Effects of Assisted and Traditional Drop Jumps on Jumping Performance

Effects of Assisted and Traditional DropJumps on Jumping Performanceby

Hubert Makaruk, Jason B. Winchester, Adam Czaplicki,Tomasz Sacewicz, Janusz Zielinski and Jerzy Sadowski

Reprinted from

International Journal of

Sports Science & CoachingVolume 9 · Number 5 · 2014

International Journal of Sports Science & Coaching Volume 9 · Number 5 · 2014 1217

Effects of Assisted and Traditional DropJumps on Jumping Performance

Hubert Makaruk1, Jason B. Winchester4, Adam Czaplicki2,Tomasz Sacewicz2, Janusz Zielinski3 and Jerzy Sadowski1

1Department of Track and Field, 2Department of Biomechanics,3Department of Basketball and Handball, Faculty of Physical Education

and Sport, Biala Podlaska, The Josef Pilsudski University of PhysicalEducation, Warsaw, Poland

E-mail: 42 Akademicka Street, Biała Podlaska, 21-500, Poland; Department ofAthletic Training and Exercise Physiology, Midwestern State University,

Wichita Falls, TX, USA.

ABSTRACT

The purpose of the present study was to evaluate the effects of assisted

and traditional drop jumps on fast stretch-shortening cycle exercises in

collegiate athletes. Participants were selected into one of three groups: 1)

the assisted drop jump (n=11); the traditional drop jump (n=11); and 3) the

control (n=11). The assisted drop jump training involved drop jumps (DJs)

with assistance of tubing, whereas the traditional DJ training was

performed without any assistance. Prior to and at the completion of 5-

week training programs, DJs from heights of both 30 (DJ30) and 60 cm

(DJ60) were conducted to determine jump height, drop jump reactivity

coefficient, contact time and peak ground reaction force. Both the

assisted DJ and traditional DJ training programs resulted in significant (p <

0.05) improvement in jump height, DJ reactivity coefficient and decreased

contact time for DJ30. Although both the assisted DJ and traditional DJ

modes also increased jump height and DJ reactivity coefficient for DJ60, an

enhancement of the assisted DJ training in DJ reactivity coefficient was

significantly greater compared to the traditional DJ training. In addition, the

assisted DJ mode allowed for a significant reduction of ground reaction

force, while the traditional DJ did not change the ground reaction force. The

results of this study support the inclusion of assisted DJ training into

jumping sports like basketball, volleyball, and track and field jumps. Our

results further suggest that incorporating assisted DJ training may be

appropriate for highly trained adult athletes due to jumping performance

improvement and impact landing forces reduction simultaneously.

Key words: Drop Jumps, Ground Reaction Force, Plyometric Training,

Vertical Jump

Reviewers: Loren Chiu (University of Alberta, Canada)Jeremy Sheppard (Surfing Australia, Australia)

INTRODUCTIONThe importance of jumping performance for many sports is well documented as well as it isknown that drop jump (DJ) exercises, which involve jumping off the box, landing andpowerful jumping, are highly efficient in improving jumping performance. The results ofstudy of Gehri [1] indicated that a 12-week DJ training significantly increased jump heightfor squat jump (SJ), countermovement jump (CMJ) and DJ tests in male and female collegestudents. Similar findings were demonstrated by Taube et al. [2], who suggested that 4 weeksof DJ training improved jump height and DJ reactivity coefficient in males and females withexperience in jumping activities. Makaruk et al. [3] have also reported that DJ training led toimprovement in jumping performance in male college students experienced in plyometricexercises.

However, DJs may result in excessive stress on muscles and joints due to eccentriccontraction and high ground reaction force [4, 5]. For this reason, non-traditional modes ofperforming DJ have been examined in an effort to reduce their potentially negativeconsequences, while at the same time still providing an appropriate stimulus which will elicitgains in jumping performance. For example, Humphries et al. [6] have demonstrated that thebraking mechanism of the plyometric power system significantly decreased the impactlanding force without a concentric force deterioration.

