The Effect of Plyometric Exercise towards Agility, Speed, Strength and Explosive Power of Leg Muscle

The aim of this research is to investigate the effect of hurdle box drill with the stick, jump and speed hurdle lateral, and lateral hurdle jump exercises on agility, speed, strength, and explosive power of leg muscles. The sample group of the study consisted of 33 students who participated in badminton FIO UNESA. The methodology used was quantitative research with quasi-experimental methods. The result showed that group I had enhancement on the muscular strength of the limbs for 2.89, speed for − 0.003, agility 0.1 and leg muscle explosive power for 1.42. Group II had the strength of the lower limbs for − 1.04, speed 0.09, agility − 0.19 and leg muscle explosive power 0.85 and group III had limbs muscle strength increased for 0.43, speed 1.18, agility 0.36 and leg muscle explosive power 0.71. Therefore, it can be concluded that these three exercises affected the agility, speed, strength and explosive power of leg muscle.


Introduction
Physics has a role which is used in enhancing athlete performance, especially in sport competition branches. Thus, a good physical condition will be considered to give a positive contribution to the athlete in mastering the sport techniques. The athlete's capacity trained privately becoming the main objective in improving the sport performance. One of the training models used to improve performance is a plyometric exercise. Plyometric exercise is considered to be effective to increase the accomplishment of an athlete's prime condition. It can be used for any kind of sports with the purpose to increase body fitness.
The explanation above is in line with Irandoust and Taheri [5] who stated that the characteristics of plyometric exercises, such as agility, speed, strength and explosive power of leg muscle, showed significant enhancement within the physical fitness performance. Kusnanik, Nasution, and Hartono [7] also claimed that plyometric was the stretching reflects to facilitate the recruitment from muscle unit and eccentric contraction. This was meant to form elastic and contractile energy of muscle component when stretching, followed by concentric contraction. Chu and Myer [2] said that plyometric exercise was the training program to increase the power and strength of an elite athlete. Plyometric exercise is efficient since it is helping to enhance training objective and able to use for a various sport such as football, tennis, or others. Furthermore, plyometric exercise also helps to increase agility that useful for an athlete [10].
Plyometric exercise such as hurdle box drill with a stick, jump and speed hurdle and lateral hurdle jump is using both unilateral and bilateral jump. According to Harrell, the phase-in stepping forward through the hurdle or gate between every leap by pushing the body forward is the phase in which speed and strength are trained [4]. Hurdle hop is defined as a high-speed movement that needs neuromuscular strength and control [11]. However, the plyometric exercise with 6 weeks duration is still contradictive. As what Lehnert, Hulka, Maly, Fohler and Zahalka [8] found that the 6 weeks duration of plyometric exercise did not produce a significant average score of vertical jump test. While Thomas, French and Hayes [16] showed the significant differentiation within 6 weeks of plyometric exercise that could enhance the agility. However, these previous researches did not point to the plyometric exercise that specifies for enhancing the physical condition components. Therefore this study is aimed to know the effect on plyometric exercise against the physical condition component such as agility, speed, strength and explosive power of leg muscle.
Regarding on the objective of this study, two hypotheses will be made in this research. The first hypothesis is the most effective exercise model to increase agility, speed, strength and leg muscle explosive power. The second hypothesis is the differentiation on the hurdle box drill with stick exercise (G1), jump and speed hurdle (G2) and lateral hurdle jump (G3) toward the enhancement of agility, speed, strength, and explosive power of leg muscle.

Subject
The subject of the research is badminton athletes of Sport Science Faculty, State University of Surabaya 2017 with the total amount are 30 people.

Protocol
This study used a quantitative using a semi quasi-experiment methodology due to finding the causality between each variable. The variables were divided into free variables, including the plyometric exercise (hurdle box drill with the stick, jump and speed hurdle, lateral hurdle jump) and bound variable which influenced by the free variables with the target on agility, speed, strength, and leg muscle leg explosive power.
Some tests were done to measure the variables, such as back leg and dynamometer to measure the strength, force plate or the Accu power test to measure leg muscle explosive power, the 30 m running test for speed and sidestep test to measure the agility. 84 I Gede Dharma UTAMAYASA, Hari SETIJONO, Oce WIRIAWAN

Statistics
The statistic in this research is dealing with the mean, standard deviation, variants, maximum and minimum score, normality test, homogeneity test and MANOVA test of leg muscle strength, explosive power, agility and speed of each group. Then the test result will be noted and counted based on the group and exercise model to which it applied. Moreover, the data description is using SPSS 23 (Statistical Program for Social Science) computer program.

