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Observation of 4-year Adaptations in Lower Body Maximal Strength and Power Output in Professional Rugby League Players.
J. Aust. Strength Cond. 16(1):3-10. 2008. © ASCA.
Peer Review
OBSERVATION OF 4-YEAR ADAPTATIONS IN LOWER BODY MAXIMAL STRENGTH AND POWER OUTPUT IN PROFESSIONAL RUGBY LEAGUE PLAYERS.
Daniel G. Baker and Robert U. Newton
School of Biomedical and Sports Science
Edith Cowan University
Joondalup, Western Australian
ABSTRACT
The purpose of this investigation was to observe changes in maximal lower body strength and power and shifts in the load-power curve across a 4-year period in experienced resistance trainers. Six young professional rugby league players who regularly performed combined maximal strength and power training were observed across a four-year period (years 1998 to 2002). Lower body strength was assessed by the one repetition maximum full squat (1RM SQ) and maximum-power during jump squats (JS Pmax) with various barbell resistances ranging from 40 to 100 kg (JS P40-100). Across the four-year period significant increases in 1RM SQ strength and JS Pmax occurred, which were strongly correlated (r = 0.96). This data indicates that over the long-term, changes in power are highly related to changes in strength for athletes of this level of resistance training experience. However as the changes in strength and power were only in the order of 12-15% over 4-years, this observation tends to verify a more limited scope for strength and power gains in already experienced, resistance trainers as compared to novice resistance trainers. As all the athletes performed large amounts of conditioning training concurrently with resistance training throughout the 4-year observation, yet still made steady progress in strength and power, it also indicates that a high volume of endurance training does not necessarily prevent such adaptations from being realized from an appropriate concurrent resistance training program.
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Key Words - Jump, Squat, Rugby League, Periodization, Strength, Power, Squat, Jump Squat, Long-term.
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INTRODUCTION
It has been theorized that considerable gaps exist in our understanding of the long-term adaptations to resistance training due to the short term nature of most university based training studies (19, 20, 40). Typically these training studies last 6-12 weeks and consist mainly of college students or athletes with limited resistance training experience serving as subjects (e.g. 16). It has been demonstrated that the effectiveness of one program over another program may take at least 8-weeks to manifest itself (19, 21) limiting the extrapolative value of a number of studies. Furthermore, how the adaptations stemming from these shorter training studies reflect the adaptations that athletes training for many years may experience has been questioned (40).
Finnish researchers have garnered considerable data examining the adaptations resulting from short-term and long-term participation in resistance training. These studies have detailed the effects training and detraining over periods of ranging from 12-weeks (21, 22) in novice resistance trainers, to 6-mths in experienced trainers (23, 24) or even in power athletes self-administering anabolic steroids (2). Furthermore, research into elite athletes in the Finnish national Olympic weightlifting team have detailed only minor or non-significant strength and power changes despite periods of one (25) and two-years (26) of intense resistance training. Overall this considerable amount of data has illustrated the relative ease with which strength may be increased in novices and those with a more limited training history compared to more experienced power athletes. For example, despite performing the same program, experienced power athletes may train twice as long for about half the strength increase exhibited by less well trained athletes (19).
While these studies starkly illustrate the great difficulty that exists in trying to increase strength in elite strength athletes despite multi-year observation periods, less data exists concerning the multi-year adaptations exhibited by other strength-power athletes who perform combined maximal strength and power training as an adjunct to their main sport training. To this date only a few multi-year tracking studies exist that report changes in strength or power in athletes. Hunter et al. (29) reported large increases in strength (> 30%) and power for collegiate basketball players but there was a diminishing degree of strength and power change observed each year across a 4-year period. French et al. (18) reported similar findings for jumping power (> 46%) in women collegiate gymnasts across 3-years. How the findings of these studies relate to larger, more powerful athletes with a greater pre-existing resistance training experience (e.g. rugby league and union players, track and field throwers, wrestlers, judo players) is unclear. Over a multiyear period, would athletes with greater resistance training experience and initial strength levels exhibit minor increases in strength and power as was exhibited by the elite Finnish weightlifters or would they still exhibit large increases in strength and power although with reducing scope similar to the collegiate basketballers and gymnasts?
