We examined the temporal changes of isokinetic strength performance of knee flexor (KF) and extensor (KE) strength after a football match. Players were randomly assigned to a control (N = 14, participated only in measurements and practices) or an experimental group (N = 20, participated also in a football match). Participants trained daily during the two days after the match. Match and training overload was monitored with GPS devices. Venous blood was sampled and muscle damage was assessed pre-match, post-match and at 12h, 36h and 60h post-match. Isometric strength as well as eccentric and concentric peak torque of knee flexors and extensors in both limbs (dominant and non-dominant) were measured on an isokinetic dynamometer at baseline and at 12h, 36h and 60h after the match. Functional (KFecc/KEcon) and conventional (KFcon/KEcon) ratios were then calculated. Only eccentric peak torque of knee flexors declined at 60h after the match in the control group. In the experimental group: a) isometric strength of knee extensors and knee flexors declined (P<0.05) at 12h (both limbs) and 36h (dominant limb only), b) eccentric and concentric peak torque of knee extensors and flexors declined (P<0.05) in both limbs for 36h at 60°/s and for 60h at 180°/s with eccentric peak torque of knee flexors demonstrating a greater (P<0.05) reduction than concentric peak torque, c) strength deterioration was greater (P<0.05) at 180°/s and in dominant limb, d) the functional ratio was more sensitive to match-induced fatigue demonstrating a more prolonged decline. Discriminant and regression analysis revealed that strength deterioration and recovery may be related to the amount of eccentric actions performed during the match and athletes' football-specific conditioning. Our data suggest that recovery kinetics of knee flexor and extensor strength after a football match demonstrate strength, limb and velocity specificity and may depend on match physical overload and players' physical conditioning level.

The purpose of the present study was to investigate the effects of a soccer training session on the balance ability of the players and assess whether the effectiveness of a balance program is affected by its performance before or after the regular soccer training. Thirty-nine soccer players were randomly divided into three subject groups (n=13 each), one control group (C group), one training group that followed a balance program (12 weeks, 3 times per week, 20 min per session) before the regular soccer training (TxB group), and one training group that performed the same balance program after the soccer training (TxA group). Standard testing balance boards and the Biodex Stability System were used to assess balance ability in the C, TxB, and TxA groups at baseline (T0) and after completing the balance program (T12). The same tests and additional isokinetic knee joint moment measurements were carried out in the TxB and TxA groups pre- and post-soccer training. Two main results were obtained: (1) No differences (p>0.05) were found in balance ability and knee joint moment production between pre- and post-soccer training. (2) The balance program increased (p<0.01) the balance ability in the TxB and TxA groups, and the improvement in the TxA group was greater (p<0.05) than that in the TxB group post-soccer training. Result (1) is in contrast to the notion of a link between fatigue induced by a soccer training session or game and injury caused by impaired balance, and result (2) has implications for athletic training and rehabilitation.

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To assess the real‐life magnitude of the heading incidence in children's and youth’ football in eight European countries with different “football cultures,” a cross‐sectional observational design, in which one match per team in 480 different teams from eight European countries (2017/18‐2018/19), was recorded by video. One training session was recorded in 312 teams. Clubs with Under‐10, Under‐12 (female/male/mixed), and Under‐16 female and male teams were eligible to participate. Heading frequencies and types were analyzed. Results are presented as headers per match/training and per team. Incidence rates (IR) per 1000 match/training hours were calculated. Under‐10 teams carried out the lowest average number of headers per match (8.8), followed by Under‐16 female (17.7), Under‐12 (18.4), and Under‐16 male (35.5). Total number of headers per match and team varied between countries. 80% of the total number of headers were single intentional headers, 12% heading duels, 3% unintentional headers by getting hit, and 5% others (trends apparent in all age groups). Three head injuries occurred during match play corresponding to an IR of 0.70 (95% CI, 0.23‐2.16). The lowest number of headers per training and team was found in Under‐10 (21.3), followed by Under‐16 females (34.1), Under‐12 (35.8), and Under‐16 males (45.0). In conclusion, this large‐scale study presents novel data about the number and type of headers in youth’ football throughout Europe. A more precise understanding of the heading incidence, specifically in young players, is mandatory for the debate of restrictions on heading in youth football.