Introduction

The literature that discusses power output and power development for athletes is a wide and varied field. Most of the literature however, will discuss power output and power development for athletes using percentage loads of explosive exercises and appropriate real-world expressions of power, such as the countermovement jump (CMJ). Consequently, this study seeks to examine the factors influencing power output and power development which is displayed in the previous literature. In service of this objective the purpose of this paper is threefold: (1) the paper will identify and justify percentage loads for power training using the CMJ, (2) look at maximal strength and its relationship with power output and development, and (3) discuss the relevance of Olympic-style weightlifting for power development.

Percentage Loads for Power Training

The term power is widely used to describe certain human abilities regarding maximal efforts in certain physical activities and sports. Power can be calculated as the product of force on an object and that object’s velocity in the direction in which the force is exerted, or the product of the object’s velocity and the force on the object in the direction in which the object is traveling (Baechle and Earle, 2008). To put this into an equation, power is equal to work divided by time.

The mechanical power produced during a movement is dependent on the external load (Zatsiorsky and Kraemer, 2006). As proven by Jandacka and Vaverka (2008) the optimum relative load, a percentage of 1RM (one rep maximum) of that exercise where maximum power is developed, varies amongst different exercises. Extensive research has been conducted using a countermovement jump (CMJ) to find percentage loads which are most effective in producing power output in the lower body.

Using a full squat 1RM Baker et al. (2001) focused on finding which percentage loads of the full squat produced maximum power in a CMJ style loaded jump squat. Using this method Baker et al. (2001) found that the load which produced maximal power was 30-40% of 1RM for men and 30-50% of 1RM for women, using the loaded jump squat. Conversely, Cormie et al. (2007) showed that maximum power during a squat jump was obtained with 0% of 1RM (no weight added to the subject), showing that peak power relative to body mass was significantly lower at 27% of 1RM. The view that maximal power during the CMJ is produced using no load is echoed by Harris et al. (2007) using well-trained rugby players and Jandacka and Vaverka (2008) using both males and females.

Jimenez-Reyes et al. (2016) highlights the importance of considering the relative power of a weighted CMJ and its corresponding height when assessing the physical state and athletic performance of elite track and field athletes. This view can allow for a different performance measure in the CMJ or squat jump, looking at height jumped rather than percentage loads. The findings of Jimenez-Reyes et al. (2016) concluded that the maximum power load in elite track and field athletes in a loaded CMJ test was achieved with a load with which the athletes could jump a height of approximately 20cm. Using height as a marker in the loaded CMJ could make monitoring loads for athletes more practical for coaches.

Maximum Strength – Relationship to Power

It has been clearly shown through research that power is a crucial factor associated with athletic performance (Baker and Nance, 1999; Cronin and Hansen, 2005; Baechle and Earle, 2008). Haff and Nimphius (2012) describes power as a mechanical quantity that expresses the rate of which work is executed. Power is also principally reliant on one’s ability to exert the highest force possible, which are their maximal strength capabilities (Cronin and Sleivert, 2005). Therefore, developing maximum strength and power that is sport specific to an athlete in their sport is of vital importance to athletes and coaches. To fulfill an athletes potential and have them peak for competition periodization strategies must be used, developing maximum strength qualities in early phases of training and using that developed maximal strength to produce high levels of power in the peaking phase (Cronin and Sleivert, 2005).

Strength can be expressed with different loads at different speeds, but with increased maximal strength in an athlete, an inverse relationship exists between force and velocity. Force and velocity with relative loads can be displayed using the force-velocity curve (figure 1) which is a continuum, with maximal force on the Y-axis and maximal velocity on the X-axis. In real world practical applications, heavier loads will be moved with a slow velocity and the lighter the loads are, the higher the velocity will be. The importance of this relationship, in relation to power, is that in the middle of the force-velocity curve is where maximal power output is produced (Toji and Kaneko, 2004). To have a positive effect on the force-velocity curve of an untrained individual, increases in maximal strength through resistance training alone will provide an adequate stimulus to positively alter the relationship (Taber et al., 2016).

Figure 1 – Force-Velocity Curve

There are correlations shown in research that maximal strength increases alone, for example in the squat, will elicit development in power production. Østerås et al. (2002) concluded that increased maximal strength after a resistance training period can produce an increased mechanical power output and positively influence the force velocity curve of an athlete. In a study by Chelly et al. (2009) junior soccer players in heavy loads (85–100% of 1-RM) back squat training protocol, which produced significant enhancements in their power related field tests (Sprint Running, Squat Jump, and Five Jump Test performances). Corresponding to the findings of Chelly et al. (2009), Comfort et al. (2012) displayed that improving maximal squat by 17.7% from (170.6 ± 21.4 kg) to (200.8 ± 19.0 kg), resulted in substantial increases in sprint performance over 5m, 10m, and 20m performances.

