Kilduff, LP - (2007) - Optimal Loading for Peak Power Output During the Hang Power Clean in Professional Rugby Players - By - Kilduff, LP - (2007)

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International Journal ofSporls P hysiology and Performance. 2007:2:260-269© 2007 Human Kinetics. Inc.

Optimal Loading for Peak Power OutputDuring theHang Power Cleanin Professional Rugby Players

Liam P. Kilduff, Huw Bevan, Nick Owen, Mike I.C. K ingsley,Paui Bunce, Mark Bennett, and Dan Cunningham

Purpose: The ability to develop high levels of muscle power is considered an

essential compunenl ot"success in many sporting activities; however, the optimal

load for the development of peak pijwcr during training remains controv ersial. T ^

aim ofthe present study was to determine the optimal load required to observe peak

power output (PPO) during the hang power clean in professional rugby players.

Methods: Twelve professional rugby players performed hang power cleans on a

portable force platform at loads of 30%. 4 0 % . SiWc 6 0 % . 70%, 80*7^. and 90 % of

their predetermined 1 -repetition maximum (I -RM ) in a randomized and balancedorder. Results: Relative load had a significant effect onpower output, with peak

values being obtained at 80% of the subject.s' I -RM (4466 ± 477 W; P< .001).

There was no signiticitnt difference, however, between the power outputs at 50%.

60%, 70% . or 90%^ 1 -RM compared wilh 8 0% I -RM, Peak force wa.s produced al

90% I -RM with relative load having a significant effect on this variable; how ever,

relative load had no eftect on peak rate of force development or velocity during

the hang power clean. Conclusions: The authors conclude thai relative load has

a significant effect on PPO during the hang power clean: Although PPO was

obtained at 80% 1-RM. there was no signiticant difference between the loadsranging from 40% to 90% 1-RM. Individual determination of the optimal load

for PPO is necessary in order to enhance individual training effects.

Key Words: force platform, relative intensity, peak rate of force development,

force-time curve

The ability to develop high levels of musele power is considered an essential

compotient of success in many sport activities. For example. Sleivert and Taingahue'

reported negative correlations between relative peak power output {PPO) during thesplit squiit and 5-m-sprint time (r= -.65) and relative PPO during the traditional





262 Kilduff et al

Subjects

Twelve professional male nigby players (Table 1) from whom written informed

consent hud been obtained volunteered to take part in the present study, whichwas approved by the local ethics committee. Players were recruited on the basisthat they had been engaged in a structured weight-training program for at least 2years before the staii of the study and were able to com plete the hang power cleanwith correct technique as assessed by a qualified strength and conditioning coach.The average resistance-training experience of the present group of subjects was2.5 ± 1.4 years.

Experimental Procedures

Before commencement of the main experimental trial, subjects visited the laboratoryto become familim- with the testing methods and to have their l-RM hang powerclean measured. Forty-eight hours after the familiarization and strength-testingsession, all subjects underwent an additional testing session.

Subjects reported to the laboratory on the morning of testing after havingrefrained from alcohol, caffeine, and strenuous exercise the day before. After themeasurement of each subject's height and weight and a standardized warm-up,subjects performed a maximal-effort hang power clean on a portable force platform

at loads of 30%, 40%. 50%, 60%, 70%. 80%. and 90% of their predetermined1-RM in a randomized and balanced order, with 3 attempts at each load. Verbalencouragement was given to maximize performance.

