Olympic Weightlifting Training Causes Different Knee Muscle–Coactivation Adaptations Compared with Traditional Weight Training

OLYMPIC WEIGHTLIFTING TRAINING CAUSES DIFFERENT KNEE MUSCLE–COACTIVATION ADAPTATIONS COMPARED WITH TRADITIONAL WEIGHT TRAINING

FOTINI ARABATZI AND ELEFTHERIOS KELLIS Laboratory of Neuromechanics, Department of Physical Education and Sport Science, Aristotle University of Thessaloniki at Serres, Serres, Greece

ABSTRACT INTRODUCTION Arabatzi, F and Kellis, E. Olympic weightlifting training causes ower performance is affected by the interaction different knee muscle–coactivation adaptations compared with between agonist, antagonist, and synergetic traditional weight training. J Strength Cond Res 26(8): 2192– muscles involved in joint movements. Although 2201, 2012—The purpose of this study was to compare the effects P the agonist muscles are able to apply a great force in a short period of time, there must be a complementary of an Olympic weightlifting (OL) and traditional weight (TW) training and simultaneous relaxation of the antagonists (25). This program on muscle coactivation around the knee joint during appears to be achieved by a neural strategy of enhanced vertical jump tests. Twenty-six men were assigned randomly to reciprocal inhibition of the antagonist musculature (26). 3groups:theOL(n =9),theTW(n = 9), and Control (C) groups However, the role of agonist and antagonist muscle interplay 21 (n = 8). The experimental groups trained 3 dwk for 8 weeks. in power movements remains unclear. The faster lifting Electromyographic (EMG) activity from the rectus femoris and speeds involved in power training may make it difficult, biceps femoris, sagittal kinematics, vertical stiffness, maximum as compared with traditional strength training, to efficiently height, and power were collected during the squat jump, control unwarranted cocontraction between agonist and countermovement jump (CMJ), and drop jump (DJ), before and antagonist muscle groups, potentially reducing power (6). after training. Knee muscle coactivation index (CI) was calculated Examination of muscle coactivation adaptations after for different phases of each jump by dividing the antagonist EMG different training programs may assist in determining optimal activity by the agonist. Analysis of variance showed that the strategies for improvement in Jump performance. Muscle coactivation is necessary to balance joint forces CI recorded during the preactivation and eccentric phases of all the and to increase muscle and joint stiffness (20). It has been jumps increased in both training groups. The OL group showed suggested that higher stiffness levels of lower-limb muscles a higher stiffness and jump height adaptation than the TW group during stretch-shortening cycle (SSC) exercises improve did (p , 0.05). Further, the OL showed a decrease or maintenance performance in terms of the greater amount of stored and of the CI recorded during the propulsion phase of the CMJ and DJs, reused elastic energy. Further, the coactivity of agonist and which is in contrast to the increase in the CI observed after TW antagonist muscles increases in the preactivation and the training (p , 0.05). The results indicated that the altered muscle braking phases of the jump (35). This coordinated activation patterns about the knee, coupled with changes of leg response would create a rebound phenomenon in which stiffness, differ between the 2 programs. The OL program improves the active tension developed in the preactivation and jump performance via a constant CI, whereas the TW training breaking phases could be released passively in the toe-off caused an increased CI, probably to enhance joint stability. phase. Further, during the toe phase, there is a decline in the activation of the knee extensors while the hamstrings KEY WORDS muscle activation patterns, stiffness, jumping maintain consistent activation in the same phase. This is performance critical for creating the take-off velocity and to transfer the stored elastic energy in the proper direction with unopposed antagonist activity from the hip flexors (33). Address correspondence to Fotini Arabatzi, [email protected]. However, it is unclear whether these changes in leg and 26(8)/2192–2201 joint stiffness are caused by changes in activation and the Journal of Strength and Conditioning Research mechanical properties of the muscle-tendon complex Ó 2012 National Strength and Conditioning Association itself. Further, it is unclear whether the type of mechanical 2192 Journalthe of Strength and Conditioning ResearchTM

