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FULL TEXT - Antropomotoryka
NR 49 AN TRO PO MO TO RY KA 2010 THE INFLUENCE OF PLYOMETRICS TRAINING ON THE MAXIMAL POWER OF THE LOWER LIMBS IN BASKETBALL PLAYERS AGED 16–18 WPŁYW TRENINGU PLAJOMETRYCZNEGO NA POPRAWĘ POZIOMU SIŁY EKSPLOZYWNEJ KOŃCZYN DOLNYCH U KOSZYKARZY W WIEKU 16–18 LAT Ryszard Litkowycz *, Kajetan Słomka **, Monika Grygorowicz ***, Henryk Król**** *****Dr, Chair of Team Sports, the Jerzy Kukuczka Academy of Physical Education in Katowice *****Dr, Department of Human Motor Behavior, the Jerzy Kukuczka Academy of Physical Education in Katowice *****Dr, Department of Physiotherapy, the Stanisław Staszic State School of Higher Vocational Education in Piła *****Dr, habil., Department of Human Motor Behavior, the Jerzy Kukuczka Academy of Physical Education in Katowice Key words: basketball, training, playometrics Słowa kluczowe: koszykówka, trening, plajometryka SUMMARY • STRESZCZENIE – 33 – - - Cel pracy. Celem pracy było określenie dynamiki zmian siły eksplozywnej przejawiającej się w biegach i skokach u koszykarzy w wieku 16–18 lat pod wpływem treningu plajometrycznego. Koszykówka należy bowiem do tych dyscyplin sportowych, w których dominującą rolę odgrywa zdolność motoryczna o charakterze siłowo-szybkościowym, a w konsekwencji – siła eksplozywna. Dzięki niej nie tylko koszykarze, ale także przedstawiciele innych dyscyplin sportowych mogą pokazać pełnię swoich umiejętności techniczno-taktycznych. Materiał i metody. Badaniom poddano 36 koszykarzy w wieku 16–18 lat, podzielonych na grupę eksperymentalną i kontrolną. Przed eksperymentem oraz po jego zakończeniu dokonano pomiarów szybkości biegowej (na dystansach 5, 15, 20 i 30 m), wytrzymałości szybkościowej (bieg 10 × 30 m), siły dynamicznej kończyn dolnych - - Aim of the work. The study was aimed at assessing the influence of plyometric training on explosive strength development dynamics in running and jumping among basketball players, since basketball is a sport discipline dominated by strength and speed abilities. The combination of these two constitutes explosive strength enables the athletes of various sport disciplines to perform at the highest level of their technical and tactical skills. Material and methods. Thirty-six basketball players aged 16–18 participated in the study. They were divided into experimental (E) and control (K) group. Running speed (5 m, 15m, 20m and 30m distance), speed endurance (10 × 30 m run), explosive strength of trunk and legs (recorded on a dynamometric platform) as well as strength endurance of leg flexors and extensors in isokinetic conditions were measured at the beginning and at the end of the experiment. Results. The training regimen did not result in any significant changes in the examined motor abilities of basketball players in the control group. The introduction of plyometric training in the experimental group resulted in a statistically significant strength torque increase in knee flexors and extensors of both joints (measured at 60º/s, 120º/s, and 240º/s angular velocity). Moreover, changes were observed in the conventional ratio of hamstrings and quadriceps muscles of the right extremity. Specific training activities positively influenced the speed endurance assessed with the use of a shuffle run (10 × 30 m). There were no significant differences in the level of running speed and explosive strength of legs. Ryszard Litkowycz, Kajetan Słomka, Monika Grygorowicz, Henryk Król i tułowia (platforma dynamometryczna), siły dynamicznej oraz wytrzymałości siłowej prostowników i zginaczy stawu kolanowego w warunkach izokinetycznych. Wyniki i wnioski. Trening sportowy nie wywołał istotnych zmian u koszykarzy z grupy kontrolnej w zakresie badanych zdolności motorycznych. Wprowadzenie ćwiczeń plajometrycznych do treningu koszykarzy z grupy eksperymentalnej w większości przypadków doprowadziło do istotnego statystycznie wzrostu wartości momentu siły zginaczy i prostowników stawu kolanowego kończyny dolnej prawej i lewej (60º/s, 120º/s, 240º/s). Ponadto stwierdzono zmiany w proporcjach wartości momentów sił zginaczy i prostowników stawu kolanowego kończyny