Healthy untrained males (age 25.4 +/- 1.7 years, n=12) gave their informed consent to take part in all experiments within the study. After 100 intermittent (every 20 s) drop jumps from the height of 0. 4 m, jumps with counter-movement to 90 degrees angle in the knee and immediate maximal rebound (eccentric-concentric exercise; E-C) and 100 continuous jumps (five bouts of 20 jumps with counter-movement to 90 degrees angle in the knee with 10 s between bouts) (maximal exercise; M) with maximal intensity, the height of vertical jump decreased in a similar way, and this decrease did not depend on the performance mode of jumps. After E-C and M jumping exercises, there was a significant (P < 0.001) decrease in maximal voluntary contraction force, as well in the force generated by electrical stimulation at all stimulation frequencies, and these values were not restored to the initial level even after 24 h. After the E-C exercise, however, the muscle contraction force generated at different stimulation frequencies and, especially, at low-stimulation frequencies (1-20 Hz) decreased to a significantly (P < 0.05-0.001) greater extent than after M exercise. Twenty minutes after the end of M exercise, there was still a greater increase in low-frequency fatigue (LFF) and it was no different from the LFF registered 20 min after the end of E-C exercise. Twenty-four hours after the M exercise, however, LFF was smaller than its respective value after E-C exercise. There was no significant relationship between the values of LFF after E-C and M exercises. This may indicate that there are differences in the origin of the LFF after the E-C and M exercises.

8 measures recorded during alternate tapping of two targets by left and right hands for 15 boys, 13 or 14 yr. old, were made during 4 30-sec. trials using a force averaging 450 gm. Mechanical and electrical activity (EMG from m. biceps brachii) of both hands suggested asymmetric characteristics of the two hands and the likely involvement of different types of muscle fibers or asymmetry of the CNS.

In the continuous research, conducted in the sports school in Tarnów (Poland) with a football profi le, the authors attempted to fi nd out whether the changes of hidden predispositions and motor abilities appear during the training process which constitute the foundation for the development of technical and tactic fi tness against the background of the similar research results carried out in the comparative groups of non-training individuals. In the research the measurements of the basic somatic traits, anthropometric indexes, VO 2 max  × kg  –1  and motor skills were taken into consideration. The observations were made every six months for three years. The comparative group consisted of the peers with attending randomly chosen schools (comparative group). The conducted factor analysis revealed the fact that there are minor quantitative differences of the motor structure between training and non-training groups during a three-year observation period. In both the sportsmen’s and less physically active boys’ groups the number of separated factors did not increase as well as the set of variables taken into account. It can be concluded then, that the applied way of sports selection as well as the process of their adaptation to a specifi c training ballast might have been the causative factor of the structure effi ciency specifi cation among children from sports schools. In this connection, they cannot deny the thesis that a talented sports master can be recognized already as a child. Still, the ways of such a selection seem controversial.