Differences in Simulated EMG Activities between a Non-Rotational Shot and an Ordinary Instep Kick Identified by Principal Component Analysis

The aim of this study was to clarify the major differences in the electromyographic (EMG) activities in the hip joint required to achieve a non-rotational (NR) shot as compared with an instep kick from the spatiotemporal data. For this purpose, simulated EMG activities obtained from NR shots and instep kicks were analyzed using principal component analysis (PCA). The PCA was conducted using an input matrix constructed from the time-normalized average and the standard deviation of the EMG activities (101 data x (15 muscles; iliacus, gluteus maximus, rectus femoris, biceos femoris, vastus lateralis, vastus medialis, vastus intermedius, semimembranosus, semitendinosus, sartorius, tensor fasciae latae muscle, adductor magnus muscle, adductor longus muscle, gasctrocnemius, and tibialis anterior)). The PCA revealed that the 3rd, 4th and 8th principal component vectors (PCVs) of the 10 generated PCVs were related to achieving the NR shot (p < 0.05).

SPEED-ACCURACY TRADEOFF OF INSTEP KICK IN YOUNG SOCCER PLAYERS

The speed-accuracy trade-off of fast movements acts inversely and as such is known as the Fitts's law. The aim of this study is to determine how instep kick (IK) speed grading instructions affect the instep kick speed and accuracy. The primary hypothesis assumes that a complex motor task such as IK has an inverse relation between speed and accuracy, and the secondary hypothesis assumes that the applied speed grading instructions are sensitive. The research involved 13 male players, the average age of 15 years (±1.6). The experimental protocol included the execution of IK at five different speeds, determined by verbal instructions to respondents. For assessment of kicking accuracy, we observed the following dependent variables: mean radial error (MRE), bivariate variable error (BVE), and centroid radial error (CRE). Comparative analysis has shown that higher accuracy (reduced MRE) and kicking consistency (reduced BVE) are achieved under lower kicking speeds, but these effects were not achieved in regard to CRE. Subsequent analyses have shown that MRE has a tendency towards a significant difference between the slowest and fastest kicks (p=0.068-0.075), while in the case of BVE it has been found that there are differences between the slowest and all other speed levels (p≤0.05). The main findings of this study have indicated a partial existence (two of three variables) of an inverse relationship between speed and accuracy in complex motor tasks such as IK (multi-joint and discrete motion).