Another potential benefit of using non-traditional DJs is because it can be a novelstimulus, especially for experienced athletes in jumping sports (e.g., basketball, volleyball ortrack and field jumps), who probably have a smaller window of adaptation for jumpingperformance development due to the high number of foot contacts that they experience on aregular basis as part of their sport. This stimulus seems to be desired, since Sheppard et al.[7] reported that male volleyball players did not change jump height in CMJ and spike jumpafter 5-week traditional jumping training. Other results of Sheppard et al. [8] showed that anon-traditional solution in jumping training (accentuated eccentric load) was superior inincreasing the jump height compared to traditional jumping training. Similarly, Rhea et al.[9] suggested rubber resistance jump training exercises to improve efficiency of jumpingperformance in jumping training. Conversely, Makaruk et al. [3] indicated that contact timemay increase when the additional load during DJ training is used, what may deteriorate thestretch shortening cycle (SSC), which has been shown to maximize jumping performance.Furthermore, assisted DJ training may allow the performer to train at a location on the force-velocity curve which is not possible at loading which is equal to or above body mass. Theimplications of this possibility remain largely unexplored.

Assisted jumping is a new non-traditional mode in plyometric training. This form oftraining uses the reduction of body weight and may lead to greater jump height by anincrease of takeoff velocity [10]. According to some researchers [7, 11] assisted jumping isa novel “overspeed” stimulus, which results in performance improvement by increasingmotor unit recruitment and motor unit synchronization. There are a few studies that haveinvestigated the effects of assisted CMJ on jumping performance. Imachi et al. [12] showedthat implementation of rubber bands for CMJ in volleyball players increased jump heightabout 8-10 cm, while improvement in traditional CMJ was only 3.5 cm. Sheppard et al. [7]reported that assisted CMJ training resulted in the greater improvement in CMJ and spikejump height compared with traditional CMJ training in volleyball players. Argus et al. [13]also observed a small difference (5.6%) in jump height for CMJ to assisted methodsadvantage.

To our knowledge, no studies have addressed the effects non-traditional DJ training inunloaded conditions with rubber bands or elastic cord assistance. Still, relatively little is

1218 Effects of Assisted and Traditional Drop Jumps on Jumping Performance

known about the effects of assisted training on ground reaction force. The purpose of thisresearch was thus to examine the effects of 5-week assisted DJ training on jumpingperformance in male athletes and compare these effects to those achieved after traditional DJtraining.

METHODSUBJECTSThirty-three male collegiate athletes who participated in basketball (n=14), volleyball (n=5),and track and field sprint (n=6) and jumping (n=8) events volunteered to participate in thisstudy. All of the athletes were experienced in plyometric exercises. None of the individualswere taking any nutritional supplements. The University’s Ethics Committee approved allexperimental methods and each participant read and signed a consent form prior to theinitiation of the study. Subjects were randomly assigned to one of three groups: assisted dropjumping (n=11), traditional drop jumping (n=11), and control (n=11). The values of selectedparameters of the groups did not differ significantly (p > 0.05) at baseline (Table 1).

Table 1. Characteristics of training and control groups at pretraining (mean± SD)

ADJ TDJ CONAge (years) 21.3 ± 1.9 21.7 ± 2.2 20.9 ± 1.8Height (cm) 186 ± 6 187 ± 7 185 ± 8Body mass (kg) 80.8 ± 6.5 81.6 ± 6.9 80.5 ± 5.71 RM squat (kg) 135 ± 14 138 ± 12 133 ± 10

None of the group differences were significant. ADJ = assisted drop jumping, TDJ = traditional drop jumping, CON= control group, 1 RM = one repetition maximum.

MEASUREMENTSKinetic data were obtained from a piezoelectric force platform (Kistler 9281CA,Switzerland) working with sampling frequency of 500 Hz. Signals from the platform wereamplified and recorded on a PC computer using a 16-bit A/D board and BioWare 3.24software. Data was filtered with a zero-lag quadratic low-pass Butterworth digital filter witha cut-off frequency of 12 Hz. Jump height, drop jump reactivity coefficient, ground contacttime and peak ground reaction force (GRF) were evaluated. Jump height was calculatedfrom the vertical velocity at the instant of the take-off, which was obtained by numericalintegration of the vertical acceleration extracted from the vertical ground reaction force [14].The DJ reactivity coefficient was estimated according to the formula of Komi [15], reactivitycoefficient = drop jump height (cm) ÷ contact time (seconds). Contact time was determinedas time from the onset of GRF to zero GRF. The peak GRF was obtained by identifying themaximal value during the landing phase [16].