Strength Testing

Before the start of the strength-testing session, all subjects underwent a standard-ized warm-up com posed of 5 minutes of light-intensity cycling followed by a seriesof dynamic movements with an emphasis on warming up the muscles associatedwith the hang power clean. Subjects then performed 3 warm-up sets of 3 repeti-

tions at approximately 50 % . 60 % . and 70% of their estimated I-RM . After thisthey attempted 1 repetition of a set toad. and. if they were successful, the liftingweight was increased until they could not lift the weight through the full range ofmotion. The hang-pow er-clean technique was carried out as previously d escribed.'^'" Subjects lowered the barbell to the hang position (iust above the knee) and thenwith triple extension of the knee. hip. and ankle lifted the barbell explosively in avertical p lane and caught the bar on Iheir shoulders in a quarter-squat pos ition. All

Table 1 Phy sical C haracteristics of Subjects at Baseline (N = 12)



Peak Power Output in Han g Power Clean 263

subjects had been previously exposed to I-RM te.sting for the hang power clean.A 5-minute rest was imposed between all attempts to allow subjects adequate

time to replenish energy stores. The 1-RM was determined after 3 or 4 attemptsby each subject.

Power Testing

On entering the laboratory for the power-testing session, subjects completed thesame warm-up us on the strength-testing day. After a lO-minute recovery periodtht-y performed maximal-effort hang power cleans on a portable force platform atloads of 30%, 40% , 50% , 60 % . 70% . 80% . and 90 % of their predetermined 1 -RMin a randomized and balanced order, with 3 attempts at each load and a 5-minute

recovery period between loads. The hang power cleans were performed in ihe samemanner as described in the strength-testing section, with subjects been instructedto lift the biu"bell as explosively as possible with correct technique.

Force Platform

A Kistler portable force platform with built-in chiirge amplifier (Type 9286AA,Kistler Instruments Ltd. Farnborough, UK) was used for data collection for theGRF time history during the hang power clean. Throughout the testing the GRF

were sampled at 5{X) Hz, and tlie force platform 's calibration was confirmed beforeand after testing.

Data Analysis

The vertical component of the GRF of a subject performing a hang power cleanwas used in conjunction with the weight of the subject-bar system (the combinedeffect of the subject and the weight of the bar) to calculate the instantaneous power,velocity, and RFD of the subject-bar's center of gravity."' Power was calculatedusing the standard relationship: Power (W) = vertical GRF (N) x vertical velocity

of the center of gravity of the subject-bar system. The velocity of the center ofgravity of the subject-bar system was calculated by numerically integrating thenet vertical GRF (Net vertical GRF = vertical GRF - weight of the subject-barsystem). Numerical integration was performed using the trapezium rule for inter-vals equal to the sample width. The area of a strip, of width equal to the samplewidth, thus represented the impulse during that time interval. Using the relation-ship that impulse equals change in momentum, the strip area was then divided bythe mass of the .subject-bar system to prixluce a value for the change in velocityof the center of gravity of the system. This change in velocity was then added to

the center of gravity's previous velocity to produce a new velocity at time equal tothat particular interval's end time.



264 Kilduff et al

Statistical Analysis

After a test for the normality of distribution, data were expressed as mean ± SD.

Statistical analysis was ciirried oui using a repeated-measures 1-way analysis of

variance (ANOVA) to determine whether there was a significant difference betweenthe relative intensities for peak power (PP ). peak ground-react ion force (PF). peakvelocity of the centerof massof the player plus bar (PV ), and PR FD. When signifi-cant F-valties were observed [P < .05). paired comparisons were used in conjunctionwith Holm's Bonferroni method for control of type I error to determ ine significantdifferences. Effect sizes (ES) are also presented in the Results .section. The levelof significance was set M P< .05 in the present study, and all statistical analyseswere performed using SPSS 13.1 (SPSS Inc. Chicago, III).

Results

Power Output During the Hang Power Clean

Statistical analysis revealed that relative load (% 1-RM) had a significant effect on

power output during the hang power clean {F = 20.56, ES 0.70, P < .00]). Peakvalues for power output during the hang power clean were observed at a relativeload of 80% I -RM in our group of players (Table 2. Figure 1 [Cl). The power outputs

generated during die hang power clean at the relative loads of 50%. 60%. 70%.and 90% 1-RM were not significantly different from tliat at 80% I-RM (Table 2,

Figure I ICI).