and neural adaptations may depend on the type of the performance after traditional resistance training would be exercise program applied. because of higher muscle strength but an increased muscle Traditional exercises, such as squats, have been de- cocontraction, whereas Olympic lifting training would termined to be excellent exercises for improving lower-body improve performance through neural adaptations, that is, strength, but they show a low correlation with vertical jump a decrease in the cocontraction index (CI) and an associated (VJ) performance (12,18). Resistance training improves the change in leg stiffness. Further, we expected that differences muscle’s ability to generate force, but this increase may in adaptations between the 2 training programs depend on not be effectively transferred to velocities that simulate the type of jump tested. the speed of jump performance (14). Toumi et al (31) reported that weight training alone did not induce any METHODS change in countermovement jump (CMJ) performance, Experimental Approach to the Problem although increases in maximal strength and squat jump The study was designed to compare the electromyographic (SJ) were observed. Similarly, it has been demonstrated (EMG) activity and training adaptations in jump perfor- that training-induced strength improvements are associated mancebetween2trainingprograms.Toinvestigatethis, with increases in jump performance (1,33). However, we matched healthy students of physical education and maximal gains can be achieved if training exercises that subsequently randomly divided them into 2 training simulate jump movement are used (1,33). This lack of groups: (a) an Olympic weightlifting (OL) group and (b) transfer from an enhanced posttraining maximum strength a traditional weight group (TW). This design enabled us to to better jump performance may also be linked with examine whether OL or TW training augmented jump different adaptations in muscle activation between antag- performance and changed the muscle interplay. The onistic muscle groups. independent variables were time (pretraining, posttraining) In contrast to traditional weight (TW) training, low-speed and training group (OL, TW, C). The dependent variables power lifts, such as Olympic lifts, are ballistic resistance were EMG activity (average EMG, coactivation), vertical exercises that involve moving an external load at high stiffness, VJ height, mechanical power, and kinematics. velocities, resulting in the acceleration of the segments Subjects through the entire movement. Olympic lifts may produce This study involved a total of 26 male students of physi- high gains in power, offering great potential for improvement cal education in Greece (age = 20.3 6 2 years, height = in VJ performance (18,27). It seems likely that weightlifting 184.8 6 8.3 cm, mass = 85.2 6 6.8 kg, maximum strength: training results in improved motor unit recruitment and 1RM/body mass = 2.11 for the OL group and 1.98 inhibition of protective antagonist muscle action, especially for the WT group) all free from any musculoskeletal given the short time frame (12). Nevertheless, the precise or neurological disease or impairment. The participants effects of such a training scheme on muscle coactivation beganthestudybyperformingthesquat,CMJ,and around a joint during sport-specific multiarticular tasks, such maximal half-squat (1RM). Based on these results, they as jumps (CMJ, DJs), are not clear. were allocated randomly into 1 of 3 groups and did not It is generally accepted that training-related increases in differ significantly (p . 0.05) in any of the dependent muscle capacity are associated with a reduction in antagonist variables. All the subjects were physically highly active coactivation (15,29). However, this adaptation may depend and experienced in performing various jumps through on the type of training program and the type of performance participation in various sport activities through their used to examine the effectiveness of training. For example, regular academic program. All the subjects had at least SJ performance may be affected by different mechanisms 1 year of experience in resistance training, but they did compared with CMJ and DJ performances. Further, DJ not systematically perform strength drills and weightlift- performance and biomechanical characteristics depend on ing exercises. The local University Ethics Committee drop height (7), whereas coactivation differs between approved the study. All the subjects were informed of any different phases of the same type of jump. Further research risk and signed a university-approved human subject’s is needed to obtain a knowledge about the relative informed consent form before their participation. involvement and functional significance of neural factors with specific types of training and examine the relative Study Design importance of these mechanisms in VJ performance. This study involved 3 groups (Table 1). The first group Neuromuscular adaptations are believed to enhance jump performed OL exercises, and the second group performed performance (13), but these need to be identified and TW drills. The last group served as the control (C) group. compared between different training stimuli. The purpose of The subjects reported to the University Neuromechanics this study was to compare the changes in muscle coactivation Laboratory. All the groups were tested before and after an during maximum jumps between an Olympic weightlifting 8-week training period (February to March). The training program with those observed after a traditional weightlifting groups attended 24 sessions (3 sessions per week) in total. program. We hypothesized that an improvement in jump Before the testing period, the subjects of the OL and TW

