Peer Review THE EFFECTS OF AN 8 WEEK SUPPLEMENTED PLYOMETRIC EXERCISE TRAINING PROGRAM ON LEG POWER, AGILITY AND SPEED IN ADOLESCENT NETBALL PLAYERS.

The effects of an 8 week supplemented plyometric exercise training program on leg power, agility and speed in adolescent netball players. J. Aust. Strength Cond. 21(3) 28-33. 2013 ASCA Peer Review THE EFFECTS OF AN 8 WEEK SUPPLEMENTED PLYOMETRIC EXERCISE TRAINING PROGRAM ON LEG POWER, AGILITY AND SPEED IN ADOLESCENT NETBALL PLAYERS. Mulcahy, R.L. & Crowther, R.G. James Cook University, Townsville ABSTRACT Objectives: Agility, speed and power are important aspects of almost every sport. One way to improve these attributes is plyometric exercise training. Plyometrics have shown to be effective for improving performance in many sports such as basketball, volleyball, and AFL. The aim of this study was to determine the effects of an 8 week supplementary plyometric exercise training program on the physical performance of adolescent athletes in the sport of netball. Methods: Participants were randomly allocated to a control group (CG, n = 8) or an intervention group (IG, n = 8). All participants completed a battery of performance tests that included 10 m sprint, 505 agility, Illinois agility, vertical jump and 5 repetition one leg bounds. Both groups undertook the same netball training. The invention group also performed supplemental plyometric exercise training program over the 8 weeks training period. The plyometric exercises performed included: skipping, countermovement jumps, depth jumps and single leg bounds or alternate leg bounds. Results: Following the 8 weeks of training all participants were retested and the intervention group demonstrated significant improvements in 505 agility (4.02%) and 5 single leg bounds (6.69%). Conclusions: It appears a supplemented plyometric exercise training program is of benefit to the adolescent netball player, for improving agility and power and it is recommended that this form of training be implemented into their normal training regime. Keywords Jumping, athlete development, performance. INTRODUCTION The ability to accelerate, sprint, change direction or jump in response to sports specific stimuli contributes to the overall performance of an athlete (1, 2). One of the most frequently used methods utilized to train these abilities is jump, or plyometric, exercise training (3). Plyometric exercise training is a popular strength and conditioning method because it trains the mechanisms involved in jumping, specifically the stretch reflex and the stretch shortening cycle (SSC). Consequently, plyometric exercise training is commonly used to improve many aspects of an athlete s fitness, including vertical jump height, power output, agility, speed and strength (3-7). The stretch reflex allows muscles to automatically adjust to the body s muscle needs (changes in load or length) and as a result of the stretch reflex, greater motor unit recruitment for a muscle contraction is facilitated (8, 9). The SSC allows more work to be done in less time due to the rapid lengthening of a muscle at the beginning eccentric phase of a plyometric movement followed immediately by a rapid acceleration in the opposite direction elicited by the concentric phase of a plyometric action (10, 11). Plyometric exercise training has been demonstrated to improve lower body power output and explosiveness, increase vertical jump height, acceleration, change of direction ability and sprint ability of elite athletes (3-7). Furthermore, these improvements were found to be significant when comparing results to control groups who performed only normal team training consisting of general fitness, skills and tactics (1-3, 9, 12-14). Plyometric exercise training has also been associated with improvements in an athlete s coordination and landing technique which may decrease the risk of certain types of injuries from occurring (3-7, 15). While performance improvements via plyometric training have been observed in many sports (basketball, volleyball, AFL etc.) limited research has investigated the effects of plyometric exercise training amongst netball players. Netball is becoming an increasingly popular sport among a large range of age groups in Australia, England, New-Zealand and South Africa. As local, national and international competition continues to develop, the requirements to be more powerful and agile is increasing and coaches are looking for a competitive edge to enhance player performance. Additionally, strength and conditioning methods such as plyometric exercise training is being implanted earlier into an athlete s training program; however, there is little evidence that this is beneficial for adolescent athletes (16). Since, an adolescent s body is still in the process of developing, this type of exercise training may not elicit sufficient performance improvements essentially due to hormonal levels, strength and coordination characteristics. Furthermore, the risk of injury associated with this type of training may be to high in this population due to this lack of strength and 28

