Physical capacity, not skeletal maturity, distinguishes competitive levels in male Norwegian U14 soccer players

Intra-observer reproducibility and inter-observer agreement of Fels skeletal age assessments among male tennis players 8-16 years

BACKGROUND

Skeletal age (SA) is an estimate of biological maturity status that is commonly used in sport-related medical examinations. This study considered intra-observer reproducibility and inter-observer agreement of SA assessments among male tennis players.

METHODS

SA was assessed with the Fels method in 97 male tennis players with chronological ages (CA) spanning 8.7-16.8 years. Radiographs were evaluated by two independent trained observers. Based on the difference between SA and CA, players were classified as late, average or early maturing; if a player was skeletally mature, he was noted as such as an SA is not assigned.

RESULTS

The magnitude of intra-individual differences between repeated SA assessments were d = 0.008 year (observer A) and d = 0.001 year (observer B); the respective coefficients of variation were 1.11% and 1.75%. Inter-observer mean differences were negligible (t = 1.252, p = 0.210) and the intra-class correlation coefficient was nearly perfect (ICC = 0.995). Concordance of classifications of players by maturity status between observers was 90%.

CONCLUSION

Fels SA assessments were highly reproducible and showed an acceptable level of inter-observer agreement between trained examiners. Classifications of players by skeletal maturity status based on assessments of the two observers were highly concordant, though not 100%. The results highlight the importance of experienced observers in skeletal maturity assessments.

Associations between biological maturity level, match locomotion, and physical capacities in youth male soccer players

INTRODUCTION

Biological maturity level has shown to affect sport performance in youths. However, most previous studies have used noninvasive methods to estimate maturity level. Thus, the main aim of the present study was to investigate the association between skeletal age (SA) as a measure of biological maturation level, match locomotion, and physical capacity in male youth soccer players.

METHOD

Thirty-eight Norwegian players were followed during two consecutive seasons (U14 and U15). Match locomotion was assessed with GPS-tracking in matches. SA, assessed by x-ray, physical capacities (speed, strength and endurance) and anthropometrics were measured in the middle of each season. Analysis of associations between SA, match locomotion, and physical capacities were adjusted for the potential confounding effect of body height and weight.

RESULTS

In matches, positive associations were found between SA and maximal speed and running distance in the highest speed zones. Further, SA was associated with 40 m sprint time and countermovement jump (CMJ) height, and with intermittent-endurance capacity after adjusting for body height (U14). Associations between SA and leg strength and power, and between SA and absolute VO_2max were not significant after adjusting for body weight. There was no association between SA and total distance covered in matches.

CONCLUSION

Biological maturity level influence match locomotion and performance on physical capacity tests. It is important that players, parents and coaches are aware of the advantages more mature players have during puberty, and that less mature players also are given attention, appropriate training and match competition to ensure proper development.

Physical characteristics of elite youth male football players aged 13-15 are based upon biological maturity

Background

Older and more mature football players have been reported to gain advantages in the selection process during adolescence. The aim of this study was to investigate the influence of skeletal age (SA) on the physical characteristics of elite male football players aged 13-15 years through a cross-sectional study.

Methods and Materials

We enrolled 167 elite players aged 13-15 from three academic football schools in China, and measured height, body mass, thigh circumference, skinfold (triceps and calf), 10 m/30-m sprint, T-tests (left and right), 5 × 25-m repeated-sprint ability (5 × 25 RSA), standing long jump, and YoYo intermittent recovery test level 1 (YYIR1). Subjects were divided into early-, average-, and late-maturity levels according to their SA and chronological age (CA) based on the following criteria: SA-CA > +1 year, SA-CA = ±1 year, and SA-CA < -1 year, respectively. The differences in parameters among the groups were analyzed using one-way analysis of variance and Bonferroni's post-hoc test, with statistical significance set at p < 0.05.

Results

Relative to the late-maturing players, the early- and average-maturing players aged 13-15 years were taller, heavier, had a larger thigh circumference, and scored higher on the standing long jump, 30 m sprint, and 5 × 25-RSA (p < 0.05). The physical (except for body-fat percentage) and athletic characteristics of players aged 13-15 were not only significantly influenced by biological maturity, but also increased significantly with CA. The influence of biological maturity on height, 30-m sprints, and 5 × 25-m RSA diminished with age and exerted no significant effect on body-fat percentage and on YYIR1. Late-maturing players exhibited the greatest increase in physical (except for body-fat percentage) and athletic performance (except for the 10-m sprint) compared to players of early and/or average maturity.

Conclusions

Although early-maturing players aged 13-15 possessed better anthropometric and physical performance than late- and average-maturing players, the growth and development of physical function of late- and average-maturing players was significantly greater, particularly with respect to height, sprint speed, and muscular power.

