To challenge current conventions in paediatric sport science and use data from recent longitudinal studies to elucidate the development of aerobic and anaerobic fitness, with reference to youth athletes.
(1) To critically review the traditional practice of ratio scaling physiological variables with body mass and, (2) to use multiplicative allometric models of longitudinal data, founded on 1053 (550 from boys) determinations of 10–17-year-olds’ peak oxygen uptake ($ {{\text{V}}\text{O}}_{2} $) and 763 (405 from boys) determinations of 11–17-year-olds’ peak power output (PP) and mean power output (MP), to investigate the development of aerobic and anaerobic fitness in youth.
The statistical assumptions underpinning ratio scaling of physiological variables in youth are seldom met. Multiplicative allometric modelling of longitudinal data has demonstrated that fat free mass (FFM) acting as a surrogate for active muscle mass, is the most powerful morphological influence on PP, MP, and peak $ {{\text{V}}\text{O}}_{2} $. With FFM appropriately controlled for, age effects remain significant but additional, independent effects of maturity status on anaerobic and aerobic fitness are negated.
Ratio scaling of physiological variables with body mass is fallacious, confounds interpretation of the development of anaerobic and aerobic fitness, and misleads fitness comparisons within and across youth sports. Rigorous evaluation of the development of anaerobic and aerobic fitness in youth requires longitudinal analyses of sex-specific, concurrent changes in age- and maturation-driven morphological covariates. Age and maturation-driven changes in FFM are essential considerations when evaluating the physiological development of youth athletes.
Jump-landing assessments provide a means to quantify an individual’s ability to attenuate ground reaction forces, generate lower limb explosive power and maintain joint alignment. In order to identify risk factors that can be targeted through appropriate training interventions, it is necessary to establish which (scalar) objective kinetic, kinematic, and performance measures are most associated with lower-extremity injury.
Online searches of MEDLINE, SCOPUS, EBSCOHost, SPORTDiscus and PubMed databases were completed for all articles published before March 2020 in accordance with PRISMA guidelines.
40 articles investigating nine jump-landing assessments were included in this review. The 79% of studies using drop jump (n = 14) observed an association with future injury, while only 8% of countermovement jump studies (n = 13) observed an association with injury risk. The 57% of studies using unilateral assessments found associations with risk of injury (n = 14). Studies using performance measures (jump height/distance) as outcome measure were only associated with injury risk in 30% of cases. However, those using kinetic and/or kinematic analyses (knee abduction moment, knee valgus angle, knee separation distance, peak ground reaction force) found associations with injury in 89% of studies.
The landing element of jump-landing assessments appears to be superior for identifying individuals at greater risk of injury; likely due to a closer representation of the injury mechanism. Consequently, jump-landing assessments that involve attenuation of impact forces such as the drop jump appear most suited for this purpose but should involve assessment of frontal plane knee motion and ground reaction forces.
There are numerous physical, social, and psychological benefits of exercise, sport and play for youth athletes. However, dynamic activities come with a risk of injury that has yet to be abated, warranting novel therapeutics to promote injury-resistance and to keep an active lifestyle throughout the lifespan. The purpose of the present manuscript was to summarize the extant literature and potential connecting framework regarding youth brain development and neuroplasticity associated with musculoskeletal injury. This review provides the foundation for our proposed framework that utilizes the OPTIMAL (Optimizing Performance Through Intrinsic Motivation and Attention for Learning) theory of motor learning to elicit desirable biomechanical adaptations to support injury prevention (injury risk reduction), rehabilitation strategies, and exercise performance for youth physical activity and play across all facets of sport (Prevention Rehabilitation Exercise Play; PREP). We conclude that both young male and females are ripe for OPTIMAL PREP strategies that promote desirable movement mechanics by leveraging a unique time window for which their heightened state of central nervous system plasticity is capable of enhanced adaptation through novel therapeutic interventions.
This cross-sectional study investigated dynamic force–time variables and vaulting performance in young female gymnasts of different maturity status.