dolnej prawej. Specyficzne zajęcia treningowe wpłynęły na istotną poprawę wytrzymałości szybkościowej ocenianej biegiem wahadłowym 10 × 30 m. Nie stwierdzono różnic, bądź też występowały sporadycznie w poziomie szybkości biegowej (5, 15, 20 i 30 m) oraz mocy kończyn dolnych (platforma dynamometryczna). to a very intensive muscle contraction – the concentric (overcoming) phase [4, 8–11]. The most important discovery of the plyometric training was that it not only develops the muscle tissue but above all, it improves the coordination of the whole neuromuscular system. Previous research results [6, 5, 10, 12–22] on plyometric training and relation between strength and speed abilities inspire to further studies. The aim of our experiment was to assess the influence of plyometric training on the explosive strength change dynamics, evident in running, jumping and in muscle torque values measured in isokinetic conditions. Introduction - - Time[s] Practical experience and various test results prove that speed-strength abilities are one of important motor abilities for an athlete, particularly for a basketball player [1–8]. Modern sport training practice attributes particular importance to strength developing exercises (dynamic, explosive). Apart from the classic methods of shaping muscle dynamics, plyometrics is an important form of sport performance. The term “plyometrics” comes from the Greek words “plio” and “metric”, meaning “more” and “measure”, respectively. The first reports about the methods and concept of plyometric exercises were provided by the coaches from the former USSR, as described by Donald and Chu [4] and Mikołajec and Rzepka [8]. Explosive force is based on a phenomenon known in the literature as the “stretch reflex”, “muscle spindle reflex” or “myotatic reflex”. Rapid muscle elongation due to a load (eccentric or landing phase) influences the stretching of fibers responsible for generating energy necessary for a contraction, which causes the activation of muscle spindles. Muscle spindle stimulation leads to the stimulation of the spinal cord, and next, - Basketball players from the team AZS Katowice who participated in youth basketball league in two age groups: older juniors (19–20 years old) and juniors (17–18 years old) took part in the study. The players were divided into two groups (experimental and control one) according to their training skills and age; more experienced players, able to handle larger training loads, were assigned to the experimental group (Fig. 1). The 1,45 1,43 1,41 1,39 1,37 1,35 1,33 1,31 1,29 1,27 1,25 E I E I I KI KII 1 - Material and methods 2 3 4 5 6 7 8 9 10 R u nn um ber Fig. 1. Comparison of mean time in 5m run for the experimental (E) and control (K) group before (I) and after the experiment (II) – 34 – The influence of plyometrics training on the maximal power of the lower limbs in basketball players aged 16–18 Table 1. Material - - - - - Group Category Number of players x± S min – max Training advancement [years] Age [years] Experimental (E) Juniors 18 16,8 ± 1,2 15,3 – 18,3 6,2 Control (K) Juniors 18 15,8 ± 0,8 14,5 – 16,4 4,7 experiment lasted from January 30 2006 to June 2 2006, and it was divided into preparation – introduction phase (8 weeks) and experiment proper phase (I and II, 8 weeks). The aim of the preparation phase, during which the subjects trained twice a week (using their own bodyweight, mats, and exercises with a partner) was to develop athletic prowess and practice the correct take-off technique in jump exercises. The experiment proper I (4 weeks) aimed at building explosive leg strength through the application of selected plyometric exercises. In the experiment proper II (4 weeks) training loads were increased on the basis of individual abilities of the players. To achieve that, basketballs as well as 1 kg and 4 kg medicine balls were used in plyometric training. The number of jumps was also increased, but the structure of particular training units did not change. The microcycle structure details in the experiment proper phase I and II are presented in Table 2. Motor ability level was assessed prior to (on 25 March 2006) and after the experiment completion (on 24 June 2006), with the following research tools: 1. Laser diode system LDM 300C-Sport, used to assess: – running speed at 5m, 15m, 20m and 30m – speed endurance in 10 × 30m run. 2. KISTLER dynamometer platform with MVJ [23] software, used to assess: – explosive leg and trunk strength measured by vertical jump with no arm swing. 