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jerk and training followed a progression essentially to TABLE 1. Exercises and volume of training for each experimental group.* the applied protocols (33) (Table 2). During the first 2 Groups Exercises Weeks 1–4 Weeks 5–8 weeks, the subjects performed Olympic weightlifting Power clean 4–6 3 6RM 4 3 4RM 4 sets of 4 repetitions of each Snatch 4–6 3 6RM 4 3 4RM exercise. The initial load corre- 3 3 Clean and jerk 4–6 6RM 4 4RM sponded to 75% of 1RM, and High pull 4–6 3 6RM 4 3 4RM Half-squat 4–6 3 6RM 4 3 4RM a 3-minute rest was provided Traditional weight Leg press 4–6 3 6RM 4 3 4RM between sets. For weeks 3 and Leg curl 4–6 3 6RM 4 3 4RM 4, the volume of training sig- Leg extension 4–6 3 6RM 4 3 4RM nificantly increased to 4 sets of 3 3 Bench press 4–6 6RM 4 4RM 6 reps at 80% of 1RM. For the Half-squat 4–6 3 6RM 4 3 4RM last 4 weeks. 4 sets of 4 reps at *6RM = 6 repetition maximum strength; R = repetitions. 80–90% of 1RM were performed. All the exercises were performed in a controlled man- ner with emphasis on the groups underwent 6 familiarization sessions (3 training eccentric-to-concentric transition, which was performed as sessions for familiarization with the movement technique quickly as possible during the lifting procedure. Initial and 3 familiarization sessions with the experimental resistance was determined from each subject’s 1RM strength. protocol). The participants in the control group performed One-repetition maximum was evaluated every 4 weeks to the laboratory familiarization only. The subjects were given adjust the training load. The loading levels were continually 2–3 days to recover between familiarization before pretesting adjusted to the intended relative levels throughout the procedures and initiation of the training period. A similar training period (4–6RM). length of recovery was given between the final training session and posttesting procedures. Traditional Weight Program. The TW training was a high- intensity (80% of 1RM) protocol that aimed to increase Training Protocol maximal muscle strength and rate of force development A standardized warm-up including jogging, stretching without inducing hypertrophy in lower-extremity muscle exercises, and several weightlifting repetitions was provided groups. The training program consisted of 5 weight for all the experimental groups before the beginning of each exercises: knee extension, knee flexion, push, pull of training session. All the subjects completed the same biceps femoris (BF), and half-squat. During the first 2 resistance training volume. A challenge was the attempt to weeks, the subjects performed 4 sets of 4 repetitions of design 2 different protocols that were comparable in terms of each exercise. The initial load corresponded to 75% of the time and effort. For this reason, in each training session, 1RM, and a 3-minute rest was provided between the sets. volumes were expressed as the total amount of work in For weeks 3 and 4, the volume of training significantly kilograms multiplied by the total number of repetitions and increased to 4 sets of 6 reps at 80% of 1RM. For the last 4 sets per exercise for the training session. Furthermore, the weeks, 4 sets of 4 reps at 80–90% of 1RM were performed. time of each specific exercise was calculated by multiplying All the exercises were performed over the range of motion, with repetitions per training sessions. The subjects repeated at a self-selected pace using cyclic concentric and eccentric these movements without a pause. The subjects performed muscle contractions and with emphasis quickly from the 4–6 repetitions per set of each exercise and 4–6 sets with beginning of the lifting movement. Initial resistance was a between-set rest interval of 3 minutes. The average total determined from each subject’s 1RM strength, which was time for each exercise was approximately 20 seconds for made every 4 weeks to adjust the training load. the OL program and 18 seconds for the TW program. Consequently, based on the total amount of work estimations, Control Group. The control group performed its standard sport the 2 training protocols were quite comparable. activities through their academic program, and no additional weight exercises over the 8-week period were performed. Olympic Weightlifting Program. The OL training protocol was designed to increase maximal muscle strength and mechan- Instrumentation ical power. The 8-week training regimes included a total of Ground Reaction Forces. All VJs were performed on a Kistler 24 training sessions. The training program consisted of piezoelectric force platform (type 9281C, Kistler Instruments, 5 Olympic-style weightlifting exercises: snatch from a squat Winterthur, Switzerland). The force platform was interfaced position, high-pull, power clean, half-squat, and clean and through Kistler amplifying units (type 233A) to an Ariel 2194 Journalthe of Strength and Conditioning ResearchTM

