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Research Notes

Transference Effect of Short-Term Optimum Power Load Training on the Punching Impact of Elite Boxers

Loturco, Irineu1; Pereira, Lucas A.1; Kobal, Ronaldo1; Fernandes, Victor1; Reis, Valter P.1; Romano, Felipe2; Alves, Mateus2; Freitas, Tomás T.3; McGuigan, Michael4,5

Author Information
Journal of Strength and Conditioning Research: September 2021 - Volume 35 - Issue 9 - p 2373-2378
doi: 10.1519/JSC.0000000000003165
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Abstract

Introduction

Punching impact is perhaps the most important performance parameter in elite boxing (15,23,32). As a knockout is a frequent goal during a fight, boxers systematically use different training strategies to maximize strength-power capabilities and thus punching impact (5,17,18). A previous study showed that Olympic boxing athletes who are able to produce higher power outputs in bench press (BP) and jump squat (JS) exercises are equally able to produce higher punch forces than their less powerful counterparts (18). Moreover, research has indicated that punching impact force is significantly greater in elite boxers than in intermediate-level boxers, as well as in intermediate level than in novice boxers (33). Therefore, the search for more practical and time-efficient power training approaches remains a challenge for investigations involving elite boxers.

The “optimum power load” (i.e., load that maximizes power output, [OPL]) has recently been shown to be an effective way to improve the physical performance of boxing athletes (17). Loturco et al. (17) reported that a 7-week OPL training program composed of BP and JS exercises performed 2 or 3 times per week could produce substantial increases in power output in Olympic team boxers, during the final phase of preparation for the Olympic games. However, despite the strong associations described between power and punching performance (16,18), to date, we cannot confirm whether meaningful increases in JS and BP power result in meaningful increases in punching impact force. Furthermore, because of the multifaceted aspect of elite boxing training (i.e., diverse and interspersed physical, technical, and tactical workouts), it would be problematic to assume that possible improvements in punching performance are directly related to the OPL intervention (and not to the interaction between many other factors).

In this regard, the transference calculation has been used to estimate the “transfer effect coefficient” (TEC) of gains in the “trained exercise” on the “untrained exercise” (22,38). For example, it was demonstrated that vertical and horizontal jumps (i.e., trained exercises) are able to transfer their specific neuromuscular gains to different speed qualities (i.e., untrained exercises) of soccer players (22). An additional study on TEC revealed that the loaded JS is superior to the Olympic push press exercise for improving speed and power capacities in young soccer players (20). According to Zatsiorsky and Kraemer (38), the TEC must only be used in cases where the athletes are not exposed to the “target ability.” Specifically, in boxing, if the target ability is punching impact force, to properly calculate the TEC on this variable, the boxer cannot be exposed to training practices where punching techniques (e.g., jabs or crosses) are executed. This is certainly a critical question when designing experiments with competitive boxers, who regularly perform several sport-specific activities on a daily basis, such as sparring, bag work, shadow boxing, conditioning training (e.g., circuit training), and technical drills (12,17).

A viable alternative to conduct this type of research with elite boxers would be to implement a short-term longitudinal design (e.g., 1 week) between 2 consecutive training weeks, during the competitive period. This approach would also be important to provide coaches with more accurate information regarding the short-term effects of a power training scheme. It is worth noting that a recent case-study performed with a professional boxer identified progressive decrements in strength, power, and punching performance during a preparation phase leading to a state title bout (12). As such, it would be of great interest to determine the “real” short-term transference effects of certain exercises executed at the optimum power zone on punching impact. The aims of this study were twofold: (a) to examine the changes in BP, JS, and half-squat (HS) power outputs induced by a short-term (1-week) OPL training scheme applied to national boxing athletes, and (b) to measure the TEC of both these exercises on punching impact forces of jabs and crosses.

