Analysis of the impact force and key technique of backward straight punch in different combat sports

Abstract

Despite the prevalence of combat sports research, a comparative analysis of backward straight punches and sEMG activation across different martial arts disciplines remains unexplored. This study examines the impact force and sEMG characteristics of backward straight punches among athletes from Boxing, Tao Lu (Chinese Wushu), Karate, and a control group (Physical Education students) under randomized signal stimulation. Twenty-eight participants performed backward straight punches while impact force and muscle activation were recorded using a pendulum system and a 16-channel Noraxon wireless sEMG system. Results indicate that the Boxing group exhibited the highest impact force (3.96 ± 0.45 times body weight), followed by the Tao Lu, Karate, and Control groups. Muscle activation patterns varied significantly among groups, with a moderate positive correlation between impact force and the deltoid (r = 0.535) and brachioradialis (r = 0.365) muscle groups. The findings highlight differences in combat philosophies, with Boxing emphasizing effectiveness, Wushu and Karate focusing on controlled strikes, and Tao Lu prioritizing precision. These insights provide a biomechanical understanding of combat sports techniques, suggesting tailored training strategies for optimizing striking performance.

Introduction

Combat sports, encompassing a wide range of competitive contact disciplines with distinct rules and strategies, have maintained enduring prominence in global athletic events. Historical data reveals they account for 20–25% of Olympic medals¹, peaking at 26.3% with karate’s inclusion in Tokyo 2020². and maintaining 23.6% of events at Paris 2024³. Combat sports is a term used to describe a wide range of competitive contact sports⁴, Technical diversity defines this category. For instance, in Chinese Wushu’s Tao Lu and Karate’s Kata, the expression of form, spirit, and energy is emphasized. Conversely, Chinese Wushu’s Sanda and Karate’s Kumite are similar to boxing, pursuing high intensity strikes to score points. Combat sports are influenced by the technical characteristics of many other sports, and Chinese Wushu is one of its important components. Events of Chinese Wushu that involve attacking an opponent’s body with techniques such as Ti (踢Kicking), Da (打Punching), Shuai (摔Wrestling), and Na (拿Grappling) can be categorized as technical attack projects⁵. Chinese Wushu, which is similar to boxing, Karate, and similar sports, has evolved differently because of its cultural heritage and competition rules.

In combat sports, the muscle strength of the upper and lower limbs is crucial to the victory of the player⁶. In addition, reaction speed and punching power are two elements in combat sports. The faster the player reacts and responds to the opponent’s attack and movement, the more likely the player is to win in the game^7,8. Impact force-related research based on reaction speed is presently limited, especially research on the impact force effect of different combat sports.

The punching effect varies in different sports. According to relevant studies, the average speed of a straight punch in Chinese Wushu is 7.30 ± 0.49 m/s⁹. Elite boxing athletes have an average punching speed between 6 and 8 m/s, and Olympic boxing athletes have a punching speed of approximately 9.14 m/s, with a peak force of approximately 3400 N^10,11. Furthermore, a greater punching power can considerably affect the opponent’s performance¹². A review summarized the striking force in full-contact combat sport athletes, including those in Muay Thai, boxing, taekwondo, and other combat sports¹³. However, the previous studies’ results were not obtained on the same test platform, making them incomparable among combat sports. Additionally, impact force tests were conducted without signal stimulation. Therefore, the results can only reflect the subjects’ impact force level under the condition of complete preparation; they may not necessarily reflect the actual status of athletes in competition or combat.

In combat sports, the fighting technique plays an important role. Excellent athletes can reasonably mobilize the muscles of the upper and lower limbs to achieve the best punching power and punching effect. High-quality fighting performance is characterized by the ability to hit a target area of the opponent’s body at different speeds and with varying degrees of strength^14–16. Surface electromyography (sEMG) is currently widely used in research on combat sports, particularly for the collection and analysis of muscle activation levels and muscle contraction effects^17–19. In this study, sEMG was used to compare and analyze the muscle contraction effect of different martial arts and further explore their technical characteristics.

The first aim of this study was to evaluate the dynamic characteristics of athletes from different combat sports disciplines using random light signals, and to collect and analyze the sEMG signals of relevant muscle groups. The second aim was to compare the muscle contraction characteristics during punching among athletes from different combat sports and to assess the techniques and power of punches with their respective dominant hands.