120 gymnasts aged 5–14 years were sub-divided into maturity groupings using percent of predicted adult height (%PAH) attained. Participants performed three jumping protocols, the squat jump (SJ), countermovement jump (CMJ) and drop jump (DJ), before completing straight jump vaults that were recorded using two-dimensional video.
Jumping performance improved with biological maturity evidenced by the most mature gymnasts’ producing significantly more absolute force (P < 0.05; all d > 0.78), impulse (P < 0.05; all d > 0.75) and power (P < 0.05; all d > 0.91) than the least mature group, resulting in the greater jump heights (P < 0.05; all d > 0.70). While, no significant differences were observed in relative peak force across multiple tests, measures of relative peak power did significantly increase with maturity. Based upon regression analyses, maturation was found to influence vertical take-off velocity during vaulting, explaining 41% of the variance in each jumping protocol. Across all tests, the DJ was found to have the highest predictive ability of vaulting vertical take-off velocity, explaining 55% of the total variance.
Biological maturation impacts jump height and underpinning mechanical variables in young female gymnasts. Vaulting vertical take-off velocity appears to be influenced by maturation and various dynamic force–time variables, particularly those during DJ, which had the highest explained total variance.
To establish the load–velocity relationships during backward sled pulling and compare this to forward sled pulling and determine the reliability of running speeds and associated load–velocity regression slopes in youth athletes.
Twenty-one boys (age, 13.6 ± 0.28 years old; height, 1.72 ± 0.09 m; mass, 66.1 ± 8.2 kg; maturity, 0.57 ± 0.72 years from peak height velocity) performed backward and forward resisted running on three occasions. Load–velocity relationships were established using an un-resisted sprint and resisted sled pull with loads of 25%–81% body mass (BM) in both directions, and the reliability of sprint times at each load and the load–velocity regression slopes were examined.
The load–velocity data was reliable across multiple testing occasions for backward (CV ≤ 7.2%; ICC 0.67–0.91) and forward sled pulling (CV ≤ 7.2%; ICC 0.66–0.91). From the regression lines (R 2 ≥ 0.99; P ≤ 0.01), it was observed that averaged loads across the sample of 31%, 46% and 61% BM resulted in 27%, 38% and 48% decrease in velocity during backward sled pulling and 23%, 33% and 43% during forward sled pulling. Increasing backward and forward loads by ∼ 13% and ~ 15% BM respectively, reliably resulted in ∼ 10% decreases in velocity.
If contractile overload of the lower limbs is a focus of training then practitioners should preferentially use backward sled pulling. Both backward and forward sled pulling can be used in a similar manner regarding loading, though backward velocity is more sensitive to load and therefore overloading backward motion should be prescribed with this in mind.
The purpose of this study was to examine the relationships among leg extension strength, explosive strength, muscle activation, and measurements of growth to predictions of vertical jump performance in youth athletes.
Height, body mass, skinfolds, and quadriceps femoris muscle cross-sectional area were measured in 39 sports active children (20 females, 19 males, age = 12.52 ± 0.62 years old). Peak torque (PT), rate of torque development (RTD), rate of velocity development (RVD), and rate of electromyographic amplitude rise (RER) were measured during isometric and isokinetic leg extensions. PT, RTD, and RVD were expressed in absolute terms and normalized to body mass. Estimated jump height (JH) and peak power (PP) were assessed during static (SJ), counter-movement (CMJ), and drop (DJ) jumps.
JH exhibited greater correlations with PT normalized to body mass (r = 0.387–0.758) than absolute PT (r = 0.338–0.417), whereas PP exhibited greater correlations with absolute PT (r = 0.368–0.837). Only negligible to moderate relationships existed between JH and PP across all jumps (r = 0.053–0.605). Over 50% of the variability in PP was predicted in 24 of 30 regression models with absolute muscle strength, muscle activation, and measurements of growth, while only 6 of 30 models predicted more than 50% of the variability in JH.
Overall, absolute static and dynamic muscle strength, muscle activation, and growth better explained PP measured during vertical jumps than estimated JH.