3. EN-Knee isokinetic dynamometer (Enraf Nonius, Holland) used to estimate the values of: – dynamic strength of knee flexors and extensors at 60º/s angular velocity (5 repetitions) and 120º/s angular velocity (10 repetitions) as well as the conventional muscle torque ratio of knee flexors and extensors, – strength endurance of knee flexors and extensors at 240º/s angular velocity (15 repetitions) as well as the conventional muscle torque ratio of knee flexors and extensors. The dynamometer had been used in previous research [24], and the evaluation of the muscle dynamic potential in isokinetic conditions (including warm-up, stabilization, rest period) was performed according to methodology described by Grygorowicz [25]. Descriptive statistics was used in data analysis. It was found out that the empirical data distribution was close to normal, which allowed for the analysis of variance (ANOVA) with repeated measures. Since the condition of data globosity was not fulfilled, the multifactor analysis was used. To assess the significance between respective test differences post hoc Tukeys’ test was done. To compare related pairs from test I and II, the Wilcoxon Matched-Pairs Ranks test was used. Statistical significance was set at p < 0.05. Statistica 5.0 software was used for statistical analysis. Results and discussion The study confirmed the effectiveness of the specific plyometric training. Subjects from the experimental group obtained significant improvement in the majority of analyzed variables. In the control group, comparing the results before and after the experiment, differences appeared in motor abilities levels; however, they were not statistically significant (p > 0.05) (Table 3–12, Fig. 1, 2). Elevating the center of body mass during a vertical jump on spot with no arm swing may be the basis for an estimate of leg and trunk strength-speed ability level in basketball players [26]. The obtained data did not show any significant difference in explosive leg and trunk strength measured on a dynamometer platform (Table 3). The analysis of strength abilities test results performed before and after the experiment in isokinetic conditions showed an improvement of strength level in the experiment group, and in the majority of players the difference was statistically significant (Table 4–8). The most noticeable is the significant difference in the level of knee flexor strength at all tested angular veloci- – 35 – - - - - – 36 – Technical exercises with balls 15min Strength exercises with medicine balls (1kg) 15 min – “multiple jumps” – “standing jumps” – “jumps on spot” (benches, lines, “hexagon”) – “depth jumps” (with the use of 3 vaulting boxes and hurdles) Day off Day off 4 5 6 7 Phase I Day off Day off 1 min after each 3 jumps 4 times longer than exercise Day off 1 min after each 3 jumps 4 times longer than exercise All jumps total (8 weeks of experiment) Day off Day off Day off Day off Strength exercises with medicine balls (1kg) 15min – “depth jumps” (with the use of 3 vaulting boxes and hurdles) 2 3 Constant run 10-15min Warm up – “core stability” on unstable ground (mats), – “bounding” Training methods 1 Day of the week Table 2. Microcycle structure - Phase II Day off Day off 2 min after each 3 jumps 5 times longer than exercise Day off 2 min after each 3 jumps 5 times longer than exercise Rest period 0 0 60 140 0 60 120 Phase I 0 0 60 200 0 60 220 Phase II Load (number of jumps) 3266 0 0 658 1182 0 353 1075 Load total (no of jumps) Ryszard Litkowycz, Kajetan Słomka, Monika Grygorowicz, Henryk Król The influence of plyometrics training on the maximal power of the lower limbs in basketball players aged 16–18 5 ,2 Time[s] 5 ,1 5 E I 4 ,9 E II K I 4 ,8 K II 4 ,7 4 ,6 1 2 3 4 5 6 7 8 9 10 R un n um b e r Fig. 2. Comparison of mean time in 30m run for the