Boxing is a sport discipline with an old Olympic tradition and a solid professional implantation worldwide (3). Reaching a competitive elite level requires the development of numerous performance factors such as aerobic and anaerobic capacities, as well as optimal levels of power and strength (6). The contribution of anaerobic endurance to boxing performance is especially important (4) because there is a great number of very high-intensity movements during the different rounds that compose a fight, in which the short breaks are insufficient for a complete recovery (11). In addition, previous research highlighted the importance of having sufficient aerobic capacity to meet the training and competition requirements (2,7,8,32). Arseneu et al. (2) reported values of VO2 uptake of 41–43 ml·kg−1·min−1 in a simulated laboratory sparring and pad work tests, which corresponded to 70% of VO2peak in 9 experienced male boxers. Furthermore, Lenestsky et al. (25) suggested that the ability to produce high levels of muscular strength is a key factor to achieve success in professional boxing. Likewise, several studies have shown that punching strength is a key factor influencing the final result of a fight (3).
Although research examining the determinant factors of boxing is limited in the scientific literature (1), contributions on aspects such as punching kinematics (35,38), load performance (27,36), or strength (6,25) have considerably increased. The latest contributions about power and force regarding the technical execution of punches in professional and amateur boxers provide conclusive data (26,28), explaining that the velocity and acceleration of the gesture are the variables that best determine punching performance (26,27).
Technical gestures in boxing require the same strength-related variables common to all sport movements (velocity, shifting, or displacement of a mass) (36). Furthermore, a complex multiarticular coordination involving arm, elbow, shoulder, hip, and lower limbs is required to achieve a successful punching gesture through a correct force transmission along the kinetic chain (26). The increase in the power of the gesture is essential in the majority of sports, and a transfer to the specific movement pattern is required to optimize boxing performance (27). Particularly, optimal power load is defined as the load that is capable of maximizing the athlete's maximum power and has been considered the best load intensity to achieve higher levels of velocity, strength, and power in professional boxers (26,28).
From a technical perspective, performance improvement of boxers should be specific to the requirements of the sport discipline (20). Movement patterns in bench press (BP) have been shown to be similar to the straight punching techniques. In this regard, Čepulenas et al. (5) found a strong and positive (large) correlation between the improvement of optimal power load in BP and the improvement in maximal punch velocity (PVmax) (r = 0.76). Similarly, another study, found a strong, positive correlation where the stronger boxers were those who reached higher power in BP (r = 0.7) (28).
Regarding the relationship between the optimal BP intensity and PVmax, only 1 study showed relevant results on a group of 15 amateur and professional boxers (30). In this study, it was determined that to favor effective punch velocity (PV) transfer in both right and left straight punches, a load of 80% of a 1-repetition maximum (1RM) was necessary. Losses in mean propulsive velocity of up to 10% were the most effective load to achieve optimal gains in maximum strength and improvements in average propulsive velocity. Considering all the above, it could be stated that success in boxing performance depends on the velocity at which the punches are executed and that BP seems a reliable method to assess PVmax (30).
To the best of the authors' knowledge, no previous study has yet analyzed the relationship between the load during a strength training session and PVmax. Therefore, the main aim of the research was to examine the association between relative intensity during the BP exercise and PVmax in professional boxers. The main hypothesis based on previous studies was that both variables would correlate positively. These results would enable the researchers to obtain a practical set of guidelines so that coaches and sports specialists can determine the optimal workload.
Experimental Approach to the Problem
For this cross-sectional study, data were collected during 2 separate days with one day in between (January 7, 2018, and January 9, 2018) to guarantee an optimal recovery between sessions.