In light of this question, Baker and Newton (14) recently reported a diminishing scope for changes in upper body maximal strength and power in elite professional rugby league players across a 4-year period. The results for multi-year (e.g. 3- or 4-year) lower body adaptations in strength and power have not been investigated in these types of sport athletes. Accordingly it is not yet known if athletes, already experienced in resistance training and who require a mixed training regimen (e.g. speed, strength, energy system conditioning, sports skill and tactics) would still make large changes in lower body strength and power across multi-year periods or would they exhibit smaller changes, similar to the changes for the more advanced athletes described above.
The purpose of this study is to report and compare the changes in lower body maximum strength and power that occur over a 4-year period for a group of professional rugby league players. Of particular interest is the potential for any increases in strength and power in these already resistance trained athletes and the relation between changes in strength and power.
METHODS
Experimental approach to the problem
The nature of the experimental design was a training observation study. Six strength-power athletes, who were reasonably experienced in combined strength and power training (2-3 years of resistance training at start of observation) were observed and tested for strength and power levels across an experimental period of 4-years. This repeated measures comparative analysis would provide information pertinent to the long-term changes in strength and power output as a result of intense resistance training by strength-power athletes. In particular, the extent and scope of adaptations in strength and power would be observed. The relation between changes in strength and changes in power would also be determined.
Subjects
The subjects were six young professional rugby league players who were recruited to be developed into potential participants in the elite national rugby league competition. All subjects were members of the same club and underwent similar training (relevant to their playing position and individual strength and power levels) for the duration of the observation. All subjects were aware of the methods and nature of the testing and voluntarily participated in the testing sessions, which were a regular part of their testing and conditioning regime. The mean (standard deviation) height, body mass and age of the subjects in 1998 were 184.7 (5.3) cm, 95.8 (9.8) kg and 19.3 (1.0) yrs, respectively. They had all completed at least 3-years of intense strength and power training prior to the initial 1998 testing sessions.
Training
Throughout the four-year period, training for the lower body was conducted on average, twice per week except in "end of season" periods where no training occurred (usually 4-6 weeks per year). The training program was periodized throughout the year with general preparation (usually 4-8 weeks per year), specific preparation (usually 6-10 weeks per year) and in-season competition (usually 24-32 weeks per year) periods. The preparation period usually consisted of two linear periodization phases separated by a two week transition period during the Christmas-New Year period. The general preparation phase contained only exercises and sets and repetitions configurations that developed hypertrophy, basic strength and agonist/antagonist muscle balance. The specific preparation phase contained explosive power development exercises as well as strengthening exercises and sets and repetitions configurations that emphasized maximal strength and power development.
In-season resistance training followed a wave-like periodization progression. The wave-like progression has been described previously (3-5, 7), but briefly it entails repeating two cycles of three weeks with an additional introductory week emphasizing hypertrophy and a concluding week emphasizing peak strength and power (eight weeks in total). The first four week block was geared slightly more towards developing basic strength and hypertrophy with a concomitant decreased volume of power exercises while the second four blocks were geared slightly more towards peaking maximum strength and power with an increased number of power exercises.
With regards to the lower body, within each training week, the first training day was oriented more towards the development of maximal strength using the full squat exercises and heavy resistances. Other exercises that aid strength development (e.g. through hypertrophy, agonist/antagonist muscle balance) as well as some lighter power exercises were also performed upon this day. The second training day within a week was oriented more towards the development of maximal power and other factors that affect power (e.g. acceleration, rapid force development, ballistic speed). The exercises performed on this day typically involved jump squats, power cleans (hang or floor), Dominator (a total body rotational power exercise) and various other exercises deemed appropriate to rugby league players (e.g. lunges, step-ups, plyometrics). This alternating of strength- and power-oriented training days also caused an undulatory pattern (a higher load and lower load-volume day) in the weekly periodization scheme throughout the year. Typically lower body workouts lasted about 50 minutes in the preparation period and 20 minutes in the in-season competition period. Examples of how sets and repetitions were manipulated in different periods and phases are contained in Tables 1 and 2. Weekly and daily examples of training scheduling are contained in Tables 3 and 4.