Copyright © National Strength and Conditioning Association Unauthorized reproduction of this article is prohibited. TABLE 2. Mean (6SD) group values for each experimental condition in the pretraining and posttraining.*

Olympic weightlifting Traditional weight Control

Test Pre Post Pre Post Pre Post

SJ Height (cm) 28.1 6 5.7 33.8 6 5.5† 28.81 6 284 29.803 6 2.99 29.5 6 4.5 31.1 6 4.6 Power (W) 1,319 6 43.3 1,335.8 6 523.4 1,604.6 6 213.5 1,639.8 6 304.5 1,306.5 6 474.7 1,294.6 6 221 CMJ Height (cm) 34.6 6 7.5 39.8 6 6.8† 31.25 6 1.97 33.38 6 3.01 33.3 6 5.2 35.2 6 5.8 Power (W) 2514.6 6 141.1 2807.6 6 270.8† 2356.66 6 107. 2461.1 6 157.8 2469 6 160.3 2571.5 6 189 1,403.3 6 571.5 2,093.6 6 587.1† 1,553.2 6 329.3 1,508.0 6 303.8 1,801.6 6 419.9 1,871 6 427.3 DJ20 Height (cm) 34.85 6 7.47 40.98 6 6.3† 30.563 6 3.4 30.67 6 3.21 32.6883 6 4.5 33.75 6 3.15 Power (W) 22,745.7 6 897 22,654.25 6 449 22,301.0 6 514 22,269.5 6 545 22,826.1 6 819 22,870 6 609 3,342.1 6 605.6 3,645.2 6 816.4 2,412.83 6 433 2,708.16 6 431 3,119.3 6 758 3,220 6 640.1

DJ40 Height (cm) 35.96 6 6.07 40.23 6 6.86† 28.05 6 3.96 29.85 6 3.127 32.98 6 6.47 33.66 6 7.37 Research Conditioning and Strength of Journal the Power (W) 24,363.75 6 773.4 24,573.12 6 775.8 23,401.5 6 726.6 23,547.1 6 7 84.6 24,239.5 6 695.4 24,484 6 545 2,588 6 457.3 3,721.2 6 629.4† 2,488.3 6 467.3 2,640.8 6 550.1 2,789.0 6 449.8 2,721.6 6 620 DJ60 Height (cm) 32.98 6 728 39.31 6 7.8† 26.11 6 3.54 29.86 6 6.0† 29.86 6 6.0 31.26 6 5.58 Power (W) 25,291.1 6 931.4 26,045.6 6 998.6† 24,959.6 6 726.8 24,652.3 6 1,139 25,364.33 6 540 25,307 6 603.8 3,081.6 6 565.8 3,497.6 6 661.2† 2,337.5 6 128.1 2,504.4 6 439.8 2,911.1 6 550.1 3,015.5 6 544 OUE2 UBR8|AGS 02| 2012 AUGUST | 8 NUMBER | 26 VOLUME *Pre = before; post = after; SJ = squat jump; CMJ = countermovement jump; DJ20 = drop jump from 20 cm; DJ40 = drop jump from 40 cm; DJ60 = drop jump from 60 cm. †Signiﬁcant difference from pre to post (p , 0.05). TM | www.nsca.com 2195