Study objectives and hypotheses

The primary objective of this study is to assess the dynamic characteristics of backward straight punches in athletes from different combat sports under randomized signal stimulation. Specifically, this research aims to:

1. Compare the impact force and sEMG activation patterns among Boxing, Tao Lu, Karate, and Control groups.

2. Investigate variations in muscle activation levels and their correlation with impact force.

3. Analyze reaction time differences across combat sports and their influence on impact force.

4. Identify biomechanical factors contributing to effective striking techniques.

It is hypothesized that athletes from high-intensity striking disciplines (e.g., Boxing, Sanda, Kumite) will demonstrate greater impact force and speed than those focused on precision and control (e.g., Tao Lu, Kata). Additionally, sEMG analysis is expected to reveal distinct muscle activation patterns across groups, reflecting the unique biomechanical demands of each sport.

Study design

Design

The subjects were required to hit the pendulum force measurement system with a straight punch using their dominant hand under experimental conditions. At this time, LED signal light was used for signal stimulation, and the subjects were required to hit the force measuring system in the shortest time possible when the LED light was randomly light up. This scheme could simulate the subject’s response to an opponent’s attack in actual combat. Then, this study explored the technical characteristics of different combat sports to reveal their varying impacts and the corresponding effects of muscle contraction. This study was conducted with the approval of the Research Ethics Committee of the Shanghai University of Sport. The registration ID is 102772020RT072, all participants signed informed consent forms and all experiments were performed in accordance with relevant guidelines and regulations.

Sample size

The sample size was estimated using the one-way measurement method in the G-power (1.G-Power 3.1.9.7, https://www.psychologie.hhu.de/arbeitsgruppen/allgemeine-psychologie-und-arbeitspsychologie/gpower) software F test by the pre-experimental results. The effect size was calculated to be between 0.75 and 0.9, and α was set to 0.05 with a test power of 90%. The resulting sample size was between 18 and 28; this study’s final sample size was 28.

The participants recruited in this study were divided into four groups: Tao Lu (Wushu Routine), Boxing, Karate, and the Control group. Each group consisted of seven male subjects.

Inclusion criteria

Each of the Tao Lu (Wushu Routine), Boxing, and Karate groups included Grade 1 and higher-level athletes from the Shanghai University of Sport. The participating groups had either won first prize in a provincial competition or belonged to the top three in a national competition. The control group comprised students majoring in physical education who study combat sports. The average training years were 10 years for the Wushu Routine group, 7 years for the Boxing and Karate groups, and less than 1 year for the Control group. Height, age, and weight were not significantly different across groups (P > 0.05). The details are shown in Table 1.

Table 1.

Basic Information of participants (Mean  ± SD) (N = 28).

Category	Tao Lu (n = 7)	Boxing (n = 7)	Karate (n = 7)	Control (n = 7)
Age (years)	21.00 ± 1.41	20.86 ± 0.69	20.29 ± 0.49	21.29 ± 0.49
Height (m)	1.70 ± 0.02	1.72 ± 0.03	1.72 ± 0.02	1.71 ± 0.03
Weight (kg)	65.99 ± 5.44	64.23 ± 6.26	65.49 ± 6.47	66.51 ± 6.85

Methods

The subjects wore boxing gloves weighing 226 g. The force-measuring pendulum system was adjusted to the subject’s shoulder height. When the subjects punched, their arm and the pendulum remained at the same horizontal height. The LED signal light was fixed on the upper edge of the pendulum (Fig. 1).

Fig. 1.

It shows the Chinese Kung Fu pendulum force measurement system, with the left figure illustrating the pendulum and the right figure showing the boxing subjects preparing their posture. The red LED signal light is randomly activated to simulate the subject completing a punch corresponding to an opponent’s attack.

The preparation position for a dominant-hand punch resembles that of a backward-hand straight punch. The feet are positioned with one foot in front of the other, approximately shoulder-width apart, with slightly bent knees, and the body weight is evenly distributed between the legs. The subjects place their right hand on their chest, with the elbow bent downward at an angle of 40° to 90°, and both hands are positioned at the same height.