Paired comparisons revealed no significant difference between 30% and 40%I -RM in terms of power output during the hang power clean (3246 ± 553 vs3495 ±

669 W, mean ± SD; P= .346), but the power outputs at these 2 relative loads weresignilicantly lower than those at other loads (Table 2. Figure 1 ICl).

Table 2 Performance Characteristics During the Hang Power Cleanat Various Relative Loads

Load

(% 1-

repetitjon

maximum)

30^ '

40%

Velocity (nVs)

1.58 ±0.23

1.50 ± 0.23

Performance Characteristics

Force (N)

2799 .6 ±422.1

2945.5 ± 372.5

Rate of force

development

(N/8)

27.999 ± 11.237

27.741 ±11.190

Power (W)

3246.0 ± 552.8

3494 .7 ±669 .1



A

B

i.73

I

o

oLJ.

iIH

n

PR

2 0 0

1.75

1.50

1.25

1.00

45004000

3500

3000

2500

2000

6000

5000

4000

3000

2Q00

50000

40000

30000

2000C

10000

t t

• • 4

30% 40% 50% 60% 70% 80% 90%



266 Kilduff et al

Velocity During the Hang Power Clean

PV during the hang power clean wu.s observed at the relative load of 5 0 ^ 1-RM,

w it h a P V o f 1.61 ± 0.21 nVs. Statistical analysis generated by the ANOVA revealedthat relative load (% 1-RM) had no significant effect on velocity produced duringthe hang power clean (F = 1.265, ES0.\2,P= .29; Table 2. Figure 11A]).

Force Outpu t and RFD During the Hang Power Clean

The repeated-measures 1-way ANOVA revealed a significant eftect of relative loadon GRF during the hang power clean (F = 28.638. ES 0.76. P < .(M)l). PF wasrecorded at the highest relative load (90% 1-RM) during the hang power clean,

which was not significantly different from the force recorded during the hang pow erclean at 80% 1-RM (Table 2, Figure i|Bl). The force produced during the hangpower clean at 80% and 90% 1-RM was significantly greater, however, than theforce produced at any of the other relative loads (Table 2. Figure I IB]}.

PRFD was also produced during the hang power clean at 90% I -RM , but againthis was nol significantly different from the RFD at any of the other relative loads(F = 0.445, ES 0.05, P = .85; Table 2. Figure 1 [D]).

DiscussionThe primary finding of the present study was that PPO was maximized at 80%1-RM during the hang power clean in our group of professional rugby players.There was no significant difference, however, between the power output at 80%I-RM and the power outputs at 50% , 60% , 70%, and 90%> 1-RM, which indicatesthat the optimal load for PPO is a very individual response (Table 2, Figure \[C]).

To maximize the power output during any exercise there must be a compromisebetween the 2 variables that contribute to power development, namely, force andvelocity. For example, if the external resistance is too high, the velocity of move-

ment will be low, and hence PPO will not be optimized.''' In the current study thiscompromise was achieved at a relative load of 80% I -RM.

This maximal PPO at 80% IRM is slightly higher than that reported byKawamori et al" '(70 % I-RM). Inthe curren tstudy . however, and that by Kawamoriet al"' there was no significant difference between the power output at a range ofloads (50% to 90% 1-RM), which indicates large intraindividual responses tooptimal loading for PPO . It is therefore difficult to determ ine whether these resultsare conflicting. If the interpretation is that they are. some researchers would sug-gest that the strength level of the athletes might have been a confounding factor.For example. Stone et al" reported that the load that maximized PPO was higherduring the squat jump in a group of stronger subjects (40% I -RM) than in their



Peak Power Output in Hang Power Clean 267

132 kg . again showing large variance in strength levels. Acco rding to Stone et al .'^thi.s magnitude of variation would lead to .subjects' attaining their PPO at different

relative loads. This point requires further investigation, however. The test-retestresults (ICCs) for all performance measures in ihe present study were good and inline with previously published values'" for these measures. We are confident thatvariability in the results is attributable primarily to (true) individual variation andnot simply to variability of testing measures.

