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Comparisons of Peak Ground Reaction Force and Rate of Force Development During Variations of the Power Clean

Comfort, Paul; Allen, Mark; Graham-Smith, Phillip

Journal of Strength and Conditioning Research: May 2011 - Volume 25 - Issue 5 - p 1235-1239
doi: 10.1519/JSC.0b013e3181d6dc0d
Original Research

Comfort, P, Allen, M, and Graham-Smith, P. Comparisons of peak ground reaction force and rate of force development during variations of the power clean. J Strength Cond Res 25(5): 1235-1239, 2011-The aim of this investigation was to determine the differences in vertical ground reaction forces and rate of force development (RFD) during variations of the power clean. Elite rugby league players (n = 11; age 21 ± 1.63 years; height 181.56 ± 2.61 cm; body mass 93.65 ± 6.84 kg) performed 1 set of 3 repetitions of the power clean, hang-power clean, midthigh power clean, or midthigh clean pull, using 60% of 1-repetition maximum power clean, in a randomized order, while standing on a force platform. Differences in peak vertical ground reaction forces (F z) and instantaneous RFD between lifts were analyzed via 1-way analysis of variance and Bonferroni post hoc analysis. Statistical analysis revealed a significantly (p < 0.001) greater peak F z during the midthigh power clean (2,801.7 ± 195.4 N) and the midthigh clean pull (2,880.2 ± 236.2 N) compared to both the power clean (2,306.24 ± 240.47 N) and the hang-power clean (2,442.9 ± 293.2 N). The midthigh power clean (14,655.8 ± 4,535.1 N·s−1) and the midthigh clean pull (15,320.6 ± 3,533.3 N·s−1) also demonstrated significantly (p < 0.001) greater instantaneous RFD when compared to both the power clean (8,839.7 ± 2,940.4 N·s−1) and the hang-power clean (9,768.9 ± 4,012.4 N·s−1). From the findings of this study, when training to maximize peak F z and RFD the midthigh power clean and midthigh clean pull appear to be the most advantageous variations of the power clean to perform.

Directorate of Sport, Exercise and Physiotherapy, University of Salford, Salford, Greater Manchester, United Kingdom

Address correspondence to Paul Comfort, p.comfort@salford.ac.uk.

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Introduction

Variations of the Clean and Power Clean are commonly incorporated into strength and conditioning programs, using different starting positions (from the floor, hang, and midthigh). The power clean has been shown to increase an athlete's performance by imitating sport-specific movements (rapid extension of the ankle, knee, and hips), while concurrently using explosive power (10). Performance in the hang-power clean has also been shown to be related to both 20-m sprint performance and countermovement jump performance (5).

Most research regarding power characteristics during performances of the clean and its variations has focused on the load that achieves the greatest peak power output (1,2,6-8). Kawamori et al. (7) determined that peak power output, during the midthigh clean pull, has been shown to be achieved at 60% of 1-repetition maximum (1RM) (power clean), although time to peak rate of force development (RFD; 99.8 ± 14.0 milliseconds) was achieved at 30% of 1RM. Time to peak RFD during midthigh clean pulls, at all loads (30, 60, 90, 120% of 1RM Power Clean), was shorter than time to peak RFD in both countermovement jump (263.3 ± 63.5 milliseconds) and vertical jump (194.7 ± 27.0 milliseconds) (7). These findings indicate that midthigh clean pulls may be preferential, over vertical jump activities, when focusing on improving RFD in an athlete.

Previously, Kawamori et al. (6) found that peak power output, during the hang-power clean, is achieved at 70% of 1RM power clean. More recently, however, Kilduff et al. (8) found that peak power output during the hang-power clean was not significantly (p > 0.05) different between loads of 50, 60, 70, 80, or 90% of 1RM power clean. Cormie et al. (1,2) demonstrated that peak power, during power cleans, is achieved at a load of 80% 1RM.

There is little evidence (3,4,9), however, to indicate which technique variations (power clean, hang-power clean, midthigh power clean, midthigh clean pull) may be optimal in the development of power and RFD. The evidence that is available has only determined that the second pull phase of the power clean results in the greatest vertical ground reaction forces (Fz) (3,4,9). However, no research to date has identified which technique variation of the power clean results in the greatest Fz or RFD.