Methods

Experimental Approach to the Problem

This study aimed to analyze the TEC between the bar-power output and punching performance in elite amateur boxing athletes. Athletes were tested before and after 3 power-oriented training sessions performed at the OPL. A schematic presentation of the study design comprising the training schedule is demonstrated in Figure 1. To properly determine the TEC among bar-power outputs and performance tests, athletes were not involved in any other type of training during the intervention period. The assessments were performed during a regular training week, within the competitive period. Subjects maintained their usual sleep and nutritional habits, which were controlled by the Brazilian National technical staff before both testing sessions (i.e., pre and post). Athletes were not involved in any type of training in the 48 hours before the physical tests performed on day 1. Pre-test and post-test were performed at the same time of the day, between 8 and 10 am.

Figure 1.
Figure 1.:
Schematic presentation of the study design. Bench press, half-squat, and jump squat exercises were all performed at the optimum power loads. No other training sessions were programmed during the interventional week.

The physical assessments comprised punching impact measurements using jabs and crosses at fixed and self-selected distances, and bar-power output in BP, HS, and JS exercises. These punching techniques were selected because they are delivered with the arms in a straight position and parallel to the ground, facilitating measurement with a force plate. In addition, they are the most frequent techniques performed during fights and have the lowest delivery time (24,34). Before performing the tests, athletes completed a 10-minute standardized warm-up, comprising 5-minute running at a moderate pace followed by 5 minutes of active stretching. Before each test, athletes performed submaximal attempts. The same experienced person conducted all testing sessions, and similar verbal motivation was provided throughout the physical measurements.

Subjects

Eight elite boxing athletes from the Brazilian National Team (age: 23.6 ± 2.2 years (±SD; age range: 21–27 years); body mass (BM): 81.8 ± 15.0 kg; stature: 182.1 ± 9.2 cm) participated in this study. Athletes had been involved in World Championships, Pan American, and South American competitions, attesting to their high level of competitiveness. Athletes were assessed during the competitive period and were all previously familiarized with the testing routines due to their constant assessments in our facilities. After being fully informed of the risks and benefits associated with the study, all athletes signed a written informed consent form. The study was approved by the Bandeirante-Anhanguera University Ethics Committee.

Procedures

Punching Impact Measurements

For punching tests, a force plate (1.02 × 0.76 m, AccuPower; AMTI, Graz, Austria) was mounted on the wall at a height of 1 m perpendicular to the floor, allowing the athletes to execute the strokes at a height of between 1.0 and 1.76 m, as described elsewhere (18). The device was covered by a rigid body shield (Jugui, São Paulo, Brazil) to prevent impact injuries to the boxers, who also used their own competition gloves to perform the impact tests (18). A pilot study revealed that the “absorption effect” provided by the body shield on the punching impact measurements was <3% (in comparison with punches performed without the shield). Boxers performed 12 punches on the target (i.e., central area of the body shield), as follows: (a) 3 jabs starting from the standardized position (FJ); (b) 3 crosses starting from the standardized position (FC); (c) 3 jabs starting from a self-selected position (SSJ); and (d) 3 crosses starting from a self-selected position (SSC). This order was fixed based on the athletes' preference and for ease of test administration (as requested by the technical staff). The standardized position was individually established before punching according to the arm length, by measuring the distance from the front foot to the wall that resulted in full extension of the dominant arm after throwing both the jab and the cross. The self-selected position was determined by each boxer to elicit optimal performance, which was also standardized for the preassessment and postassessment. A 15-second and 1-minute resting interval were allowed between attempts in each condition and between conditions, respectively. Verbal motivation was provided to each boxer to elicit maximal impact in every attempt. The peak forces were determined for all trials using a force plate with custom-designed software (AccuPower 3.0; AMTI), which sampled at a rate of 2,000 Hz. The highest impact of each punch mode was retained for analysis.