Performance System (4), and ground reaction forces were contact rebounded immediately as high as possible, while A/D converted at a sampling rate of 1,000 Hz. keeping their hands on their hips. The starting position was with the knee at 180° (full extension). The technique used for Bipolar surface electrodes (Motion Con- Electromyography. the drop was the bounce DJ where a small amplitude trol, Iomed Inc., voltage range: 64to612V) analog movement is typical (9). Neither verbal nor visual amplifier (sampling frequency 1,000 Hz, common-mode motivation was provided during the tests. The rest interval rejection ratio 100 dB at 50/60Hz, bandwidth 8,500-Hz gain between trials was 3 minutes, whereas a 5-minute interval 400) were used to record the EMG activity of the rectus was given as the height of the jump was altered. The femoris (RF) and BF muscles. Electrode locations were repeatability of the jump height measurements was in- prepared by shaving the skin of each site and cleaning it with vestigated in a preliminary study with 10 young men by alcohol wipes. Electrode placement was carefully measured performing 2 sessions, separated by a week’s interval. The and marked with permanent nonremovable ink to exactly intraclass correlation coefficient was 0.90 for SJ, 0.89 for ensure that the same position was used before and after CMJ, and 0.83 for DJ power, respectively. training. The GRF and EMG data were averaged over 0.60 intervals, Kinematics. For motion analysis, 2 video cameras (Panasonic yielding 600 data points per second. This was performed AGI88 Tokyo, Japan, frame rate 60 Hz with a high-speed to achieve the simultaneous examination and display of shutter) and a video recorder (Panasonic S500) were used. kinematic and kinetic data. The average EMG (millivolts) for The cameras were placed at a 90° angle at a focal distance the 1RM and the jumps (squats, CMJs, DJs) was calculated by of 8 m. Skin markers were placed at 5 body locations on the full-wave rectification and averaged over precontact, eccen- body: trunk (midaxillar line at umbilicus height), hip (superior tric, and concentric phases. For each jump, GRF, EMG, and part or greater trochanter), knee (lateral epicondyle), ankle joint displacement values were used for analysis. For CMJ (lateral malleolus), and foot (head of fifth metatarsal). The and DJ, the movement was divided into preactivity, video image of a calibration frame was recorded before each concentric, and eccentric phases, and for SJ the movement, measurement, and 8 calibration points were digitized to it was divided into preactivity and concentric phases. These determine the 3 dimensional position of any point in space. phases were determined using the changes in the angular The coordinates for these markers were digitized using the position of the knee and the contact time as proposed by Aura Ariel Performance Analysis System (Ariel dynamics Co, and Vitasalo (5) and Vitasalo et al. (34). San Diego, CA, USA). For synchronization of the force and Statistical Analyses video data, the computer trigged a stroboscopic light, which From GRF data, the maximum VJ height was determined was visible on the camera’s field of view. for the highest jump (36). Furthermore, power was Three dimensional marker position data were generated obtained by integrating the vertical GRF for each phase using the direct linear transformation method. The of the jump ([concentric SJ power (Cpower)], [eccentric resulting displacement-time data of each marker were power (Epower)], concentric [Cpower] for CMJ, DJ from filtered using a second-order Butterworth digital filter with 20, 40, 60 cm, respectively). From the kinematic raw a zero-order phase lag (38). Optimal cut-off frequencies angular displacement values, knee (maximum angle of knee were chosen by comparing the residuals of the difference [MAK]) maximum values were further analyzed. The raw between filtered and unfiltered signals at several cut-off EMG was full-wave rectified and averaged over eccentric frequencies (37). From the smoothed angular displace- (EMGecc) and concentric phases (EMGcon) for all the ment data, the hip and knee extension-flexion position jumps or during the whole movement (SJ). data were further analyzed (37,38). Cocontraction Index Testing Procedure The EMG raw data were full-wave rectified and low-pass The subjects underwent a standardized warm-up consisting filtered at 6 Hz yielding the linear envelopes of each muscle of submaximal cycling (5 minutes), stretching exercises, and EMG. The EMG of each muscle was then expressed as a severalVJs.Betweenwarm-upandhabituationtests,and percentage of the EMG value during the maximum voluntary again between the individual tests, 3–6 minutes was given to contraction (MVC). allow recovery. The main protocol included performance of The CI was calculated using the following equation: 3SJsandCMJsand3dropjumps(DJs)from20cm(DJ20), 40 cm (DJ40), and 60 cm (DJ60) in a randomized order, and I CI ¼ ant 3100%; the best performance was analyzed. The SJ test was I ang performed from the seated position with the knee secured where Iagn= EMGRF and Iant= EMG BF. at 90° of knee flexion (180° = full extension) while keeping their hands on their hips. The starting position for the CMJ Vertical Stiffness (Kvert) was with the knee at 180° (full extension). The subjects Vertical stiffness (Kvert) was calculated by dividing the jumped from a stand on the platform and after bilateral change in force (DF) by the change in displacement of 2196 Journalthe of Strength and Conditioning ResearchTM

