Development of Physical Fitness in Young Athletes: A Longitudinal Meta-analysis
Sports medicine - open · 2026
Boys' jump and endurance fitness spurt around age 13-14 while sprint speed climbs linearly with no growth spurt; useful benchmarks, male-only data.
Part of: Endurance performance and physiology: training the aerobic engine · Youth and adolescent athletes: training, injury and development
The paper
Longitudinal meta-analysis, 28 studies / 41 independent samples, male youth athletes (ages ~12-17) across nine sports.
What they found
Vertical jump and endurance performance followed curvilinear growth curves, with the fastest rate of improvement (peak velocity) occurring at 13.2 years (68% CrI 13.0-13.5) for jump and 13.8 years (68% CrI 13.6-14.2) for endurance, both overlapping typical peak height velocity timing; sprint performance improved linearly from age 12-17 with no distinct acceleration period.
Study design
Systematic review and longitudinal meta-analysis (PRISMA-guided, PROSPERO-registered) of repeated-measures studies tracking vertical jump, 10m sprint and endurance in male youth athletes across nine sports; 28 studies, 41 independent samples, synthesised with Bayesian multilevel growth curve modelling.
Methodology
The search (MEDLINE, Web of Science, Scopus), Cochrane-adapted risk-of-bias assessment, and funnel plot/Egger's test for publication bias are solid synthesis practice. But the underlying data are observational longitudinal cohorts, not trials, so maturation, training exposure, sport-selection and drop-out are all confounded with age; the abstract reports credible intervals only on the age of peak velocity, not on the magnitude of improvement or between-athlete spread, so a clinician can't judge how tight or individually useful the benchmark actually is.
The appraisal
Finding a curvilinear, earlier growth spurt in jump and endurance versus a flat linear climb in sprint is a genuinely useful descriptive result for age-referencing, but it describes natural development, not a training effect, so it cannot support causal claims about what drives faster development. Note too that the reported 68% credible intervals are roughly plus or minus one posterior SD, not the more conventional 95% band, so the true uncertainty around these peak-velocity ages is wider than the headline figures suggest, think closer to a year either side rather than a few months. Whether that true width is clinically distinguishable from normal individual variation is not something a pooled, population-level model can answer.
The gap
The analysis is male-only because of insufficient female data, so none of this generalises to female youth athletes, and the abstract gives no absolute performance values or individual-level variability needed to place a specific athlete against the curve.
Landmark context
This extends the peak height velocity/biological maturation tracking literature (the Mirwald-style PHV framework) into sport-specific fitness testing, and sits alongside youth physical development models (e.g. Lloyd and Oliver) that propose trainability windows tied to maturation; it adds pooled, age-referenced curves rather than overturning that framework.
What to do Monday
Not a change to Monday's session, but a reference point: when a boy's vertical jump or endurance testing plateaus or surges around age 13-14, these curves offer a population benchmark for whether that's expected maturation timing versus something to investigate, while sprint speed should be judged against steady linear progress rather than an expected spurt. Applies to male athletes only.
In practice
Use this as an expectation-setting and screening reference for boys roughly 11-16 across multi-sport development squads, not as a training manual. In clinic, if a 13-14 year old's jump or endurance testing plateaus well outside this window, or a 15-16 year old is still climbing steeply when the curve says they should be flattening out, that's a prompt to screen for maturation status, training load, illness, or injury rather than reassure by age alone; on the performance floor, don't programme a dedicated 'jump block' at age 13 expecting an automatic spurt, since this curve reflects pooled natural development across sports, not a trainable window, and individual timing varies widely around these means. Caveat in application: the abstract gives no absolute jump height, sprint time or endurance values and the credible intervals are the narrower 68% band, so you cannot anchor one athlete's result against this paper alone, you still need your own normative data or the full paper's tables before making a monitoring decision off it.
The five papers that matter — every week, free.
We read the whole sports-medicine, rehab & performance literature and appraise the papers worth your time.
Get the free weekly issue