al Effects Of Plyometric Training On Leg Muscle Strength, Endurance And Power Characteristics Of Nigerian University Undergraduates Abstract Ademola O. Abass Department of Human Kinetics And Health Education Faculty of Education University of Ibadan, Ibadan Nigeria. E-mail: dokidemo@yahoo.com Phone: +2348055436276 This study focused on the relationship among strength, endurance and power performance characteristics of untrained university undergraduates following three different modes of plyometric training. Participants were 40 untrained volunteer male undergraduates, randomly assigned to three experimental plyometric training of depth, rebound and horizontal over a distance, and a fourth group which served as the control. The three experimental were made to go through a 12-week exercise programme based on plyometric training procedures. Interval training method was adopted while the progressive resistance training principle was considered to determine the duration and intensity of training. Data collected were analyzed using the mean, standard deviation and range. Relationship between variables was determined using the Pearson Product Moment Coefficient. Results show that there were no significant relationships among the in strength and endurance performance characteristics. Significant correlations were recorded in power performance between horizontal and rebound group [0.672; P= 0.033]. All other interactions among the on leg power were not significant. On relationship among the three variables based on pooled data across the, significant correlation was recorded only between muscle strength and power [0.327;P= 0.039]. between all other variables was found not to be significant. Based on the finding of the study it was concluded that plyometrics training with repeated jumps horizontally and that which involves rebound on the spot, are capable of improving leg muscle power in similar ways. Moreover, the study also concluded that, plyometrics training is capable of improving leg muscle strength and power significantly. Introduction Sports science generally aims at identifying and developing performance variables essential for competitive excellence. Performance indices like muscle strength, endurance and power, play cardinal role in achieving athletic excellence. According to Guyton (1991), the final common denominator in athletic events is what the muscle can do for you - what strength they can give when it is needed, what power they can achieve in the performance of work and how long they can continue in their activity. The leg muscles play important roles in the successful execution of skills in many games and sports. Although, apart from soccer, combat sports, running and events in athletics, the direct use of legs is not common to most other sports. Most of these other sports that utilizes mainly the arms directly for skill execution, still require strength, and
43 endurance of the leg muscle to generate force and carry them through the stress and duration of their activity. Plyometric exercises have been used successfully over the years to elicit training responses from athletes. According to Chu, (1998) plyometrics are training techniques used by athletes in all types of sports to increase strength and explosiveness Plyometrics training is almost exclusively applied to extensor Muscle of the legs, and consists of a vigorous lengthening of the active extensor muscles (eccentric contraction) immediately followed by a maximal concentric contraction. It consists of a rapid stretching of a muscle (eccentric action) immediately followed by a concentric or shortening action of the same muscle and connective tissue (Baechle and Earle, 2000). They are most frequently used as a means of increasing speed and anaerobic power output in sprinters and jumpers, but the techniques may also be of value to other types of sportsmen (Watson, 1993; Wausen, 1990). Sharkey (1986) described plyometric exercises as explosive callisthenic-like exercises which involve the conditioning of the neuromuscular system to permit faster and more powerful changes of direction such as moving from up and down in or switching leg positions as in running. The stored elastic energy within the muscle is used to produce more force than can be provided by a concentric action alone ( Komi, 1992; Miller, et al., 2002; Pfeiffer, 1999; Wathen, 1993). Researchers have shown that plyometric training, when used with a periodized strength-training program, can contribute to improvements in vertical jump performance, acceleration, leg strength, muscular power, increased joint awareness, and overall proprioception (Harrison and Gaffney, 2001; Hennessy and Kilty, 2001; Miller et al., 2002; Paasuke et al., 2001). The fundamental reason to train with plyometrics is to reduce the ground contact time that an athlete spends when running or. This time is reduced as the athlete matures, gets stronger, and practices the skills of their game. To further enhance resistance training the athlete spends considerable time practicing the specific movement skills they wish to improve; namely, running and. These two movement patterns are often thought of as genetic endowments and affected little by outside influences such as training programs. To the contrary, research has shown that virtually all athletes can positively influence their performance outcomes by using plyometric training on a regular basis.(chu, 2004). The training modes derived for this study were based on the principle of plyometrics training. This study focused on the correlational effect of depth, rebound and horizontal over a distance (three modes of plyometrics training) on the leg muscle strength,, endurance and power performance of untrained University males. The hypotheses tested in this study are as follows: 1. There is no significant relationship in the leg-muscle strength, endurance and power performance characteristics among the various under study. 2. There is no significant relationship in the post- test leg muscle strength, endurance and power performance of all subjects across the. Method and Procedures Participants Forty apparently healthy untrained male undergraduates of the University of Ibadan, Nigeria, participated in the study. Subjects were volunteers, certified medically and physically fit to take part in the training programme. They were randomly divided into four of 10 participants each. Three of these served as the experimental that participated in the depth, rebound and horizontal exercises, while the fourth was the control group.