TESTINGSubjects were tested during DJ at heights of 30 (DJ30) and 60 cm (DJ60) respectively. Priorto the performance of the DJ exercise, each subject was instructed to: “drop off the box, andjump immediately as high as you can”. Upon initial ground contact, the arms first swungbackwards and then high upwards to facilitate the following jump. Subjects were allowed toself-select their achieved depth prior to jumping. The greatest jump height among 3 trials


was used for data analysis. The interval between trials was approximately 1 minute and foreach test was 5 minutes. Measurements were made 3 days before and after the completion ofthe program. A standardized warm-up consisting of a low-intensity 8-minute jog as a warm-up exercise was followed by 5-minute dynamic stretching exercises, and rope jumps 6 x 15.

The reliability of DJ30 and DJ60 measurements were evaluated two weeks before the studyby testing 12 subjects. The trial-to-trial reliability of the three trials of DJs was examinedusing intraclass correlation coefficients (ICC). The ICCs were strong for all testedparameters in DJ30 and DJ60: for jump height (0.94 and 0.93), for DJ reactivity coefficient(0.91 and 0.91), for contact time (0.95 and 0.96), and for peak ground reaction force (0.91and 0.93), respectively.

TRAINING PROCEDURE The training intervention was performed during off-season periods for each sport and wascompleted three times a week (Monday, Wednesday, and Friday) for 5 weeks, with theexception of the last week of training (only Monday and Friday). Training consisted of anassisted or traditional DJs performed with two boxes of varying heights. The DJ heightswere increased on a weekly basis in the following progression: 30-30 cm in back and fortharrangements (1 week), 30-45 cm (2 week), 45-45 cm (3 week), 45-60 cm (4 week), 60-60 cm (5 week). For each training session, 7 sets of 6 DJs were performed with 4-5 minutesof rest between sets. The DJ exercise required the subject to drop off a box, and double-legjump onto the box in front of him as soon as possible after double-leg landing. Subjects wereinstructed to take off with full extension in the hip and knee joints, and the feet were slightlyoutwards. All training sessions were performed indoors on a synthetic surface. The trainingprograms were identical except for the assisted DJ mode, where Theraband “heavy” grey


Figure 1. Unloading procedure


tubing was used. The tubing, fixed between the body harness and the bay roof of the traininghall. The distance between two points (ground and roof) was about 3.5 m. The adjustment oftension was made by grips secured to the harness to allow for a body weight unloading of10% for each subject. Proper adjustment was verified prior to the first set of DJs for eachtraining session using a portable force platform (AMTI AccuGait System, model ACG, USA)(Figure 1).

STATISTICAL ANALYSISThe mean and SD were calculated for all results and they were initially tested for normalityand homogeneity of variance assumptions. The significance of differences between dependentvariables was assessed with a 3 x 2 (group x time) repeated-measures ANOVA. Whensignificant effects were observed, Tukey post hoc tests were applied. The difference in themagnitude of changes between the pre- and post-tests was analyzed by separate one-wayANOVA’s. An alpha level of p ≤ 0.05 was used as a criterion for significance in all statisticalcomparisons. Cohen’s effect size (ES) was calculated by determining the difference betweenpre- and post-test means, divided by the pre-test SDs of control group [17]. The thresholds forsmall, moderate, and large ES were set at 0.4, 0.6, and 1.0, respectively.

RESULTSChanges in jump height, drop jump reactivity coefficient, contact time and peak groundreaction force for DJ30 are shown in Table 2. Both the assisted DJ and traditional DJ groupssignificantly improved jump height, DJ reactivity coefficient and decreased contact time. Allthese changes were significantly greater compared to the control group. Neither the assistedDJ group nor traditional DJ group changed peak ground reaction force.

Table 2. Effects of plyometric training on jumping height, drop jumpreactivity coefficient, contact time and peak ground reaction force in dropjump (DJ30) from height of 30 cmData are presented as the mean (± SD) and effect size (ES).

Test Parameter Mode Pre Post Change ESAbsolute %

DJ30 h (cm) ADJ 37.9 ± 4.7 41.1 ± 4.1*‡ 3.2 8.4 0.8TDJ 39.1 ± 4.5 42.6 ± 3.6*‡ 3.5 9.0 0.9CON 37.5 ± 3.8 37.8 ± 4.1 0.3 0.4 0.1

DRC ADJ 93 ± 11 111 ± 16*‡ 18 19.5 1.6TDJ 92 ± 12 110 ± 15*‡ 18 19.8 1.6CON 87 ± 12 89 ± 14 2 2.4 0.2

CT (s) ADJ 0.41 ± 0.05 0.37 ± 0.05*‡ -0.04 -8.6 0.7TDJ 0.43 ± 0.06 0.39 ± 0.04*‡ -0.04 -8.7 0.7CON 0.43 ± 0.05 0.43 ± 0.06 -0.004 -0.8 0.1