Table 1 - Typical example of the sets and repetitions periodisation for lower body exercises such as the maximal strength full squat (SQ) and various assistant strength exercises (AS) and maximal power jump squat (JS), power clean from hang (PC) and various assistant power (AP) exercises during the preparation period.
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Gen. Prep.
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Gen. Prep.
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Transition
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Spec. Prep.
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Spec. Prep.
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Test Week
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Exercise
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Wks 1-2
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Wks 3-4
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Wks 5-6
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Wks 7-10
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Wks 11-12
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Wks 13
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Squat
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4 x 10
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4 x 8
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2 x 10
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3 x 5
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3 x 2-3
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Test 1RM
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AS Exercise
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3 x 10
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3 x 8
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2 x 10
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3 x 8-10
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3 x 5-6
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JS & PC
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NA
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NA
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NA
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4 x 5
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4 x 2-4
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1RM PC & JS Pmax
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AP Exercise
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NA
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NA
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NA
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3 x 5-8
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3 x 3-6
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Table 2 - Typical example of the sets and repetitions periodisation for lower body exercises such as the maximal strength full squat (SQ) and various assistant strength exercises (AS) and maximal power jump squat (JS), power clean from hang (PC) and various assistant power (AP) exercises during the in-season competition period.
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Exercise
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Wk 1
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Wk 2
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Wk 3
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Wk 4
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Wk 5
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Wk 6
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Wk 7
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Wk 8
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Squat
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2 x 8
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8, 6
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6, 5
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5, 3
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8, 6
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6, 5
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5, 3
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3, 2
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AS Exercise
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2 x 10
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2 x 8
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2 x 6
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2 x 5
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2 x 8
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2 x 6
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2 x 5
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2 x 5
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JS & PC
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3 x 5
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3 x 5
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5, 4, 3
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4, 3, 2
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3 x 5
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5, 4, 3
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4, 3, 2
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3, 2, 2
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AP Exercise
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3 x 6
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3 x 6
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3 x 5
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3 x 4
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3 x 6
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3 x 5
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3 x 4
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3 x 3
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Table 3 - Typical weekly training plan for the preparation period. No training occurred on week-ends.
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Monday
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Tuesday
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Wednesday
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Thursday
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Friday
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7.00-8.00 am Skills
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7.00-8.00 am Skills
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10-11.00 am. Upper body strength
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10-11.00 am. Lower body strength
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10-11.00 am. Lower body strength
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10-11.00 am. Upper body strength
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5-6.30 pm Running Conditioning & tactics
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12-12.30pm Wrestling conditioning
1.30-2.15 pm Recovery massage
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5-6.30 pm Running Conditioning & tactics
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12-12.30pm Wrestling or upper body conditioning
1.30-2.15 pm Recovery massage or Hot/cold therapy
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5-6.30 pm Running Conditioning & tactics
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Table 4 - Typical weekly training plan for the in-season competition period with a seven day turnaround between games (Sunday to Sunday).
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Sunday
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Monday
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Tuesday
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Wednesday
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Thursday
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Friday
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Saturday
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8.00 am Recovery of pool + stretching
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10-11.45 am
Whole body strength + skills
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9-10.30 am
Skills + recovery
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10-11.45 am
Whole body strength + skills
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Off
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9-10.00 am
Team tactical training
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3. pm Game
+ recovery
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2.00-3.30 pm Conditioning + tactics
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2.00-3.30 pm Conditioning + tactics
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Testing
Testing consisted of maximum lower body strength as assessed by the one repetition maximum full squat (1RM SQ) according to the methods previously outlined described (8, 13). Essentially this entailed the athletes working up to progressively heavier resistances until a 1RM had been achieved. The depth of the squat was defined as top of thigh below parallel, which was visually assessed by an experienced strength and conditioning coach.
