The ability to generate high levels of muscular strength and power are considered important physiological characteristics in many sporting disciplines, with strength and power qualities clearly distinguishing between different levels of athlete performance (16). Elite professional rugby league players have been shown to exhibit significantly greater strength and power output compared with subelite college-aged (2,3) or state-level players (4), while similar differences in strength and power levels also exist across different levels of rugby union players (1). Body mass was shown to increase significantly with age and training experience in these studies, and it appears that these body mass differences underpin some of the strength and power disparity between these groups. However, body mass alone is not responsible, with other muscular and neural adaptations likely to have an impact on strength and power differences with differences in strength and power reported between different levels of college-aged American footballers (9) and elite Australian footballers (AFs) (26), despite no differences existing in body mass.
Australian football is a sport that requires a vast array of physiological qualities, including high levels of strength and power (10,26). Previous investigations show that lower-body power measures have the ability to differentiate between selected and nonselected players in an elite AF environment (26). Selected players produced better scores than nonselected players in all leg extensor power tests, with the differences either statistically significant or having an effect size (ES) of 0.97 or more (26). Lower-body strength and power measures, and the eccentric utilization ratio (EUR), a ratio of countermovement jump (CMJ) to squat jump (SJ) performance, provide valuable information that can be used to track athletic performance in AF (19,21). Longitudinal examination of power performance in AF players shows that with periodized program design, elite AF players continue to increase muscular power and velocity over a 3-year period (21). The increase observed in peak power output and peak velocity over the 3-year period in both CMJ and SJ was significant, with the ESs showing that changes were large in magnitude. McGuigan et al. (21) suggested that the results were both statistically and practically significant; consequently, an understanding of the power characteristics of AF players is important so that power performance can be monitored and improved by coaches and sports scientists working within the sport.
The power characteristics of AF players, particularly at the subelite level have not been extensively studied with further investigation warranted. Therefore, the aim of this investigation was to develop a lower-body power profile of elite and subelite AF players, by measuring jump profile characteristics of AF players competing in the Australian Football League (AFL) and Victorian Football League (VFL). This will provide coaches and sport scientists with important and original information about the power capabilities and training requirements of elite and subelite AF groups.
Experimental Approach to the Problem
Testing in this cross-sectional study took place during the competitive football season, with all players from both groups completing 3 testing sessions over an 8- to 10-week period at similar intervals and during parallel points in the competitive football season. A 1 repetition maximum (1RM) squat was performed to assess maximal lower-body strength, with the results also used to determine individual loads for lower-body power tests. Countermovement jump and SJ were performed at subsequent testing sessions to assess lower-body power performance. The measures obtained were analyzed to assess the power capabilities of AF players and to determine whether there were differences present between elite and subelite AF players at each load of 0, 20, 30, and 40% of 1RM for CMJ and SJ. Given that both elite and subelite players were within the competitive phase of the season, it was important that the study design emphasized efficiency of testing to ensure that any disruptions to normal training were minor, player safety was maximized, recorded data were accurate, and to allow replication of testing for future training and monitoring purposes.
Thirty AFs participated in this research. Eighteen players (21.4 ± 2.5 years, body mass 86.4 ± 7.6 kg, and height 1.87 ± 0.07 m) were classified as elite AFs, as they were contracted to an AFL club as a senior or rookie player. Twelve players (20.4 ± 1.5 years, body mass 82.7 ± 6.5 kg, and height 1.84 ± 0.07 m) were classified as subelite AFs, as they were registered on a VFL club playing list. Institutional board approval was granted for this research and appropriate consent was obtained pursuant to law before the commencement of the investigation.
After familiarization, initial testing required players to undertake a health screening and a 1RM squat test to assess maximum lower-body strength. All players had been involved in at least 6 months of strength training before the study and were familiar with plyometric and power training as part of their regular training for AF. All testing sessions were conducted at similar points in the afternoon, while verbal encouragement and reinforcements were provided to all participants by the same tester to ensure comparable arousal levels were reached during testing. Given the highly applied nature in which the study took place, factors such as hydration, nutritional intake, and prior sleep were unable to be controlled before testing.
