The Effects of Tapering on Power-Force-Velocity Profiling and Jump Performance in Professional Rugby League Players

Abstract

de Lacey, J, Brughelli, M, McGuigan, M, Hansen, K, Samozino, P, and Morin, J-B. The effects of tapering on power-force-velocity profiling and jump performance in professional rugby league players. J Strength Cond Res 28(12): 3567–3570, 2014—The purpose of this study was to investigate the effects of a preseason taper on individual power-force-velocity profiles and jump performance in professional National Rugby League players. Seven professional rugby league players performed concentric squat jumps using ascending loads of 25, 50, 75, 100% body mass before and after a 21-day step taper leading into the in-season. Linear force-velocity relationships were derived, and the following variables were obtained: maximum theoretical velocity (V0), maximum theoretical force (F0), and maximum power (Pmax). The players showed likely-to-very likely increases in F0 (effect size [ES] = 0.45) and Pmax (ES = 0.85) from pre to posttaper. Loaded squat jump height also showed likely-to-most likely increases at each load (ES = 0.83–1.04). The 21-day taper was effective at enhancing maximal power output and jump height performance in professional rugby players, possibly as a result of a recovery from fatigue and thus increased strength capability after a prolonged preseason training period. Rugby league strength and conditioning coaches should consider reducing training volume while maintaining intensity and aerobic conditioning (e.g., step taper) leading into the in-season.

Introduction

Rugby league is a collision sport that involves high-intensity bouts of exercise exertion (⁹). Players are required to complete frequent bouts of high-intensity activity (e.g., sprinting and tackling) separated with short bouts of low-intensity activity (e.g., walking and jogging) (^8,9). Because of these activities, players require high levels of muscular strength and power in addition to well-developed aerobic capacity (^9,11). Professional rugby league players typically have a scheduled match every 5–10 days during the in-season, and thus, recovery is an important aspect in reducing an athlete's fatigue that can be accumulated before and throughout the in-season. The season structure typically involves a 4-month preseason, 6-month in-season, and 1 month for the playoffs if the team makes it.

A key element to an athlete's preparation for competition is the taper. A taper is a reduction in training load over a period that allows an athlete to recover from the stress of training. In doing so, performance benefits can be enhanced after a tapering period, such as maximal power, vertical jump, 10- to 40-m sprint times, and isoinertial strength (^4–6). Although these traditional strength and speed measures allow some diagnostic information, they do not incorporate the entire force-velocity spectrum. The force-velocity mechanical capabilities of the neuromuscular system are well described by the inverse force-velocity and parabolic power-velocity relationships when multijoint movement is considered (¹³). Maximum theoretical force (F0) and velocity (V0) are extreme values identified as the x- and y-intercepts of the force-velocity relationship, and the ratio between F0 and V0 determines the individual F-v profile (S_fv). The F-v profile and maximal power (Pmax) have been shown to have independent influences on performance during squat jumping (¹⁶). No previous research has investigated the effect of tapering on force-velocity profiling in addition to performance measures in team sports. Such information is vital for determining the efficacy of tapering in team sports, which could potentially influence individualized programming. Therefore, the purpose of this study was to determine the effects of tapering on power-force-velocity profiling and jump performance.

Methods

Experimental Approach to the Problem

To investigate the effects of tapering on power-force-velocity profiling and loaded squat jump performance in a group of 7 professional rugby league players, all subjects performed loaded squat jumps with 25, 50, 75, and 100% of their body mass (BM) before and after a step taper. The step taper occurred during the final 21 days of a 4-month preseason training period leading into the Australian National Rugby League (NRL) in-season. Jump height was measured for each load, and linear force-velocity profiles were derived. The measures of F0, V0, Pmax, and jump height at each load were compared before and after taper.

Subjects

Seven professional male rugby league players (age, 24 ± 3.6 years; height, 183.0 ± 6.1 cm; weight, 99.0 ± 12.2 kg), including 2 international players, from an NRL club volunteered as participants for this research. Each participant signed an informed consent before participation. The Auckland University of Technology Ethics Committee approved all procedures undertaken in this study (12/159).