During the first day, subjects attended the laboratory for the PVmax assessment and 1RM test in the BP exercise (laboratory conditions: air temperature 20° C and relative humidity 65%). During the second testing session, the PVmax from each submaximal intensity was determined. All boxers who participated in the study were familiarized with the exercises and the test protocol used in the study before the testing day. All assessments were performed in the same facilities where the subjects trained regularly (gym conditions: air temperature 23° C and relative humidity 67%). The warm-up performed on day 1 was conducted according to the findings by Lambert et al. (24). For 1RM assessment, the protocol designed by Kraemer was used as described in the 1RM prediction section (23). Finally, maximal velocity during submaximal BP was assessed following the protocol specified by Jidovtseff et al. (19).
Twelve Spanish male professional boxers voluntarily participated in this study (Table 1). The sample comprised from light to super welterweight (56–72 kg). All of the boxers were ±3 kg within the permitted margins of their competitive body mass. Inclusion criteria were as follows: (a) to have competed in a minimum of 5 national fights as a professional boxer and (b) to have previously followed at least 5 years of boxing specific training and 2 years of controlled strength training. All subject characteristics were measured mean ± SD.
Subjects and coaches were fully informed of the aims, benefits, and potential risks of the study. The procedures were in accordance with the latest version of the Declaration of Helsinki (Fortaleza 2013) (17) and were approved by the ethical committee from Aragón, Spain (CEICA; ref No 02/2019). A written informed consent form was signed by all boxers; all of them underwent a previous physical examination by the team physician and declared not to be under medication, drugs, or to be suffering from cardiac and metabolic disorders that could confound or limit their ability to fully participate in the study.
The subjects were evaluated during 1 week in the middle of the competitive period. All data were collected between 10:00 am and 12:00 am: day 1: PVmax assessment and 1RM test in the BP exercise and day 2: velocity test with different %loads.
Maximum Punching Velocity
Maximum punching velocity: PVmax was determined over the rear arm (RA) and lead arm (LA) punch. All exercises were performed with the help of an accelerometer (Crossbow; Willow Technologies, Sussex, United Kingdom) that had been validated in a previous study (24). This system monitors the real output of the punch with a cutoff frequency of 12 Hz and a sampling rate of 1,000 Hz, with all subjects performing the same specific warm-up that consisted of 20 shadow punches and a regime of introductory punch on the heavy bag (140 × 35 cm; Charlie Equipment, Hard-core heavy bag, Madrid, Spain) (24). The accelerometer was attached to the wrist with a Velcro strap in the interior surface of the boxing glove. Each boxer executed 3 repetitions at the maximum possible velocity for each jaw punch. Notably, the assessment of reliability of these tests showed excellent values, with intraclass correlation coefficients of 0.898 for LA PVmax and 0.910 for RA PVmax in this group of boxers. Raw data collected from the Crossbow system were computed for further analyses.
One-Repetition Maximum Maximal Test
All subjects were familiarized with the BP exercise. One-repetition maximum assessment was tested according to the standard methods established by Kraemer (23) to assess the maximum load by using a direct methodology on a Smith machine (Atlantis, Laval, Canada). A standard dynamic warm-up was performed before the start of the maximal test. First, subjects performed 8 repetitions with their estimated 50% of 1RM, following 3 repetitions at 60% of estimated 1RM, and 2 repetitions at 70% of estimated 1RM. After the warm-up, subjects rested for ∼3 minutes and performed 1 repetition at 80% of their estimated 1RM, followed by 1 repetition at 90% of the estimate 1RM. From this point, attempts were performed to achieve the highest possible load (16). Subjects rested a minimum of 3 minutes and a maximum of 5 minutes between sets. An expert coach supervised the test. During the eccentric phase of the exercise, a gentle contact of the barbell with the chest was permitted, although the attempt was considered unsuccessful if the chest movement helped the execution.
Maximum Velocity during Submaximal Bench Press Tests
Submaximal loads in BP were calculated based on the maximum load from the 1RM test. The number of attempts performed at each load was as follows: 4 attempts at 30 and 40% of 1RM; 3 attempts at 50, 60, and 70% of 1RM; and 2 attempts at 80% of 1RM (19). Three minutes of passive recovery were allowed between each attempt with different loads. Boxers were encouraged to push the bar as fast as possible without releasing it or losing contact with it at the end of the concentric phase. Maximum velocity during submaximal BP tests was recorded with an infrared sensor (MUSCLELAB, Ergotest, Norway), which had been previously validated (16). The best attempt was selected for further statistical analysis (19).
