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Original Research

Load Absorption Force-Time Characteristics Following the Second Pull of Weightlifting Derivatives

Suchomel, Timothy J.1; Lake, Jason P.2; Comfort, Paul3

Author Information
Journal of Strength and Conditioning Research: June 2017 - Volume 31 - Issue 6 - p 1644-1652
doi: 10.1519/JSC.0000000000001634
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Abstract

Introduction

Implementing weightlifting movements and their derivatives into strength and conditioning programs has become increasingly popular. This is likely the result of the superior training adaptations (strength, vertical jump height, sprint speed, etc.) that result from their inclusion compared with other training methods (10,17,31). Most of the research that has examined weightlifting derivatives has investigated the kinetic and kinematic characteristics of the second pull (2–5,19–21,29,30). This is not surprising given that the second pull phase of the clean and snatch, which is characterized by the triple extension of the hips, knees, and ankles (plantar flexion) and the shrugging of the shoulders, results in the greatest production of force and power (6–8) and transfers to sport tasks with similar joint movements (22). Although this information is important for exercise prescription, less is known about the force-time characteristics after the second pull. If additional benefits could be obtained from weightlifting derivatives in the form of the mechanical demands made after the second pull, indicated by the force-time characteristics, an even stronger case could be made for the inclusion of weightlifting derivatives into resistance training programs of sports or events that do not typically use them.

A purported benefit of weightlifting derivatives that involve the completion of the catch phase is the ability to train the individual to “accept,” “decelerate,” or “absorb” a load (22). Furthermore, although not supported by evidence, some may believe that the catching action may simulate receiving an impact in sports such as American football or rugby. Research by Moolyk et al. (14) examined strategies used to absorb force during a jump landing, a drop landing, a clean (i.e., squat or full clean), and a power clean (i.e., clean caught in a semisquat position). Their results indicated that the clean resulted in more overall joint work compared with the power clean, but it was not different from the drop landing. They concluded that the clean and power clean could be used to train the muscular strength required for impact actions, such as jump landing. Although the previous study examined the load absorption differences between 2 weightlifting movements that involved the catch phase, no research has compared the load absorption phase of weightlifting catching derivatives and weightlifting pulling derivatives that exclude the catch phase.

Previous research has indicated that the weightlifting pulling derivatives that omit the catch phase may produce similar (i.e., small-moderate effect sizes) (2,3) or superior (i.e., large-very large effect sizes) (27,29,30) force and power characteristics compared with weightlifting catching derivatives. Moreover, several weightlifting pulling derivatives may allow an individual to train with loads that are greater than the maximum weight lifted during a catching derivative (4,5,9,12), which may emphasize force production. As a result, practitioners may consider implementing weightlifting pulling derivatives as a substitute to the clean or snatch or as an additional exercise to train triple extension (22,26). Because of the potential training benefits of weightlifting pulling derivatives during the concentric phase (i.e., force production and external power characteristics) (2,3,27,29,30), further research is needed to examine their force-time characteristics after the second pull to determine if they provide an eccentric loading stimulus similar to traditional weightlifting exercises. Previous research that examined post–second pull force-time characteristics of the jump shrug (JS) indicated that landing forces decreased as the external load increased (28). Although this information is beneficial to practitioners who may question the mechanical consequences of the JS landing, further research is needed to understand force-time characteristics after the second pull of the JS and other weightlifting catching and pulling derivatives. Comparisons of the load absorption force-time characteristics after the second pull of weightlifting catching and pulling derivatives may be beneficial from a programming standpoint for those interested in implementing weightlifting derivatives to train both the concentric and eccentric phases of the lift. Therefore, the purpose of this study was to compare the load absorption force-time characteristics of the hang power clean (HPC) catch phase, JS landing phase, and hang high pull (HHP) landing phase. It was hypothesized that the JS would produce the greatest load absorption demands as a result of the landing characteristics associated with the exercise (28).

