The effects of an accentuated eccentric load drop jump training program on neuromuscular performance

A case study investigating the effects of anaccentuated eccentric load drop jump trainingprogram on strength, power, speed and change ofdirectionLee A. Bridgeman 1, Michael R. McGuigan 2, and Nicholas D. Gill 3 4

1Department of Sport and Exercise Science, Solent University, Southampton, England,2Sports Performance Research Institute New Zealand, Auckland University of Technology,

Auckland,3New Zealand Rugby Union, Wellington, New Zealand, and 4Adams Centre for High Performance, Faculty of Health, Spirt and Human Performance, University of

Waikato, Tauranga, New Zealand

Case Study | Drop Jump | Accentuated Eccentric Load

Headline

Previously it has been reported that the use of drop jumps(DJs) improves sprint (1-3), agility (4), 2.4 km time trial

(2), jumping (2, 5-8), throwing (9) performance and acute1RM back squat strength (10). A method which can increasethe intensity of a DJ is the addition of load during the eccen-tric portion of the exercise only, termed accentuated eccen-tric loading (AEL) (11). Previously Bridgeman et al. (12)reported that 5 DJs with an AEL of 20% body mass (BM) re-sulted in acute enhancements in subsequent countermovementjump (CMJ) jump height and peak power (PP). However, todate, no one has investigated the use of an AEL DJ as part ofa longer-term training programme.

AimThis case study aimed to investigate the effects of a four-weektraining block of AEL DJ training on strength, jump perfor-mance, speed and change of direction (COD) performance.

MethodsAthletes.Eight strength-trained male academy rugby unionathletes (mean ± SD; age: 18.7 ± 1.0 years; height: 180.5± 5.9 cm; mass: 92.7 ± 10.7 kg; 1RM squat relative to BW= 1.65 ± 0.24) volunteered to participate in this study. Allsubjects provided written informed consent and the Auck-land University of Technology Ethics Committee approved thisstudy.

DesignSpeed and Change of Direction Assessment. Subjects initiallycompleted a dynamic warm-up followed by three maximal 30msprints. SWIFT Speedlight gates (Speed Light V2 gate, Swift,Wacoi, QLD, Australia) were set up at the start line and at 10and 30m to capture timing splits. The mean times for the 10mand 30m splits were then calculated. After five minutes, thesubjects then completed four 5-0-5 runs in a randomised or-der as described previously (13). The mean times for each legwere calculated, and the fastest COD leg was used for furtheranalysis.

Jump and Strength Assessment (48 hours later).After awarm-up subjects completed three CMJ and three squatjumps (SJ) (15 seconds between jumps, 3 minutes betweenconditions). All jumps were completed utilising the Swift-SpeedMat (Swift, Wacoi, QLD, Australia) the mean jumpheight (cm) was used in further analysis. After a rest period,

subjects completed three DJs from a height of 52cm onto theSwiftSpeedMat (30 seconds between jumps). The variable ofinterest during these DJs was jump height (cm). The meansof the three jumps were used in further analysis. After a finalfive-minute rest period, each subject’s peak force (PF) was as-sessed utilising the Exerbotics squat device using the methoddescribed previously (14).

At the end of testing, all subjects completed AEL DJs witha load of 20% BM (Two sets of eight repetitions). This wasdone to ensure the subjects were familiar with the AEL DJexercise before commencing training.

Training interventionDuring the training intervention, the subjects were randomlyassigned to one of two groups. One group completed resistancetraining with unloaded DJs (n = 3) and the other completedAEL DJs (n = 5). All subjects attended ≥90% of the train-ing sessions during the intervention period. The AEL DJswere completed as usual but when each subject hit the bot-tom position of the CMJ (thighs parallel to the ground) thedumbbells providing the AEL (20% of each subjects BM) werereleased allowing the subjects to complete the concentric phaseof without additional load. This 20% load was based on theprevious finding by Bridgeman et al. (12) that this resulted

Table 1. Group performance variables before and after thetraining interventions

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The effects of an accentuated eccentric load drop jump training program on neuromuscular performance

Table 2. Targets for each subject based on initial pre-intervention testing and test results achieved post intervention high-lighting improvements

Table 3. Individual subjects concentric and eccentric peak force production (N)

in the greatest acute enhancement in CMJ performance. The52cm drop height utilised during the intervention was basedon our previous finding that this resulted in minimal exercise-induced muscle damage with a 20% AEL (15). The trainingintervention is provided here.

