Periodic body composition (BC) measurements can be used to assess the effectiveness of exercise and monitor changes in BC associated with growth and maturation or disease state. Determination of BC provide useful information on the nutritional status and on the predispositions for physical exercise. The specific BC is a predisposition for specific sport, let us say specific sports want also specific change in BC. Although BC, as well as the age-related changes in it, has a strong genetic component, it is also influenced by enviromental factors. The primary influences are nutrition, disease, and physical activity. Regular physical activity is an important factor in the regulation of body weight. Regular training generally results in a decrease in fatness and an increase in fat free mass (FFM). The magnitude of changes in BC with regular training varies with the type, intensity, and duration of the program. The increase in FFM observed in youth regularly trained over several years seems to suggest an increase greater then that expected with normal growth and maturation. Physical activity is one of many factors that may influence growth and maturation. An individual´s growth and maturity status also influence physical performance. Clearly, growth, maturation, and performance are related. The characteristics of the performer affect the performance. The bioelectrical impedance analysis (BIA) seems to be one of the most used methods for determination of BC in the field conditions. The most frequently used variables for characteristing the adaptation to a physical training are those related to the ventilatory threshold (VT). The laboratory testing of functional parameters can be used to assesment of predisposition for exercise, to check the level of performance and to observe the effects of passed physical training with using for preparing an individual training program, also to predict achievement and choose youth for exercise. The aim of this study was to determine the differences in the level of physical performance and body composition parameters after six months preparatory training period of skiing season 2003/2004 in group of Czech pubescent cross-country skiers. Methods The tests were realized two times, second one after six months preparatory training period of skiing season 2003/2004 in group of Czech pubescent intensive regularly trained cross-country skiers (n=20 - 6 girls and 14 boys, spring 2003: age=13.5±1.7 years, total body mass (BM)=46.3±12.0 kg, height=160.4±13.9 cm, body mass index (BMI)=17.6±1.8 kg.m-2, fat mass (FM)=12.7±1.5 %, fat free mass (FFM)=40.6±10.1 kg, ECM/BCM=0.88±0.12, body cell mass (BCM)=22.5±6.3 kg, total body water (TBW)=30.6±7.5 l, maximal oxygen uptake (VO2max.kg-1)=61.4±6.0 ml.kg-1.min-1). Multi-frequency BIA method (B.I.A. 2000M, Data Input, Germany) was used for determination of body composition. The adaptation to a physical training was estimated during a progressive running test until subjective exhaustion on the treadmill with a slope of 5 %, initial speed was increased each minute by 1 km.h-1 in the laboratory conditions. The subjects trained during the preparatory period five times per week, in case of training camp two times per day. One training block lasted minimal 1 hour. The all followed subjects passed the minimal one year of regular training load before testing. Results We have found the significant improvement in the level of submaximal functional variables. The results of differences of anaerobic threshold (AT) and maximal functional variables show no significant increase, in some case stagnancy or also tendency to downgrade of functional maximum (VO2max.kg-1=-1.4 %, %VO2max=-1.3 % - p<0.05). The total volume of the training load, type and ratio of the training resources, means running, cycling, roll-ski etc. reflect the standard and recommendation for the several age divisions from the Ski federation of Czech Republic. In spite of this, the analysis of the training system indicated the trend to more volume load by intensity lower than anaerobic threshold, let us say lower than intensity approaching to the competitive load. We have found no significant nevertheless downgrade of predisposition to physical exercise means increased in ECM/BCM by 2.9 % and increased in FM by 3.9 % after followed training period. Besides we have found the significant relation between BCM and age (R=0.8659 - p<0.001). No significant relation was found among the other selected body composition parameters as ECM/BCM, FM, FFM and age or BC parameters and functional variables. In addition we can recognize that some of our subjects have the high level of adaptation to a physical training (VO2max=73.8 ml.kg-1.min-1), the high level of predisposition to physical exercise (ECM/BCM=0.69) and the low level of fat mass (till FM=8.9 % in girls, till FM=11.6 % in boys). Discussion/Conclusion The presented differences in the level of physical performance related to the effects of regular physical training during the six months training period. The applied training system seems to be inadequate regarding to using of intensity of physical exercise and probably have affected also the decline of predisposition to physical exercise. The increase of FM can be probably associated above all with natural ontogenetic evolution. Except in used of training intensity, the above presented total volume of the training load (five times per week, in case of training camp two times per day and one training block lasted minimal 1 hour) is sufficient for long-term development of the level of physical performance in followed young subjects and the detected training structure can be used in preparing system of Sport elementary school with a specialization to cross-country skiing, above all in followed region.
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