Enoka (3) studied experienced weightlifters' techniques during the pull portion of a clean; findings showed that subjects created a peak ground reaction force (Fz) of 2,471 N during the first pull phase, whereas the second pull phase created a greater peak Fz with an average of 2,809 N. These findings were supported by Häkkinen et al. (4) who found that the second pull displayed the greatest peak Fz at 150% of the system load. More recently, Souzam et al. (10) also found that the second pull phase of the power clean resulted in significantly higher peak Fz compared to the first pull, unweighting and catch phases. However, as aforementioned, no research has compared the force characteristics of the power clean (performed from the floor-Figure 1), the hang-power clean (performed from the knee-Figure 2), the midthigh power clean (performed from midthigh-Figure 3), and the midthigh clean pull (performed from midthigh, without the catch-Figure 3). Therefore, the aim of this study was to compare peak Fz and instantaneous RFD during the power clean, hang-power clean, midthigh power clean, and midthigh clean pull. The findings of this study should aid the Strength and Conditioning Coach in determining which variation of the power clean should be used to achieve the specific goals during different phases of a periodized program. It was hypothesized that the midthigh variations would result in higher peak Fz and instantaneous RFD, because previous research has identified that the second pull phase of a power clean results in the greatest Fz (3,4,9).

Figure 1

Figure 1

Figure 2

Figure 2

Figure 3

Figure 3

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Methods

Experimental Approach to the Problem

This study employed a within-subjects repeated-measures research design, whereby peak Fz and instantaneous RFD were determined during the power clean, hang-power clean, midthigh power clean, and midthigh clean pull. Peak Fz and RFD were measured by the athlete performing all lifts while standing on a force platform (Kistler, Winterthur, Switzerland, Model 9286AA, SN 1209740).

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Subjects

Eleven healthy male elite rugby league players (age 20 ± 1.63 years; height 181.56 ± 2.61 cm; body mass 93.65 ± 6.84 kg) participated in this study. The investigation was approved by the Institutional Review Board, and all subjects provided informed consent before participation. The study conformed to the principles of the World Medical Association's Declaration of Helsinki. Participants had just completed preseason training and were at the end of a power mesocycle. All participants had previously conducted technique sessions to allow familiarization with the specific protocols of each lift.

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Testing

Before testing all subjects performed a standardized dynamic warm-up, including each variation of the power clean (4 repetitions, 3 sets) using a standardized load (40 kg) (Ivanco Olympic bar and weights, San Pedro, CA, USA). Participants were then randomly assigned to perform 1 cluster set of 3 repetitions (30-second rest between repetitions to minimize fatigue) of each exercise, starting with the power clean, hang-power clean, midthigh power clean, or midthigh clean pull. All lifts were performed using a standardized load of 60% of previously determined 1RM power clean, because previous research has demonstrated that this load results in peak power output during midthigh cleans and hang-power cleans (6-8). All lifts were performed with subjects standing on a force plate (Kistler, Model 9286AA, SN 1209740), sampling at 1,000 Hz, interfaced with a laptop. Data were later analyzed using Bioware (Version 3.22; Kistler Instrument Corporation) to determine peak vertical ground reaction force. Instantaneous RFD was determined by dividing the difference in consecutive vertical force readings by the time interval (0.001 seconds) between readings. Data were smoothed using a moving average window of 400 milliseconds.

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Statistical Analyses

Intraclass correlations were performed to determine the reliability of performances between repetitions of each exercise. A 1-way analysis of variance and Bonferroni post hoc analysis were conducted using SPSS (Version 16.0) to determine if there were any significant differences in Fz and RFD, within subjects, between lifts. The alpha level was set to p ≤ 0.05.

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Results

Intraclass correlation for Fz demonstrated high reliability for each of the exercises (r = 0.925, p < 0.001, Power Clean; r = 0.966, p < 0.001, Hang-Power Clean; r = 0.880, p < 0.001, Midthigh Power Clean; r = 0.957, p < 0.001, Midthigh Clean Pull). Similarly intraclass correlations for RFD also showed high reliability for each of the exercises (r = 0.916, p < 0.001, Power Clean; r = 0.947, p < 0.001, Hang-Power Clean; r = 0.926, p < 0.001, Midthigh Power Clean; r = 0.958, p < 0.001, Midthigh Clean Pull).