Result
The table 1 below will describe the estimated marginal mean and multiple comparative to answer the hypotheses 1. Afterwards, Table 2 below will show the answer of hypotheses 2. The Table above answers the second hypothesis that there is differentiation on the hurdle box drill with stick exercise (G1), jump and speed hurdle (G2) and lateral hurdle jump (G3) toward the enhancement of agility, speed, strength, and explosive power of leg muscle. Because they are showing some different number of mean on each category. And the highest number comes from strength.

Discussion
The result of table 2 above contains a significant value for each group toward the variables -strength, speed, agility and explosive power of leg muscle for sig < 0.05, which meant Ho was rejected or there was significant differentiation in each group toward the variables. It showed that every exercise would be able to influence the bound variables differently. The differentiation occurred since there was a different physiologic mechanism in each exercise. The hurdle box drill with the stick, jump and speed hurdle, and lateral hurdle jump, physiologically, might affect the tense in the leg muscle, respiration, anaerobic capacity, and lactic acid which increase the strength and leg muscle explosive power optimally.
Jump and speed hurdle, according to Harrell, was when the respondent steps forward through the hurdle between every jump, and push himself forward due to produce the speed and strength [4]. Richter et Marshall, Franklin-Miller, King, Falvey, Moran claimed that hurdle hops were a movement with high speed that needs the neuromuscular strength and control [11]. Different from lateral hurdle jump that focused on enhancing agility. With jump movement, cognitive ability and strength can be increased and causes speed. The sudden change in movement direction could happen in a very quick motion that can increase the agility. The effect of plyometric exercise on explosive strength through lower extremity had a positive effect on strength and power [3,6,9,13]. This finding showed that plyometric exercises has became a valuable tool to be entered in a structural program to increase sports performance. Based on the MANOVA test using four statistic models, including Pillai's trace, Wilks lambda, Hotelling, Tace, and Roy's largest root, had showed significant results for p < 0.05. It meant that the hurdle box drill with the stick, jump and speed hurdle, and lateral hurdle jump had a significant effect on the enhancement of agility, speed, strength and explosive power of leg muscle when these came together. Hence, Ho was rejected, or there was interaction among these exercises toward the improvement of agility, speed, strength and explosive power of leg muscle. Senthil stated that plyometric exercises could increase the strength of abdominal muscle, cardiovascular, pulse reduction and thinking ability [14]. Plyometric exercise started from low intensity to high intensity.
These three exercise models utilized the elastic energy and myopic reflect on strength development. Elastic energy is energy when an object is given a force and then the force is removed; hence the object will be back to its former form. While myopic energy is related to athlete energy derived from the combustion within the body. Myopic energy is obtained from the sports training which done with load or weight that change each day with a purpose that the strength and energy came out more, thus the myopic energy can be formed. Besides, the plyometric exercise can increase the spindle muscle system. Elastic energy used to make the concentration becomes stronger. The combination of the unilateral and bilateral leap was more profitable to induce a significant performance within the plyometric exercise [15].
Plyometric exercise is a stretch-shortening cycle or SSC which started from a long contraction of tendon muscle followed directly with shortening muscle contraction. Kusnaik et Nasution, Hartono said that plyometric exercise had stretching reflect from unit muscle with eccentric contraction due to form the elastic energy when the muscle is stretching, followed with concentric contraction [7]. Plyometric exercise combined the strength and speed to produce power that involves more of fibre muscle to obtain spindle muscle.
Plyometric exercise is one of the exercise models with the purpose to increase athlete's power and speed [2]. Chelly et Ghenem, Abid, Hermassi, Tabka, Shephard stated that plyometric exercise could increase the leg muscle explosive power and speed [1]. Therefore it can be concluded that plyometric exercise, generally, can contribute to enhancing the leg muscle speed and explosive power, especially in badminton which tends to require a high-speed level, agility, and jump ability.

Conclusion
From the analysis above, it can be concluded that there was significant differentiation on and interaction among plyometric exercise models -hurdle box