44 Instrument and Measures The main variables measured in this study were leg muscle strength, leg muscle endurance, and leg muscle power. Additional variables include age, height and weight of participants. Leg muscle strength was measured using the back and leg dynamometer. The test protocol for using the instrument was followed as described by Johnson and Nelson, (1986) They reported a reliability value of.86 to.90 for the instrument. Leg muscle endurance of subjects was measured using the half-squat jump test as described by Johnson and Nelson, (1986A reliability of.82 was recorded for the test. The Vertical jump (Sergeant chalk jump) test was used to measure leg muscle power. The measurement and scoring procedure adopted were those of Johnson and Nelson, (1986, who recorded a reliability of. 93 for the test. The stadiometre and its weighing scale were used to measure height and weight; three locally manufactured boxes, each of which were, 35cm, 40cm, and 45cm in height were used for depth training, a training wall was used for rebound training; a marked ground of nine metres in length with 6 rings placed alternately on the ground were used for horizontal training; while stopwatches and measuring tape were used to measure time and distance respectively. The entire training programme was designed according to the recommendations of experts in plyometrics training. Data collection All the tests were administered by the researcher with the help of four research assistants who helped in recording, observing and timing the subjects as the need arose. Subjects were informed of the nature of the test and each of them signed an informed consent form before commencement of training. Training The training programme lasted for a period of 12 weeks. Participants were trained three times a week between 3 pm and.6pm. Subjects were randomly divided into four of ten subjects each. Group one engaged in depth as their training mode, participants in two and three engaged in rebound and horizontal bounding with rings respectively, while the fourth group served as the control group which received no treatment. The training programme was based on the interval training principle, which comprised series of plyometrics exercise work intervals, interspersed with relief intervals with a work - relief ratio of 1:3. The progressive resistance training principle was used in determining the dosage at every period of training. The intensity and duration of exercise were gradually increased every two weeks, when training was assumed to have become less challenging to the leg muscles of the subjects. The plyometrics - training modes, developed for this study are described as follows: Depth Jumping: This exercise was performed by using three wooden boxes that were 60cm in width, and 35cm, 40cm and 45cm in height. The subject was expected to climb the box and stand straight in the front edge of the box. He steps down and rebound from his jump after landing to the height of the box. He then moves quickly to the back of the box and repeats the exercise all over until the stipulated time. Rebound Jumping: - This exercise was performed near a training wall. It involved continuous with the two feet leaving the ground at the same time. The subject was expected to rebound after landing from each jump. To ensure efficiency in this exercise, a
45 20cm distance from the standing - reach height of the performer was marked against the wall in front of the performer. This served as the minimum height he can get to with his arms raised when he is. bounding with rings: - This exercise was performed on a marked ground of 9- metres in distance. Six rings were alternately placed on each side of the marked line. The subject jogs into the start of the drill for forward momentum. After a few feet, forcefully push off with the left foot and bring the right leg forward. At same time swing left arm forward and land into the first ring, which is 3-4 feet out and to the left, with the right foot. He continue and repeat with other leg and arm into the second ring, which is now 3-4 feet up and to the right. This exercise is an exaggerated running motion focusing on foot pushoff and air time. Research Design and Methodology. The design for this research was the randomized pre- test - posttest control group design. Participants were randomly assigned to experimental and control after the selection, to eliminate selection bias as a threat to internal validity. The descriptive statistics of mean, standard deviation and range were used. Also Pearson Product Moment Coefficient was used to determine whether significant relationships existed among the on each of the variables tested in the study; and also to determine whether there was any significant correlation in the posttest strength, endurance and power performance of subject across all the. Variables. All variables were tested at 0.05 level of significance. Results GROUPS AGE [years] Height[metres] Weight [kg] Depth Jumping Group X ± SD 21.90±3.07 1.74±0.05 65.27± 6.48 Rebound Jumping Group X ± SD 21.90 ± 4.82 1.76 ± 0.06 64.90 ± 3.74 bounding with rings Group X ± SD 24.50 ±2.01 1.70+ 0.07 64.54 ± 6.24 Control Group X ± SD 24.30 ±5.48 1.69 ± 0.07 66.42 ± 8.05