Lower-body maximal strength was determined with a 1RM squat test using free weights. Players completed a multiple set warm-up protocol that required the completion of 5 repetitions at 30% of 1RM, 4 repetitions at 50% of 1RM, 3 repetitions at 70% of 1RM and 1 repetition at 90% of 1RM (20). Warm-up loads were individualized based on previous testing results and training history. Once players had completed the warm-up protocol, a 1RM was achieved with players completing 3–5 single maximal lifts until the point where they failed to complete a successful repetition as assessed by the investigators. A lift was successful when the movement was completed through a full range of motion without deviating from proper form, with players required to flex the knees and hips to the point where the thighs were parallel to floor, and then return back to a standing position (25). Loading was increased after each successful lift through player feedback and the experience of the investigators, with a minimum of 3 minutes rest given between each lift.
Countermovement jumps were performed with players starting in a standing position holding a broomstick (unloaded jumps) or barbell (loaded jumps) across the shoulders. Players initiated a downward countermovement to a self-selected depth, before immediately jumping to reach maximum height in an attempt to maximize power output (19). Players completed the SJ by holding a broomstick (unloaded jumps) or barbell (loaded jumps) and descending to a visually monitored knee angle of 90–100°. This position maintained for 3 seconds before players jumped to reach maximal height in an attempt to maximize power output, without any further descending movement (19). Players performed 3 repetitions of CMJ and SJ at each load of 0, 20, 30, and 40% of 1RM squat, with a minimum of 3 minutes rest given between each jump trial. For each jump trial, the best jump was that corresponding to the greatest jump height. Peak power, peak velocity, and peak force corresponded to those recorded during the best jump at each load of 0, 20, 30, and 40% of 1RM.
All jump trials were performed on a force plate (400 Series Force Plate, Fitness Technology, Adelaide, Australia), allowing vertical ground reaction forces to be recorded at a sample rate of 200 Hz and with a linear position transducer (PTA5; Celesco, Chatsworth, CA, USA) attached to a broomstick or barbell held by players to record displacement data, also sampled at 200 Hz. The force plate and linear position transducer were interfaced with computer software (Ballistic Measurement System Version 2011.0.1, Fitness Technology, Adelaide, Australia), and raw data were saved to the laptop hard drive. Raw data were analyzed using the Advanced Jump Analysis Package (AJAP) (TLAD Solutions, Melbourne, Victoria, Australia) which reported maximum power and jump height for each trial (7). Jump height and force values were extracted directly from the raw data using AJAP. Power values were extracted from AJAP and calculated in accordance with previously published research (7). Reliability of this type of testing has been reported elsewhere and has demonstrated that this type of testing produces reliable results (7). Eccentric utilization ratio was then calculated as the ratio of CMJ peak power to SJ peak power and CMJ jump height to SJ jump height for both unloaded and loaded jumps using the results obtained from AJAP (19).
Statistical analyses were performed using SPSS (version 15; SPSS Inc., Chicago, IL, USA). Normality was assessed visually and statistically for all data before analysis, and data were summarized as mean ± SD. In accordance with previous similar research 1-way analysis of variance was used to assess differences between groups at each jump and load (19,26), with significance set at p ≤ 0.05. The magnitude of the differences between groups for each outcome measure was interpreted using ES (6). As per Cohen (6), ES of ≥0.2, ≥0.5, and ≥0.8 were considered small, moderate, and large, respectively.
Maximal lower-body strength, as determined by a 1RM squat was 131.4 ± 18.1 and 121.0 ± 16.7 kg for elite and subelite players, respectively. Maximal lower-body strength was not significantly different between elite and subelite players (p = 0.13).
Peak power for both CMJ and SJ were significantly different between elite and subelite players for all loads except CMJ 20% of 1RM (Table 1 and 2). Squat jump maximal force, peak velocity, and jump height were significantly different between groups for all loads, with the exception of peak velocity at 0 and 30% of 1RM (Table 2). In contrast, CMJ were significantly different between groups for maximal force at 40% of 1RM, peak velocity at 0% of 1RM, and jump height at 20, 30, and 40% 1RM (Table 1).