Bar-Power Outputs in Bench Press, Half-Squat, and Jump Squat Exercises

Maximum bar-power outputs were assessed in BP, JS, and HS, all performed on a Smith machine (Hammer Strength Equipment, Life Fitness, Rosemont, IL). Subjects were instructed to execute 3 repetitions at maximal velocity for each load, starting at 30% of their BM in the BP and 40% of their BM in the HS and JS exercises. For the BP, athletes were instructed to lower the bar in a controlled manner until the barbell lightly touched their chest and then to move the load as fast as possible, without losing contact with the bar. In the JS, subjects executed knee flexion until the thigh was parallel to the ground and, after the command to start, jumped as fast as possible without their shoulders losing contact with the bar. The HS was executed in a similar fashion to the JS, except that the subjects were instructed to move the bar as fast as possible without losing foot contact with the ground, keeping their heels on the floor. In both exercises, a load of 5% of BM for the BP and 10% of BM for the JS and HS was progressively added for each set until a clear decrement in mean power (MP), mean propulsive power (MPP), or peak power (PP) was observed (21). The maximum MPP value was considered as the OPL for all exercises and thus used for the training purposes. A 5-minute rest period was allowed between sets. To determine the power outputs, a linear position transducer (T-Force, Dynamic Measurement System; Ergotech Consulting S.L., Murcia, Spain) was attached to the Smith machine bar, and values were automatically derived by the custom-designed software as follows: MP—value calculated during the entire concentric phase of each repetition; MPP—value calculated during the propulsive phase, defined as that portion of the concentric action during which the measured acceleration is greater than acceleration due to gravity; and PP—the highest bar-power value registered at a particular instant (1 ms) during the concentric phase (29,30). The bar position data were sampled at 1,000 Hz. The maximum MP, MPP, and PP values obtained in each exercise were used for analysis. To account for the differences in the BM of the athletes, values were normalized by dividing the absolute power value by the BM (i.e., relative power = W·kg−1).

Statistical Analyses

All values are reported as mean ± SD. Normality was checked using the Shapiro-Wilk test. To analyze the differences in the physical performance tests comparing preassessment and postassessment, the differences based on magnitudes were calculated (3). This method was chosen in place of traditional null-hypothesis testing methods based on an arbitrary p value as it allows for the emphasis of effect magnitudes and estimate precision, focusing on noneffect interpretation rather than on absolute effect (28). In addition, the “traditional method” does not deal with the real-world significance of an outcome (3), whereas the magnitude-based method defines the practical effect, allowing the researcher to qualify and quantify the probability of a worthwhile effect with inferential descriptors to aid interpretation (28). Although traditional inferential statistics can be misleading, depending on the magnitude of the statistic, error of measurement, and sample size (3), magnitude-based inferences recognize sample variability and provide scientists and professional coaches with an indication of the practical meaningfulness of the outcomes. The quantitative chances of finding higher, similar, or lower values for the variables tested were assessed 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%, almost certain. A meaningful difference was considered using a clinical inference, based on threshold chances of harm and benefit of 0.5 and 25% (3,13). To determine the magnitude of the differences before and after training, effect size (ES) was calculated (6,13). The ES magnitudes were interpreted using the following thresholds: <0.2, 0.2–0.6, 0.6–1.2, 1.2–2.0, 2.0–4.0, and >4.0 for trivial, small, moderate, large, very large, and near perfect, respectively (13). The TEC was calculated as previously described (20,22,38), by the ratio between the result gain (ES) in the untrained exercises (e.g., FJ, SSJ, FC, and SSC) and the result gain in the trained exercises (e.g., HS and JS). The TECs were only calculated for variables presenting an ES of at least 0.2, considered a small ES based on Cohen's principle (6,13). All performance tests used in this research presented good levels of absolute and relative reliability (coefficient of variation <5% and intraclass correlation coefficient >0.90) (13).

Results

Table 1 shows the comparisons of the bar-power outputs between preassessment and postassessment. Possible to very likely increases in all bar-power outputs were observed in the HS and JS. No meaningful changes were observed for the power assessments in the BP. Figure 2 shows the comparisons of the punching impact between pre-test and post-test. Possible increases in the punching impact forces were observed for the 4 distinct punch types assessed (ES [90% confidence limits] = 0.36 [−0.29 to 1.02], 0.38 [−0.32 to 1.09], 0.39 [−0.23 to 1.01], and 0.26 [−0.22 to 0.74], for FJ, SSJ, FC, and SSC, respectively). Figure 3 depicts the TEC between the bar-power outputs in the HS and JS exercises and the punching impact. The JS MPP demonstrated the highest TEC values in the 4 punching techniques analyzed (TEC = 1.60, 1.69, 1.71, and 1.15, for FJ, SSJ, FC, and SSC, respectively). The other TEC values between bar-power outputs and punching impact forces varied between 0.36 and 0.99.