As discussed by Prue et al. (2010), the stronger the athlete is, the greater advantage they will have in gaining power. On the opposite side of the spectrum, it has been proven that if weaker athletes increase their maximum strength it will result in greater increases in the rate of force development and power than if they were doing only power (Prue et al., 2010). This expresses a close relationship between maximal strength and power. Rate of force development can be seen to be a bridge between strength and power, binding the two together, as the majority of sport specific skills occur in a time frame which does not portray maximal force production (Zatsiorsky and Kraemer, 2006). Moreover, maximal strength is crucial when seeking to develop power in an athlete, while the rate of force development is the application of high forces in sport (Taber et al., 2016).

Olympic-style Weightlifting

Olympic-style weightlifting includes the snatch and the clean and jerk. To be successful in both lifts, besides technique factors, an athlete must have a high level of strength, as well as the ability to produce high power outputs (Helland et al., 2017). High power outputs and rate of force development have been shown in the literature (Helland et al., 2017; McBride et al., 2011). Consequently, Olympic weightlifting exercises and derivatives of those exercises are often used for a range of athletes in different sports to improve lower body muscle power. “Weightlifting training produces many benefits, including: injury prevention, improved flexibility, improved inter- and intramuscular coordination and sharpened psychological abilities” (Newton and Jenkins, 2013). Olympic-style weightlifting has also been shown to be an effective training method to improve vertical jump height of athletes (Hori et al., 2008). Similar effects have been observed of Olympic-style weightlifting and plyometric training on vertical jump improvements showing that both methods are both beneficial, but for maximal results, both should be used (Hackett et al., 2016).

For Sports Performance

One of the most common exercises used in strength and conditioning training for athletes is the power clean and its derivatives, which include starting with the barbell at various positions from the hang or off blocks. These exercises are used because of their similarities to certain sports-specific movements, as the power clean and its derivatives allow for maximal force to be produced over a short period of time, while performing a triple extension of the ankles, knees, and hips (Kelly et al., 2014). Judge et al. (2013) used a general linear model analysis shown in figure 2 and figure 3 which revealed significant linear and quadratic trends in the data for both male and female shot-put athletes when comparing their 1RM power clean to personal best shot-put distances. These results show that there is a significant correlation between 1RM power clean performance and shot-put performance. Within this study by Judge et al. (2013) the power clean showed a stronger correlation related to shot put performance as compared with squat and also with bench press, which is the least related. Using the results of this research, a strength and conditioning program for shot-put athletes should include power exercises such as power cleans, in addition to strength exercises such as the squat and bench press, to optimise performance.

Figure 2: “Scatterplot for Personal Best Throw (m) in the shot put by 1RM Power Clean (kg) for male participants. Dashed line represents quadratic regression, the solid line represents linear regression (linear: p≤0.001, quadratic: p=0.003)” (Judge et al., 2013).

Figure 3: “Scatterplot for Personal Best Throw (m) in the shot put by 1RM Power Clean (kg) for female participants. Dashed line represents quadratic regression, solid line represents linear regression (linear: p≤0.001, quadratic: p≤0.001)” (Judge et al., 2013).

As stated previously the power clean and its derivatives are some of the main Olympic-style weightlifting movements used for power development in athletes. McBride et al. (2011) reported that the highest power output produced in the jump squat was at low loads (0% of bodyweight) whereas the study showed the opposite for power cleans, showing that the highest power output was reached at 90% of 1RM. Athletes training for explosive power should be performing exercises that involve rapid acceleration extended through the entire movement, including triple extension, and weightlifting exercises and their derivates are a perfect match for this need (Kelly et al., 2014).

The results of 29 semi-professional Australian Rules football players 1RM hang power clean performance relative to the body mass in which Hori et al. (2008) collected using can be seen in table 1. Table 2, also from the study by Hori et al. (2008), presents strong correlations between the 1RM power clean, strength and power measurements. In Table 1 we can observe that those who are in the top 50% of 1RM hang power clean display significantly greater scores in other tests compared to the bottom 50% group.

These findings are in line with those in other studies by Judge et al. (2013) and Carlock et al. (2004) who both concluded that participants with higher 1RM in weightlifting exercises were able to jump higher and produce more power output in a vertical plane.

Table 1: Hori et al. (2008). Comparison between the top 50% and bottom 50% in the 1RM hang power clean, p.414.

Table 2: Hori et al. (2008). Relationships between each measurement (Pearson’s r), p.415

When looking to develop power output in an athlete programming and load considerations must be made, for example, one must consider the loads necessary with certain exercises that will appropriately represent specific markers of the force-velocity curve (figure 1) within the speed–strength part of the curve. Research has identified that loads between 70–80% of 1RM provides the suitable optimal load to develop power in weightlifting derivatives, for example, in the power clean (Soriano et al., 2015) and the hang power clean (Soriano et al., 2015; Kawamori et al., 2005). However, within the literature it is shown that there are no significant differences in power output in the power clean and hang power clean from 50 to 90% 1RM (Cormie et al., 2007; Kawamori et al., 2005; Newton and Jenkins, 2013).

Adam Swan – APEC Olympic Weight Lifting Coach

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