experimental (E) and control (K) group before (I) and after the experiment (II) ties, both in left and right extremity (Table 4, 5). Identical number of jumps performed by both lower extremities in the proper phase of the experiment resulted in a greater strength increase in the right knee flexor. The strength level of knee extensor increased as well, however not at all tested velocities; no significant difference was recorded in the dynamic strength of the lower right extremity (tested at 60º/s and 120º/s angular velocity) or left extremity (tested at 60º/s angular velocity) (Table 6, 7). Before the experiment, at 60º/s and 120º/s angular velocity, the strength level of right knee extensor in basketball players was on a similar level to the strength level of left knee extensor; only the level of strength endurance of left knee extensor was slightly higher than that of the right knee extensor. It seems that the right lower extrem- ity is more often used to perform the long step in layup (opposing and take-off phase) while the left lower extremity makes a short dynamic step (take-off phase). As a result of the plyometric training there was a change in strength endurance (tested at 240º/s angular velocity) of knee extensors in both lower extremities. Changes in dynamic strength levels were observed only in left lower extremity at 120º/s angular velocity. One may ask why before and after the experiment there were no significant differences in the level of dynamic strength of right and left lower extremity extensors (at 60º/s and 120º/s, and 60º/s angular velocity, respectively). Perhaps motor activities in the regular basketball training resulted in the development of high strength level of knee extensors, and the experiment was not Table 3. Descriptive statistics and significance level of the differences in vertical jump [cm] N x± S min – max Sk Ku I 18 40,2 ± 4,86 30,9 – 52,1 0,494 1,050 II 18 40,0 ± 4,30 32,3 – 47,7 –0,350 –0,525 I 18 40,2 ± 4,86 30,9 – 52,1 0,494 1,050 III* 18 39,7 ± 4,44 32,4 – 47,4 –0,152 –1,122 II 18 40,0 ± 4,30 32,3 – 47,7 –0,350 –0,525 III* 18 39,7 ± 4,44 32,4 – 47,4 –0,152 –1,122 T p 0,235 0,817 0,992 0,335 1,022 0,321 - - - - - Test * Having observed no statistically significant changes in the level of explosive leg and trunk strength, the researchers decided to carry out test III believing that a longer rest period will allow the subjects to show the real level of the tested ability. – 37 – Ryszard Litkowycz, Kajetan Słomka, Monika Grygorowicz, Henryk Król Table 4. Descriptive statistics and significance level of the differences for the right lower extremity flexor muscles [Nm] Test Angular velocity I 60 deg/s x± S min – max Sk Ku 171,8 ± 49,53 93,8 – 303,0 1,304 2,631 197,3 ± 55,06 125,0 – 322,0 1,298 1,059 158,8 ± 36,82 79,4 – 243,0 0,533 2,205 177,6 ± 44,03 120,0 – 279,0 1,304 1,270 127,1 ± 23,97 90,7 – 175,0 0,841 0,045 145,2 ± 28,79 99,6 – 204,0 0,631 –0,009 N 18 II 60 deg/s I 120 deg/s 18 II 120 deg/s I 240 deg/s 18 II 240 deg/s a sufficient stimulus to bring about the intended effects. Statistically significant differences between the values of muscle torque of flexors (6 cases) and extensors (3 cases) may suggest that in basketball training insufficient attention was devoted to the muscles responsible for knee flexion, which confirms their susceptibility to the stimulus of the plyometric training (Table 4–7). According to Wilkerson et al. [11] the value of conventional knee flexors/extensors ratio should be equal to 2:3. However, varied values of this ratio (Hamstring/ Quadriceps) have been reported in scientific research, depending on the tested velocity, the subject’s position, the test muscle group [27, 28]. Nevertheless, many authors accept 0.6 as the normative value of the knee conventional ratio at 60°/s angular velocity; it increases to 0.8 at higher velocities of the isokinetic assessment [29–31]. It should be noted that before the experiment most of the subjects had a correct conventional ratio of knee T p –4,610 0,000 –3,984 0,001 –5,698 0,000 extensor and flexor muscles (Hcon/Qcon) (Table 8), and the statistically significant changes caused by the plyometric training