Further supptirt of our findings comes from the study by Haff et al.̂ " wh oreported that PPO was attained at 8{)''/r I-RM during the hang power clean. In thatstudy, however, the authors only examined the power outputs againsl 3 externalresistances (80% , 90 % , and 100% 1-RM) and failed to present statistical informa-tion on the comparison between the 3 measured relative intensities. Therefore, il

cannot be discounted that PPO might have been attained at a relative load of lessthan 80% 1-RM.

The main finding of the present study will provide athletes with appropriatedirection in the development of peak power during the hang-power-clean exercise.Training at the load that pnxiuces PPO can be effective in improving maximalmuscle power, which in turn can lead to improvem ent in a range of dynam ic perfor-mance v ari ab les /' For exam ple. Kaneko et al-' reported that subjects training at avariety of relative intensities (0%. 30%, 60%, and I0()% maximum isometric force)produced their greatest gains in PPO at the relative intensity equal lo the intensity

at which PPO was produced during ihis elbow-extension exercise (30% ).The results of the current study indicate ihal higher relative loads are required

to generate PPO during the hang power clean than during the more traditionalsquat Jumps (40% to 80% l-RM)"*'^ and ballistic bench press (40% to 70% I-RM).'•**•** The potential factors contributing to Ihese difterences include the typeof muscle action involved, strength level of subjects, and single- versus multiple-joint exercises."'

Subjects in the present study produced PPO of 4554 ± 551 W at 80% 1-RM,which is higher than the PPO reported for Ihe same players during the ballistic

bench press (873 ± 24 W) and squat jum p (4291 ± 84 W; unpublished data). Thi.sfinding supports the work of Stone et al'-* and emphasizes the need to incorporateOlym pic lifts during power training of rugby pla ye rs." In addition, this highlightsthe need to individually determine the optimal load for PPO for all major exerc isesu.sed during training (eg, squat jump.s. bench press).

Peak ground forces increa.sed as a function of load (Table 2), which is in agree-ment with previous studies.^"' In the study by Kawamori et al'^ and in the presentstudy PRFD w as unaffected by relative load, which is in agreement with Ihe findingsof Schmidtbleicher.'' who reported that PRFD is equal for all loads higher than25% of maximum force. Subjects in the present study pr<xluced a PRFD of 287 ±147 N-s'^-kg"' compared with 234.5 ± 95 N s ' - k g ' in the study by Kaw amori etal""; however, direct com parison between the 2 studies is very difficult in terms of



268 Kilduff et al

settings altering the PRFD values, so direct comparison is not necessarily m eaning -ful unless the same titter settings were used. The filter setting used in the study byKawamori et al"' was not stated in their Methods section.

In conclusion, the results from the current study indicate that relative inten-sity had a signiticani ettect un PPO during the hang power clean and ihat peakvalues were obtained in our athletes when they were working aguinst un externalload equivalent to 80% 1 -RM of their hang power clean. There was no significantdifference, however, between the power outputs at the loads ranging from 40% to90% I-RM. which indicates that individual determination of ihe optimal load forPPO is necessary to enhance individual training effects. In addition, because of thevarious physiological dem ands placed on rugby union players during gam es, theyrequire ail Ihe components of strength and power along the strength continuum.

Therefore, players might benefit from training against a variety of training loads,for example, <30% I-RM for speed-strength development and >80% 1-RM forstrength-speed development.

Practical Application

The power output during Olympic-style lifts is greater than the power outputsduring the more traditional squat and bench-press activities, so power-based training

programs should incorporate Olympic lifts and their various derivatives. Trainingat the optimal load for PPO can be beneficia! in improving maximal power outputand athletic performance. It is important that coaches be aware of the optimal loadfor peak power production. This study highlights the large individual responses tothe optimal load for PPO. Individual determination of athletes' optimal load forPPO is required to effectively develop their power-generating capabilities.

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Kilduff, LP - (2007) - Optimal Loading for Peak Power Output During the Hang Power Clean in Professional Rugby Players - By - Kilduff, LP - (2007)