Methods

Experimental Approach to the Problem

A repeated measures design was used to compare the load absorption force-time characteristics after the second pull phase of the HPC, JS, and HHP. Subjects performed sets of the HPC, JS, and HHP with 30, 45, 65, and 80% of their 1-repetition maximum (1RM) HPC. Load absorption phase work, mean force, and duration were calculated from the force-time data and were compared to quantify between-exercise differences. The work performed during the load absorption phase was studied to establish the effect that exercise and load had on the absorption of potential energy during the loading phase after the second pull of each movement. Mean force during the load absorption phase was examined as opposed to peak force to provide a greater understanding of the magnitude of force produced over the duration of the loading phase of each weightlifting derivative. Finally, load absorption duration was studied to examine the length of time over which force was produced to decelerate the system center of mass during each weightlifting derivative.

Subjects

Twelve resistance-trained men participated in this study (age, 21.4 ± 1.2 years; height, 180.3 ± 6.2 cm; body mass, 83.2 ± 8.4 kg; 1RM HPC, 108.5 ± 14.6 kg; relative 1RM HPC, 1.3 ± 0.2 kg·kg−1). All of the subjects participated in the National Collegiate Athletic Association Division III track and field (short sprints, jumps, or throws) or collegiate club or intramural sports and had at least 2 years of training experience with weightlifting derivatives. Each subject read and signed a written informed consent form. The current study was approved by the Institutional Review Board at the University of Wisconsin-La Crosse. Twelve subjects were recruited based on an a priori power analysis that indicated that 12–14 subjects would be needed to establish a moderate effect (Cohen's d = 0.60) (11) at a statistical power level of 0.80.

Procedures

All subjects attended 4 sessions that included a 1RM testing and practice session and 3 subsequent exercise testing sessions. Each session was performed at the same time of day (2–7 days apart) with the subjects refraining from physical activity that could affect their performance at least 24 hours before each testing session.

Upon arrival for the 1RM testing and practice session, subjects completed a standardized dynamic warm-up and submaximal HPC sets before making 1RM attempts, following a previously described protocol (20,29). Briefly, subjects attempted progressively heavier loads (minimum 2.5 kg increase) until a failed attempt occurred. The largest successfully lifted load was recorded as each subject's 1RM. All HPC repetitions were performed using previously described technique (20), and repetitions caught in a squat position where the upper thigh of the subject was below parallel to the floor were considered unsuccessful. Following a self-selected rest period, subjects practiced the JS and HHP and were coached on proper technique. Specifically, each subject performed submaximal sets of the JS and HHP using 30% of their 1RM HPC in accordance with previous research (29). All JS and HHP repetitions were completed using the technique previously described by Suchomel et al. (23,24). It should be noted that a 1RM JS and HHP were not performed because no criteria exist on what constitutes a successful 1RM attempt of weightlifting pulling derivatives (25).

The order of the remaining exercise testing sessions was randomized. Before testing, each subject performed the same dynamic warm-up, as previously described, followed by submaximal sets (i.e., 1 set of 3 repetitions with 30 and 50% 1RM HPC) of the exercise that was to be tested during that session (HPC, JS, or HHP). To clarify if the subjects were going to test the JS during that particular testing session, they would perform a set of 3 JS repetitions with 30 and 50% of their 1RM HPC as part of their warm-up before performing testing repetitions. After the warm-up, subjects performed 2 maximal effort repetitions of the testing session exercise with 30, 45, 65, and 80% of their 1RM HPC on a force platform (Kistler, Type 9290AD; Kistler, Winterthur, Switzerland) sampling at 500 Hz with 1 minute of rest between repetitions and 2 minutes between loads. It should be noted that no additional instructions were given to the subjects before or after each repetition regarding their landing technique because extra instruction or feedback may impact the ground reaction forces produced (13,15,16). The order of loads was randomized in an attempt to prevent a fatigue or potentiation order effect during the first testing session. The same randomized order of loads was used during each subsequent testing session with the remaining exercises. Subjects rested for 1 minute between repetitions and 2 minutes between loads.