Figure 1. Training-associated changes in the coactivation index (CI) as assessed through the squat jump (SJ) and in the countermovement jump (CMJ) and the drop jump (DJ) from 20 and 60 cm, respectively, in the precontact (PR), eccentric phase (ECC), and concentric phase (CON). *Signiﬁcant differences from pre to post (p , 0.05).

center mass (DL) during the eccentric phase in the jump (35). RESULTS The negative phase was defined between the initiation of Cocontraction index the movement (the instant at which vertical force began to The EMG results are presented in Figure 1. There was decrease continually) and the deepest excursion of the a significant Group 3 Training interaction effect on CI in SJ knee joint: DF =DL; (p , 0.05). Post hoc analysis showed that CI decreased after both programs in the preactivation phase, but it was where DF is the range of the vertical component of the unchanged for the TW group during the concentric phase ground reaction force and DL is the range of the center of (p . 0.05). For CMJ, the ANOVA indicated a significant mass displacement. Group 3 Training interaction effect on CI (p , 0.05). Post Mean and SD were calculated from individual measure- hoc analysis showed that CI increased for the 2 groups ments for the 3 groups. An analysis of variance (ANOVA) in the preactivation and eccentric phases, but it increased in with repeated measures was used to examine the effects of the concentric phase only after TW training. Similarly, for training (PRE-POST) between the 3 groups (OL, TW, C) on the DJ20cm, post hoc analysis showed that the CI each dependent variable. Post hoc Tukey tests were applied increased only for the TW group, but it was unchanged for comparisons between individual means, when required. after the OL training (p , 0.05). The CI during the The level of significance was set at p # 0.05. preactivation and concentric phases of the DJ60cm

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decreased signiﬁcantly after TW training, but it increased during the eccentric phase (p , 0.05).

Stiffness The results for the stiffness are presented in Figure 2. There was a signiﬁcant Group 3 Training interaction effect on stiffness in the SJ for the OL group (p , 0.05). In the CMJ, the ANOVA indicated a signiﬁ- cant Group 3 Training interaction effect on stiffness (p , 0.05). Post Hoc analysis showed that both groups increased joint stiffness after training (p , 0.05). For DJ20cm and DJ60cm, post hoc analysis showed that only the OL group increased leg stiffness (p , 0.05).

Vertical Jump Height and Power Figure 2. Training-associated changes in stiffness as assessed through the squat jump (SJ) and in the The results for the VJ height countermovement jump (CMJ) and drop jump (DJ) from 20 and 60 cm, respectively. *Signiﬁcant differences from and mean power for each pre to post (p , 0.05). testingconditionarepre- sented in Table 2. The ANOVA indicated a signiﬁcant Group 3 Training interaction effect on

TABLE 3. Training-associated changes in angle displacement of the knee and hip as assessed through SJ, CMJ, and in the DJ20, DJ40, and DJ60.*†