coordination ability. Therefore, research is needed to investigate the impact of plyometric exercise training on young (15-17 yrs. old) athletes. METHODS Approach to the problem Following baseline testing, participants (females N = 16) were divided randomly into two groups, intervention group (IG) (n = 8; age = 16.4 ± 0.5 yrs; height = 165.0 ± 6.7 cm; weight = 57.0 ± 7.9 kg; body fat = 22.5 ± 3.5 %) and control group (CG) (n = 8; age = 15.6 ± 0.7 yrs; height = 171.9 ± 9.0 cm; weight = 70.0 ± 18.2 kg; body fat = 28.6 ± 7.6 %). All participants had previously participated in 8 weeks of netball training prior to the beginning of this study. Both groups played a competitive game of netball on Wednesday of each week and performed normal strength and conditioning workouts 2 additional days per week, for approximately 1 hour each (15 minutes of various warm-up and ball drills, 30 minutes of skill work, 15 minutes of game play and cool down). Subjects Female senior school students (N = 16) (Table 2) who played in the local netball competition volunteered to participate in this study. All participants were informed of their roles and responsibilities throughout the study and all participants plus their parents/guardians signed a consent form showing their approval to participate. All the procedures that were used in this study were approved by the institution s Human Ethics Committee. The participants filled out a prescreening medical history questionnaire prior to testing which screened the participants for disease or injury that could result in the athlete being harmed further by participating in the study. Procedures Testing was conducted in a random fashion and performed on a concrete netball playing surface. Participants were required abstain from physical activity for the 24 hrs. leading up to testing. All tests were clearly explained to the participants before they performed each of the tests. A practise attempt was used to ensure correct technique and to lessen the chance of a learning effect from occurring. Before testing was carried out, a 10 min dynamic warm-up was completed by all participants. The warm up consisted of 6 laps of slow jogging, high knees (walk back) x 2, butt kicks (walk back) x 2, grapevine x 2, side step x 2, change of direction x 2, 3 x 10 m sprints and 10 x leg swings (forward and side direction) for each leg. All participants were given three trials in each of the following tests. Only the best result was taken for statistical analysis. Anthropometric data Height and weight were assessed for comparison of groups. Height was measured using a wall mounted tape measure. Participants weight was assessed using TANITA scales (Model BF-522, Tokyo, Japan). Vertical jump Vertical jump height was measured using the Swift Vertec apparatus (Swift Performance Equipment, NSW, Australia). Lower body power output was calculated using the Lewis formula (Average power (watts) = 4.9 x body mass (kg) x jump-reach score (m) x 9.81) (17). Speed The speed of the athletes was measured during a 10 m sprint test with time to complete the 5 m and 10 m splits recorded using speed light timing gates (Swift Performance Equipment, NSW, Australia) connected to an IBM Thinkpad Microsoft laptop with Speed light wireless timing gate software (Swift Performance Equipment, NSW, Australia). Participants began in the 3 point start position and on a go command, sprinted as fast as possible. Markers were placed 2 m after the last timing gate and participants were instructed to keep running until they were past the markers. Agility Agility was measured using the 505 agility test and the Illinois agility test. The 505 agility test (18) required the participant to accelerate over the first 10 m and be at full pace by the time they ran through the timing gates for the first time. They then had to continue running and pivot on the 15 m line then return as fast as possible through the timing gates (Swift Performance Equipment, NSW, Australia). The Illinois agility test (19) required the athletes to run as fast as possible through a series of cones. To perform this test the athlete runs straight to the first cone and back the same distance (10 m), zig-zags through the second series of cones and runs straight again to another cone and back through the timing gate system (Swift Performance Equipment, NSW, Australia). 29