Motion Analysis of Match Play in U14 Male Soccer Players and the Influence of Position, Competitive Level and Contextual Variables

This study aimed to investigate match running performance in U14 male soccer players in Norway, and the influence of position, competitive level and contextual factors on running performance. Locomotion was monitored in 64 different U14 players during 23 official matches. Matches were played at two different competitive levels: U14 elite level (n = 7) and U14 sub-elite level (n = 16). The inclusion criterion was completed match halves played in the same playing position. The variables’ influence on match running performance was assessed using mixed-effect models, pairwise comparisons with Bonferroni correction, and effect size. The results showed that the U14 players, on average, moved 7645 ± 840 m during a match, of which 1730 ± 681 m (22.6%) included high-intensity running (HIR, 13.5–18.5 km·h⁻¹) and sprinting (>18.5 km·h⁻¹). Wide midfielders (WM) and fullbacks (FB) covered the greatest sprint distance (569 ± 40 m) and, in addition to the centre midfield position (CM), also covered the greatest total distance (TD) (8014 ± 140 m) and HIR distance (1446 ± 64 m). Centre forwards (CF) performed significantly more accelerations (49.5 ± 3.8) compared other positions. TD (7952 ± 120 m vs. 7590 ± 94 m) and HIR (1432 ± 57 m vs. 1236 ± 43 m) were greater in U14 elite-level matches compared with sub-elite matches. Greater TD and sprint distances were performed in home matches, but, on the other hand, more accelerations and decelerations were performed in matches played away or in neutral locations. Significantly higher TD, HIR and sprinting distances were also found in lost or drawn matches. In conclusion, physical performance during matches is highly related to playing position, and wide positions seem to be the most physically demanding. Further, competitive level and contextual match variables are associated with players’ running performance.

Validity of Force-Velocity Profiling Assessed With a Pneumatic Leg Press Device

PURPOSE

The aim of this study was to examine the concurrent validity of force-velocity (FV) variables assessed across 5 Keiser leg press devices.

METHODS

A linear encoder and 2 independent force plates (MuscleLab devices) were mounted on each of the 5 leg press devices. A total of 997 leg press executions, covering a wide range of forces and velocities, were performed by 14 participants (29 [7] y, 181 [5] cm, 82 [8] kg) across the 5 devices. Average and peak force, velocity, and power values were collected simultaneously from the Keiser and MuscleLab devices for each repetition. Individual FV profiles were fitted to each participant from peak and average force and velocity measurements. Theoretical maximal force, velocity, and power were deduced from the FV relationship.

RESULTS

Average and peak force and velocity had a coefficient of variation of 1.5% to 8.6%, near-perfect correlations (.994-.999), and a systematic bias of 0.7% to 7.1% when compared with reference measurements. Average and peak power showed larger coefficient of variations (11.6% and 17.2%), despite excellent correlations (.977 and .952), and trivial to small biases (3.9% and 8.4%). Extrapolated FV variables showed near-perfect correlations (.983-.997) with trivial to small biases (1.4%-11.2%) and a coefficient of variation of 1.4% to 5.9%.

CONCLUSIONS

The Keiser leg press device can obtain valid measurements over a wide range of forces and velocities across different devices. To accurately measure power, theoretical maximal power calculated from the FV profile is recommended over average and peak power values from single repetitions, due to the lower random error observed for theoretical maximal power.

Sprint Interval Running and Continuous Running Produce Training Specific Adaptations, Despite a Similar Improvement of Aerobic Endurance Capacity-A Randomized Trial of Healthy Adults

The purpose of the present study was to investigate training-specific adaptations to eight weeks of moderate intensity continuous training (CT) and sprint interval training (SIT). Young healthy subjects (n = 25; 9 males and 16 females) performed either continuous training (30-60 min, 70-80% peak heart rate) or sprint interval training (5-10 near maximal 30 s sprints, 3 min recovery) three times per week for eight weeks. Maximal oxygen consumption, 20 m shuttle run test and 5·60 m sprint test were performed before and after the intervention. Furthermore, heart rate, oxygen pulse, respiratory exchange ratio, lactate and running economy were assessed at five submaximal intensities, before and after the training interventions. Maximal oxygen uptake increased after CT (before: 47.9 ± 1.5; after: 49.7 ± 1.5 mL·kg^-1·min^-1, p < 0.05) and SIT (before: 50.5 ± 1.6; after: 53.3 ± 1.5 mL·kg^-1·min^-1, p < 0.01), with no statistically significant differences between groups. Both groups increased 20 m shuttle run performance and 60 m sprint performance, but SIT performed better than CT at the 4th and 5th 60 m sprint after the intervention (p < 0.05). At submaximal intensities, CT, but not SIT, reduced heart rate (p < 0.05), whereas lactate decreased in both groups. In conclusion, both groups demonstrated similar improvements of several performance measures including VO_2max, but sprint performance was better after SIT, and CT caused training-specific adaptations at submaximal intensities.