Methodology

Athletes attended 1 testing session at the start of the taper and 1 testing session at the end of the taper. During the first testing session, each athlete lay on his or her back for extended leg length measurement. This measurement was made on the right leg from the greater trochanter to the end of the participant's toes, which were pointed toward the floor (i.e., plantar flexed) to simulate the take off position during a squat jump. The participant then stood up and squatted down to a 90° knee angle, which was measured by a goniometer. From this position, a measurement was taken from the greater trochanter to the floor (Hs) and the crease between the glutes and hamstrings to the floor (¹⁴). The second measurement was made to provide the height of the box the athlete would touch before exploding vertically. After a general 5-minute warm-up, the testing protocol consisted of 2, concentric-only squat jumps at 5 different additional loads at a percentage of BM (25, 50, 75, and 100% BM). Jump height was measured with a linear position transducer (GymAware; Kinetic Performance Technology, Canberra, Australia) attached to the barbell sleeve and placed outside the rack, so the wire would be vertical once the athlete stepped back to the box with the barbell across his shoulder. To control the depth of the concentric-only loaded squat jump, a box was placed in the squat rack for the participant to touch before exploding vertically. The height of the box was determined by the measurement taken from the crease between the glutes and hamstrings to the floor while in the 90° knee angle squat position. Once the participants warmed up, they each had 2 body weight concentric-only squat jumps to familiarize themselves with the testing protocol. During each jump throughout the testing, the investigator signaled when to jump after the pause on the box through verbal cueing. This minimized the likelihood of participant jumping too early and using the stretch shorten cycle.

Statistical Analyses

The vertical push-off distance (H_PO) during the squat jump was determined by the difference between Hs and the extended leg length. With only measures of H_PO, jump height (h) and moving mass (BM + additional mass), mean force and velocity over the push-off were calculated at each load with the following equations (¹⁴):

Then, linear force-velocity relationships were calculated through least squares regressions, and S_fv was determined as the slope of the force-velocity relationship (¹³). The force-velocity curves were extrapolated to identify F0 and V0 as the x- and y-intercepts on the force-velocity curve (¹⁵). Finally, Pmax was calculated as follows:

Taper

A step taper was used during the final 21 days of a 4-month preseason training period, where the volume of strength training rapidly decreased, whereas intensity remained high and conditioning remained unchanged (¹²). Strength training was performed 3 to 4 times a week averaging approximately 60 minutes a session before the taper. Field sessions were performed 3 to 4 times a week averaging approximately 60 minutes a session. During the taper, strength training was reduced to 1 session per week taking approximately 45 minutes, whereas field sessions remained at pretaper levels. Intensity relative volume (IRV) per session was used to quantify resistance training load and volume during these training phases (¹⁰). The first 7 weeks of the preseason was the strength-hypertrophy phase, where an IRV of 358.4 per week was calculated. During this phase, the athletes typically performed high repetitions (6–15 repetitions) with moderate loads (65–83% 1RM). The following 6 weeks were a strength-power phase, where an IRV of 156.87 per week was calculated. During this phase, athletes typically performed moderate repetitions (3–6 repetitions) with moderate to heavy loads (80–95% 1RM). The 3-week taper leading into the season had an IRV of 40.8 per week, which is shown in Table 1.

Table 1: Resistance training program used during the taper period.*

Statistical Analyses

For practical significance and because of the small sample of professional rugby league players, magnitude-based inferences were determined with a modified statistical Excel spreadsheet (⁷). Effect size and 90% confidence limits were calculated to compare the difference between pre and postmeans. The value 0.2 was prespecified as the smallest worthwhile difference (SWD) for between-subject SDs. Threshold values of 0.2, 0.6, 1.2, 2.0, and 4.0 were used to represent small, moderate, large, very large, and extremely large effects. Probabilities that differences were higher, lower, or similar to the SWD were evaluated qualitatively as follows: ≤1%, almost certainly not; >1–5%, very unlikely; >5–25%, unlikely; >25–75%, possible; >75–95%, likely; >95–99%, very likely; and >99%, most likely. If the chance of both higher and lower values was >5%, the true difference was assessed as unclear.

Results

F0, V0, Pmax, and jump performance at each load before and after taper are presented in Table 2. F0 had a likely small increase from pre- to posttaper, although any improvements in V0 and S_fv were unclear. Pmax and 4 jump heights at 25, 50, 75, and 100% BM showed likely-to-most likely moderate increases from pre- to posttaper.