46 TTable 1: Descriptive Data on Age, Height, Weight Characteristics of Subjects. Table 1 shows the mean and standard deviation of age, height and weight of participants. The horizontal bounding with rings group was the oldest with a mean age of 24.50 + 2.01 years followed by the control group (24.30 + 5.48). The depth and rebound- group had the lowest age (21.90+ 3.07years and 21.90+4.82years respectively. The rebound group was tallest with a mean height of 1.76+ 0.06 metres, followed by the depth- group with 1.74+ 0.05 metres. The horizontal bounding with rings group had a mean height of 1.70+ 0.07 metres, while the control group had the lowest mean height of 1.69+ 0.07 metres. The control group recorded the heaviest mean weight of 66.42+8 05kg, followed by the depth - group[ 65.27+6.48kg], the rebound group [64.90+ 3.74kg] and the horizontal bounding with rings group [64.54+ 6.24kg] respectively. This showed that the control group was heaviest, while the horizontal bounding with rings group recorded the lowest weight. Groups N Mean Standard Deviation Depth group 10 64.00 21.18 Rebound group 10 55.60 19.01 bounding with rings 10 41.00 25.95 group Control group 10 34.90 10.59 Table 2: Descriptive statistics on posttest Leg muscle strength performance of subjects Table 2 shows that the depth group had the highest posttest leg muscle strength mean performance (64.21± 21.18); followed by the rebound group, (55.60± 19.01); and horizontal bounding with rings group (41.00 ± 25.95),and the control group(34.90± 10.59) respectively. Groups N Mean Standard Deviation Depth group 10 42.50 9.63 Rebound group 10 38.10 13.31 bounding with rings 10 43.40 14.58 group
47 Control group 10 23.30 11.93 Table 3: Descriptive statistics on posttest Leg muscle endurance performance of subjects Results from the above table shows that horizontal bounding with rings group had the highest mean leg endurance performance (43.40±14.58), followed by depth group (42.50±9.63), and rebound group (38.10±13.31), while the control group (23.30±11.93), recorded the lowest performance. Groups N Mean Standard Deviation Depth group 10 105.70 12.09 Rebound group 10 104.10 12.06 bounding with rings 10 110.50 8.73 group Control group 10 101.70 12.19 Table 4: Descriptive statistics on posttest leg muscle power performance of subjects Results from the above table revealed that horizontal bounding with rings group recorded the highest posttest relative leg power (110.50±8.73),followed by the depth group (105.70±12.09), and the rebound with rings group (104.10±12.06). The control group again recorded the least performance (101.70±12.19) in posttest leg power performance. Group scores on all variables N Mean Standard Deviation Leg strength score across all 10 48.88 22.46 Leg endurance score across all 10 36.83 14.52 Leg power score across all 10 105.50 11.39 Table 5: Descriptive statistics of performance on all variables across all the experimental The above table shows that the mean leg strength performances of subjects across the experimental is 48.88±22.44, while their mean leg muscle endurance performance is 38.83±14.52, and mean relative power performance is 105.50±11.39. depth (post-test Pearson Depth (post-test (posttest Rebound (posttest 1.000.69.290-346 Sig. (2-..851.416.327 Control gp(posttest
48 (posttest Rebound (posttest Pearson.069 1.000.096-307 Sig. (2-.851..791.388 Pearson.290.096 1.000-201 Sig. (2-.416.791..577 Control (posttest Pearson -.346 -.307 -.201 1.000 Sig. (2-.327.388.577. * is significant at the 0.05 level (2- Table 6: coefficients matrix of muscle strength performance among all the The above correlation coefficient matrix table reveals that there was no significant relationship in leg muscle strength of subjects in the three-plyometric and the control group. This shows that there was no significant association in the muscle strength training effects generated by the three-plyometric training modes used in this study following 12weeks of training Depth (post-test (posttest Rebound (posttest Pearson Depth (post-test (posttest Rebound (posttest 1.000 -.504.066.041 Sig. (2-..137.857.910 Pearson -.504 1.000 -.295.083 Control gp(posttest Sig. (2-.137..409.820 Pearson.066.-295 1.000 -.626 Sig. (2-.857.409..053
49 Control gp(posttest Pearson.041 -.083 -.626 1.000 Sig. (2-.910.820.53. * is significant at the 0.05 level (2- Table 7: coefficients matrix of muscle strength performance among all the The correlation matrix table above also reveals no significant relationship in leg muscle endurance of subjects among the three plyometric and the control group. This shows that there was no significant correlation in the training effects elicited by the three plyometric training modes following 12 weeks of training. depth (post-test (posttest relative power) Rebound (po sttest relative power) Control gp(posttest relative power) Pearson Depth (post-test (posttest Rebound (posttest 1.000.198.363.098 Control group (posttest Sig. (2-..583.302.788 Pearson.198 1.000.672 -.350 Sig. (2-.583. *.033.321 Pearson.363.672 1.000.074 Sig. (2-.302 *.033..840 Pearson.098 -.350.074 1.000 Sig. (2-.788.321.840.
