49 figures, each with the population it was measured in and the source with DOI: drop-out, menstrual cycle, injuries, sleep, iron, pain. A number without its population is not a fact.
Among girls registered with a club at ages 10-14, 71% drop out of sport without ever returning.
Source: Eime et al., 2020
77% of elite athletes report that their menstrual cycle has negatively affected their performance. Population: 128 ADULT athletes, mean age 28.
Source: Jones et al., 2024
The effect of menstrual cycle phase on performance is of trivial magnitude (ES 0.5 = -0.06; 95% CrI -0.16 to 0.04), with evidence quality rated low under GRADE. Population: 78 studies, 1,193 ADULT women aged 18-40; no equivalent data exists for adolescents.
Source: McNulty et al., 2020
Among adolescents aged 10-18, between 25.2% and 61.1% avoid or reduce physical activity during their period.
Source: Harvey et al., 2025
The prevalence of dysmenorrhoea (period pain) is 71.1%; 20.1% report absence from school or university because of the pain and 40.9% an impact on concentration or classroom performance. Population: 38 studies, 21,573 young women UNDER 25, largely students — not adolescents only.
Source: Armour et al., 2019
Among athletes, dysmenorrhoea is the most frequent menstrual disorder, with a prevalence of 32.3%. CAUTION: the range across studies runs from 7.8% to 85.6% because definitions and measurement methods differ widely — the order of magnitude is reliable, the figure is not. Population: systematic review of 60 studies and 6,380 athletes not using hormonal contraception.
Source: Taim et al., 2023
Exercise can substantially reduce the intensity of period pain compared with doing nothing (SMD -1.86; 95% CI -2.06 to -1.66), roughly 25 mm on a 100 mm visual analogue scale; the dose used in the studies is 45-60 minutes at least 3 times a week, at any intensity. Evidence quality LOW; whether the benefit persists after stopping is unclear. Population: 12 studies and 854 women (10 studies and 754 women in the meta-analysis).
Source: Armour et al., 2019 (Cochrane)
Only 11% of athletes discuss their menstrual cycle with their coach: 4% if the coach is a man, 55% if a woman; 88% learned about it on their own. Population: 1,086 athletes, adults and adolescents together, data not broken down by age.
Source: Höök et al., 2022
44% of adolescent female athletes mistakenly believe that losing their period is a normal response to heavy training loads. Population: 90 adolescent female athletes.
Source: Armento et al., 2021
In adolescent female athletes (aged 11-18) the prevalence of mild iron deficiency (ferritin ≤30 µg/L) is 53.2%, while iron-deficiency anaemia affects 4%.
Source: Nicotra et al., 2023
At 13-14, 51% of girls say their breasts affect their participation in sport, yet only 10% always wear a sports bra. Population: 2,089 British girls aged 11-18.
Source: Scurr et al., 2016
The consensus recommendation for ages 13-18 is 8-10 hours of sleep per night.
Source: Paruthi et al., 2016
In adolescent athletes, sleeping fewer than 8 hours a night is associated with being injured 1.7 times as often (95% CI 1.0-3.0; p=0.04). Population: 112 adolescent athletes of both sexes, results not broken down by sex; an association, not a demonstrated cause.
Source: Milewski et al., 2014
Insomnia symptoms rise from 3.4% to 12.2% in girls between Tanner stage 1 and stage 5, against 4.3%-9.1% in boys. Population: 7,507 children and adolescents aged 6-17.
Source: Zhang et al., 2016
Only 6% of sport and exercise science studies are conducted exclusively on women.
Source: Cowley et al., 2021
In high-school football (soccer), female athletes have 1.88 times the concussion risk of male peers (95% CI 1.69-2.09). The leading mechanism differs: contact with an object in girls (41.9%), with another player in boys (48.4%); boys are 1.54 times as likely to be removed from play immediately. Population: 83,378 US high-school athletes, 2016-2019.