One-way analysis of variance demonstrated significant differences (p < 0.001) in peak vertical ground reaction forces between variations of the power clean. Bonferroni post hoc analysis revealed a significantly (p <0.001) greater peak Fz during the midthigh power clean (2,801.7 ± 195.4 N) and the midthigh clean pull (2,880.2 ± 236.2 N) compared to both the power clean (2,306.2 ± 240.5 N) and the hang-power clean (2,442.9 ± 293.2 N) (Figure 4).

Figure 4

Figure 4

No significant (p > 0.05) differences were found when comparing the peak Fz between the midthigh power clean (2,801.7 ± 195.4 N) and the midthigh clean pull (2,880.2 ± 236.2 N). The hang-power clean resulted in greater peak Fz (2,442.9 ± 293.2 N) when compared to the power clean (2,306.2 ± 240.5 N) although this was not statistically significant (p >0.05) (Figure 4).

Significant differences (p < 0.001) in instantaneous RFD were found between variations of the power clean. Bonferroni post hoc analysis revealed a significantly (p < 0.001) greater RFD during the midthigh power clean (14,655.8 ± 4,535.1 N·s−1) and the midthigh clean pull (15,320.5 ± 3,533.3 N·s−1) compared to both the power clean (8,839.7 ± 2,940.4 N·s−1) and the hang-power clean (9,768.9 ± 4,012.4 N·s−1) (Figure 5).

Figure 5

Figure 5

No significant (p > 0.05) differences were found when comparing the RFD between either the midthigh power clean (14,655.8 ± 4,535.1 N·s−1) and the midthigh clean pull (15,320.6 ± 3,533.3 N·s−1), and between the hang-power clean (9,768.9 ± 4,012.4 N·s−1) compared to the power clean (8,839.7 ± 2,940.4 N·s−1) (Figure 4).

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Discussion

The results of this study demonstrate significantly (p < 0.001) greater peak Fz during the midthigh power clean (2,801.7 ± 195.4 N) and the midthigh clean pull (2,880.2 ± 236.2 N) compared to both the power clean (2,306.2 ± 240.5 N) and the hang-power clean (2,442.9 ± 2,93.2 N), when performed at a load of 60% 1RM power clean. This is in line with findings from previous research that has demonstrated that the second pull phase of the clean results in greater Fz compared to the other phases of the lift (3,4,10). Fz during the power clean (2,306.2 ± 240.5 N) and midthigh power clean (2,801.7 ± 195.4 N) were also comparable to Fz during the first pull (2,471 N) and second pull (2,809 N) of the clean, respectively, in the study by Enoka (3).

Comparisons of instantaneous RFD demonstrate similar trends across the clean variations, with the midthigh power clean and the midthigh clean pull demonstrating significantly (p < 0.001) greater instantaneous RFD (14,655.8 ± 4,535.1 and 15,320.6 ± 3,533.3 N·s−1, respectively) than both the power clean (8,839.7 ± 2,940.4 N·s−1) and the hang-power clean (9,768.9 ± 4,012.4 N·s−1), when performed at a load of 60% 1RM power clean.

As with the peak Fz results, there were no significant (p > 0.05) differences between the instantaneous RFD of the midthigh power clean (14,655.8 ± 4,535.1 N·s−1) and the midthigh clean pull (15,320.6 ± 3,533.3 N·s−1), or between the hang-power clean (9,768.9 ± 4,012.4 N·s−1) compared to the power clean (8,839.7 ± 2,940.4 N·s−1).

The similarity in peak Fz and the instantaneous RFD between the midthigh power clean and the midthigh clean pull may be explained by the fact that the concentric phases of the lifts are kinematically identical, whereas the hang-power clean and power clean exhibit noticeably different kinematics.

The midthigh power clean and the midthigh clean pull demonstrate both higher Fz and higher instantaneous RFD when compared to the hang-power clean and the power clean. It can therefore be assumed that because of a combination of greater Fz and higher instantaneous RFD that both the midthigh power clean and the midthigh clean pull result in greater peak power outputs when compared to the hang-power clean and the power clean. Furthermore, the lower limb kinematics during both of these exercises, performed from midthigh, replicate the joint angles achieved during the drive phases of both running and jumping activities. It is therefore recommended that when power output is the main goal, midthigh variations of the power clean appear to be advantageous. In contrast, the clean from the floor may be better suited to the general preparation phase of a periodized training plan.

