The present study aimed to investigate positional differences in 744 high-level soccer players, aged 8 to 18 years. Players were assigned to six age groups (U9-U19) and divided into four playing positions (goalkeeper (GK), defender (DEF), midfielder (MF) and attacker (ATT)). MANOVA and effect sizes were used to examine anthropometrical and functional characteristics between all positions in all age groups. The main findings of the study were that GKs and DEFs were the tallest and heaviest compared with MFs and ATTs in all age groups. Further, between U9-U15, no significant differences in functional characteristics were found, except for dribbling skill, which MFs performed the best. In the U17-U19 age groups, ATTs seemed to be the most explosive (with GKs), the fastest and the more agile field players. These results suggest that inherent physical capacities (i.e., speed, power, agility) might select players in or reject players from an attacking position, which is still possible from U15-U17. Apparently, players with excellent dribbling skills at younger age are more likely to be selected to play as a MF, although, one might conclude that the typical physical characteristics for different positions at senior level are not yet fully developed among young soccer players between 8 and 14 years.

The purpose of this study was to gain an insight into the physical and physiological profile of elite Belgian soccer players with specific regard to the player's position on the field. The sample consisted of 289 adult players from 6 different first division teams. The players were divided into 5 subgroups (goalkeepers, center backs, full backs, midfielders, and strikers) according to their self-reported best position on the field. The subjects performed anaerobic (10-m sprint, 5 × 10-m shuttle run [SR], squat jump [SJ], and countermovement jump [CMJ]) and aerobic (incremental running protocol) laboratory tests. The strikers had significantly shorter sprinting times (5-, 5- to 10-m time, and SR) compared with the midfielders, center backs, and goalkeepers, whereas the full backs were also significantly faster compared with the goalkeepers and the center backs. The goalkeepers and the center backs displayed higher jumping heights (total mean SJ = 40.7 ± 4.6 cm and CMJ = 43.1 ± 4.9 cm) compared with the other 3 positions, whereas the strikers also jumped higher than the full backs and the midfielders did. Regarding the aerobic performance, both full backs and the midfielders (61.2 ± 2.7 and 60.4 ± 2.8 ml · min(-1) · kg(-1), respectively) had a higher VO2max compared with the strikers, center backs, and goalkeepers (56.8 ± 3.1, 55.6 ± 3.5, and 52.1 ± 5.0 ml · min(-1) · kg(-1), respectively). From this study, it could be concluded that players in different positions have different physiological characteristics. The results of this study might provide useful insights for individualized conditional training programs for soccer players. Aside from the predominant technical and tactical skills, a physical profile that is well adjusted to the position on the field might enhance game performance.

Purpose This study aimed to investigate the effects of different work and recovery characteristics on the W′ reconstitution and to test the predictive capabilities of the W′BAL model. Methods Eleven male participants (22 ± 3 yr, 55 ± 4 mL·kg−1⋅min−1) completed three to five constant work rate tests to determine CP and W′. Subsequently, subjects performed 12 experimental trials, each comprising two exhaustive constant work rate bouts (i.e., WB1 and WB2), interspersed by an active recovery interval. In each trial, work bout characteristics (P4 or P8, i.e., the work rate predicted to result in exhaustion in 4 and 8 min, respectively), recovery work rate (33% CP or 66% CP), and recovery duration (2, 4, or 6 min) were varied. Actual (W′ACT) and model-predicted (W′PRED) reconstitution values of W′ were calculated. Results After 2, 4, and 6 min recovery, W′ACT averaged 46% ± 2.7%, 51.2% ± 3.3%, and 59.4% ± 4.1%, respectively (P = 0.003). W′ACT was 9.4% higher after recovery at 33% CP than at 66% CP (56.9% ± 3.9% vs 47.5% ± 3.2%) (P = 0.019). P4 exercise yielded a 11.3% higher W′ACT than P8 exercise (57.8% ± 3.9% vs 46.5% ± 2.7%) (P = 0.001). W′ACT was higher than W′PRED in the conditions P4-2 min (+29.7%), P4-4 min (+18.4%), and P8-2 min (+18%) (P < 0.01). A strong correlation (R = 0.68) between the rate of W′ depletion and W′ recovery was found (P = 0.001). Conclusion This study demonstrated that both the work and recovery characteristics of a prior exhaustive exercise bout can affect the W′ reconstitution. Results revealed a slower W′ reconstitution when the rate of W′ depletion was slower as well. Furthermore, it was shown that the current W′BAL model underestimates actual W′ reconstitution, especially after shorter recovery.

During ramp exercise the deoxy[Hb + Mb] pattern follows a sigmoid model [f(x) = f (0) + A/(1 + exp(-(-c +dx))], indicating a non-linear muscle blood flow (Qm)/oxygen uptake (VO25)-relationship. We hypothesised that in trained cyclists the sigmoid would display a rightward shift, due to an increased oxidative capacity and/or higher percentage of slow-twitch fibres. A total of 10 cyclists and 11 physically active students (PA students) performed a relative ramp exercise (+/-12 min) and a ramp25-exercise (25 W min(-1)). Deoxy[Hb + Mb] was measured at the M. Vastus Lateralis by NIRS, normalized to the total amplitude of the response and expressed as a function of absolute and relative (%peakP) work rate. The work rate corresponding to c/d (i.e.50% of the amplitude of the deoxy[Hb + Mb] response) was the only parameter of the sigmoid that differed significantly between cyclists (57.9 +/- 4.4% and 60.1 +/- 4.1%peakP in the relative and ramp25, respectively) and PAstudents (49.6 +/- 4.2% and 48.2 +/- 5.1%peakP, respectively), indicating a rightward shift of the sigmoid in the cyclists. These results suggest a change in the time course of C((a-v))O(2) as a function of aerobic fitness status.