Horizontal leg power Leg power was measured using the 5 single repetitive leg bound test. Each participant was instructed to hop 5 times on each leg and aim for maximum distance. Distance was measured with a 100 m fibreglass tape measure that was placed on the ground. TRAINING PROGRAMS CG training program The CG completed 2 sessions a week of their normal training sessions on Tuesday and Friday. Each session lasted approximately 1 hour. During the training session the participants completed a warm up that consisted of jogging, stretches and sprints that lasted for approximately 15 mins. The athletes then completed 20 minutes of ball skills and ball activities followed by 15 mins of game play followed by a 10 minute cool down period. IG plyometric exercise training program None of the participants in the IG had any previous experience with plyometric exercise training, so before the first session an experienced athlete demonstrated how to perform each of the exercise utilized in this research with proper form and technique. A supervisor was present throughout each training session for the entire intervention period to ensure the safety of the athletes. Plyometric exercise training took place 2 d.week-1 for a total of 8 weeks (Monday and Friday). Each plyometric exercise session lasted for a duration of 30 minutes and was comprised of the same 4 plyometric exercises; skipping, hops, counter movement jump (CMJ) and depth jumps (DJ) off a 40 cm high box. The volume of plyometric training was altered by increasing the number of foot contacts at week 2 and again at week 6 (Table 1). The plyometric exercise training was completed at the beginning of each training session. Once the IG completed their plyometric session they joined the CG group. Both groups then completed the general strength and conditioning workout together. Table 1 - Plyometric exercise training program undertaken by IG participants. Week Contacts Exercises Volume Rest 1-2 52 Skipping DJ (40 cm) CMJ Single Leg Bounds 1 x 20 2 x 5 2 x 5 2 x 3 (each leg) 30 secs between sets 2 mins between exercises 3-5 66 Skipping DJ (40 cm) CMJ Single Leg Bounds 6-8 80 Skipping DJ (40 cm) CMJ DJ Depth jump CMJ Countermovement jump Single Leg Bounds 1 x 20 3 x 5 3 x 5 2 x 4 (each leg) 1 x 20 4 x 5 4 x 5 2 x 5 (each leg) 30 secs between sets 2 mins between exercises 30 secs between sets 2 mins between exercises Statistical analysis Statistical analysis was performed using SPSS version 18 (IBM, PASW Statistics). All performance measures (baseline vs. 8 week & IG vs. CG) were analysed using non-parametric tests (Kruskal-Wallis test). The significance level was set to p < 0.05. RESULTS Both groups showed similar performance results at baseline testing for almost all tests. The IG had significantly better performance results than the CG in 5 m, 10 m, 5 bound test off the right foot and vertical jump tests. At the completion of the intervention period, the IG showed significantly better results than the CG in the 10 m, 505 off the left foot, Illinois, 5 bound off both the right and left foot and the vertical jump test. Significantly better results were seen in the IG compared to baseline testing in 505 off the left foot and Illinois test and the CG in the Illinois test (Table 3). 30

Table 2 - Results of performance tests at baseline and 8 weeks. Test CG IG CG IG Baseline Baseline 8 week 8 week Sprint 5 m (s) 1.32 ( 0.09) * 1.22 ( 0.03) 1.24 ( 0.09) 1.23 ( 0.06) Sprint 10 m (s) 2.31 ( 0.17) * 2.07 ( 0.04) 2.18 ( 0.14) 2.07 ( 0.08) 505 Agility Test Right (s) 2.82 ( 0.12) 2.77 ( 0.08) 2.77 ( 0.10) 2.68 ( 0.10) 505 Agility Test Left (s) 2.82 ( 0.12) 2.79 ( 0.07) 2.86 ( 0.16) 2.68 ( 0.07) Illinois Agility (s) 18.67 ( 1.24) 17.97 ( 0.5) 17.29 ( 0.78) ** 16.2 ( 0.29) 5 Bound Right (m) 7.1 ( 1.19) * 8.41 ( 0.83) 6.97 ( 1.20) 8.93 ( 0.71) 5 Bound Left (m) 6.99 ( 1.22) 8.3 ( 1.11) 6.90 ( 1.15) 8.64 ( 0.86) Vertical Jump (cm) 32.9 ( 5.03) * 42.0 ( 4.1) 33.9 ( 6.3) 41.3 ( 5.7) Power Output (Watts) 866.3 ( 224.0) 802.8 ( 131.6) 876.0 ( 257.3) 804.0 ( 146.9) Values are mean ( SD) * p < 0.05 vs. IG baseline p < 0.05 vs. IG 8 week p < 0.05 vs. IG baseline ** p < 0.05 vs. CG baseline Percentage changes The CG demonstrated a significant improvement in percentage change in 5 m and 10 m sprints compared to baseline. The IG displayed a significant improvement in percentage change in 5 bound right and 505 agility left at baseline (Table 4). Table 3 - Percentage change in performance variables over the 8 weeks. Test CG IG %Δ %Δ Sprint 5 m (s) -5.80 ( 4.94) * 1.25 ( 4.44) Sprint 10 m (s) -5.37 ( 3.63) * -0.01 ( 2.92) 505 Agility Test Right (s) -1.76 ( 2.56) -3.11 ( 3.86) 505 Agility Test Left (s) 1.46 ( 3.50) * -4.02 ( 1.76) Illinois Agility (s) -7.2 ( 4.49) -9.83 ( 2.73) 5 Bound Right (m) -2.56 ( 2.59) * 6.69 ( 10.56) 5 Bound Left (m) -1.46 ( 3.58) 5.23 ( 12.33) Vertical Jump (cm) 2.69 ( 8.57) -1.02 ( 17.59) Power Output (Watts) 0.21 ( 9.37) 0.66 ( 4.87) Values are mean ( SD) * p < 0.05 vs. IG DISCUSSION Vertical and horizontal jumps, agility, speed and power are all very important skills that are needed for many sports. Plyometric exercise training is a form of training that has been shown to potentially enhance the ability of an