Testing of lower body maximum-power (Pmax) was assessed during jump squats (JS) using the Plyometric Power System (PPS, Plyopower Technologies, Lismore, Australia) and the methods previously described (8, 11-13). Jump squats in a Smith machine weight training device such as the PPS result in much higher power outputs than traditionally performed squats making this exercise more suitable for power testing (39). Briefly, the PPS is a device whereby the displacement of the barbell is limited to the vertical plane, as in a "Smith" weight training machine. The linear bearings that are attached to each end of the barbell allow the barbell to slide vertically along two hardened steel shafts with a minimum of friction. A rotary encoder attached to the machine produced pulses indicating the displacement of the barbell. The number of pulses, denoting barbell displacement, and the time of the barbell movement were measured by a counter timer board installed in the computer. The PPS software calculated the average power output of the concentric flight phase of each jump squat based upon the displacement, time and mass data. Each subject performed three repetitions of jump squats with barbell resistances of 40, 60, 80 and 100 kg (JS P40, JS P60, JS P80 and JS P100), with only the highest power output at each resistance recorded. This battery of resistances allowed for generation of a load-power profile or curve (10, 13, 14, 36), similar to what has been done previously (22-26). The
highest power output for and individual from these jump squat sets, irrespective of the resistance, was deemed the JS Pmax for that testing occasion.
Statistical procedures
Means and standard deviations for each dependent variable were calculated using standard [analysis of variance (ANOVA) to determine if any of the test scores in 2002 differed from the base-line scores of 1998. No control group was used as it is not plausible to require elite professional athletes to not train for 4-years to serve as a control group in the traditional sense.
Accordingly the “pre-test” scores serve as “time-based” control. Pearson's product moment correlations were used to determine the strength of relationships between variables. Statistical significance was accepted at an alpha level of p < 0.05. Research on elite athletes is rare and difficult and this study involved only six subjects. For this reason no adjustment of the alpha level was made for multivariate comparisons. This is acknowledged as a necessary limitation.
RESULTS
The results for changes in 1RM SQ and power output during JS are contained in Table 5. The correlations between changes in 1RM SQ and changes in power output with the various barbell resistances are contained in Table 6. Only changes in JS P60 and 80 were statistically significant, although the JS P40 approached significance (p=0.09). The effect size was quite large for the change in JSP40 (E.S. = 0.94) however the low subject numbers precluded sufficient statistical power to achieve criterion significance. There was a significant increase of 3.2% in body mass from 95.8 to 98.8 kg, kg across the 4-year period.
Table 5 - Results for changes in body mass, 1RM SQ and JS Pmax between 1998 and 2002 expressed as mean (standard deviation) with effect size and percentage change 1998 to 2002 total and per annum.
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Body Mass
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1RM SQ Strength
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JS Pmax Power
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JS P40 Power
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JS P60 Power
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JS P80 Power
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JS P100 Power
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1998
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95.8 (9.8)
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160.0
(25.9)
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1805 (222)
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1657 (171)
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1738 (225)
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1758 (271)
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1798 (206)
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2002
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98.8 (9.5)
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182.5 (30.0) *
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2045 (362)*
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1911 (343)*
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2003 (295)*
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1970 (372)*
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1894 (423)
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Effect Size
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0.31
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0.80
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0.80
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0.98
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1.01
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0.66
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0.30
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Total % Change
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3.1%
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14.1%
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13.3%
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15.3%
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15.2%
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12.1%
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5.3%
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% Change/Year
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0.8%/yr
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3.5%/yr
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3.3%/yr
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3.8%/yr
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3.8%/yr
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3.0%/yr
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1.3%/yr
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* denotes significantly different in 2002. + denotes approached significance (p = 0.09)
Table 6 - Relationships between changes in strength and changes in power across the 4-year period. All correlations were significant, p< 0.05.