Eccentric utilization ratio values, as calculated from peak power and jump height measures can be seen in Table 3. The only significant difference existing between groups for EUR occurred at 20% of 1RM when EUR was calculated with peak power measures; with subelite players having a higher EUR in comparison to their elite counterparts (p = 0.04).
In this study, lower-body strength and power of elite AF players was compared with those competing at the subelite level to develop a lower-body power profile for both groups. The primary findings of this investigation were that elite players produced higher power at all loads for SJ and CMJ (large ESs), with the exception of 20% of 1RM, in comparison to subelite players, despite no differences existing in maximal lower-body strength or body mass. This demonstrates that there is an improvement in the power production of AF players as playing level increases from subelite to elite. The contrast in power output between elite and subelite players was more pronounced as jumping loads increased, with these differences even more pronounced when comparing SJ to CMJ.
Elite players producing greater levels of power output in comparison to their subelite counterparts is in agreement with the findings of previous work investigating the physical and performance characteristics of athletes competing across differing levels of competition in football-based team sports (1,4,26). The difference in maximum force and peak power output between elite and subelite players in this study was more pronounced as external load was added to jumps in comparison to measures at 0% of 1RM in both the CMJ and SJ. These results suggest that elite AF players are better equipped to produce force and, consequently, power with greater loads in the CMJ and SJ compared with subelite players. In contrast, examinations of lower-body power output with multiple loading conditions in athletic populations (23,26) have found that the difference in power output between high- and low-ranked athletes did not rise, as the external resistance increased. However, these investigations involved athletes from the same club (26) or institute (23), with athletes taking part in similar training programs regardless of their level of ranking. This was not the case in the present study, where an elite AFL club and their subelite VFL affiliate team trained independently, with strength and power training between groups not equivalent.
Eccentric utilization ratio, a useful method to track change in lower-body power performance in athletes (12,19), was only significantly different between groups at 20% of 1RM when calculated using peak power measures, with subelite players having a higher EUR in comparison to elite players (large ES). Although this may suggest that subelite players are using the stretch shorten cycle as, or more efficiently than elite players, it is important to remember that the EUR simply describes the relationship between CMJ and SJ performance, with different training programs likely to impact the results. This was not controlled for in this study, with both teams continuing their regular training regimes. Previous research has shown EUR measures to be sensitive to different phases of resistance training programs (19), although it has also been theorized that a larger difference between CMJ and SJ performance may be expected in individuals who generate force slowly in comparison to individuals who generate force at a higher rate (5).
Elite players producing greater levels of lower-body power compared with subelite players was not unexpected given the findings of previous investigations (1,4,26). Garstecki et al. (9) speculate that the distinction across differing levels of athletes in team sport may be partly attributed to variances in staff and support personnel, facilities, and the recruitment of players with a high level of physical fitness into the elite environment. In AF, clubs competing in the AFL typically use a team of full-time strength and conditioning and sport science professionals to assist with the physical preparation and development of each senior and rookie player. Conversely, clubs competing in the VFL are typically not as well staffed in the strength and conditioning and sport science areas, meaning strength and power training is likely to be less specific to an individual's needs. It is also worthwhile considering that as coaches have less time to spend with part-time VFL players, more emphasis is likely to be placed on skill, tactical, and conditioning elements of AF, before aspects of strength and power are considered.
The elite players involved in this study regularly perform loaded jump power training, in addition to performing Olympic lifts (and their variations), shown to result in improvements in jump performance and power output (13,24). The subelite players involved in this investigation are prescribed general resistance training programs with a key focus on performing compound strength training exercises to ensure a sufficient strength base exists, with less focus given to power-specific training. The results of the present study suggest that this has been adequate for strength development given that maximal lower-body strength was not significantly different between groups, although it seems that this has been at the expense of power development.