Data Analyses

Force-time data were exported from Bioware and analyzed using a custom LabVIEW program (Version 10.0; National Instruments, Austin, TX, USA). Force-time data from each repetition were analyzed to obtain load absorption phase work, mean force, and duration after completion of the second pull phase. The transition from pulling to load absorption was represented by 2 distinct force-time curves (Figures 1–3): the most obvious where subjects left the ground (JS and HPC, Figures 1 and 2) and when this occurred a force threshold of 10 N was used to indicate both take off and load absorption in accordance with the previous work by Owen et al. (18). In the event that the subjects did not leave the ground (e.g., HHP), the lowest post–pull force was identified, and the same 10-N threshold used to identify the beginning of load absorption (lowest force + 10 N; Figure 3). The load absorption phase ended when the system (lifter plus bar) center of mass reached its lowest postlanding displacement (Figures 1–3). Acceleration-time data were calculated by dividing net force by system mass, and this was integrated with respect to time using the trapezoid rule to first yield velocity-time data and then again to yield displacement-time data. Mean force was calculated by averaging the force produced over the duration of the load absorption phase. The displacement of the system center of mass was calculated by subtracting the position of the system center of mass at the end of the load absorption phase from its position at the beginning of the phase. Work was then calculated as the product of the mean force and displacement. The load absorption phase work, mean force, and duration of each HPC, JS, and HHP repetition was used to assess trial-to-trial reliability and then averaged for further statistical analyses.

Figure 1.
Figure 1.:
Example hang power clean force-time and displacement-time curves. The shaded area denotes the load absorption phase duration.
Figure 2.
Figure 2.:
Example jump shrug force-time and displacement-time curves. The shaded area denotes the load absorption phase duration.
Figure 3.
Figure 3.:
Example hang high pull force-time and displacement-time curves. The shaded area denotes the load absorption phase duration.

Statistical Analyses

Intraclass correlation coefficients (3, 1) were used to determine the test-retest reliability of load absorption phase work, mean force, and duration based on the recommendations from Weir (33). The normality of the data distribution was tested using the Shapiro-Wilk test. To compare the differences in load absorption phase work, mean force, and duration between the HPC, JS, and HHP, a series of 3 × 4 (exercise × load) repeated measures analyses of variance were used. If the assumption of sphericity was violated, Greenhouse-Geisser adjusted values were reported. When appropriate, post hoc analysis was performed applying the Bonferroni correction. The alpha value was set at ≤0.05 for all statistical measures. Statistical power (c) was calculated for all main effect comparisons. In addition, Cohen's d effect sizes and 95% confidence intervals (CI) were calculated for all pairwise comparisons. Effect sizes were interpreted as trivial, small, moderate, large, very large, and nearly perfect if values were equal to 0.00–0.19, 0.20–0.59, 0.60–1.19, 1.20–1.99, 2.00–3.99, and 4.00 or greater, respectively (11). All statistical analyses were performed using SPSS 22 (IBM, Armonk, NY, USA).

Results

The intraclass correlation coefficient statistics for load absorption phase work, mean force, and duration during the HPC, JS, and HHP are displayed in Table 1.

Table 1.
Table 1.:
Reliability (intraclass correlation coefficients) of load absorption phase variables across exercises and loads.*

Significant exercise (F2,22 = 154.598; p < 0.001; c = 1.00), load (F1.54,16.88 = 17.947; p < 0.001; c = 0.99), and exercise × load interaction (F6,66 = 7.027; p = 0.001; c = 0.97) effects existed for load absorption work. Post hoc analysis revealed that significantly more load-averaged work was performed during the JS (647.3 ± 111.1 J) compared with the HPC (129.9 ± 93.7 J; p < 0.001; d = 5.03; 95% CI, 415.6–619.4) and HHP (448.8 ± 123.4 J; p < 0.001; d = 1.69; 95% CI, 147.5–249.5). In addition, significantly more load-averaged work was performed during the HHP compared with the HPC (p < 0.001; d = 4.81; 95% CI, 229.2–408.7) (Figure 4).

Figure 4.
Figure 4.:
Load absorption work comparison between exercises (A) and loads (B). *Statistically greater than the HPC (p < 0.001). #Statistically greater than the HHP (p < 0.001); a = statistically greater than 30% (p ≤ 0.05); b = statistically greater than 45% (p = 0.033); c = statistically greater than 65% (p = 0.001).