GRF (N) ADJ 2832 ± 554 2664 ± 691 -168 -6.0 0.3TDJ 2709 ± 406 2841 ± 382 132 4.9 0.3CON 3078 ± 504 3145 ± 463 67 2.2 0.1

DJ30 = drop jump from height of 30 cm; h = jumping height; DRC = drop jump reactivity

coefficient; CT = contact time; GRF = peak ground reaction force; ADJ = assisted drop

jumping training; TDJ = traditional drop jumping training; CON = control. * Significant difference

from pre values (p < 0.05). ‡ Significantly different change than in TDJ (p < 0.05).

‡ Significantly different change than in CON (p < 0.05).

Differences in jump height, DJ reactivity coefficient, contact time, and peak groundreaction force for DJ60 are shown in Table 3. Follow-up analysis revealed that both theassisted DJ and traditional DJ groups significantly enhanced jump height. These changeswere greater than in control group. Both the assisted DJ and traditional DJ group increasedDJ reactivity coefficient, but an increase of the assisted DJ group was significantly greaterthan in traditional DJ and control groups. The assisted DJ group significantly decreasedcontact time and this change was significantly greater compared to the control group. Theanalysis also indicated that the assisted DJ group significantly reduced peak ground reactionforce. These changes were greater than in the traditional DJ and control groups.

Table 3. Effects of plyometric training on jumping height, drop jumpreactivity coefficient, contact time and peak ground reaction force in dropjump (DJ60) from height of 60 cmData are presented as the mean (± SD) and effect size (ES)

Test Parameter Mode Pre Post Change ESAbsolute %

DJ60 h (cm) ADJ 39.6 ± 4.0 43.0 ± 3.8*‡ 3.4 8.5 0.9TDJ 41.0 ± 3.8 43.5 ± 3.4*‡ 2.5 6.0 0.7CON 38.4 ± 3.6 38.2 ± 3.4 -0.2 -0.5 0.1

DRC ADJ 104 ± 13 125 ± 14*‡† 21 19.8 1.3TDJ 103 ± 16 112 ± 13* 9 8.7 0.5CON 98 ± 16 97 ± 18 1 0.5 0.2

CT (s) ADJ 0.38 ± 0.04 0.34 ± 0.03*‡ -0.04 -9.8 0.7TDJ 0.40 ± 0.06 0.39 ± 0.04 -0.01 -3.2 0.2CON 0.40 ± 0.05 0.41 ± 0.06 0.01 1.8 0.1

GRF (N) ADJ 4464 ± 478 3927 ± 460*†‡ -536 -12.0 0.9TDJ 4095 ± 665 4282 ± 751 187 4.5 0.3CON 4509 ± 573 4645 ± 536 136 3.0 0.2

DJ60 = drop jump from height of 60 cm; h = jumping height; DRC = drop jump reactivitycoefficient; CT = contact time; GRF = peak ground reaction force; ADJ = assisted dropjumping training; TDJ = traditional drop jumping training; CON = control. * Significant differencefrom pre values (p < 0.05). † Significantly different change than in TDJ (p < 0.05).‡ Significantly different change than in CON (p < 0.05).

DISCUSSIONThe main findings of this study are associated with the assisted DJ training, which providedthe greater jumping performance in short time overloaded conditions compared to traditionalDJ training. In particular, we demonstrated that 5-week assisted DJ training significantlyincreased DJ reactivity coefficient and decreased contact time for DJ from height of 60 cmin male athletes. In addition, the greater decrease of peak ground reaction force after assistedDJ training has also occurred from height of 60 cm.

The current study was based on a premise that training for success in jumping sportsrequires jump height enhancement. Achievement of a greater jump height in basketballallows for advantage in field goals and rebound, in volleyball provides gains in attack andblock, and in high jump directly increases performance. Both the assisted and traditional DJtraining programs were equally effective in increase jump height. These results may suggestthat assisted method in DJ training does not produce an added benefit for increasing jump


height and there is not a need to replace a traditional DJ training by assisted DJ when onlyimprovement of jumping ability is required. This is in line with previous study [3] wherebyother non-traditional (resisted) DJ training provided similar gains in jumping performancecompared to traditional DJ training.