athlete to perform these skills (20). However, to the author s knowledge, the effect of plyometric exercise training in netball and adolescent athletes is not documented. The results of this study suggest that performing two plyometric exercise training sessions, in addition to their normal netball training, for 8 weeks is of some benefit to adolescent female netball players seeking to improve performance. The athletes in this study that engaged in the plyometric training intervention improved their agility performance and power measured by the 505 agility and Illinois tests. In addition significant changes in the percentage of improvements for the 5 repetition single leg bound test were also observed. Similar results have also been found in previous research that has followed similar plyometric exercise training protocols (1, 21). Agility is a fundamental skill needed in the game of netball. In recent years the most common way to measure agility for a netball player has been the 505 agility test (22). The 505 agility test is the standard agility test used by national netball associations to test their netball athletes. This test and the Illinois Agility test are used because the movements that are performed in these tests are similar to those used in the game of netball. Therefore, it is believed that if there are improvements in these tests, then there would be improvements in agility on the court. However, both these agility 31

tests use pre-determined movements and although these movements are used in the game of netball, there is always outside stimuli that effect the movements of athletes during a game situation. Therefore, although these are currently the agility tests of choice for the sport of netball, further research needs to be done into the options available to test the perceptual and decision making components of agility performance. The results of this study showed that an 8 week supplementary plyometric exercise training program may improve agility characteristics to a larger extent than vertical jump power amongst adolescent (15-17 yr old) female athletes. However, other research has demonstrated improvements in both power and agility utilizing an 8 week of plyometric exercise training program, with 2 sessions per week (2, 3). It is suspected that the reasons for increases in power seen in these studies are due to the neural adaptations that take place in the body during plyometric exercise training, these adaptations being; the specific activation of motor units in specific muscles to enhance the performance of the jump, increases in the number of motor units recruited and the ability to synchronise the activation of these motor units (2). Perhaps the reason why these studies showed greater improvement may be due to their participants having a weight training foundation prior to plyometric exercise training. This is a limitation of the current study, as none of the participants had engaged in weight training prior to plyometric exercise training. Some of the results obtained in this study differ from results of previous research that implemented 2 plyometric exercise training sessions a week for 8 weeks. Previous research has shown improvements in CMJ, maximal force and sprint velocity (2, 3, 23, 24); however, the average contacts that were performed at each session in these studies were approximately 85 foot contacts. It should be noted that the average number of contacts in the current study was 66. Thus, the volume of plyometric training may be a reason why significant improvements in VJ and sprint times did not occur. Furthermore, these studies that demonstrated improvements in VJ and sprint times were performed by participants between the ages of 19-24 yrs old whereas the current study the participants had an average of 16 yrs. This may explain the difference between results due to age and its relationship to muscle development. Other research conducted using adolescent athletes has found significant improvements in sprints, agility, CMJ, squat jump and rate of force development (1, 25-27). These studies were conducted between 6-10 weeks in duration and had varying volume per session. One study had an average of (21) 66 foot contacts per session over an 8 week period, which is similar to the current study and similar results were obtained to the current study (i.e. significant improvement in agility) (1). However, it should be noted that this study used only male participants and gender consideration should be taken into consideration. Other research has had participants complete 60 100 contacts over the intervention period and it was discovered that significant improvements were found in CMJ and squat jump as well as sprint results (25, 27). Perhaps a longer program with more contacts would elicit greater improvements in CMJ in this studies population. 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