Table 2: Mechanical and performance variables of professional rugby league players pre- and posttaper.*

Discussion

An interesting observation from the present findings was that V0 was not enhanced while F0 was likely to increase after the taper. S_fv became slightly more negative from pre to posttaper, which shows the slope of the force-velocity profile moving in the direction toward force capabilities, although the change was unclear. It could be speculated that velocity capabilities would change more so than force capabilities, as shown in the study by Anderson et al. (²). The greater change in F0 rather than V0 may have occurred as a result of the short tapering period that was used in the present study. The taper in the present study lasted 21 days, whereas Andersen et al. (²) used a 3-month detraining period. If the taper in the present study was longer, a greater change in V0 may have taken place because of the overshoot phenomenon (^1,2). However, Coutts et al. (⁴) observed similar findings to the present study with their short 7-day taper, where no significant changes were observed with higher-velocity isokinetic strength (5.25 rad·s⁻¹). Thus, velocity capabilities may have improved if the taper had occurred over a longer duration. Furthermore, the training done before the taper was predominantly heavy loaded strength training with a few low and unloaded explosive movements. If velocity was the prominent quality being developed pretaper, we may have observed a greater change in V0.

The initial benefit of increased force production may have been the result of recovery of fatigue from prolonged training. This has been shown by Coutts et al. (⁴) where both isoinertial strength and isokinetic strength at slower velocities (1.05 rad·s⁻¹) significantly increased from pre to post 7-day taper. Furthermore, Elloumi et al. (⁵) reported a total score of fatigue significantly lower during and after their 2-week taper in 16 national level 7-second rugby players compared with 6 weeks of intense training. Previous tapering literatures in rugby and rugby league have used 7-day and 14-day tapers, showing significant increases in performance measures (i.e., 10-m sprint and 5 jump test) (^4,5). This may have been the result of a potential increase in maximal power gained from the tapering period. Coutts et al. (⁴) attributed the increase in strength, power, and endurance to a change in muscle fiber properties: increased anabolism and a decrease in muscle damage. Elloumi et al. (⁵) attributed their performance increases to a reduction in fatigue. The present study also saw improvements in performance that can potentially attribute this to the very likely increase in Pmax. Both the present study and that of Coutts et al. (⁴) used a step taper, whereas Elloumi et al. (⁵) used a progressive taper. Training time decreased by 55% during the 7-day step taper in the study by Coutts et al. (⁴), whereas Elloumi et al. (⁵) had weekly duration of training sessions decrease by 33% over the 2-week taper. The present study decreased weekly repetitions by approximately 80%. The current literature suggests either a step or progressive taper for increasing or maintaining maximal power (³). Both the present study and that of Coutts et al. (⁴) have shown that a step taper is effective at improving performance variables.

A limitation of the present and previous studies was that there was no control group used (^4,5). In addition to this, testing was only performed once pretaper and once posttaper, so long-term effects of the taper were not investigated. Further research should investigate how long these improvements in Pmax last following the taper and how they affect athletic performance (e.g., 1RM strength, repeat sprint ability, sprinting, and jumping). Furthermore, alternative modes of tapering should be considered because they may potentially influence performance variables in a different manner.

Practical Applications

These findings suggest that a 21-day taper is long enough to elicit a positive change in maximal power and performance. Furthermore, it seems that strength training is the driving factor in the change of force, velocity, and power variables where running-based conditioning does not have an adverse effect. This is important to note for strength and conditioning coaches as fitness and conditioning does not have to be sacrificed to see positive changes in maximal power during a taper. Most importantly, during the taper, volume should be reduced, whereas intensity is kept high. From a practical standpoint, future researchers and practitioners should consider investigating individual responses to tapering.

It is still not known the optimal length for a taper in rugby league that produces the greatest change in maximal power. When implementing a step taper where strength training volume is greatly decreased, we suggest starting earlier than the traditional 1-week training load reduction leading into the in-season. This step taper would start 3 weeks before the in-season, and therefore, coaches should consider starting in-season strength training during the last phase of preseason strength training (i.e., 1–2 strength sessions a week while the training intensity and aerobic conditioning levels remain high). This would allow adaptations in maximal power to take place and the athlete's to recover from prolonged training while still improving conditioning specific to the sport. Thus, coaches can implement a step taper to potentially improve Pmax and performance leading into a season while avoiding fatigue and still improving or maintaining aerobic and anaerobic conditioning.