occurred only in the lower right extremity. It might be said that the plyometric training to a greater extent affected the weaker muscle group, that is hamstrings (semimembranosus muscle, semitendinosus muscle, biceps femoris muscle), causing compensation changes. Changes leading towards the proper muscle ratio were particularly visible in the lower extremity, which – as it was already mentioned above – performs particular work during training and game. After the experiment the results of the described ratio of right lower extremity exceeded the normative values at 240º/s angular velocity, mostly due to the large increase of the flexors’ strength endurance level. It should be remembered that before the experiment the right lower extremity demonstrated correct values of conventional knee flexors/extensors ratio (60°/s – 0. 63, 120°/s – 0.76, 240°/s – 0.86). After the experiment Table 5. Descriptive statistics and significance level of the differences for the left lower extremity flexor muscles [Nm] Angular velocity N 60 deg/s x± S min – max Sk Ku 172,57 ± 43,39 129,0 – 272,0 1,516 1,700 187,50 ± 43,52 139,0 – 290,0 1,288 1,039 157,25 ± 30,21 114,0 – 218,0 0,855 0,366 169,00 ± 32,93 136,0 – 234,0 1,133 0,084 123,09 ± 20,13 93,5 – 157,0 0,108 –0,983 134,00 ± 16,12 107,0 – 161,0 0,168 –0,945 18 p –4,151 0,000 –2,964 0,009 –2,971 0,009 - 60 deg/s T 120 deg/s - 18 - 120 deg/s 240 deg/s 18 - - 240 deg/s – 38 – The influence of plyometrics training on the maximal power of the lower limbs in basketball players aged 16–18 Table 6. Descriptive statistics and significance level of the differences for the left lower extremity extensor muscles [Nm] Test Angular velocity I 60 deg/s II 60 deg/s I 120 deg/s II 120 deg/s I 240 deg/s II 240 deg/s N 18 18 18 x± S min – max Sk Ku 259,56 ± 62,41 162,0 – 416,0 1,001 1,650 267,06 ± 60,41 178,0 – 411,0 0,948 1,034 211,25 ± 39,50 160,0 – 317,0 1,499 2,526 223,44 ± 43,87 172,0 – 319,0 0,937 0,341 150,56 ± 26,45 105,0 – 187,0 –0,080 –1,140 164,94 ± 23,54 126,0 – 218,0 0,518 0,495 this ratio was incorrect and at 240º/s angular velocity it exceeded normative data (0.98) (Table 8). Out of 40 parameters describing speed and speed endurance, its derivative, statistically significant changes were observed in the values before and after the experiment in 19 cases in the experiment group; no such changes were recorded in the control group (Table 9–12, Figure 1 and 2). It should also be noted that what improved was endurance abilities, not speed abilities, as could be suggested by the type of the training experiment. All significant differences in the running test were only noticed in the 6th or 7th repetition (when the subjects had already run 5 × 30m). The differences were not recorded in any of the first runs at 5 m, 10 m, 20 m or 30 m distance, which confirms the above mentioned observation on the endurance type of changes in motor abilities of basketball players. According to Wachowski et al. [13] there was no correlation between the running speed and the power and strength tests. The obtained results show that there is a small relation (too many components) between running speed and strength and power. Therefore, it should not be assumed that a plyometric training focused on power development will result in better results in running tests. T p –1,205 0,246 –2,674 0,017 –3,560 0,002 Moreover, the authors claim that in optimal conditions for strength and power development, running speed level depends on the running technique (the length and frequency of step). Changes in motor abilities in the experiment group resulted from the plyometric training structure, as well as from the subjects susceptibility to training impulses (sensitive periods). Thus the research question should be considered from two perspectives; that is, from the educational and ontogenetic perspective. Literature analysis [5, 13, 14, 17, 32–36] allows for a conclusion that the slowest is the annual speed increase (5%) which grows best up to age 16. Faster development can be observed in the case of jumping abilities (7%) and power (6%), and the sensitive period for these abilities occurs at age 13–15. The development of