When striking, subjects from different combat sports should strike according to the specific characteristics of their respective events. Although the basic action route and process of striking are similar, the power characteristics of striking should meet the technical requirements of each event. The subject stands in front of the pendulum in the mentioned preparatory position, with the striking distance determined according to the subject’s arm length. Each subject was instructed to perform three or more strikes, with a two-minute rest interval between strikes.

Materials

A martial arts pendulum force measuring system was used to measure the impact force, this device has been used and validated for its reliability by several studies²⁰. The force signal was collected using a four-channel YE6231 (IEPE, https://www.china-yec.com/show-186-420-1.html) sensor with a sampling frequency of 1500 Hz. Raw EMG signals were recorded at the same frequency, and each electrode was connected using a Telemyo DTS wireless transmitter (Noraxon 1.08, https://www.noraxon.com/). Then, the activity characteristics of the brachioradialis, triceps, biceps, and deltoid muscles were analyzed. A randomized LED light was utilized with the light-emitting diode varied 5 mm with a microcontroller. The duration of the random light was between 1 and 3 s. The experiment was recorded using a Japanese Panasonic GS-400 digital camera with a sampling frequency of 30 f/s. Synchronization was ensured by connecting the signal light, EMG, and force measuring system to the YE6231 data collector.

The pendulum force measurement system used in this study was developed by Jiangsu Lian Neng Technology Co., Ltd. The system was modified based on the principle of mechanics and the calibration-test system of Chinese Kung Fu Engineers (Patent No. CN203915999U). The system consisted of a support, pendulum rod (adjustable length), pendulum (diameter: 20 cm; weight: 20 kg), pendulum surface rubber, and internal adhesion sensor, with a sensor sensitivity of 2.24 pC/N and a range of 10 kN. The input and output error of the system was 0.34%. The system was calibrated before the test.

Procedure

Preparation: The test order was randomly assigned. A warm-up period of approximately 20 min was conducted so that subjects could familiarize themselves with the experimental movements and procedures.

Formal test:EMG electrode placement. The skin was cleaned, and electrodes were placed longitudinally in the middle of each muscle with a spacing of 2 cm. The wireless EMG transmitter was secured with a bandage.

MVC test. The test followed the protocol described in “The ABC of EMG”²¹.As shown in Table 2, a Maximum Voluntary Contraction (MVC) test was conducted for various muscles of the upper and lower limbs. The subjects were asked to perform maximum voluntary muscle contraction and hold it for 5 s. The experimental staff encouraged subjects to try their best verbal cues. Each movement was tested twice, with a 2-min interval between tests.

Table 2.

MVC test position.

Muscle	Test	Comments
Brachioradialis		Seat in front of a bench and arrange a stable forearm support. Use manual resistance and belt.
Bicipital brachii		Seat in front of a bench and arrange a stable forearm support. Elbow and trunk are fastened securely.
Triceps brachii		Same instruction as biceps brachii.
Anterior deltoid		Select a seated position with the back in a fixed position. Fasten the straps near the arms close to the 90° position.
Ectopectoralis		Do push up and performe in 90°elbow position.
External oblique		A side lying position with the leg and hip restrained. Let the subject flex up and remain fixed early in the flexion position.
Rectus abdominis		Sit-up styled movements with the legs securely fastened. Let the spine flex by around 30° and use a belt restraint for that position.
Erector spinae		The prone lying position on a bench.

Action acquisition. The pilot provided the zero-drift value, and the subjects were instructed to perform strikes in the prepared position. The subjects were required to perform three successful strikes with a two-minute rest interval in between. The data were checked for validity via manual monitoring and camera recording, ensuring the accuracy of strike action and position.

Yep7600 software (Yep7600,https://www.china-yec.com/show-186-420-1.html), provided by Jiangsu Lian Neng Technology Co., Ltd., was used for kinetic data processing. The best performance of punching was selected for analysis, and the impact force was standardized by weight (impact force: N ÷ weight kg ÷ 9.8 N/kg) to normalize the subjects’ weight difference²².