Post hoc analysis revealed that significantly more exercise-averaged work was performed with 80% 1RM (451.5 ± 229.6 J) compared with 30% (366.8 ± 229.1 J; p = 0.001; d = 0.37; 95% CI, 33.9–135.5), 45% (406.0 ± 253.7 J; p = 0.033; d = 0.19; 95% CI, 3.0–88.0), and 65% (410.3 ± 250.0 J; p = 0.001; d = 0.17; 95% CI, 17.1–65.3) 1RM. In addition, the work performed with 65% 1RM was significantly greater than work performed with 30% 1RM (p = 0.035; d = 0.18; 95% CI, 2.6–84.4) but was not different than 45% 1RM (p = 0.011; d = 0.02; 95% CI, −29.6 to 38.1). Finally, the work performed with 45% 1RM was significantly greater than work performed with 30% 1RM (p = 0.001; d = 0.16; 95% CI, 17.6–60.9) (Figure 4).

The HPC, JS, and HHP exercise and load interaction for load absorption work is displayed in Figure 5.

Figure 5.
Figure 5.:
Exercise and load interaction for load absorption work (p = 0.001). 1RM = 1-repetition maximum; HPC = hang power clean; JS = jump shrug; HHP = hang high pull.

Significant exercise (F1.23,13.48 = 89.575; p < 0.001; c = 1.00), load (F1.63,17.97 = 21.734; p < 0.001; c = 1.00), and exercise × load interaction (F6,66 = 7.038; p < 0.001; c = 0.99) effects existed for load absorption mean force. Post hoc analysis revealed that the load-averaged mean force for the JS (2,674.1 ± 420.6 N) was significantly greater compared with the HPC (1,488.1 ± 411.6 N; p < 0.001; d = 2.85; 95% CI, 782.3–1,589.7) and HHP (1,359.6 ± 259.9 N; p < 0.001; d = 3.75; 95% CI, 1,031.1–1,597.9), whereas the HPC and HHP were not significantly different (p = 0.253; d = 0.37; 95% CI, −62.5 to 319.4) (Figure 6).

Figure 6.
Figure 6.:
Load absorption mean force comparison between exercises (A) and loads (B). *Statistically greater than the HPC (p < 0.001). #Statistically greater than the HHP (p < 0.001); a = statistically greater than 30% (p ≤ 0.05); b = statistically greater than 45% (p ≤ 0.05); c = statistically greater than 65% (p = 0.015).

Post hoc analysis revealed that exercise-averaged mean forces with 80% (2,061.6 ± 629.2 N) were significantly larger than mean forces with 30% (1,683.7 ± 747.0 N; p = 0.002; d = 0.55; 95% CI, 144.4–611.44), 45% (1,751.2 ± 731.6 N; p = 0.001; d = 0.45; 95% CI, 124.7–496.0), and 65% (1,865.8 ± 650.1 N; p = 0.015; d = 0.31; 95% CI, 33.8–357.7) 1RM. In addition, mean forces with 65% 1RM were significantly larger than mean forces with 30% (p = 0.015; d = 0.26; 95% CI, 32.2–332.2) and 45% (p = 0.011; d = 0.17; 95% CI, 24.5–204.8) 1RM. Mean forces with 30 and 45% 1RM were not significantly different (p = 0.297; d = 0.09; 95% CI, −30.7 to 165.7) (Figure 6).

The HPC, JS, and HHP exercise and load interaction for load absorption mean force is displayed in Figure 7.

Figure 7.
Figure 7.:
Exercise and load interaction for load absorption mean force (p < 0.001). 1RM = 1-repetition maximum; HPC = hang power clean; JS = jump shrug; HHP = hang high pull.

Significant exercise (F2,22 = 126.694; p < 0.001; c = 1.00) and exercise × load interaction (F3.02,33.24 = 7.901; p < 0.001; c = 0.98) effects existed for load absorption phase duration; however, no significant load main effects existed (F1.78,19.54 = 0.330; p = 0.698; c = 0.093). Post hoc analysis revealed that the load-averaged load absorption duration of the HHP (0.76 ± 0.13 seconds) was significantly longer compared with the HPC (0.27 ± 0.13 seconds; p < 0.001; d = 3.77; 95% CI, 0.35–0.58) and JS (0.22 ± 0.05 seconds; p < 0.001; d = 5.48; 95% CI, 0.43–0.60), whereas the HPC and JS were not significantly different (p = 0.573; d = 0.51; 95% CI, −0.05 to 0.15) (Figure 8).