Source: Bretzin et al., 2021
Athletes had not reported 60% of the concussion events they recalled to a responsible adult; for minor blows («bell-ringers») the non-reporting share rises to 87%. Population: 167 high-school athletes of both sexes, mean age 15.7; preliminary study.
Source: Register-Mihalik et al., 2013
Adolescent athletes removed from play immediately after a concussion recover in a mean of 22.0 days, against 44.4 days for those who keep playing (p=0.003); those who stay on are 8.8 times as likely to have a prolonged recovery beyond 21 days. Population: 69 athletes aged 12-19 of both sexes, recruited at a specialist centre — a small, selected sample.
Source: Elbin et al., 2016
In high-school sport, girls sustain 0.084 anterior cruciate ligament ruptures per 1,000 exposures against 0.060 in boys (ratio 1.40; 95% CI 1.25-1.57); the widest gap is in basketball (RR 4.14) and the highest absolute rate is in girls’ football/soccer (0.166).
Source: Bram et al., 2021
Preventive neuromuscular training reduces ACL rupture risk from roughly 1 in 54 to 1 in 111 (OR 0.51; 95% CI 0.37-0.69); among athletes aged 13-19 the odds ratio falls to 0.38 (95% CI 0.24-0.60), about 60% lower risk. Mean effective dose: 24.1 minutes per session, 2.51 times a week. Population: 27,231 female athletes aged 13-24, with the 13-19 subgroup reported separately.
Source: Petushek et al., 2019
After ACL reconstruction, 23% of athletes under 25 who return to sport sustain a second ACL injury. Population: athletes of both sexes.
Source: Wiggins et al., 2016
In young female athletes the estimated mean age at peak height velocity (PHV) is 11.18 years, with a 90% credible interval from 8.62 to 12.94 years: the width of that interval is the finding, not a flaw in the estimate — one age category holds athletes years apart biologically. Population: Bayesian longitudinal meta-analysis of 14 studies and 21 independent samples of young female athletes.
Source: Lima et al., 2024
Peak bone mineral content accrual occurs roughly 6 months AFTER peak height velocity: in that window the bone is already longer but not yet as dense. Population: 53 Canadian girls and 60 boys followed for 6 years.
Source: Bailey et al., 1999
In young female athletes the evidence supporting an association between biological maturation and injury is LIMITED; the evidence linking maturation to potential risk factors is moderate, above all in jumping and landing biomechanics and knee injury risk. Population: systematic review of 31 studies (10 on injury, 21 on risk factors) in girls and young women in sport.
Source: Zoellner e Whatman, 2026
Among adolescent female athletes the prevalence of urinary incontinence during sport ranges from 18.2% to 80% depending on the discipline, with a mean of 48.58%; the highest values are in trampolining (80%), rope skipping (75%) and football/soccer (62.8%). Population: 9 studies, 633 athletes under 19, mean age 16.15.
Source: Rial Rebullido et al., 2021
87% of adolescent female athletes say they would not discuss their urinary incontinence symptoms with their coach, and between 69% and 90% have never heard of pelvic floor training.
Source: Rial Rebullido et al., 2021
Among 219 female athletes aged 13-18, those highly specialised in a single sport report a history of injury 2.93 times as often as low-specialisation peers (95% CI 1.38-6.24) and a history of concussion 5.00 times as often (95% CI 1.86-13.42). Cross-sectional questionnaire study, wide confidence intervals.
Source: Okoruwa et al., 2022
Young athletes who play more hours of organised sport per week than their age in years have 2.07 times the odds of a serious overuse injury (95% CI 1.40-3.05); a ratio of organised sport to free play above 2:1 raises it to 1.87 times (95% CI 1.26-2.76).
Source: Jayanthi et al., 2015
American Academy of Pediatrics guidance for under-18s: play multiple sports at least until puberty, specialise later (late adolescence), keep weekly hours of organised sport below the athlete’s age in years and under 16 in any case, take 1-2 days a week free from the specific sport, and at least 3 months a year off in one-month blocks. This is consensus guidance on limited evidence, written for the US sporting context.