Table 1 - Comparison of the bar-power outputs between preassessment and postassessment.*
Pre Post ES (90% CL) rating
BP MP (W·kg−1) 4.58 ± 0.79 4.65 ± 0.85 0.09 (−0.13 to 0.44) trivial
BP MPP (W·kg−1) 6.88 ± 1.17 6.80 ± 1.28 −0.06 (−0.27 to 0.02) trivial
BP PP (W·kg−1) 11.65 ± 2.56 11.60 ± 2.35 −0.02 (−0.23 to 0.10) trivial
HS MP (W·kg−1) 5.73 ± 1.48 6.55 ± 1.84VL 0.56 (0.31 to 0.80) small
HS MPP (W·kg−1) 7.20 ± 2.04 8.00 ± 2.25L 0.39 (0.18 to 0.60) small
HS PP (W·kg−1) 16.70 ± 4.24 19.80 ± 4.90VL 0.73 (0.48 to 0.99) moderate
JS MP (W·kg−1) 6.17 ± 1.58 6.88 ± 2.13L 0.45 (0.22 to 0.68) small
JS MPP (W·kg−1) 8.74 ± 2.42 9.29 ± 2.68P 0.23 (0.08 to 0.38) small
JS PP (W·kg−1) 20.93 ± 4.75 24.41 ± 6.99VL 0.73 (0.41 to 1.05) moderate
*ES = effect size; CL = confidence limits; BP = bench press; MP = mean power; MPP = mean propulsive power; PP = peak power; HS = half-squat; JS = jump squat; P = possible difference from prevalues; L = likely difference from prevalues; VL = very likely difference from prevalues.

Figure 2.
Figure 2.:
Comparison of the punching impact forces before and after assessments. Symbols and lines represent individual changes and bars demonstrate mean values. *Possible difference between pre-test and post-test.
Figure 3.
Figure 3.:
Transference effect coefficients between bar-power outputs in the half-squat (HS) and jump squat (JS) exercises and the punching impacts. MP = mean power; MPP = mean propulsive power; PP = peak power; FJ = jab performed at a fixed distance; SSJ = jab performed at a self-selected distance; FC = cross performed at a fixed distance; SSC = cross performed at a self-selected distance.

Discussion

This is the first study to assess the TEC of BP, JS, and HS exercises executed at the optimum power zone on punching performance of national boxing athletes. The main findings were (a) short-term OPL training (3 workouts performed over 1 week) elicited small-to-moderate increases in both JS and HS power output (∼12 and ∼14%, respectively), but not in BP power output, and (b) there was an effective transference (TEC ∼0.80, on average) of JS and HS power performance gains to punching impact force.

Although a previous study showed that a 7-week OPL training approach was able to increase power output in Olympic boxers (17), it was still unclear whether a 1-week training period could improve physical or punching performance in these athletes. With this research, we demonstrated that meaningful increases in lower-limb power, obtained through short-term OPL training, can be directly transferred to meaningful increases in punching impact. These findings have crucial implications for the development of future training strategies, especially for those designed for the weeks preceding boxing competitions. Because it has been reported that both power and punching forces of a professional boxer tend to progressively decrease throughout a preparation phase leading up to a bout (12), it can be speculated that the use of a short-term OPL training scheme would be able to avoid or at least minimize the decrements in performance over this decisive period. It is worth emphasizing that the training scheme used in this study has a very low volume of exercises (Figure 1) (4,27), being suitable for implementation during periods with reduced (or very reduced) training content (e.g., tapering) (25,26). As aforementioned, “knockout power” is one of the most relevant performance indicators in boxing (17,23,24,37). Therefore, the possibility of maintaining or even enhancing this ability in critical training phases (i.e., weeks close to competitions) is of great importance when dealing with elite amateur boxers.