Figure 8.
Figure 8.:
Load absorption duration comparison between exercises (A) and loads (B). *Statistically greater than the HPC (p < 0.001). #Statistically greater than the JS (p < 0.001).

The HPC, JS, and HHP exercise and load interaction for load absorption duration is displayed in Figure 9.

Figure 9.
Figure 9.:
Exercise and load interaction for load absorption duration (p < 0.001). 1RM = 1-repetition maximum; HPC = hang power clean; JS = jump shrug; HHP = hang high pull.

Discussion

This study compared the load absorption phase work, mean force, and duration differences of the HPC, JS, and HHP across a range of loads. The primary findings included the following: (a) greater load absorption work was performed during the JS compared with the HPC and HHP, whereas greater work was also performed during the HHP compared with the HPC, (b) the JS produced greater load absorption mean forces compared with the HPC and HHP, and (c) the HHP produced a longer load absorption phase duration compared with the HPC and JS.

Because the work completed during the load absorption phase of weightlifting derivatives may improve the capacity of an individual to absorb forces during impact tasks (14), examining the work completed during multiple derivatives may assist the practitioner in making programming decisions. The JS produced the largest magnitude of load absorption work compared with the HPC and HHP, with large practical effects being present. These findings are likely more attributed to the mean forces produced during the JS landing as opposed to the displacement. In contrast, the HHP produced the lowest magnitudes of mean force but still achieved the second highest magnitude of work, resulting in large practical significance when compared with the HPC. However, it should be noted that the barbell is traditionally caught before the barbell has any downward momentum by gravity during the HPC (32). As a result, the downward momentum to be absorbed during the HPC should be smaller than that of the JS and HHP. Our findings may have training implications, especially considering that the JS and HHP have previously been shown to produce superior performance characteristics during the second pull or propulsion phase compared with the HPC (27,29,30). Collectively, it appears that the JS and HHP may benefit both the concentric and eccentric phases of a weightlifting derivative to a similar or greater extent, compared with the HPC. From a loading perspective, the exercise-averaged work during the load absorption phase at 80% 1RM was the largest; however, it should be noted that only trivial-small effects were present between all the loads examined.

The largest load absorption phase mean forces were produced during the JS and were followed, in order, by the HPC and HHP. Large practical effects were present when comparing the JS and both the HPC and HHP, whereas only a small effect existed between the HPC and HHP. The JS is unique compared with the other weightlifting derivatives examined in the current study because it requires the individual to jump as high as possible (24). Although this may enable high force, velocity, and power during the concentric phase (19,29,30), the results of this study suggest that the individual must absorb larger mean forces upon landing. This notion is supported by previous research that indicated that higher jump heights during the JS coincided with larger landing forces (28). Interestingly, the final load absorption phase deceleration position of the JS and HHP mimics the second pull position (i.e., midthigh position), which may enable the individual to effectively absorb forces in the strongest position that is achieved during weightlifting derivatives (6–8). Although a purported benefit of a commonly prescribed weightlifting exercise (i.e., HPC) may be the rapid acceptance of an external load (22), our findings indicate that the JS may produce a greater training stimulus in this regard because of its shorter load absorption duration and larger mean forces. This suggests that the JS demands a greater eccentric rate of force development to decelerate an external load. Combining our findings with previous research, the JS may enable the individual to further develop the magnitude and rate of force production during both the concentric (27,29) and eccentric (28) phases of the lift. However, practitioners should note the training phase in which the JS is implemented because repetitive high-force eccentric loading, such as that produced during landing activities from maximal jumps, has been noted as a mechanism of delayed onset muscle soreness (1). Therefore, it is important to implement the JS, as well as other weightlifting derivatives, in a progressive manner to prevent an excessive volume of eccentric loading during training periods, where the dissipation of accumulated fatigue is important (e.g., competition phase). Regarding the loads examined, the greatest load absorption mean force was present with the highest load (i.e., 80% 1RM). However, it should be noted that the effect sizes that existed between all loads produced trivial-small magnitudes of practical significance, indicating that the external load does not appear to have much of an effect on load absorption mean forces. This is likely because of the interaction between decreased loads and increased displacements. For example, a greater displacement would provide additional time for gravitational acceleration, potentially resulting in a similar force required to decelerate the system mass.

