The purpose of this study was to examine the effects of fatigue on biomechanical indices of soccer kick performance. Ten male amateur soccer players performed maximal instep kicks prior to, in the middle and after the implementation of a 90 min intermittent exercise protocol. Three-dimensional data, ground reaction forces (GRFs) and segmental moments were measured during the kick while blood lactate and ammonia concentrations were monitored throughout the protocol. Analysis of variance designs with repeated measures indicated a significant increase in ammonia (P<0.01) and lactate levels (P<0.01) following fatigue. The GRFs and joint displacement curves during the kick remained unaltered after fatigue (P>0.01). However, post-fatigue maximum angular velocity of the shank, the net moments acting on the shank and the resultant joint moments were significantly lower compared with the corresponding pre-exercise values (P<0.01). The velocity of the ball was 24.69 m/s prior to the protocol and significantly decreased to 21.78 m/s after (P<0.01). Similarly, the ball/foot speed ratio significantly (P<0.01) declined from 1.40+/-0.12 (pre-fatigue) to 1.33+/-0.18 (post-fatigue). The present results suggest that an exercise protocol that simulates soccer game conditions results in significant impairment of soccer kick performance. This could be attributed to alterations of the function of the neuromuscular system and force generation capacity, which may have altered the mechanics of soccer kick performance.

Soccer kicks using a high angle of approach increase the medial and posterior GRF, which is indicative of an altered stance during the kick, resulting in an altered balance. Such kicks are accompanied by significant alterations in knee joint kinematics and an increased BF activation around ground contact. Soccer kicks from an angled approach may induce significant loads to knee joint structures of the support leg.

Soccer kicking training should be adjusted to the characteristics of the athletes. Therefore, examination of differences in kicking kinematics of females and pubertal players relative to males is worthwhile. The purpose of the study was to compare kicking kinematics and segmental sequence parameters between male, female, and pubertal players. Ten adult male, ten adult female, and ten male pubertal players participated in the study. Participants performed five consecutive kicking trials of a stationary ball, as powerful as they could. Analysis of variance showed significantly higher ball velocity, higher joint linear velocities for the knee and the hip, and higher angular velocities of the knee and the ankle for males compared to female and pubertal players (p < 0.05). Similarly, the peak joint velocity was achieved significantly closer to ball impact in males compared to other groups (p < 0.05). Males also showed a more plantarflexed ankle immediately before ball impact (p < 0.05). Females and pubertal players may benefit from skill training aiming to increase ankle plantarflexion and hip flexion prior to ball impact, and to adjust thigh and shank motion, such that the shank-foot segment travels through a higher range of motion and with a greater velocity.

The purpose of the present study was to compare the three-dimensional kinematics of the lower extremities and ground reaction forces between the instep kick and the kick with the outside area of the foot (outstep kick) in pubertal soccer players. Ten pubertal soccer players performed consecutive kicking trials in random order after a two-step angled approach with the instep and the outstep portion of the foot. Three-dimensional data and ground reaction forces were measured during kicking. Paired t-tests indicated significantly higher (P < 0.05) ball speeds and ball/foot speed ratios for the instep kick compared with the outstep kick. Non-significant differences in angular and linear sagittal plane kinematic parameters, temporal characteristics, and ground reaction forces between the instep and outstep soccer kicks were observed (P > 0.05). In contrast, analysis of variance indicated that the outstep kick displayed higher hip internal rotation and abduction, knee internal rotation, and ankle inversion than the instep kick (P < 0.05). Our results suggest that the instep kick is more powerful than the outstep kick and that different types of kick require different types of skill training.

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