Olympic weightlifting Traditional weight Control

Test Pre Post Pre Post Pre Post

SJ Knee 143.3 6 4.6 149.6 6 16.1‡§ 144.58 6 10.4 146.8 6 6.05 148.1 6 6.1 145.1 6 10.4 Hip 147.2 6 7.1 150.5 6 11.4 148.5 6 8.5 142.5 6 6.8‡§ 149.1 6 11.8 144.2 6 11.2 CMJ Knee 146.22 6 5.8 149.2 6 7.6 145.27 6 21.8 146.4 6 5.95 154.8 6 9.9 152.71 6 9.40 Hip 135.93 6 15.9 145.7 6 19.7‡§ 144.42 6 13.4 140.4 6 17.3 149.61 6 15.6 146.4 6 9.29 DJ20 Knee 140.45 6 11.9 132.5 6 26.2‡§ 140.3 6 13.3 137.8 6 9.71 152.43 6 14.0 154.5 6 14.9 Hip 160.9 6 11.4 153.9 6 14.0‡§ 147.45 6 9.53 154.9 6 5.4‡§ 149.9 6 9.7 151.0 6 7.5 DJ40 Knee 146.2 6 12.3 142.76 6 10.6 139.03 6 7.8 142.16 6 6.2 144.62 6 6.55 146.5 6 5.2 Hip 157.63 6 9.0 156.28 6 9.32 153.4 6 5.6 153.8 6 11.3 162.4 6 7.5 160 6 6.8 DJ60 Knee 146.6 6 8.1 149.16 6 9.6 139.02 6 5.0 138.79 6 5.5 149.86 6 14.6 147.65 6 9.8 Hip 159.5 6 8.37 156.44 6 11.4 154.36 6 12.4 146.6 6 13‡§ 155.80 6 9.8 157.8 6 12.9

*Pre = before; post = after; SJ = squat jump; CMJ = countermovement jump; DJ20 = drop jump from 20 cm; DJ40 = drop jump from 40 cm; DJ60 = drop jump from 60 cm; C = control group; OL = Olympic weightlifting training; TW = traditional weight training. †Mean (6SD) group values for each experimental condition in the pretraining and posttraining. ‡Signiﬁcant differences from pre to post (p , 0.05). §Signiﬁcant differences between groups (p , 0.05).

2198 Journalthe of Strength and Conditioning ResearchTM

SJ and CMJ height (p , 0.05). Post hoc analysis showed group, the vertical stiffness and CI were unchanged (Figures 1 that only the OL group improved the SJ and CMJ height and 2) as both RF and BF EMG increased. This increase (p , 0.05), whereas the SJ power did not increase for all the might explain the absence of significant SJ height improve- groups (p . 0.05). For CMJ, the ANOVA indicated ments (Table 2) as any benefits from a higher quadriceps a significant Group 3 Training interaction effect on CMJ activity are probably counteracted by a higher BF activation, power (p , 0.05). Post hoc analysis showed that the OL thus leading to a more extended hip joint (Table 3) (31,32). group improved CMJ, eccentric and concentric power but It could be suggested that strength improvements in both not the other groups. The OL group showed a significant knee extensors and flexors after TW training were equally increase in the DJ height from 20 and 40 cm after training transferred to SJ movement. In contrast to the TW group, (p , 0.05), but both training groups showed a significant the OL group showed a decline of CI (Figure 1). This might improvement in the DJ height from 60 cm (p , 0.05). indicate an increase in the net joint knee extension torque Eccentric power in DJ from 60 cm and concentric power in at propulsion, because of a reduction in antagonist (BF) DJ from 40 and 60 cm improved significantly (p , 0.05) cocontraction (17). This, in association, with the increase in only in the OL group. vertical stiffness may contribute to a greater gain in the SJ jump height and power, which is in agreement with Kinematics the findings of previous studies on ballistic resistance The results for knee and hip angles are presented in Table 3. training adaptations (2,21,28,35). There was a significant Group 3 Training interaction effect In CMJ, there was an increase in the CI during the on the knee and hip angle in SJ (p , 0.05). Post hoc analysis preactivation and breaking phases after both training showed an increased knee angle after OL training (p , 0.05) programs (Figure 1). However, an increase of CI during and a decreased hip angle after TW training (p , 0.05). For the propulsion CMJ phase was found for the TWgroup but CMJ, the ANOVA indicated a significant Group 3 Training not for the OL group (Figure 1). A higher CI and stiffness interaction effect on hip angle (p , 0.05). Post hoc analysis during the transition phase, seen after TW training, may showed that the OL group increased the hip joint angle after not be sufficient for the transfer of elastic energy from the training (p , 0.05). For DJ20cm, the ANOVA indicated eccentric-to-concentric phase (8,33,35). For this reason, a significant Group 3 Training interaction effect on knee and traditional resistance exercises are thought to be beneficial hip angle (p , 0.05). Post hoc analysis showed a decreased for enhancing joint stability and the functional capacity of knee and hip angle after OL training and an increased Hip the activated muscles (19) but not jump performance. In angle after TW training (p , 0.05). There was no significant contrast, the OL group improved CMJ height by means of Group 3 Training interaction effect on the knee and hip a lower CI and an altered hip joint angle (Tables 2 and 3). angle in DJ40cm (p . 0.05). For the DJ60cm, the ANOVA Particularly, the combination of a higher BF EMG activity indicated a significant Group 3 Training interaction effect and hip flexion angle (Table 3) during the stretch phase can on the hip angle (p , 0.05). Post hoc analysis showed that explain the increase in vertical stiffness (Figure 2). In turn, the TW group showed a lower hip joint angle after training a higher stiffness facilitates the release of greater amounts (p , 0.05). of stored elastic energy during the propulsion phase (3,10,24), with a relatively unopposed antagonist activity DISCUSSION from the hip flexors (35). The results of this study showed that the OL group showed Muscle coactivation in DJs showed variable responses, better improvements in jump height than the TW group did. depending on training group and dropping height. As far as Further, OL training resulted in a reduction or maintenance of the TW group is concerned, the results showed that CI, hip CI and an increase in leg stiffness during the push-off phase of flexion angle, and leg stiffness increased during the DJ20 all jumps, whereas TW training increased in CI and leg without increases in performance (Figures 1 and 2, Tables 2 stiffness. This partly confirms our initial hypothesis indicating and 3) which is in line with previous findings (13,23). Bobbert that TW exercises may be appropriate for enhancing joint et al (8) reported that stronger muscles do not necessarily stability, whereas OL exercises are better for improving result in greater jumping ability. The increased muscle power performance through better coordination of antago- coactivation in DJ after TW training may assist knee stability nistic muscle groups. Because the mechanisms that contribute especially during the breaking phase, but it may have no to performance differ among the 3 types of jumps tested, effect on the propulsion and the reuse of elastic energy (23). training adaptations must be examined separately for each Thus, it appears that the central nervous system counter- jump. balances force production and joint stability to ensure joint During the SJ, the CI in the preactivation phase decreased integrity (by increasing joint stiffness via elevated antagonist for both training groups (Figure 1), mainly because of a higher coactivation) in unstable movement conditions, such as DJs agonist EMG, which is frequently observed after training (16). Although TW training increased CI in DJ20, the (30,31). However, changes in CI during the main SJ opposite was found for DJ60 (Figure 1). This agrees with the movement differed between the 2 groups. For the TW findings of previous studies, and it could be explained by an