This is the first study that has compared the load absorption phase duration of weightlifting derivatives. Interestingly, the HHP produced the longest load absorption duration compared with the HPC and JS (both large effects). These findings may be the result of the required constraints of each exercise. As opposed to the JS, the HPC and HHP require the elevation of the barbell after the second pull (20,23). Although the barbell elevation is similar between these exercises, it is likely that individuals performing the HPC will only elevate the bar to a height where they can drop under the bar and rack it across their shoulders. In contrast, the HHP requires the individual to finish the movement with the barbell elevated to chest height while the triple extension of the hip, knee, and ankle (plantar flexion) joints is being completed (23). Although this may emphasize the triple extension movement, it creates a larger displacement of the load, and as a result, the individual must spend more time absorbing the external load when it is lowered from its maximum height and the bar returns to the midthigh position. The load absorption duration differences between the HPC and JS were not statistically significant (small effect). This may the result of similar landing techniques as both the HPC and JS require the individual to land in a stiff semisquat position to absorb the load because it either decelerates from its maximum height after the second pull (HPC) or as the center of mass decelerates, it lowers from peak jump height (JS). From a practical standpoint, our findings indicate that the HPC and JS appear to affect the magnitude and duration of landing force the individual is exposed to. In contrast, the HHP may facilitate greater absorption of forces during the load absorption phase compared with the HPC and JS. The latter findings indicate that the HHP may allow an individual to effectively dissipate the magnitude of force experienced after the second pull, potentially leading to a decreased accumulation of stress during multiple sets and repetitions.

A limitation of the current study may be the inclusion of load absorption phase variables only associated with the lifter plus bar system. Although this limitation does not lessen the value of the results of the current study, future research should include the collection and analysis of 3-dimensional kinetic and kinematic data to determine if similar trends exist at the joint level. The information within the current study combined with joint-level measurements may provide a better understanding of the similarities and differences between the load absorption phase of weightlifting catching and pulling derivatives. A second possible limitation to the current study was the exclusion of the lowering phase of the barbell during the HPC. If an athlete is performing multiple HPC repetitions, they must lower the barbell from a racked position across their shoulders to the midthigh position before the subsequent repetition. However, it should be noted that this may also be accomplished by dropping the barbell onto training blocks. Although this may add to the overall work performed by the individual, the focus of the current study was to compare the catch phase of the HPC with the landing phases of the HHP and JS. Additional analyses were outside of the scope of this study.

Practical Applications

Weightlifting pulling derivatives that exclude the catch phase may be used as effective training stimuli to improve force absorption after the second pull. Although a purported benefit of weightlifting catching derivatives is the rapid acceptance of an external load, the results of this study show that the exclusion of the catch does not diminish this effect but rather increases it. The load absorption characteristics of each exercise may dictate what training phase may be the most appropriate. For example, the JS produced the greatest load absorption work and mean forces, while also producing the shortest load absorption phase duration. To prevent excessive eccentric loading from repetitive landing but also effectively benefit from the propulsion characteristics of JS (19,27,29), the JS may be best implemented during a low volume, speed-strength training block. Finally, the external load prescribed does not appear to have much practical significance on the load absorption work, mean forces, or duration characteristics of the HPC, JS, or HHP. Therefore, practitioners may implement a variety of loads to train the load absorption characteristics of their athletes.

Acknowledgments

The results of this study do not constitute endorsement of the product by the authors or the National Strength and Conditioning Association. There is no conflict of interest. There are no professional relationships with companies or manufacturers who will benefit from the results of the present study for each author.

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Keywords:

hang power clean; jump shrug; hang high pull; eccentric loading; catch phase

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