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% Change 1RM SQ
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Versus
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% Change JS Pmax
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% Change JS P40
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% Change JS P60
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% Change JS P80
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% Change JS P100
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R =
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0.96
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0.93
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0.89
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0.91
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0.83
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DISCUSSION
Initial subject strength/power levels. The initial data from 1998 detailing the strength and power scores are indicative for rugby league players of this age, playing status and level of training (8, 12, 13). Previous research indicated that rugby league players of this age and level of training possessed 1RM SQ and JS Pmax scores of 155.8 kg and 1794 w, respectively (8), which is very similar to the scores possessed by the current group of athletes in 1998. Over a 4-year period these athletes progressed from being sub-elite athletes playing in the second-division state-league into elite players participating in the first division national league. During this time they improved strength and maximum power by an average of 3.5% per year till they attained the strength and power levels indicative of elite young national league participants (8, 13).
Changes in maximum strength. The results of this long-term observation suggest that maximum lower body strength can still be increased in athletes who possess a 2-3 year combined strength-power training history. However there appears to be diminishing degree of positive adaptation with increased training experience. For example, in regards to 1RM SQ, Hakkinen and Komi (22) reported 30-40% increases in 16 weeks in relatively inexperienced resistance trainers, Hunter et al. (28) reported changes of about 32% across 4-years in collegiate basketball players as compared to the 14% increase across 4-years in the present study and 2% across 2-years in elite weightlifters by Hakkinen et al (26). By analysing the degree of strength change, it is clearly observable that with increased strength levels and training experience comes diminished scope for improvement in lower body strength.
Changes in maximum power. The power data provides further support of the concept of diminishing scope for increases in muscular functioning with increased training experience. In the current study changes of about 12-15% across 4-years were reported for the different resistances, except for the JS P100 where only a 4.7% non-significant result occurred. Hakkinen and Komi (23, 24) reported 10-25%+ changes in performance during jump squats with various barbell resistances across 6-months in men accustomed to resistance training compared to the 4% (non-significant) changes in jump squat performance with barbell resistances of up to 140 kg in elite weightlifters across 2-years reported by Hakkinen et al (26) . Again by analysing the average yearly rate of power change and comparing it to the pre-existing strength/power levels of the athletes it is clearly observable that a reduced scope for improvement in lower body power exists with increased resistance training experience.
Changes in load- power curve. Changes in the load-power curve in the present study tended to reflect the nature of training. It has been shown that in experienced resistance trainers different types of resistance training can exert differing effects upon maximal strength and power. For example, studies (23) have illustrated that heavy, strength-oriented training (with resistances of 70-100% 1RM) resulted in large increases in strength and improvements in various speed-strength measures towards the heavier end of the load-power spectrum whereas explosive power training with lighter resistances (10-60% 1RM) results in small changes in 1RM strength but considerably larger changes in speed-strength measures towards the lighter end of the load-power spectrum (24). These findings were further validated by the work of Wilson et al (39) and Moss et al (33).
In the 4-years of training the athletes performed jump squats mainly with resistances of 60-80 kg (approximately 35-50% 1RM SQ), but only once or twice per 8-week cycle with resistances of 100 kg or more. These resistances of 60 to 80 kg were typically the resistances that allowed the athletes to attain JS Pmax and were accordingly believed the most optimal resistances which to be performing maximal-power training (39). The fact that no significant increase in JS P100 occurred perhaps reflects the fact that it was not a resistance used much during JS training and is simply a reflection of the load specific training adaptation previously reported (23, 24). While the percentage change in JS P100 was much less than for the other loads tested, it could be stated that large inter-subject variation in JS P100 can preclude statistical significance being achieved when there are low sample numbers. This is evident in the size of the standard deviation for the subjects' JS P100 data in 2002. However the effect size statistics reveal that the changes with resistance were small (in comparison to the very large effect size changes for Pmax, JS P40 and JS P60 and medium effect size for the JS P80). Based upon the low effect size ratio and lack of statistical change observed in the JS P100 test, it would probably be prudent to include JS with 100 kg or greater more frequently into the training regime in a bid to improve this aspect of power output.