Statistical analyses

The original sEMG signal was processed using Myo Research XP Master Edition (Noraxon 1.08, https://www.noraxon.com/). The collected signals were rectified, filtered (FIR, frequency selected to be 20–500 Hz), and smoothed (RMS, window set to 100 ms). The EMG signal of the subject was intercepted and retained for 0.2 s before the movement start point. Then, the integral EMG value and muscle contribution rate of the subjects were analyzed.

Data analysis was performed using SPSS 27.0 statistical software(SPSS 27.0, https://www.ibm.com/spss). When the data did not follow a normal distribution, a one-sample K-S test was used for nonparametric testing. To determine the appropriate statistical tests, the normality of the data distribution was assessed using the Shapiro–Wilk test. The results indicated that all data met the assumption of normality (p > 0.05). Therefore, parametric tests were utilized for further analysis. A one-way ANOVA was used to compare the force and sEMG results of the straight-punch performance by athletes from different groups. Pairwise comparison (post hoc tests) was conducted using the Least Significant Difference (LSD) test, and Pearson’s two-sided test was used for correlation analysis. The mean and standard deviation were expressed as the mean ± SD, and the significance level was set at P < 0.05.

Results

Punch impact force

Reaction time was not significantly different across groups (P > 0.05). The results of the punching force showed that the group focused on boxing training achieved the highest impact force at 3.96 ± 0.45 body weight (BW). The four groups of subjects had punching effects in the following order: Boxing > Tao Lu (Wushu Routine) > Karate > Control (Fig. 2). The punching effects of the Tao Lu (Wushu Routine), Boxing, and Karate groups were significantly higher (P < 0.01) than that of the Control group. The punching force of the Boxing group was significantly higher than those of the Karate group (P < 0.01). The difference between the Tao Lu and Karate groups was not significant (P > 0.05), the details are shown in Tables 3 and 4.

Fig. 2.

Mean value of impact force.

Table 3.

Characters of standardized impact force and reaction time.

	Group	Mean	SD	CV/%	SWC
Reaction time (s)	Tao Lu	0.6217	0.10786	17.355	0.0216
	Boxing	0.5514	0.06797	12.33	0.0136
	Karate	0.6056	0.16744	27.65	0.0335
	Control	0.6775	0.07575	11.18	0.0152
Impact force (BW N/kg)	Tao Lu	3.183	0.36523	11.48	0.0731
	Boxing	3.9611	0.44737	11.29	0.0895
	Karate	2.8234	0.66455	23.54	0.133
	Control	1.9788	0.31334	15.84	0.0627

Table 4.

Comparison of peak force and reaction time between boxing and Tao Lu, Karate and control group.

			Mean difference	Standard error	P	95% confidence interval
						Upper limit	Lower limit
Boxing	Impact force (BW N/kg)	Tao Lu	0.778	0.25	0.005**	0.2627	1.2936
		Karate	1.138	0.25	0.000**	0.6223	1.6533
		Control	1.982	0.25	0.000**	1.4668	2.4978
	Reaction time (S)	Tao Lu	− 0.070	0.06	0.251	− 0.1936	0.0531
		Karate	− 0.054	0.06	0.374	− 0.1775	0.0692
		Control	− 0.126	0.06	0.046*	− 0.2494	− 0.0027

*p < 0.05; **p < 0.01.

These results indicate that the Boxing group exhibited the shortest reaction time and the highest standardized impact force, reflecting greater performance efficiency and strength. The Karate group, despite showing a relatively higher mean impact force than the Control group, demonstrated the highest variability in both reaction time and impact force, as indicated by their CV values. The Tao Lu group showed a moderate performance with relatively balanced CV values, suggesting consistent performance. The Control group had the lowest mean impact force and higher reaction time, indicating lower performance compared to the trained groups. For the differences in strength and reaction time between the groups, it is possible that the boxing group underwent higher intensity and more targeted training to enhance explosive power, whereas the Wushu Routine and Karate groups may have placed more emphasis on technique and speed.