Training programs that include Olympic lifts are thought to not only increase maximal power output but also increase maximal power output against heavy loads (8) and can be effective at improving athletic power capacity (14). Furthermore, load specificity dictates that power output is most pronounced at, and around, the load, which is used when training (15). This may explain why elite players produced more force and power at greater loads for CMJ and SJ compared with subelite players. The wider range of difference in power between elite and subelite groups in SJ, compared with CMJ, could also be partly attributed to the differences in training emphasis between elite and subelite groups. Specifically, the elite players involved in the present study regularly perform concentric only (SJ) movements, as part of their regular strength and power training and, therefore, are better physically prepared to generate higher levels of power during such movements compared with subelite players, as force and power are greatest for tasks that are similar to exercises regularly performed during training (22). These differences in training emphasis between groups may have attributed to the contrast in power output between elite and subelite players. Therefore, it may be of benefit for coaches and scientists to include individualized and sports specific power training in subelite training programs.
That no differences in maximal lower-body strength were found between elite and subelite players, despite significant differences existing in power output, suggests that neuromuscular adaptations may also account for some of the discrepancy seen in power output between elite and subelite players. Training programs with a focus on power development bring about neuromuscular adaptations that lead to improvements in the realization of force generation in a short time frame and, therefore, a high-power output (16,18). The specific mechanisms driving adaptation to regular periodized power training are not clear, with sparse research investigating the responsible mechanisms. It has been theorized that regular performance of Olympic lifts, and ballistic and plyometric exercises elicit changes in neural drive, neural activation rates, and intermuscular coordination (8). These neural adaptations contribute to improvements in the rate of force generation that results in the ability to generate high levels of force in a short length of time, thereby, increasing maximal power production (17).
To what extent these neuromuscular adaptations played in explaining the findings of the present study, if any, cannot be known, as appropriate testing was not conducted to allow the influence or contribution of such adaptations to be determined. Due to availability of elite and subelite playing groups and our primary research question, we did not track the neuromuscular changes as a result of training differences throughout the phases of a season. Despite this, based on previous literature, it is reasonable to speculate that some of these neuromuscular adaptations may be present in the elite players and could potentially account for some of the differences seen in power output between elite and subelite players (11).
Future research may investigate the mechanisms that cause these neuromuscular adaptations to occur to enable a complete understanding of the contribution these changes may make to the difference in power capacity between elite and subelite athletes, as observed in this study and by others (1,4,26). Also, longitudinal research profiling AF players across different levels of competition, including those competing at the elite junior level may provide valuable information to assist in the development and progression of subelite or junior level athletes to the elite level.
This study is the first to profile power across a range of loads for both CMJ and SJ in elite and subelite AF players. The findings show that lower-body power can differentiate between AF players competing at elite and subelite levels. These results provide insight into the strength and power characteristics required to compete in AF at the elite and subelite level, and add to the increasing body of research on the physiological characteristics of AF players.
The findings of this study may be used by coaches and sport scientists who are responsible for developing training programs to improve the strength and power capacity of AF players at the elite and subelite level, whilst also assisting the identification of AF talent from subelite competitions. As lower-body power levels clearly differentiate elite and subelite AF players, emphasis may be placed on improving the power levels of subelite players, particularly those aspiring to reach the elite level. The insight gained from this investigation may help demonstrate the necessity to develop the lower-body power of new draftees, typically recruited from elite junior or subelite competitions.
Given that the differences in training emphasis between groups may have attributed to the contrast in power output between elite and subelite players, particularly at heavier loads and during concentric only movements, coaches and scientists should consider the importance of training specificity when programming to target definitive adaptations in an athlete's power capacity.
At the elite level, coaches and sport scientists should regularly, where possible, continue to conduct strength and power testing, allowing training programs to be as individualized as possible to match the requirements of each training phase and the athlete's weaknesses.
The authors would like to thank the players and staff members of the Carlton Football Club and Northern Bullants Football Club for their assistance in this study, particularly, Steuart Livingstone. The results of the present study do not constitute endorsement by the authors or the NSCA of any product or equipment used to conduct this investigation. There was no external funding provided by any organization to conduct this study.
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Keywords:Copyright © 2013 by the National Strength & Conditioning Association.
countermovement jump; squat jump; eccentric utilization ratio; athletic performance; team sport