The short-term OPL training did not elicit meaningful improvements in BP performance. This occurrence seems to be commonplace even in long-term interventions including lower- and upper-limb exercises, where the BP usually presents lower rates of improvements than, for example, squat exercise (1,14). Accordingly, Hunter et al. (14) observed increases of 24 and 32%, respectively, in BP and squat 1 repetition maximum (1RM) across a 4-year period in collegiate basketball players. Another investigation examined the effects of creatine supplementation in conjunction with a 12-week heavy-resistance training in resistance-trained men, reporting increases of 24 and 32%, and 16 and 24% in BP and squat 1RM, respectively, in the creatine and placebo groups (36). Moreover, changes in strength and power performance have been shown to be directly influenced by the training background, with highly trained subjects (e.g., national boxing athletes) generally achieving smaller improvements over time than untrained and moderately trained subjects (1,2,31). Together, these factors may explain the absence of changes in BP power observed in this research.

The meaningful increases in both JS and HS power outputs (∼14%) are similar to those obtained in longer investigations (e.g., 6–7 weeks) performed with athletes who also trained under optimum loading conditions (10,17,19). These greater gains (in relative terms) are possibly associated with the very particular training scheme adopted in this work. Throughout the intervention, the boxers did not execute any additional workouts, performing the OPL training sessions exclusively. Thus, it is highly probable that the “specificity” (7) of this power microcycle in conjunction with the complete absence of concurrent training sessions (e.g., aerobic-based boxing drills) (8,11) boosted the neuromechanical training adaptations, producing substantial improvements in power-related qualities. Future studies should analyze whether these effects are generalizable across distinct athletic populations.

Leg power plays a pivotal role in punching performance (15,16,18); when punching, boxers initiate the movement by applying force onto the ground, then rotating the hips and trunk before extending the arm and, finally, hitting the opponent (9,15). As a result, the ability to transfer substantial amounts of force at high velocities from the lower to the upper limbs is essential to produce greater impact forces (15,18,35). Given the lack of improvements in BP power, and considering that the boxers did not execute any additional type of exercise during the intervention, it is rational to assume that the increases in impact forces (∼8%) in both techniques (i.e., jabs and crosses) and conditions (i.e., fixed or self-selected position) were related to the improvements in HS and JS performances. These assumptions may be supported by the high levels of transference to punching impact presented by both exercises in both punching techniques. Therefore, practitioners interested in enhancing the punching performance of boxers are recommended to implement HS and JS exercises performed at the optimum power zone in their training routines (even in short training periods).

In summary, we demonstrated that a short-term OPL training scheme is able to improve HS and JS power, but not BP power output. Of note, the increases in lower-limb power can be directly transferred to punching impact, which seems to be independent of punching technique (i.e., jabs or crosses). This may have important implications in boxing, especially in prebout phases, when athletes commonly present important decreases in power and punching performance (12). This study is limited by its very short duration, small sample size, and the absence of a control group (to verify in what extent the performance gains are only related to the training intervention). To some extent, this also reinforces our findings because it provides coaches with valuable information about how to rapidly (1-week) and effectively (+8%) increase the punching impact force of elite amateur boxers. Future research should be directed to determining whether different training approaches are capable of increasing the BP power production in the same period (i.e., 1 week). Finally, studies conducted during “cutting periods” (i.e., rapid weight reduction) are warranted to examine the effectiveness of the OPL training scheme in reducing the gradual decrements in neuromechanical performance regularly observed throughout these phases.

Practical Applications

Given the meaningful increases in power output and punching performance reported here, coaches and sport scientists are encouraged to regularly include HS and JS exercises in the strength-power training routines of elite amateur boxers. To optimize the transference effects on punching impact force in both jabs and crosses, these exercises can be executed at the optimum power zone (i.e., using the load capable of maximizing power output). According to our findings, this training strategy is useful and effective even in very short training periods, which may be an important and decisive advantage in some competitive scenarios, such as prebout phases.

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Keywords:

combat sports; power training; muscle power; punches

© 2019 National Strength and Conditioning Association