jumping abilities is mainly related to the training of the capability of fast and economic use of muscle strength (neuromuscular coordination) of lower extremities. It depends, among others, on the elastic elements acting within the ankle joint. It can thus be said that the experiment was too short to cause any significant changes in the level of relative strength, Table 7. Descriptive statistics and significance level of the differences for the right lower extremity extensor muscles [Nm] Test Angular velocity I 60 deg/s N x± S min – max Sk Ku 261,56 ± 54,69 187,0 – 400,0 1,105 1,483 268,81 ± 64,72 181,0 – 412,0 0,948 0,224 209,81 ± 49,46 145,0 – 333,0 1,324 1,312 218,37 ± 47,48 154,0 – 327,0 0,971 0,589 141,81 ± 26,28 101,0 – 202,0 0,705 0,363 152,69 ± 23,64 116,0 – 194,0 0,434 –0,700 II 60 deg/s I 120 deg/s 18 - - - 18 II 120 deg/s I 240 deg/s 18 240 deg/s - - II – 39 – T p –0,978 0,343 –1,593 0,131 –2,193 0,044 Ryszard Litkowycz, Kajetan Słomka, Monika Grygorowicz, Henryk Król Table 8. Descriptive statistics and significance level of the differences for conventional knee flexors/extensors ratio Angular velocity Conventional index x± S min – max Sk Ku T p 47,5 0,289 67,5 0,979 62,0 0,756 9,0 0,006 25,0 0,084 27,5 0,036 Left lower extremity 60 I 0,68 0,68 ± 0,10 0,50 – 0,91 0,495 0,507 60 II 0,70 0,70 ± 0,07 0,60 – 0,84 0,355 –0,532 120 I 0,76 0,76 ± 0,08 0,59 – 0,9 –0,161 –0,345 120 II 0,76 0,76 ± 0,08 0,62 – 0,92 0,195 –0,670 240 I 0,86 0,86 ± 0,16 0,61 – 1,25 0,791 0,994 240 II 0,87 0,87 ± 0,13 0,64 – 1,14 0,254 0,040 - - - - - Right lower extremity 60 I 0,63 0,63 ± 0,07 0,48 – 0,74 –0,772 0,131 60 II 0,70 0,70 ± 0,10 0,51 – 0,94 0,262 0,755 120 I 0,76 0,76 ± 0,09 0,55 – 0,89 –0,699 0,650 120 II 0,81 0,81 ± 0,11 0,66 – 1,05 0,696 –0,142 240 I 0,86 0,86 ± 0,21 0,21 – 1,21 –1,867 6,068 240 II 0,98 0,98 ± 0,17 0,61 – 1,19 –0,733 –0,004 responsible for the elevation of the body mass center during a vertical jump on a platform. It also seems that boys aged 11–14 are more capable of perfecting their strength-speed abilities [17]. As a result of the exercises the greatest annual changes can be observed in endurance and absolute power training (more than 20%) [33, 17]. It can be expected that the time of the experiment and training load allowed only for the development of endurance changes in running tests (Table 9–12, Figure 1 and 2). Such interpretation of the results is confirmed by the high level of running endurance and strength endurance of knee flexors and extensors. Significant changes in the muscle torque values in tests performed on the isokinetic dynamometer at 240º/s angular velocity characterize changes in strength endurance, while the value of muscle torque at 60º/s angular velocity suggests changes of dynamic strength. Basketball players from the experiment group performed more than 3000 jumps during the proper phase of the experiment (I and II). That is a lot, taking into consideration the time span of the experiment: eight weeks (Table 2). One may ask whether three days of rest were enough for four days of plyometric training. To com- pare with other research, in a study by Kubaszczyk and Litkowycz [10] basketball players were subject to a plyometric training twice a week for five months, performing approximately 2500 jumps. As a result, there were significant changes in the dynamic strength level measured by a vertical jump, long jump from a spot and triple jump. It should be noted that in spite of the fact that the training load was divided into five months, during the second measurement (out of three), in the middle of the experiment, the authors recorded a regress of results. What occurred was a common phenomenon observed in all tests: a decrease in the level of strength-speed abilities value, after which a significant improvement occurred, with values higher than those before the experiment. After the fatigue accumulation effect, supercompensation occurred. It can thus be said that prolonging the experiment at the expense of one training unit would allow for achieving satisfactory results not only in the level of endurance abilities but, above all, of speed abilities. Another reason for