Visual inspection of data and the Shapiro-Wilk test applied to all variables confirmed that data met the assumption of normality. Descriptive statistics were reported as mean ± SD (range). Age-adjusted Pearson partial correlations and their 95% confidence intervals were calculated to assess the association between PVmax for both arms (RA and LA) and the maximal velocity in each percentage of the BP (30, 40, 50, 60, 70, and 80% of 1RM). Correlation coefficients were interpreted according to Cohen (9): 0.1 = small effect, 0.3 = medium effect, and 0.5 = large effect. In a secondary analysis, main correlations of the previous stage were further investigated in a multiple univariate regression. Body mass and age were included in the models as potential covariates. Before model fitting, data were standardized for easier interpretation of the regression estimates of effect (βδ). Adjusted coefficient of determination (R2) was used to assess the goodness of fit, and Cook's distance (18) was used to verify the absence of influential data. Coefficients of determination were interpreted according to Cohen (9): 0.01 = small effect, 0.09 = medium effect, and 0.25 = large effect. Analyses were performed using the SPSS 24.0 software, and significant differences were assumed when p ≤ 0.05.
Descriptive statistics are shown in Table 1. Correlation analysis revealed a large association between RA PVmax and BP velocity in all load percentage, especially at 80% of 1RM (r = 0.815; p < 0.01) (Table 2). On the other hand, PVmax in LA was not associated with BP velocity for any percentage of 1RM.
Multiple univariate regression confirmed that PVmax in RA could be predicted by BP velocity at 80% and the boxer's body mass, with a goodness of fit of R2 = 0.65 (p = 0.006, large). Standardized regression coefficients appear in Table 3, and this linear trend can be seen in Figure 1.
To the best of the author's knowledge, this is the first study examining the relationship between PV and the velocity at which different loads are lifted during the BP exercise. Although RA PVmax correlated with BP velocity at all submaximal loads, the main findings of this study reveal that the maximum velocity shown during 80% of 1RM in BP might explain a 75% of the variance of the RA PVmax. However, although we obtained such a correlation for the RA, the LA does not seem to correlate with BP velocity. This discrepancy might be attributed to differences in the technical execution performed by both arms because the RA movement during punching is more similar to the BP execution than the LA. The limited sample size of this study might have also played a role in this outcome.
Bench press is commonly used in a variety of sports for both assessing strength and improving athletic performance (19,23). Specifically in boxing, the movement pattern seems to mimic straight punches (20,27). This statement is in agreement with previous research that after comparing power characteristics during BP and straight punches concluded that it is necessary to incorporate BP into the boxer's strength training programs to improve power during technical executions (6,27,28). The moderate correlation between power and strength production (r = 0.391; p < 0.001) during punching (29) must be taken into account. The authors have only found 1 previous study that showed information related to the increase in optimal power load in BP after a 3-week resistance-training period. Results showed moderate improvements for mean power (effect size [ES] = 0.42) and mean propulsive power (ES = 0.46), as well as small improvements in peak power values (ES = 0.22) (27).
The association between power and strength or velocity increases (33,34) suggests that a key aspect of strength training in boxing would consist in controlling the execution velocity during strength training (14). A main limitation of the BP exercises when analyzing boxing-specific actions is that a symmetrical exercise might lack specificity for an asymmetrical pattern of movement such as a boxing punch. Therefore, a possible alternative would be to train with specific exercises to favor an artificial asymmetry condition (12).