Surface EMG results

Comparison of iEMG results

As shown in Fig. 3, within the Boxing group, the integrated sEMG (iEMG) measurements of the brachioradialis and deltoid muscles were notably elevated compared with other muscles. Similarly, the iEMG levels in the anterior bundle and triceps muscles of the Boxing group surpassed those of the other groups. In particular, the anterior bundle’s sEMG values were most prominent within the Boxing group, and a statistically significant difference was found between the Karate (p < 0.05) and Control (p < 0.01) groups. The Karate group exhibited substantial muscle discharge in the brachioradialis and triceps, similar to the trunk muscles, resembling the patterns for the Boxing group. Overall, the Control group demonstrated the lowest sEMG values. The external abdominal oblique muscles of subjects in the Control group exhibited a significant decrease in contrast to those in the Karate group (P < 0.05); their rectus abdominis displayed a notable increase in contrast to those in the Karate and Control groups (P < 0.05); and their erector spinae muscles exhibited significantly higher readings than those in the Boxing group (P < 0.05).

Fig. 3.

The mean value of the iEMG.

Comparison of the muscle contribution rate

Within each group, the primary muscles that generally contributed to the force generated in a straight punch were the brachioradialis, triceps brachii, and anterior deltoid muscles (Fig. 4).

Fig. 4.

Contribution rate of the upper limb muscles.

The contribution rates of the torso muscles of subjects in the Boxing and Control groups were similar (Fig. 5). The contribution rates of the external oblique muscle and erector spinae muscle of subjects in the Boxing group were nearly identical. The Tao Lu (Wushu Routine) group exhibited dissimilarities from the other groups.

Fig. 5.

Contribution rate of the torso muscles.

In summary, during the execution of the backward straight punch, the primary muscles engaged in the torso region were the ectopectoralis and erector spinae muscles. The Karate group predominantly utilized the ectopectoralis and external oblique muscles.

Correlation between the contribution rate of each muscle and the impact force

The results obtained from the analysis of punching force and muscle contribution rate indicate differences in the punching force and utilized muscle groups depicting high contribution rates, further suggesting that the difference in muscle contribution rate is attributable to the difference in punching force. In the further investigation of this relationship, a correlation analysis between the muscle contribution rate and punching force was conducted using the Pearson two-sided test (Table 5).

Table 5.

Correlation between the contribution rate of each muscle and the impact force.

	Muscles	Brachioradialis	Bicipital brachii	Triceps brachii	Anterior deltoid	Ectopectoralis	External oblique	Rectus abdominis	Erector spinae
Impact force	Pearson correlation	0.365*	0.248	− 0.219	0.535**	0.127	0.268	0.061	0.054
	Significance (two-sided)	0.031	0.151	0.206	0.001	0.466	0.12	0.73	0.757

*p < 0.05; **p < 0.01.

The results of the correlation analysis revealed a moderate positive correlation between punching force and the deltoid and brachioradialis muscle groups, with correlation coefficients of 0.535 and 0.365, respectively, at p = 0.05 and p = 0.1. Among the torso muscles, the external oblique muscle had a slightly higher correlation with the punching force than the other muscles.

Discussion and analysis

Muscle contribution rate

iEMG represents the original EMG after data processing; thus, iEMG was used to obtain the entire area per unit time, which could reflect the number of recruited muscle fibers and the discharge intensity of these muscle fibers¹⁴. The muscle contribution rate represents the percentage of the iEMG value of a certain measured muscle within a certain period when the subject completes a certain action, reflecting the proportion of a particular muscle to the measured muscle when completing an action. The muscle contribution rate measured in this study was calculated by iEMG. For the Wushu Routine and Boxing groups, the contribution rates of the brachioradialis, deltoid anterior, and triceps muscles were greater than those of other muscles, which is consistent with previous results^11,23–25. This finding indicates that the muscle fibers of the brachioradialis, deltoid anterior bundle, and triceps were increased when performing straight punches. Some researchers have measured the posterior-hand straight punch by karate athletes, and the most prominent muscle contraction measured by iEMG was the deltoid or triceps^26,27. This finding differs from the results measured in this experiment, and the varying analyses may be due to the different ways of punching.