Relationship between changes in strength and changes in power. Of most interest are the results for changes in strength and changes in power output with different barbell resistances detailed in Table 6. While the strong relationship between strength and power has clearly been established before (8-14, 33, 37) and was again in this study (r = 0.86 in 1998 and r = 0.79 in 2002), changes in strength largely accounting for changes in power over long-term periods have been more difficult to substantiate. Over the course of this 4-year observation the relationship between changes in 1RM SQ strength and changes in JS Pmax was extremely high (r = 0.96). Relationships of a similar magnitude were observed between changes in 1RM SQ and changes in JS P40-100 as well. While we recognize the low statistical power of having only six subjects, this data supports previous results that clearly indicate that increases in strength largely account for increases in power in athletes of this caliber. This strong relationship between changes in strength largely accounting for changes in power has also been observed for the upper body for periods ranging from 5-months (r = 0.73, ref. 9 ) to 4-years (r = 0.73, ref. 14) with experienced rugby league players. Due to this agreement in the literature regarding changes in strength apparently under-pinning changes in power across long-time periods in experienced athletes, we feel that this result is valid despite the low statistical power.
Based upon this data, coaches of athletes who need to overcome large external resistances such as the body mass of an opponent (rugby league, rugby union, American football, wrestling, judo, ju jitsu and other mixed martial arts) must stress the development of strength as well as performing the appropriate power exercises. The judicious combination of both strength and power exercises may act to train the neuromuscular system to contract both forcefully and rapidly (6, 14, 35, 37).
Relationship between changes in body mass and changes in strength and power. While it has been shown that changes in body mass or lean body mass are strongly related to increases in maximal strength in males accustomed to resistance training (5), that finding was not confirmed in this research. The correlation between changes in body mass and changes in 1RM SQ and JS Pmax were not significant. It must be assumed that various neural, fibre or other morphological adaptations largely accounted for the changes in 1RM SQ (see ref. 3, 20, 38 for reviews of the area).
Concurrent endurance and resistance training. While not being the primary focus of this observation, it is important to note that despite some current beliefs that strength and power cannot be improved or are severely compromised when a large amount of conditioning and heavy resistance training are performed concurrently (17, 27, 29, 30) the results of this long-term observation emphatically illustrate otherwise. Rugby league players cover distances of a minimum of 5 km to over 10 km in each eighty-minute game (31, 32) and typically distances of 3-10 plus km per session during the preparation period and 2-6 km per conditioning/team training session during the in-season period (unpublished data from GPS monitoring). It has been recently shown that elite national league players can maintain upper-body strength and power throughout a 29-week in-season period containing such running volumes mentioned above as well as resistance training and other training (e.g. sprint/agility, tackling, wrestling) (9). Younger college-aged players can actually increase upper-body strength over a 19-wk in-season despite similar workloads (7, 9). This current observation has shown increased lower-body strength and power by around 14% across four years, despite the large total concurrent workloads. It has been suggested previously that better conditioned athletes and more efficient periodization and sequencing of training may allow athletes to perform concurrent strength and endurance training without significant negative results (1, 9, 14). Detailing exactly what is efficient periodization and sequencing of training is beyond the scope of this manuscript, however the periodization structure for strength can be seen in Tables 1 and 2 while weekly and daily sequencing of training can be seen in Tables 3 and 4.
CONCLUSION
This long-term observation of experienced resistance trainers has illustrated that lower body strength can still be improved in experienced strength-power athletes but that there may be a more limited scope for improvement with increased training experience. Maximum lower body power, because it is strongly related to maximum strength, appears to follow a similar pattern in terms of diminishing increases in power with increased training experience and strength levels. Emerging elite athletes, such as in the current study, appear to rely heavily on increases in maximum strength to account for increases in maximum power. This would not mean that maximum strength training alone will necessarily transfer to increases in maximum power, because statistically many other factors must contribute to the multi-faceted nature of muscular power. Accordingly power exercises, which entail rapid lifting speeds and acceleration throughout the entire range of motion, must also be performed in the training regime.