Similar PV differences between limbs were found previously by Dyson et al. (10). These authors assessed the relative power produced during straight punches in 3 different categories of boxers: professionals (p), intermediates, (i) and beginners (b), concluding that RA straight punches were executed at a higher power than LA straight punches, regardless of the performance level of the boxer. Technical execution during punches might be a key determinant of power production due to differences in traveled distance between rear and lead fists (6). Two key aspects have been suggested to explain this finding: on the one hand, the differences in punching distance between RA and LA have an influence on the amount of strength generated (31). On the other hand, the relationship between strength and velocity would likely cause the differences in strength observed between right and left hands as a consequence of having trained at different velocities (34). Therefore, it is considered that different training methods should be applied to improve PVmax with both LA and RA.
These results agree with previous research (28,30) highlighting the relevance of training at diverse training loads (between 40 and 80%) to reach optimal improvements for both strength and velocity. These results also show an agreement with previous studies that reported an optimal training load of 85% of 1RM to improve punching performance (10). Moreover, the relevance of being able to maintain certain velocity during RA straight punching strengthens the idea of training with higher loads even during fast exercises without overload (26,28). Nevertheless, the literature studying the relationship of different loads with PV is still limited, which makes these results preliminary. González-Badillo et al. (13) stated that maximal explosive strength could be enhanced regardless of the external load, provided that the velocity is always maximal or submaximal at any load. Other authors such as Kraemer et al. (21) supported the previous statement by studying other sport disciplines. Kraemer et al. (21) found a high correlation between 1RM BP and the force used during a tennis stroke and reported a significant relationship between maximal strength levels and execution velocity (p < 0.005). Harris et al. (15) also concluded that comparable velocities could be achieved in a group of sprinters after a training period with loads that represented either 80% of 1RM or maximal power.
In summary, this study shows that PVmax in RA is correlated with the BPVmax at all submaximal intensities (p < 0.05). However, no significant relationship between upper-body strength as measured through BP and LA PVmax was found. In addition, and from a practical point of view, professional boxers might benefit from using different loads for both left and right arms. Besides punching velocity, future research should measure power outputs during technical gestures to find clearer correlations between optimal power during basic strength exercises such as BP and power during punching executions. To find differences in correlations, both arms should be analyzed independently and a different range of movement, characteristic of this punching action, should be used for LA. This study was conducted with a small sample size, a limitation that could have also been present in previous studies in which it was truly difficult to recruit subjects from this very specific population (22,37). Therefore, future research with more sophisticated methods of analysis is needed to confirm these results. Future studies should emphasize the importance of asymmetrical force production, punch impact, and also the potential role of lower extremities in the development of straight punching velocities. The evolution of acute fatigue after several fighting rounds or the influence of lower limb fatigue on the punching velocity could be other potentially interesting factors that should be taken into account.
Improvements in execution velocity in the BP exercise with loads varying between 30 and 80% of 1RM translate to improvements of straight RA punching velocity. This confirms the importance of strength training in professional boxing. These loads should be considered when scheduling training periods to improve the relationship between strength and the velocity during the sports-specific action. Thus, lower loads should be applied to improve velocity with low resistance, and higher loads should be used to ameliorate strength related to higher resistance. It should also be remarked that execution speed at loads of 80% of 1RM should be considered as a reference for developing the RA PVmax performance.
Insignificant correlations when comparing with the LA imply that a different methodological approach should be considered when training this technical gesture. As boxing implies different technical executions, training exclusively based on BP should be avoided and should always be complemented with other tasks that recruit other muscle groups and patterns of movement. The authors consider that asymmetric exercises with different loads should also be included in training regimes as strength imbalances are both joint-specific and task-specific (12).
Finally, the differences between RA and LA punches obtained in this study could be explained by lack of a clear and standardized position when executing LA punches. In this regard, RA punches have a similar execution and starting position, whereas the technical execution of LA punches varies. It should be considered that strength and conditioning professionals should study the technical execution of both punches in their boxers to find the best efficiency in positioning, length, and execution.
The authors are grateful to Pablo Iniesta Lon for the support in the data collected with boxers.
This research did not received any economic resources from any organization.
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