycles reversing mode of leg work or, otherwise, on athletes' sprint abilities. But qualification in bobsledder crews according to body-weight ratio, its distribution in view of specialization (side, back brakemen), synchronism of efforts at sliding off and accelerating of the bob followed by seating in the bob without losing the speed gained by the bob are of special importance.

The purpose of the study was to analyze synchronous team actions of elite bobsledders when performing the starting slide off of the bob and determine the influence of the latter on passing time closings during the starting stride.

For this purpose, three four-man crews were tested in 19 races (qualification - MS and MSIG) on the acceleration ice flyover “Paramonovo" in August 2011.

Materials and methods: stationary and portable electronic timing system by the company “Brower Timing Systems, USA, 2011", the registration of acceleration using a linear accelerometer of the type MMA 7260Q with signal filtering at the input by the first order filter with the range 200 cyclic Hz.

In our case, we consider only linear acceleration along the acceleration axis in 19 races of three crews (Tab. 1). At the same time, there were analyzed the time to maximum acceleration, the very magnitude of this acceleration, sharpness as the ratio of maximum acceleration and time to achieve it and took the time of passage of time cutoffs at the 15 and 45 m distances from the starting bar and the time of passing the 30 m area between 15 and 45 m.

Table 1, where the strongest "most well-trained” crew took part in the races № 4, 7, 10, 13, 16, 19, shows how much higher the magnitude of the maximum acceleration of these bobsledders is and how to achieve it faster as compared with other four-man crews. Moreover, these figures vary greatly in the sample by the coefficient of variation, especially sharpness as a derivative of the first two, reflecting the heterogeneity of sampling for different crews. Indirectly such fast (almost in 0,2 seconds) maximum acceleration of the strongest four-man crew in the very first moment of the starting stride reflects nothing but the speed of recruitment of motor units, and in all four athletes simultaneously. Working so synchronously on the first meters of acceleration the bob speed reaches over 5-6 m/s, allowing to sit in the bob after a 15 m acceleration "section” of the track.

Table 1. Parameters of bob acceleration for different races

Table 2.

As follows from Tab. 2, the value of maximum acceleration in the very first moment of acceleration greatly determines the time for passage of all cutoffs. It would seem that the initial acceleration should primarily influence the passage of a 15-meter cutoff, however, next 30 m are completely dependent on the first 200-400 ms.

It should be noted that bigger value of а_max stipulates for less time to achieve it. And this is nothing but the confirmation of previous results on the basis of electromyographic and tenzodynamographic researches in the late 80-s of the last century in Riga, where the amount of effort being developed was also determined by the time of recruitment of motor units (MU). The more ME are involved in the time unit of elite bobsledders in the very first moment of muscle contraction, the larger the magnitude of the motor effort is. In addition, it turned out that the higher the contractile muscle properties are, the greater their relaxation characteristics are. In other words, the faster an athlete, using central neuromechanisms of innervation of muscles, involved them in the work, the faster he could relax them. And this is extremely important during the starting stride of bob, which starts to move with a sprint speed. At high speed of movement in cyclic locomotions, when the duration of the support phase is only 90-120 ms [1], each subsequent muscle involvement in the work can be effective only if they have previously been completely relaxed, otherwise the rapid recruitment of MU will not occur [5].

Conclusions

Registration of the apparatus acceleration when teams perform the starting stride revealed a very strong dependence of time results at time closings and power of the initial slide off of the bob, which, in its turn, is related to synchronous actions of the whole crew in general.

The results of the measurements of accelerations have clearly proved the leading role of explosive muscle strength, especially its starting component at the very beginning of acceleration (in the first 200-400 ms).

In order to get an objective assessment of sports technical skills of bobsledders in crews and their recruitment, research and development are required, focused on design of devices that can register acceleration of the apparatus and the devices enabling measure straining the bob and simulators' handles to get information on the manner of applied efforts of each of the crew members.

References

1. Ozolin, E.S. Sprint / E.S. Ozolin. – Moscow: Fizkultura i sport, 1986. – 159 P. (In Russian)
2. Frolov, V.I. The manner of interaction of the processes of muscle contraction and relaxation in elite bobsleders / V.I. Frolov, L.V. Chuprik. – Book of abstr. of theor.-pract. conf. – Riga: LSIPC, 1989. (In Russian)
3. Frolov, V.I. Key bobsledder’s motor abilities and factors limiting their manifestation in the starting stride / V.I. Frolov, L.V. Chuprik / Research report. – Riga: LSIPC, 1990. (In Russian)
4. Frolov, V.I. The factors limiting special exercise performance of bobsledders of different qualifications in the starting stride of the bobsled / V.I. Frolov, L.V. Chuprik / Book of abstracts of the. scient. conf. – Riga: LSIPC, 1991. (In Russian)
5. Yashchaninas, I.P. The influence of different levels of muscle tension on the manifestations of explosive isometric contractions / I.P. Yashchaninas, Yu.V. Verkhoshansky et al. // Teoriya i praktika fizicheskoy kultury. – 1988. – № 4. (In Russian)

Corresponding author: fvi1945@mail.ru, 89036904297