significant differences in the level of dynamic strength of lower extremities in basketball players tested by Kubaszczyk and Litkowycz [10] is the age of subjects (16 years) and thus their greater susceptibility to strength-speed training impulse. – 40 – The influence of plyometrics training on the maximal power of the lower limbs in basketball players aged 16–18 - - - - - Table 9. Descriptive statistics and significance level of the differences for 5m run [s] Test Run N x± S min – max Sk Ku I 1 188 1,34 ± 0,07 1,18 – 1,48 –0,404 0,572 II 1 18 1,27 ± 0,04 1,20 – 1,35 0,112 0,014 I 2 18 1,35 ± 0,10 1,17 – 1,55 –0,029 –0,411 II 2 18 1,30 ± 0,05 1,21 – 1,38 –0,295 –0,296 I 3 18 1,35 ± 0,09 1,16 – 1,51 –0,282 –0,523 II 3 18 1,30 ± 0,05 1,24 – 1,40 1,142 0,331 I 4 18 1,37 ± 0,08 1,24 – 1,49 0,113 –1,456 II 4 18 1,30 ± 0,05 1,22 – 1,40 –0,019 –0,482 I 5 18 1,38 ± 0,10 1,19 – 1,58 –0,245 –0,371 II 5 18 1,33 ± 0,04 1,23 – 1,39 –0,927 0,835 I 6 18 1,39 ± 0,07 1,29 – 1,58 1,091 1,507 II 6 18 1,31 ± 0,07 1,15 – 1,38 –1,389 2,091 I 7 18 1,39 ± 0,07 1,25 – 1,57 0,428 0,988 II 7 18 1,31 ± 0,04 1,27 – 1,39 1,318 0,924 I 8 18 1,41 ± 0,08 1,28 – 1,63 0,732 1,628 II 8 18 1,32 ± 0,02 1,30 – 1,36 0,360 –1,474 I 9 18 1,42 ± 0,08 1,23 – 1,55 –0,698 1,047 II 9 18 1,32 ± 0,05 1,26 – 1,41 0,421 –0,507 I 10 18 1,42 ± 0,08 1,32 – 1,60 0,772 –0,081 II 10 18 1,31 ± 0,06 1,25 – 1,42 1,066 0,014 Cossor et al. [22] described the effect of 20 weeks of plyometric training. During the study subjects (12–16 year old swimmers) performed a total of 2700 jumps. After the experiment there were no significant changes in the values of explosive leg strength in the young swimmers. The authors suggest two most probable reasons for such a situation: first, physical load imposed by the plyometric training turned out to be too low, as the authors used load recommended for training children. Out of the two components of training load, the body of a young athlete better tolerates volume better than intensity. The second reason is the young swimmers’ growth process. Authors [12, 15, 18–21, 37] of some research papers have not observed any significant increase of sport achievements after applying the plyometric train- T p 11,5 0,055 31,5 0,893 25,0 0,798 11,5 0,055 27,0 0,593 11,5 0,055 2,0 0,005 12,5 0,068 6,5 0,018 5,0 0,021 ing, which was most probably due to a too short plyometric program. Burr and Young [20] believe that the plyometric training should be carried out for at least 18 weeks for the positive effects to appear. High intensity exercises which affect the nervous system should only be applied in individuals where the growth process is completed. Particular plyometric exercises should be performed with maximum strength (when the subject is not fatigued), and rest periods should take at least as much time as the exercises. The conclusions concerning the application of plyometric exercises in a training process can be now formed. Basketball training should be supported by plyometric training, and its intensity, one of the components of load, should exceed average values appropriate to the subject’s age. Increasing the training volume and – 41 – Ryszard Litkowycz, Kajetan Słomka, Monika Grygorowicz, Henryk Król Table 10. Descriptive statistics and significance level of the differences for 10m run [s] x ± S min – max Sk Ku 188 2,81 ± 0,11 2,59 – 3,00 –0,208 –0,123 18 2,71 ± 0,08 2,61 – 2,89 0,952 1,103 2 18 2,84 ± 0,16 2,56 – 3,14 0,097 –0,461 II 2 18 2,76 ± 0,08 2,66 – 2,91 0,585 –0,972 I 3 18 2,87 ± 0,15 2,61 – 3,15 0,197 –0,717 II 3 18 2,78 ± 0,10 2,64 – 2,99 0,877 0,603 I 4 18 2,90 ± 0,14 2,71 – 3,23 0,801 –0,177 II 4 18 2,79 ± 0,09 2,64– 3,95 0,529 –0,016 I 5 18 2,91 ± 0,16 2,64 – 3,23 –0,021 –0,484 II 5 18 2,81 ± 0,09 2,65 – 2,95 0,074 0,360 I 6 18 2,93 ± 0,13 2,77 – 3,22 0,908 0,570 II 6 18 2,79 ± 0,09 2,64 – 2,92 –0,302 –0,640 I 7 18 2,94 ± 0,13 2,69 – 3,22 0,436 0,065 II 7 18 2,79 ± 0,10 2,70 – 3,03 1,745 2,267 I 8 18 2,97 ± 0,15 2,76 – 3,34 0,844 0,993 II 8 18 2,81 ± 0,07 2,72 – 2,96 0,874 0,834 Test Run N I 1 II 1 I I 9 18 2,98 ± 0,12 2,70 – 3,18 –0,511 0,502 II 9 18 2,82 ± 0,09 2,72 – 3,04 1,399 2,519 I 10 18 2,98 ± 0,15 2,77 – 3,33 