Coaches need not be overly concerned about the possible negative effects of concurrent strength and endurance training if their athletes are well conditioned, the periodization plan is appropriately designed and sequencing of training allows resistance training before any extensive endurance training in the daily schedule.
REFERENCES
- Abernethy, P.J. Influence of acute endurance activity on isokinetic strength. J. Strength Cond. Res. 7:141-146. 1993.
- Alen, M., Hakkinen, K. and Komi, P. Changes in neuromuscular performance and muscle fiber characteristics of elite power athletes self-administering androgenic and anabolic steroids. Acta Physiol. Scand. 122: 535-544. 1984.
- Baker, D. Periodization of strength training for sports: A review. Strength & Conditioning Coach. 1(3):15-21. 1993.
- Baker, D. Strength training for rugby league. Proceedings of the 1995 Australian Strength and Conditioning Association National Conference and Trade Show. pp 135-155. ASCA, Toowong, QLD, Australia. 1995.
- Baker, D. Effect of a wave-like periodised strength training cycle on maximal strength and lean body mass. Strength & Conditioning Coach 3(3):11-16. 1995.
- Baker D. Selecting the appropriate exercises and loads for speed-strength development. Strength & Conditioning Coach. 3(2):8-16. 1995.
- Baker, D. Applying the in-season periodisation of strength and power training to football. NSCA Journal. 20(2):18-24. 1998.
- Baker, D. Comparison of lower body strength and power between national, state and city level rugby league football players. Strength & Conditioning Coach. 8(4):3-7. 2000.
- Baker, D. The effects of an in-season of concurrent training on the maintenance of maximal strength and power in professional and college-aged rugby league players. J. Strength Cond. Res. 15(2): 172-177. 2001.
- Baker, D. A series of studies on the training of high intensity muscle power in rugby league football players. J. Strength Cond. Res. 15(2): 198-209. 2001.
- Baker, D and S. Nance. The relationship between running speed and measures of strength and power in professional rugby league players. J. Strength Cond. Res. 13(3):230-235. 1999.
- Baker, D. and S. Nance. The relationship between strength and power in professional rugby league players. J. Strength Cond. Res. 13(3):224-229. 2001.
- Baker D, S. Nance and M. Moore. The load that maximises the average mechanical power output during jump squats in power-trained athletes J. Strength Cond. Res. 15(1):92-97. 2001.
- Baker, D. and R. U. Newton. Adaptations in upper body maximal strength and power output resulting from long-term resistance training in experienced strength-power athletes. J. Strength Cond. Res. 20(3):541-546. 2006.
- Balyi, I. and A. Hamilton. The concept of long-term athlete development. Strength & Conditioning Coach. 3(2): 3-4, 1995.
- Berger, R. Effect of Varied Weight Training Programs on Strength. Res. Q. 33:168-181. 1962.
- dos Remedios, K. A., R. L. dos Remedios, S. F. Loy, G. J. Holland, W. J. Vincent, L. M. Conley and M. Hing. Physiological and field test performance changes of community college football players over a season. J. Strength Cond. Res. 9(4):211-215. 1995.
- French, D. N., A.L. Gomez, J.S. Volek, M.R. Rubin, N.A. Ratamess, M.J. Sharman, L.A. Gotshalk, W.J. Sebastianelli, m. Putukian, R.U. Newton, K. Hakkinen, J.S. Fleck and W.J. Kraemer. Longitudinal tracking of muscular power changes in NCAA Division 1 collegiate women gymnasts. J. Strength Cond. Res. 18(1):101-107. 2004.
- Hakkinen, K. Factors influencing trainability of muscular strength during short term and prolonged training. NSCA Journal. 2: 32-37. 1985.
- Hakkinen, K. Neuromuscular and hormonal adaptations during strength and power training. A review. J. Sports Med. 29: 9-26. 1989.