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offset of the positive (increased muscle function) and negative improved mainly by weightlifting training. These results (decreased prestretch augmentation) effects on DJ perfor- suggest that weightlifting training increases the jump height mance (23,32). Furthermore, the lower CI coupled with via an increase in leg stiffness and constant CI. Finally, the a change in the hip flexion angle might signify a higher cocontraction increase in the breaking phase after both activity of the back thigh muscles, which has a direct role in training protocols may be seen as an attempt for dynamic landing and in assisting knee stability (13). restrain and functional knee stability. According to our initial hypothesis, it was expected that the increase in vertical stiffness during the DJs would be the PRACTICAL APPLICATIONS result of neural adaptations after OL training. However, there An implication of the present findings is that a proper were no significant changes in muscle activity (Figure 1). This periodized training program should focus on the specific suggests that DJ performance gains after OL training are training stimulus either to avoid possible injury or improve the because of a change in the mechanical properties of muscle- use of SSC. In a practical sense, coaches might prefer to use tendon complex rather than caused by muscle coactivation. It hierarchical OL programs when there is a need to improve is interesting as to why the OL group showed a lower CI SSC. Alternatively, when there is a need to improve joint during CMJ and SJ but in the DJ the CI did not change. This stability, TW programs are more beneficial. Because in most could be because of the following factors: first that the faster cases both injury avoidance and performance improvements SSC (DJ) depends more on the mechanical properties of are desirable, we propose that TW training may precede OL the muscle than the slower SSC jumps (CMJ, SJ) and, second, training exercises so that participants first achieve a muscle the greater need for enhanced joint stability prevents any strength increase and joint stability and then perform power- reductions in CI after OL training. The above result is specific exercises to achieve better performance. accompanied by kinematic (as interpreted through hip

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