From the analysis of the movement structure, the straight punch by boxing athletes mainly includes the torsion of the waist around the vertical axis, the rotation of the shoulder joint, and the flexion and extension of each joint of the upper limb²⁸. Among them, lumbar torsion is mainly reflected in the external oblique, erector spine, and rectus abdominis. The main muscles involved in shoulder and elbow movement are the deltoid anterior bundle and pectoralis major, triceps, and biceps. The brachioradialis muscle is divided into two parts. First, the subject completes the internal rotation of the wrist. Second, at the moment of hit, the subject receives the reaction force of the pendulum, corresponding to the strong passive contraction caused by the strong reaction force. These actions can mainly explain the contribution of the brachioradialis, deltoid, and triceps brachii in the process of beating.

The backward straight punch involves a complex kinetic chain that requires efficient energy transfer from the lower body through the torso to the upper body. While our study primarily focused on muscle activation and contribution rates, it is important to consider how these muscles work together to achieve biomechanical efficiency. For example, the torsion of the waist and the rotation of the shoulder joint not only involve local muscle activation but also facilitate the transfer of momentum generated by the lower limbs to the upper body. Inefficiencies in this chain, such as delayed activation or over-reliance on certain muscle groups (e.g., the brachioradialis), may lead to reduced force output.

Joint kinetics

Such as angular velocity at the hip and torque at the shoulder, play a crucial role in determining the efficiency of energy transfer during a straight punch. While the current study did not measure these parameters directly, previous research has highlighted their significance in generating maximal punching force. For instance, optimal hip rotation and shoulder joint torque are essential for maximizing the contribution of lower-body momentum to the final impact force. Future studies should integrate these biomechanical measurements to provide a more comprehensive understanding of punching efficiency.

Biomechanical efficiency

The observed differences in muscle activation patterns across groups suggest varying strategies for energy transfer and biomechanical efficiency. For example, the reliance on torso muscles (e.g., external oblique and erector spinae) in the Boxing group may indicate a more efficient kinetic chain compared to the Wushu Routine group, which exhibited greater variability in activation patterns. These differences could impact punching effectiveness, with more efficient strategies likely resulting in higher impact forces and better performance.

Analysis of the key muscle groups affecting the impact force

The athletes’ reaction time, which represents the time between the signal light and hitting the target, was tested using a signal stimulus, ensuring the effectiveness of a strike. A recent study found significant differences in the motor time and reaction time of Gyaku Tsuki between elite and sub-elite athletes²⁹. If the athletes’ reaction time is extremely long, then they have enough time to prepare before hitting, or they are slow to respond, putting them at a disadvantage in actual combat.

Muscle contribution size, limb speed, and impact force during exercise are correlated with each other³⁰. Higher speed improves the recruitment of muscle fibers³¹ and enhances muscle firing. Therefore, an important relationship exists between the muscle contribution rate and the strike force. The analyzed correlation between the contribution rate of each muscle and the strike force (Table 5) revealed that the anterior bundle of the deltoid and the brachioradialis are significantly associated with the strike force, indicating their close relationships.

According to several studies, boxing involves extensive movements of the shoulder and elbow³⁰. The deltoid muscle plays a critical role in these movements, as it is the main muscle of the shoulder joint. In the increased range of motion of the shoulder and elbow joint, the anterior bundle of the deltoid muscle has a significant contribution. The deltoid muscle quickly drives the shoulder joint, and the triceps assists in transmitting the movement from the proximal to the distal end. This feature completes the explosive elbow extension movement, increasing the strength of the fist. Therefore, the anterior bundle of the deltoid muscle is crucial in straight boxing to improve the strike force³². Additionally, some studies suggest that the large contribution rate of the anterior deltoid muscle may protect the shoulder joint from the impact of a strong reaction force while hitting the target³³.

The biceps and triceps are activated in elbow extension, and the size of the work determines whether elbow extension is explosive. The angle of elbow extension is related to the acceleration of the straight fist³⁴. Both movements require antagonistic muscles. Studies have shown that in rapid exercise, antagonistic muscles usually contract at the end of the exercise, indicating the important role they play in stabilizing the elbow joint and ensuring movement accuracy³⁵.

Relation between muscle force characteristics and the concept of strike

Relation to the boxing group

This study found that boxing athletes have the highest contribution rates of the deltoid and triceps muscles, which are crucial for explosive punching, combined with coordinated movements of the waist, shoulder, and elbow. This technique underscores the effectiveness of punching in boxing, aimed at maximizing strike power³⁶.