Statistical AnalysisDescriptive statistics (mean ± SD) were calculated for all thedependent variables (Table 1). Due to the small number ofsubjects in this study changes in the coefficient of variation(CV) were used to calculate meaningful changes in individualsubjects performances (Table 2) from pre to post intervention(16). This method was chosen as it accounts for the variationbetween trials. Whereas Turner et al (16) propose that usingthe smallest worthwhile change calculation may result in er-rors of measurement being recorded rather than real change.

The following calculation was used to determine targets foreach subject post intervention:

Individual best pre-intervention performance in a test +/-(individual best pre-intervention performance in a test *((overall mean group CV for each test * 2) * 100)).

+ for jump tests and PF tests – for speed tests and CODtests

ResultsGroup Results. Post intervention the AEL DJ group had anincrease of 13.2% and 13.8% in concentric and eccentric PFrespectively. Compared to 9.4% and 7.3% in the unloaded DJgroup. The AEL group had an increase of 13.0% and 14.8%in the CMJ and SJ, respectively. Whilst the unloaded groupshowed an increase of 6.4% and 12.5%. The AEL group hada mean decrease in 10m sprint time of 2.2% compared to a0.5% increase in the unloaded group. When examining the30m sprint the AEL group achieved a 2.0% decrease in timecompared to no mean change in the unloaded group. In the

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The effects of an accentuated eccentric load drop jump training program on neuromuscular performance

COD test, the AEL DJ group had a decrease in test time of5.6% compared to 2.5% in the unloaded group.

Individual Results. Utilising the methods described by Turner(16) meaningful changes were calculated for each individualsubject. These targets and whether the subjects achievedthem are displayed in table 2. The results of each subject’spost intervention PF testing are displayed in table 3.

DiscussionThis case study investigated the effects of a short AEL DJtraining intervention. Improvements in jump performancewere found post intervention in both groups in agreement withstudies which have utilised the DJ as part of a training inter-vention (17, 18). One explanation for the greater jumpingimprovements in the AEL group compared to the unloadedgroup (13% vs 6.4% CMJ and 14.8 vs 12.5% SJ) is that dur-ing the four week training period they were exposed to greatereccentric loads, which resulted in greater enhanced neural ex-citability and selective recruitment of high threshold motorunits (19). This may have resulted in the subjects being ableto utilise these high threshold motor unit to a greater degreepost training and therefore perform better during explosivemovements such as the CMJ. Another possible explanation isthat improved eccentric control and coordination as a result ofexposure to AEL enhanced performance in stretch shorteningcycle (SSC) function by modulating the eccentric phase of themovement during the CMJ (20).

Studies have reported enhancements in DJ performance (DJheight and RSI) after a DJ training intervention (17, 21). Inagreement with these findings, the current study also foundchanges in DJ height post training in both groups and RSIin the AEL group (table 1). Previously Antonio et al. (18)reported that vertical unilateral DJs showed greater improve-ments in vertical jump height and horizontal, unilateral DJsshowed greater enhancements in sprint and COD performance(18). The authors concluded that force orientation should bea key consideration when planning the inclusion of plyometricactivities (18). Although meaningful individual improvementsin the AEL groups speed occurred the magnitude of the over-all groups improvements was small (2.2% and 2% at 10 and30m respectively) in comparison to the improvements seen invertical jump performance. Therefore, it is proposed that fu-ture research may wish to investigate the effects of AEL duringhorizontal-orientated DJs.

Previously Spiteri et al. (22) investigated the relationshipsbetween eccentric strength and COD performance reportinga strong relationship between them. The authors concludedthat the ability to tolerate greater eccentric loads might resultin improved COD performance (22). When examining the re-sults of this current study, the subjects in the AEL group hadthe greatest increases in eccentric PF (13.8% vs 7.3%) andalso the greatest improvement in COD performance. How-ever, it should be noted that the subject in the AEL groupwith the largest individual increase in eccentric PF (27.4%)did not achieve any meaningful change in his COD perfor-mance. Therefore, more research is required to examine the re-lationships between eccentric force production and COD per-formance.

Practical ApplicationsBased on the study findings, it is proposed that the inclu-sion of AEL DJs warrants further investigation. If Strengthand Conditioning coaches wish to incorporate AEL DJs into

a training program starting with a smaller volume (week 1 –four sets of eight repetitions twice a week) before progressingto higher volumes as training progresses (week 4 – four sets of12 repetitions twice a week) is recommended (see appendix).

LimitationsThe authors acknowledge that the sample size in this currentstudy was small. A combination of factors such as injury anddevelopmental players being called up to the first team con-tributed to this small sample size. However, this case studyadds to the literature, as it is the first to investigate the chroniceffects of an AEL DJ program.

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