The assisted DJ training demonstrated, however, superior results due to increase of DJreactivity coefficient influenced by decrease of contact time for DJs from the height of 60 cmcompared to traditional DJ training. This observation suggests that assisted DJ training maybe very advantageous for sports where shorter time to reach the greater jump height allowsto overtake an opponent and therefore favorable to sport success. For example, efficiency ofmany actions in basketball and volleyball is associated with performing maximum jumpimmediately after landing from a high jump height. It is also logical to expect benefits fromassisted DJs to another specific actions like landing technique “land and go” because of shortcontact time. This technique is used in volleyball, when a player serves and has to play indefense or when attacking from the back row [18]. Furthermore, the assisted DJ training canbe strongly recommended for athletes who have to overcome high ground reaction force invery short time when high horizontal velocity requirements are needed; for example, in triplejump [19]. We speculate that the assisted method during DJ training might induce positiveneuromuscular changes by forcing more rapid muscle action in concentric phase without lossof force. The mechanisms underlying this beneficial effect should be examined in the futurestudies. The coaches must also consider the negative implications due to shortened contacttime in DJ training. Makaruk and Sacewicz [20] found no increase in jump height for DJafter plyometric training, when the subjects were instructed to perform jump as fast aspossible with the minimum contact time. There is some empirical evidences that too short atime for execution of exercise may cause decrease in the jump height because of insufficientforce development [21].

The assisted DJs should be, however, viewed with caution because of other reason. Theassistance methods are often associated with supramaximal velocities [7, 22] and thereforesome athletes; e.g. long-distance runners or swimmers may not be adequately prepared totolerate high velocity movements such as those experienced in assisted DJs; and this methodof training may not properly prepare them for success in their chosen sport. We believe thatassisted DJs are highly specific methods and should be employed by athletes whose sportperformance requires high velocity development or cutting maneuvers. We also suggest thatcoaches should take into consideration both the assisted and traditional DJs to eliminatespecific adaptation to only assisted mode of training. This recommendation is supported byKristensen et al. [22], where assisted, traditional, and resisted methods in speed training wereused. It was observed that every method guaranteed improvement in running velocityindividually, but mostly for specific training conditions.

The changes in peak ground reaction force as a consequence of traditional DJ trainingwere non-significant, but a significant decrease were noted for assisted DJ training in theDJ60 condition. Considering the high number of jumps under high impact landing forces;e.g., in triple jump more than (15 times the body mass of an athlete) [19] or in NBA players(landing after a lay-up jump shot is about 9 times the body mass [23]), it is a valuableobservation for coaches. In other words, assisted DJs may be preventive of body impairmentssuch as shin splints and tendinitis caused by repetitive landing forces. On the other hand, toolarge a reduction of eccentric load may compromise the SSC mechanism and jumpingperformance due to a decrease of muscle activation [24]. An interesting solution to thisproblem in assisted DJ training is proposed using a higher drop height, which allows forsimilar eccentric demands to traditional DJs from lower height [7]. Due to decreasing large



landing impact forces observed by Kilgallon and Beard [25], more studies are needed toclarify the underlying mechanism of these muscle actions before an assisted method forbeginners or children can be recommended.

There is an important limitation to the present study. This limitation provides furtherevidence of the need for continued experimentation to validate the approach presented here.There were no measures of neuromuscular adaptation, therefore it is not possible to ascertainwhat caused the changes in performance. Other new research might examine the effect ofassisted jump training on neuromuscular adaptation in athletes. Mero and Komi [26]indicated that speed exercises in the assistance conditions are associated with greaterneuromuscular response in comparison of traditional exercise.

CONCLUSIONThe results of this study provide support for the usefulness of assisted DJ training in jumpingsports. Logically, it seems that track and field jumpers, and basketball and volleyball playerswould be good candidates for the use of assisted DJs due to an increase jump height andpossibility of shortening time of performance jumping exercise in high overload condition.In addition, the results of this study indicated that the inclusion of assisted DJs into thetraining programs may improve jumping ability when the eccentric phase of the exercise isunloaded. Therefore, reduction of injury may be expected with the incorporation of assistedDJs compared to traditional DJs. Further studies are needed to determine the benefits ofcombined assisted DJ training with traditional methods for these athletes.

ACKNOWLEDGEMENTSThis study was supported in part by Jozef Piłsudski University of Physical Education inWarsaw, grant BW III/26.

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Effects of Assisted and Traditional Drop Jumps on Jumping Performance