0,765 0,225 II 10 18 2,80 ± 0,12 2,69 – 3,06 1,322 1,056 T p 9,5 0,066 30,5 0,824 21,0 0,858 9,5 0,066 19,0 0,386 5,0 0,012 4,5 0,011 2,0 0,009 5,0 0,012 3,0 0,007 T p 10,5 0,083 30,5 0,824 31,0 0,858 10,0 0,040 17,5 0,308 6,0 0,016 5,0 0,012 6,0 0,016 4,5 0,011 3,0 0,007 Table 11. Descriptive statistics and significance level of the differences for 20m run m [s] Test Run N x± S min – max Sk Ku I 1 188 3,47 ± 0,14 3,21 – 3,70 –0,260 –0,555 II 1 18 3,36 ± 0,10 3,23– 3,58 0,929 1,046 I 2 18 3,51 ± 0,19 3,19 – 3,86 0,171 –0,587 II 2 18 3,42 ± 0,10 3,32 – 3,61 0,778 –0,819 I 3 18 3,55 ± 0,18 3,26 – 3,91 0,355 –0,622 II 3 18 3,45 ± 0,12 3,27 – 3,70 0,709 0,076 I 4 18 3,59 ± 0,18 3,37 – 4,04 0,926 0,338 II 4 18 3,46 ± 0,12 3,27 – 3,66 0,616 0,307 I 5 18 3,60 ± 0,19 3,28 – 4,01 0,119 –0,534 II 5 18 3,48 ± 0,11 3,27 – 3,67 0,295 0,836 6 18 3,62 ± 0,17 3,42 – 4,03 0,874 0,424 6 18 3,46 ± 0,10 3,31 – 3,62 0,215 –0,373 I 7 18 3,63 ± 0,17 3,35 – 3,99 0,519 –0,195 II 7 18 3,46 ± 0,13 3,36 – 3,79 1,867 2,948 I 8 18 3,67 ± 0,18 3,43 – 4,07 0,801 0,518 II 8 18 3,48 ± 0,10 3,35 – 3,71 1,147 1,724 I 9 18 3,68 ± 0,14 3,36 – 3,93 –0,258 0,102 II 9 18 3,49 ± 0,11 3,36 – 3,76 1,534 2,784 I 10 18 3,69 ± 0,19 3,41 – 4,15 0,780 0,333 II 10 18 3,48 ± 0,15 3,34 – 3,82 1,542 1,717 - - - - - I II – 42 – The influence of plyometrics training on the maximal power of the lower limbs in basketball players aged 16–18 Table 12. Descriptive statistics and significance level of the differences for 30m run [s] Run N x±S min – max Sk Ku I 1 18 4,79 ± 0,20 4,48 – 5,16 0,278 –0,947 II 1 18 4,64 ± 0,15 4,45 – 4,98 1,086 1,530 I 2 18 4,85 ± 0,25 4,43 – 5,36 0,285 –0,655 II 2 18 4,71 ± 0,15 4,56 – 5,00 0,917 –0,362 I 3 18 4,92 ± 0,26 4,56 – 5,47 0,539 –0,610 II 3 18 4,77 ± 0,18 4,53 – 5,11 0,708 –0,366 I 4 18 4,99 ± 0,29 4,67 – 5,73 1,089 0,909 II 4 18 4,78 ± 0,17 4,55 – 5,10 0,927 0,457 I 5 18 4,99 ± 0,28 4,57 – 5,51 0,185 –0,908 II 5 18 4,80 ± 0,16 4,54 – 5,09 0,808 0,771 I 6 18 5,02 ± 0,26 4,70 – 5,67 0,949 0,481 II 6 18 4,79 ± 0,14 4,61 – 5,08 0,918 0,524 I 7 18 5,03 ± 0,25 4,65 – 5,57 0,614 –0,424 II 7 18 4,79 ± 0,20 4,62 – 5,28 1,945 3,402 I 8 18 5,09 ± 0,24 4,74 – 5,67 0,823 0,583 II 8 18 4,82 ± 0,15 4,65 – 5,17 1,434 1,867 I 9 18 5,10 ± 0,22 4,65 – 5,48 0,011 –0,225 II 9 18 4,82 ± 0,17 4,61 – 5,23 1,614 3,131 I 10 18 5,13 ± 0,30 4,67 – 5,77 0,699 0,275 II 10 18 4,80 ± 0,21 4,62 – 5,31 1,685 2,410 reducing rest periods will adversely affect the release of elastic energy during exercises and decrease the explosive strength level. Prolonging the transition phase (stance phase) leads to the diffusion of elastic energy accumulated in tissues into chemical energy and heat [8]. Duda [38] claims that if we shorten ground contact time during take-off, jump height will increase; an identical mechanism is performed in specific plyometric exercises. Future research including the plyometric training should consider the intensification of youth training by exercises that do not burden the motor system, that is the so-called ‘hexagon’: skipping rope, jumps over a line, depth jumps from low heights (e.g. from a bench, not higher) stressing the short stance phase with jump up and short acceleration phase. In mature athletes similar exercises should be used, increasing the height of accessories (vaulting boxes, hurdles), adding medicine balls – enforcing short ground contact time after landing. - T p 15,0 0,109 26,5 0,563 29,5 0,755 12,5 0,068 17,0 0,154 2,0 0,009 5,0 0,012 2,0 0,005 3,0 0,007 1,0 0,004 The research results and the discussion presented above allow us to present the following conclusions: 1. Plyometric training increases knee flexor and extensor muscle strength, but its effects are greater in the case of weaker muscles – hamstrings (semimembranosus muscle, semitendinosus muscle, biceps femoris muscle). 2. Weekly plyometric training load turned out to be too much (mainly due to the volume component), causes endurance changes in general physical ability of the subjects. 3. Changes in knee flexor and extensor muscles in basketball players ought to be considered in the aspect of lateralization. 4. 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