According to the characteristics of the movement required, all sports lead to development of muscles of the participants. In athletes, the muscles responsible for the movement of specific joints that are repeatedly exercised become thicker. Such muscles can be used as indicators to predict athletes' performance and to obtain information about their functional ability. Various studies have reported that anatomical cross-sectional area and muscle-volume data can be used to predict strength [1, 2, 5, 6, 8, 24]. In addition, it has been reported that a combination of MT and morphological limb length is useful for estimating muscle volume [9]. Through these prior studies, it can be inferred that the developmental form or structure of the muscle directly affects exercise power.
In previous studies, CT and MRI were used to measure muscle volume and anatomical cross-sectional area, and comparisons by sex or comparisons between non-athletes and athletes were made accordingly. In most studies, EMG measurement using electromyography was used for muscle strength [8, 25].
Through US examination and image analysis, it is possible to obtain valuable information about muscle structure; however, most previous studies performed and reported on morphological comparisons using results of CT, MRI, or simple observation of US images of muscles [1, 26]. In addition, there are few reports on the association between muscle and specific sports ability. Thus, it was not possible to determine whether this result could explain the general relationship for various sports. A previous study compared the differences in muscle structure between swimmers and soccer players. The VL thickness was thicker in swimmers than in soccer players, and there was no significant difference in Gm thickness between the two samples. VL thickness and fascicle length were significantly correlated in both these sports categories [9]. Based on this, the authors confirmed the need for further investigation into the characteristics of each sports category. Therefore, in this study, we attempted to determine the relationship between muscle architecture and anaerobic power in six categories of athletes.
According to the results, there was a statistically significant difference between the muscle structure and various measurement parameters. Moreover, a similar tendency was observed in most sports categories. The muscle development architecture of the anterior thigh region showed a significant correlation with most of the anaerobic power metrics, and the MT contribution to the exertion of anaerobic power was especially high.
The interpretation of each result is as follows:
The mean thickness and anaerobic power of the RF was approximately 29 mm, and no significant difference was observed at 30% and 50% levels of RF. The average VM and VL values were 33 and 28 mm, respectively. The TA had a mean thickness of 31 mm, and the gastrocnemius was 21 mm and 14 mm in the medial and lateral head, respectively. In addition, MT and FA were higher in Gm than in Gl.
Athletes’ muscle architecture and anaerobic power comparison based on sport category showed statistically significant differences between each sports category in all muscle items except the gastrocnemius. Upon comparing the anaerobic power items, a statistically significant relationship was observed among all values except for the arrival time to peak power. In the early stages of the Wingate test, traditional Korean wrestlers showed the highest values, but a decreasing trend was observed over time. In addition, Judo athletes showed the highest peak power; however, soccer players showed the shortest time to reach peak power and the strongest peak power calculated by weight. Wrestlers showed the highest mean power value, but were calculated by weight, showing a slight drop in the value.
In recent studies, VL has been reported to be the muscle, from among the thigh muscles, that contributes most to the exertion of propulsion [12, 27]. However, according to the results of the present study, it is apparent that the main muscle responsible for reaching maximum power can differ according to the category of the athlete.
This study demonstrated a clear correlation between muscle characteristics and anaerobic power in athletes. This finding was corroborated by a previous report that found that the physiological cross-sectional area and the maximum power generation capacity increased with an increase in the MT and FA [1–4, 12].
According to the results of the present study, the factors that influence the exertion of maximum power in athletes are the MT of the RF, VL, and gastrocnemius, and the FA of RF and Gm. The results analyzed according to the six sports categories showed similar tendencies to those obtained without classifying them into categories.
Based on these results, coaches can develop training programs that include resistance training based on the characteristics of each sports category. Programs designed to intensively develop the maximum power exerting muscles for sports that require explosive power, and to intensively develop the mean power exerting muscles for sports that require endurance, can be expected to improve athletes' performance. In addition, such programs can facilitate prediction and improvement of performance.
The correlation between muscle architecture and the anaerobic power of athletes according to sports category was analyzed in this study. The results analyzed according to the six sports categories showed similar tendencies to those obtained without classifying them into categories. The main findings of this study are as follows.
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In the case of boxers, the factor that contributes to the maximum power is the thickness of Gm. The thicknesses of the Gm and RF work together to exert the mean power.
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In the case of Judo athletes, the MT of Gl contributes to the maximum power and the MT of Gm contributes to the mean power.
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In the case of Taekwondo athletes, the MT of RF and Gm acts together to exert maximum power and mean power.
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In the case of soccer players, the MT of VL and the FA of Gm are common factors contributing to both maximum and mean power.
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In the case of wrestlers, a statistically significant relationship was found between the MT of VM and mean power exertion. No statistical significance was observed between maximum power and muscle structure.
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In the case of traditional Korean wrestlers, the FA of the RF and MT of VL and Gl were found to be factors that contribute to reaching maximum power exertion. No statistical significance was observed between mean power and muscle structure.
Therefore, on this basis, it can be concluded that the muscles that contribute to reaching the maximum power and mean power in each sport can be predicted accordingly. (Fig. 2).