**3. Results**

Statistically significant differences were found in the results of measurements before and after the experiment in the experimental group. Significant improvements in performance were noted in all tests except for the Cooper test. The analysis of the results (Table 3) indicated a statistically significant increase in abdominal muscle strength (5% difference), handgrip strength, an increase in the number of pull-ups (12% difference), an increase in the number of clap push-ups (9% increase), and an increase in the length of the long jump (1.8% difference), as well as a decrease in the time of the shuttle run (3% difference) and an increase in the results of the sit-and-reach test (8% difference) compared to the results of the initial test (pre-test compared to post-test). No statistically significant differences in the results of the Cooper test were observed (*p* > 0.05). In the control group, the only significantly improved result was the static strength test (handgrip test on a dynamometer). A comparison of the difference between the groups after the experiment revealed statistically significant differences in abdominal strength, clap push-ups, standing long jump, sit-and-reach, and tapping (Table 3).

The analysis of the changes in special fitness induced by the experiment showed a significant improvement in all the parameters measured in the experimental group. Furthermore, there were significant adverse changes in the control group in punch speed and hip-turning speed. The difference between the groups after completion of the experiment on the special kickboxing fitness test (SKFT) and the total number of punches in the test and the hip-turning speed were also found to be statistically significant (Table 4).

There were statistically significant relationships of endurance as measured by the Cooper test, total number of punches in the SKFT, speed of upper limb movements (tapping) with punching speed, and agility run with hip-turning speed. All the correlations were high and statistically significant at *p* < 0.001 (Table 5).


#### **Table 3.** General physical fitness of the participants before and after the experiment.

**group** t 0.84 *p* 0.40 d 0.22 **t 1.14** *p* **0.05** d 

> E—experimental group, C—control group, SD—standard deviation, CI—confidence intervals, statistically significant values are bolded.

**Table 4.** Special physical fitness of the participants before and after the experiment.


*p* *p* 

E—experimental group, C—control group, SD—standard deviation, CI—confidence intervals, statistically significant values are bolded.


**Table 5.** Relationships between special physical fitness and general physical fitness of kickboxers after the experimental program.

Statistically significant values are bolded.

## **4. Discussion**

In this study, we attempted to determine the effect of CrossFit training on the general and special physical fitness of kickboxers. The results presented in this study allow for the verification of an experimental program based on CrossFit training. The idea of CrossFit training is to introduce a component of competing with a training partner or oneself, which increases the intensity and effectiveness of exercise [24]. The findings of the study show that the experiment had a positive effect on the fitness level in the experimental group, which was confirmed by statistically significant changes. Improvements were observed in abdominal muscle strength, shoulder girdle strength, and handgrip strength. The development of general body strength is a basic component of the preparation of a kickboxer to effectively use hand and foot techniques and to improve performance during the fight [4,48,49]. Furthermore, strength training is effective in protecting against injuries that are common in contact sports [50,51]. The results of our research show that it is advisable to use CrossFit training as a supplement to basic kickboxing training in the preparation period. The experimental training also improved dynamic upper and lower limb strength as measured by standing long jump and clap push-ups. Muscle strength of both upper and lower limbs is essential for the athlete to win in full-contact formulas in kickboxing such as K1, low kick, and full contact [52,53]. Taking into account the significant changes, it can be concluded that the training used in the experiment led to the increase in dynamic strength in the experimental group despite the lack of exercises with additional external resistance. A high level of dynamic power allows for the effective use of technical actions that affect the level of technical and tactical indices and thus fighting performance [16,33]. Another effect of the implemented training program was a progression in speed, as confirmed by statistically significant changes recorded in the test of speed of hand movements (plate tapping test) in the experimental group. Accordingly, the authors' program induced improvements in upper limb speed in plate tapping and special fitness tests (punching speed). The relationship between these two components was confirmed by the high correlation between each other. It is worth noting that these abilities play a key role in full-contact formula (K1, low kick, full contact), light forms (kick light, light contact), and intermittent forms (point fighting) [54], as well as in any fight using upper limbs (boxing, karate, etc.). According to Kimm and Theil, hand speed is especially important in boxing, both to protect against attack and throw punches [55]. A kickboxer who delivers punches at a fast pace can effectively attack the opponent, anticipate their intentions, and effectively defend against the opponent's attack. A high frequency of upper

limb movements and punches is highly desirable, especially in limited-contact formulas where a point advantage determines victory [9]. The observed progression can be explained by the use of plyometrics in the experimental training involving the upper limbs, such as burpees, combined with dynamic, explosive boxing actions on a bag. The purpose of these actions was to develop the muscles' ability to generate a large force in a short time (high force rate) or improve dynamics [56]. In addition to these characteristics, agility, balance, and coordination also play an important role in the training process [15]. An improvement in the results after the experimental training was also observed in the agility test (shuttle run). This ability determines the speed of movement, which is a precondition for effective movement in the fighting area and defense. Furthermore, the ability to move quickly and the footwork speed are the basis for meeting the technical and tactical objectives of the fight [57].

In the present study, a high correlation was observed in the experimental group between the hip-turning speed in the special fitness test and shuttle run results. Interpretation of the relationships leads to the conclusion that the kick speed, associated with hip turning, is determined by agility, with its components being coordination and speed [2,15]. There was a significant increase in flexibility in the experimental group after the experimental training program. Flexibility is one of the elements needed to master technical skills [15]. The sit-and-reach test showed the progression of flexibility in athletes in the study group. The improvements may be due to the training used, which included high kicks that required a large range of motion. The Cooper Test, which measures the athlete's aerobic endurance level, showed small and statistically insignificant improvements in both groups. This may be explained by high baseline levels of running endurance in the kickboxers tested, whereas the specific kickboxing training and experimental training did not allow for significant development of this ability. It is worth noting that the higher level of the Cooper test results translates directly into higher special fitness, as evidenced by the high positive correlation with the total number of punches in the test. Furthermore, the experimental group showed a statistically significant reduction in the physical fitness index in the SKFT test, which indicates an improvement in the athletes' special endurance. Favorable changes were found in all special fitness parameters, i.e., the total number of punches, punching speed, and hip-turning speed. This leads us to assume that the applied training based on the components of CrossFit has a positive impact on the athlete's performance, which is measured by the results of special fitness tests [45,58].

#### *Limitation in the Study*

A major limitation of our study was the lack of detailed verification of the study groups. We were unable to conduct the experiment in a closed facility where both groups would have the same conditions for functioning and training. Furthermore, we did not perform a direct test to evaluate VO2max based only on running endurance.