The midthigh variations of the clean may also provide further advantages in terms of improving RFD as Kawamori et al. (7) found that time to peak RFD during midthigh clean pulls, at all loads (30, 60, 90, 120% of 1RM Power Clean) was shorter (Peak at 30% 1RM, 99.8 ± 14.0 milliseconds) than time to peak RFD in both vertical jumps (194.7 ± 27.0 milliseconds) and countermovement jumps (263.3 ± 63.5 milliseconds). These findings and the findings of the present study indicate that midthigh clean variations may be preferential, over vertical jump activities, when focusing on improving RFD in an athlete.

Hori et al. (5) found that performance in the hang-power clean is related to both 20-m sprint performance and countermovement jump performance; however, no research has made such comparisons using the midthigh power clean and midthigh clean pull, both of which may demonstrate a stronger relationship to such performances based on the Fz and instantaneous RFD findings of this study. Furthermore, Weyand et al. (11) found that faster top running speeds are achieved through greater Fz rather than the development of limb speed; therefore, the use of midthigh power clean variations may assist with the development of sprint speed. Research into the relationship between Fz during midthigh power clean variations and top running are recommended.

It is recommended that further research determine if these findings are similar at different loads or if Fz and instantaneous RFD is greater during the hang-power clean and power clean when performed at the loads that have previously been reported to result in peak power output (70 and 80% 1RM, respectively) (1,2,6,8).

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Practical Applications

From the results of the present study, the most advantageous variations of the clean, when training to maximize Fz and RFD, appear to be the midthigh power clean and midthigh clean pull. These 2 clean variations, especially the midthigh clean pull, also offer the practical benefit that both are easier for less experienced athletes to learn and require less technical excellence. It is suggested that when optimal Fz, RFD and power output are the main goal, midthigh variations of the power clean should be used. In contrast, the clean from the floor may be better suited to the general preparation phase of a periodized training plan, when Fz, RFD and peak power output are not the primary focus.

Further research investigating performance in these lifts, ideally incorporated into a training study, and their relationships to sprint and jump performance are also recommended.

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References

1. Cormie, P, McBride, JM, and McCaulley, GO. The influence of body mass on calculation of power during lower-body resistance exercises. J Strength Cond Res 21: 1042-1049, 2007.
2. Cormie, P, McCaulley, GO, Triplett, NT, and McBride, JM. Optimal loading for maximal power output during lower body resistance exercises. Med Sci Sports Exerc 39: 340-349, 2007.
3. Enoka, R. The pull in Olympic weightlifting. Med Sci Sports 11: 131-137, 1979.
4. Häkkinen, K, Kauhanen, H, and Komi, P. Biomechanical changes in the Olympic weightlifting technique of the snatch and the clean and jerk from submaximal to maximal loads. Scand J Sports Sci 6: 57-66, 1984.
5. Hori, N, Newton, RU, Andrews, WA, Kawamori, N, McGuigan, MR, and Nosaka, K. Does performance of hang power clean differentiate performance of jumping, sprinting, and changing of direction? J Strength Cond Res 22: 412-418, 2008.
6. Kawamori, N, Crum, AJ, Blumert, PA, Kulik, JR, Childers, JT, Wood, JA, Stone, MH, and Haff, GG. Influence of different relative intensities on power output during the hang power clean: Identification of the optimal load. J Strength Cond Res 19: 298-708, 2005.
7. Kawamori, N, Rossi, SJ, Justice, BD, Haff, EE, Pistilli, EE, O'Bryant, HS, Stone, MH, and Haff, GG. Peak force and rate of force development during isometric and dynamic mid-thigh clean pulls performed at various intensities. J Strength Cond Res 20: 483-491, 2006.
8. Kilduff, LP, Bevan, H, Owen, N, Kingsley, MIC, Bunce, P, Bennett, M, and Cunningham, D. Optimal loading for peak power output during the hang power clean in professional rugby players. Int J Sports Physiol Perf 2: 260-269, 2007.
9. Souzam, AL, Shimada, SD, and Koontz, A. Ground reaction forces during the power clean. J Strength Cond Res 16: 423-427, 2002.
10. Stone, MH. Explosive exercise and training. Natl Strength Cond Assoc J 15: 7-15, 1993.
11. Weyand, PG, Sternight, DB, Bellizzi, MJ, and Wright, S. Faster top running speeds are achieved with greater ground forces not more rapid leg movements. J Appl Physiol 89: 1991-1999, 2000.
Keywords:

hang power clean; mid-thigh power clean; performance

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