50 * is significant at the 0.05 level (2- Table 8: matrix of muscle performance among all the plyometric and control Table 8 shows that there was significant relationship in leg muscle power (0.672; P=0.033) between subjects in the horizontal bounding with rings and rebound subjects. However, no significant correlation was recorded in all other inter-group comparisms on leg-muscle power. This shows that only horizontal bounding with rings and rebound plyometric training modes have similar capacity to develop leg muscle power out of the three modes used in the study. Strength score across all the Endurance score across all the Absolute power score across all the Relative power score across all N 40 40 40 correlation is significant at the 0.05 level (2- Table 9: matrix of strength, endurance and power performance across all the following plyometric training Table 9 presents the relationship that existed in strength, endurance and power performance of subject across all the. Results shows there was significant relationship only between leg muscle strength and power (0.327;P = 0.039). correlations between all other variables were found not to be significant. This shows that there was relationship only in the strength and power effects generated in the athletes following plyometric training. Discussion Pearson Strength score across all the Endurance score across all the 1.000.189.327 Sig. (2-..243 *.039 N 40 40 40 Pearson.189 1.000.160 Sig. (2-.243..324 N 40 40 40 Pearson.461.371.517 Sig. (2-.003.018.001 N 40 40 40 Pearson.327.160 1.000 Sig. (2- *.039.324. Relative power score across all the
51 Results of this study revealed a non-significant correlation among the plyometric and control used in this study on strength and endurance performance characteristics of subjects. This shows that there were no significant interactions in the muscle strength and endurance training effect generated by the various plyometric training modes used in the study. A significant relationship was however recorded in leg power performance of horizontal and rebound group. This result may not come as a surprise because the real essence of plyometric training is not development of strength but explosive power. According to Gambetta (2003) plyometric training is specific work for the enhancement of power. It deals with the rate and not magnitude of the stretch to determine the utilization of elastic energy and the transfer of chemical energy into mechanical work. Also in determining whether relationships exists among the variables under study based on performance across all the, a significant relationship was recorded only between muscle strength and power (0.327; 0.039 2 tail sig.). This result only confirms the fact that strength has a significant contribution in power performance. Power performance has been found to be a product of efficient strength and speed development. Conclusion Based on the findings of this study, it was concluded that only the horizontal bounding with rings and rebound training used in this study have similar capacity to develop leg power attributes. This implies that these two plyometrics training can be used interchangeably in developing leg muscle power in various sports. Moreover, the plyometric training techniques used in this study only exhibited relationship in leg muscle power and leg muscle strength attributes of athletes. Based on the findings of this study, it is recommended that plyometric mode should be included in all trainings that involve the development of explosive power and strength of the leg muscles either for recreation, competition, or rehabilitation purposes. REFERENCES Baechle, T.R. and Earle, R.W. (2000) Essentials of strength training and conditioning. 2nd edition.champaign, IL: National Strength and Conditioning Association. Brown,M.E,Garbutt, G Reilly, T.Linge, K & Troup, J.D.G (1988). The effects of gravity inversion on exercise induced spinal loading. Ergonomics, 31,(1631-1637). 22-23. Brzyckim M (1986), Plyometrics : A giant step backwards. Athletics Journal,72, (86), Chu, D.A. (2004).Plyometric Training for Youth. http//www.donaldchu.com Guyton, A.C. (1991). Textbook of medical physiology (8 th ed.) Philadelphia:W.B.Saunders co. Harrison, A.J. and Gaffney, S. (2001) Motor development and gender effects on stretch-shortening cycle performance. Journal of Science and Medicine in Sport 4, 406-415. Hennessy, L. and Kilty, J. (2001) Relationship of the stretch-shortening cycle to spring performance in trained female athletes. Journal of Strength and Conditioning Research 15, 326-331.
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