The aim of this study was to determine the modulatory roles of biological maturity and age on the predictors of performance in youth swimmers and their stability over a six-month training cycle.
In total, 28 swimmers (10 pre-pubertal [6 boys], 11.1 ± 1.8 years; 18 pubertal [8 boys], 15.2 ± 2.0 years old) and 26 untrained controls (15 pre-pubertal [10 boys], 9.7 ± 1.5 years; 11 pubertal [6 boys], 14.4 ± 0.5 years old) were recruited. At baseline, 3- and 6-months, participants completed an incremental ramp cycle test, isometric handgrip strength test and countermovement jumps, with speed assessed as a measure of performance in swimmers. Principle component analysis (PCA) identified factors that described youth swimmers’ physical profile, with linear mixed models subsequently used to determine their interaction with age and maturity on performance.
Aerobic fitness and upper body strength were significantly higher in the trained participants, irrespective of maturity status or time-point. Four key factors were identified through PCA (anthropometrics; strength; aerobic capacity; aerobic rate), accounting for 90% of the between parameter variance. Age exerted a widespread influence on swimming performance predictors, influencing all four factors, whilst maturity only influenced the aerobic factors. The key age of divergence was 13 years.
Overall, the present study found no evidence of a maturational threshold in the aerobic or strength-related response to training in youth. The influence of age on performance predictors suggests that utilising a single or select group of parameters to inform selection and/or talent identification throughout the dynamic processes of growth and maturation should be avoided.
Individual differences in biological maturation present challenges for coaches involved with youth soccer players. Youth in the same chronological age group vary in terms of stage of maturity (pre, circum- and post-pubescent) and rate of growth, but how this affects coaches’ evaluations of player performance is unknown. The aim of this study was to compare youth soccer coaches’ evaluations of players match performances before, during and post growth spurt in a professional English soccer academy across four seasons. Two hundred and seventy-eight male soccer players in the under-9 to under-16 age-groups had their performances evaluated by their coach on a 4-point Likert scale. For each game, players were categorised by their maturity status estimated using percentage of predicted adult height at the time of observation. A one-way ANCOVA controlling for the level of opposition and game outcome revealed that coaches’ evaluations declined from the pre- to during growth spurt stages, however, this was only significant in the under 12 age-group. Further, coaches’ evaluations increased again in the post-growth spurt stage, although only significant in the under 15 age-group. Coaches evaluations of player performance appear to vary in accordance with stage of maturity and rate of growth. Practitioners in youth soccer should understand the extent to which maturity status may adversely impact performance and consider this when making talent selection decisions.
It is well recognised that injury prevention training can reduce injury incidence, however current coach education pathways do not provide grass-root coaches with the knowledge and confidence to deliver such training to youth players. The aim of this study was to explore differences in knowledge, understanding, attitude and confidence to deliver such injury prevention training in three European countries.
A total of 269 grass-root soccer coaches from 3 European countries (Czech Republic, UK, Spain) were recruited for this study. A validated questionnaire exploring knowledge, understanding, attitude towards and confidence to deliver youth injury prevention training was completed prior to a 2 h workshop on injury prevention training. Differences between countries was examined using Bayesian factors to quantify the evidence for and against the hypothesis of independence (H0) by assuming a Poisson sampling scheme (as there was no a priori restriction on any cell count, nor on the grand total) (BF10 Poisson).
Current knowledge, attitude and confidence to deliver injury prevention training to youth players was poor across all three European countries. Relatively few coaches were currently using injury prevention training in their coaching sessions (23%). There were some country specific differences for attitude towards injury prevention training and confidence to deliver injury training, with Spanish coaches reporting a more positive attitude and confidence to deliver such training. Significantly fewer coaches in the UK were using injury prevention training compared to coaches in Spain and the Czech Republic.
As coaches identified a need for coach education and few were delivering injury prevention training, there is a clear need to embed and implement this programme into the grassroots coaching framework of sports governing bodies to improve adoption, implementation and maintenance.