- Hakkinen, K. & Komi, P.V. Effect of different combined concentric and eccentric muscle work regimens on maximal strength development. J. Hum. Move. Stu. 7: 33-44. 1981.
- Hakkinen, K. & Komi, P.V. Electromyographic changes during strength training and detraining. Med. Sci. Sports Exerc. 15: 455-460. 1983.
- Hakkinen, K. & Komi, P.V. Changes in electrical and mechanical behaviour of leg extensor muscles during heavy resistance strength training. Scand. J. Sports Sci. 7(2):55-64. 1985.
- Hakkinen, K. & Komi, P.V. Effect of explosive strength training on electromyographic and force production characteristics of leg extensor muscles during concentric and various stretch-shortening cycle exercises. Scand. J. Sports Sci. 7(2): 65-76. 1985.
- Hakkinen, K., Komi, P.V., Alen, M. and Kauhanen, H.. EMG, muscle fiber and force production characteristics during a one year training period in elite weightlifters. Eur. Jour. Appl. Physiol. 56:419-427. 1987.
- Hakkinen, K., Pakarinen, A., Alen, M., Kauhanen, H. and Komi, P. Neuromuscular and hormonal adaptations in athletes to strength training in two years. J. Appl. Physiol. 65(6):2406-2412. 1988.
- Hickson, R. Interference of strength development by simultaneously training for strength and endurance. Eur. J. Appl. Physiol. 45:255-263. 1980.
- Hunter, G., Demment, R and Miller, D. Development of strength and maximum oxygen uptake during simultaneously training for strength and endurance. J Sports Med. Phys. Fit. 27:269-275. 1987.
- Hunter, G.R., J. Hilyer, and M.A. Forster. Changes in fitness during 4-years of intercollegiate basketball. J. Strength Cond. Res. 7(1):26-29. 1993.
- Legg, D & Burnham, R. In-season shoulder abduction strength changes in football players. J. Strength Cond. Res. 13(4):4381-383. 1999.
- Meir, R., D. Arthur and M. Forrest. Time and motion analysis of professional rugby league: A case study. Strength & Conditioning Coach. 1(3):24-29. 1993.
- Meir, R., Colla, P and C. Milligan. Impact of the 10-meter rule change on professional rugby league: Implications for training. Strength Condit. J. 23(6):42-46. 2001.
- Moss, B. M., P. E. Refsnes, A. Abildaard, K. Nicolaysen and J. Jensen. Effects of maximal effort strength training with different loads on dynamic strength, cross-sectional area, load-power and load-velocity relationships. Eur. J. Appl. Physiol. 75:193-199. 1997.
- Nelson, A.G., D.A. Arnall, S.F. Loy, L.J. Silvester and R.K. Conlee. Consequences of combining strength and endurance training regimens. Phys. Ther. 70:287-294. 1990.
- Newton, R., and Kraemer, W. Developing explosive muscular power: Implications for a mixed methods training strategy. Strength Condit. J. October:20-31. 1994.
- Newton, R., A. Murphy, B. Humphries, G. Wilson, W. Kraemer and K. Hakkinen. Influence of load and stretch shortening cycle on the kinematics, kinetics and muscle activation that occurs during explosive bench press throws. Eur. J. Appl. Physiol. 75(4). 333-342. 1994.
- Stone, M.H, H.S. O'Bryant, L. McCoy, R. Coglianese, M. Lehmkuhl, and B. Schilling. Power and maximum strength relationships during performance of dynamic and static weighted jumps. J. Strength Cond. Res. 17(1): 140-147. 2003.
- Tidow, G. Muscular adaptations induced by training and de-training - a review of biopsy studies. New Studies in Athletics. 10(2):47-56. 1995.
- Wilson, G., R. Newton, A. Murphy and B. Humphries. The optimal training load for the development of dynamic athletic performance. Med. Sci. Sports Exerc. 23:1279-1286. 1993.
- Wilks, R. Limitations in applied strength training research: Current dilemmas and recommendations for future studies. Strength & Conditioning Coach. 3(2):17-21. 1995.