Furthermore, the contribution rates of the rectus abdominis, erector spinae, and other abdominal muscles were balanced in the Boxing group, suggesting that subjects could maintain a stable trunk while punching. Maintaining a balanced center of gravity is crucial for executing powerful strikes, and a stable body is necessary for boxers to deliver effective punches³⁶.

Relationship between the Tao Lu and Karate groups

Tao Lu and Karate are classic oriental martial arts. These disciplines emphasize the “touch” or “convincing people by virtue,” focusing on controlled strength rather than the goal of knocking down an opponent. In practical terms, Karate employs a non-contact “inch stop” combat form, halting one inch before striking the opponent. This technique, known as “hanging without hitting” and “point up,” promotes precision and control. Studies have shown that elite Karate athletes exhibit superior control over their punching force²⁹. In this study, the contribution rate of the vertical spinal muscles in the trunk was higher than that of the external oblique muscles and rectus abdominis. This may be attributed to the slight forward lean of the body during a punch, with the trunk tensed to meet the requirement of “moving fast and stopping motionless (动迅静定).” Conversely, Karate athletes’ rectus abdominis showed the highest contribution rate in the trunk, possibly due to the “lean back” posture adopted in the “suspension without strike” technique and the breath-hold at the moment of impact²⁹.

Relation to the control group

Subjects in the Control group did not undergo professional combat training. During the punching process, the triceps muscles of the Control group exhibited significantly higher activity than those of the other groups. This suggests that the Control group primarily used their arms to execute straight punches, rather than engaging their whole body power. In contrast, athletes from Tao Lu and other combat sports utilize a comprehensive “punching” movement chain. Consequently, the punching force in the Control group was the lowest.

Limitation

1. The 1–3s LED randomization window may enable athlete anticipation during repeated trials, requiring extended randomization protocols in future designs;

2. Participant homogeneity (male athletes from a single institution) limits technical diversity assessment, necessitating multi-center recruitment with gender-balanced cohorts;

3. Laboratory conditions simplified combat dynamics by omitting lower-body mechanics and evasive footwork—critical determinants of punching biomechanics;

4. Cross-sectional design precludes analysis of training-induced neuromuscular adaptations.

The exclusion of lower-limb kinetics particularly constrains force generation analysis, as power transfer from lower extremities fundamentally modulates punching efficiency. While our single-session approach enables group comparisons, longitudinal tracking could reveal how coordinated upper-lower body biomechanics evolve with training—essential for optimizing energy transfer patterns and strike efficiency. Future work should integrate 3D motion capture with force plates to quantify full kinetic chain contributions.

Conclusion

This study highlights significant differences in impact force and muscle activation patterns during backward straight punches across different combat sports. The findings indicate that boxing athletes generate the highest impact force, likely due to their emphasis on explosive striking. In contrast, Tao Lu and Karate athletes exhibit more controlled muscle activation patterns, consistent with their training philosophies that prioritize technique over force.

The results emphasize the role of specific muscle groups in optimizing impact force. A moderate positive correlation was observed between impact force and activation of the deltoid and brachioradialis muscles, underscoring their importance in generating power. Additionally, differences in torso muscle engagement suggest varying biomechanical efficiencies across disciplines.

These insights offer practical applications for combat sports training. Boxers may benefit from targeted strength training to enhance explosive power, while Tao Lu and Karate athletes should focus on improving precision and reaction time. The incorporation of signal-based reaction training may further optimize striking efficiency across all disciplines.

Future research should address the limitations of this study by expanding participant diversity, including female athletes, and integrating lower-body mechanics into analysis. A longitudinal study design could also provide deeper insights into how training adaptations influence striking performance over time.

In conclusion, this study provides a biomechanical foundation for understanding the technical nuances of backward straight punches in different combat sports, with implications for performance enhancement and sport-specific training methodologies.

Author contributions

X.X.Y. and S.Y.K. wrote the main manuscript, Z.D. revised the manuscript, X.X.Y. and S.Y.K. completed the experiment and prepared all the figures. All authors reviewed the manuscript.

Data availability

The datasets used and analysed during the current study available from the corresponding author on reasonable request.

Declarations

Competing interests

The authors declare no competing interests.