Source: Brenner e AAP, 2016
In sex-comparable US high-school sports, female athletes sustain 2.22 stress fractures per 100,000 exposures against 1.27 in male peers (ratio 1.75; 95% CI 1.38-2.23) and account for 63.3% of all cases; the highest rates are in girls’ cross-country (10.62) and girls’ gymnastics (7.43). Population: 389 stress fractures out of 51,773 injuries, 2005-2013.
Source: Changstrom et al., 2015
As female athlete triad risk factors accumulate, the incidence of bone stress injury rises: with low bone density (Z-score < -1.0) and ≥12 training hours a week, 29.7% sustained one; combining ≥12 hours, a «leanness» sport and dietary restriction takes it to 46.2%, against 10.8% overall. Population: 259 active girls and young women, MEAN AGE 18.1; observational study, associations rather than causation.
Source: Barrack et al., 2014
10 minutes of jumping replacing the PE warm-up, twice a week for 8 months, increased femoral neck bone mineral content in girls by 13.9% against 4.9% in controls. Population: randomised controlled trial of 99 adolescents (53 girls, 46 boys), mean age 13.8; sex-specific effects.
Source: Weeks et al., 2008
Weight training does not stunt growth: in a review of 22 experimental programmes in children and preadolescents, the programmes significantly improved strength, did NOT affect growth in height or weight, and across the 10 studies that systematically monitored injuries a total of three were reported (estimated rates 0.176 / 0.053 / 0.055 per 100 hours). The conclusion is conditional: it holds for SUPERVISED protocols with a low instructor-to-participant ratio.
Source: Malina, 2006
Only 38.51% of children and adolescents meet the WHO recommendation of muscle-strengthening activity on at least 3 days a week (95% CI 34.35-42.75); being male is among the predictors of meeting it. Population: meta-analysis of 29 studies, 1,273,544 children and adolescents across 36 countries, 49.40% girls, mean age 13.40.
Source: García-Hermoso et al., 2025
Strength training alone as primary prevention is associated with a relative risk of sports injury of 0.338 (95% CI 0.238-0.480), with high strength of evidence, no publication bias and a dose-response relationship. CAUTION: 6 randomised studies, 7,738 participants aged 12-40, results not broken down by age band — this is not an estimate specific to adolescents.
Source: Lauersen et al., 2018
The estimated annual prevalence of patellofemoral pain in adolescents is 28.9%, against 22.7% in the general population; among amateur adolescent athletes, incidence over a season runs from 5.1% to 14.9%. The authors flag few studies and heterogeneous definitions.
Source: Smith et al., 2018
Five years after baseline, 40.5% of adolescents with knee pain still have it (95% CI 35.4-45.6) against 13.2% of controls; among those still in pain, 60% have stopped or cut back on sport because of the knee. Population: 504 Danish adolescents aged 15-19 of both sexes.
Source: Rathleff et al., 2019 (BMJ Open)
In adolescent patellofemoral pain what works is load management, not complete rest: 12 weeks of activity modification, home exercises and graded return to sport produced 86% self-reported positive outcomes at 12 weeks and 81% at 12 months. Population: 151 adolescents aged 10-14; prospective study WITHOUT a control group, so not proof of efficacy.
Source: Rathleff et al., 2019 (AJSM)
Among 2,953 Danish adolescents aged 12-19, knee pain was reported by 35.0% of girls against 27.9% of boys, and near-daily pain at any site by 23.8% against 13.3%.
Source: Rathleff et al., 2013
In young female athletes the ankle is the most affected site: 23% of all injuries, ahead of the knee (16%) and thigh (13%), within 67% of injuries occurring at the lower limb. Population: systematic review with meta-analysis of 32 studies, 15,908 athletes under 19.
Source: Beech et al., 2024
Among high-school athletes aged 14-18 the prevalence of chronic ankle instability is 20.0%: 23.6% in girls against 16.3% in boys. Yet only 26.1% reported ever having sprained an ankle: the share with an unstable ankle is almost equal to the share who remember the injury. Population: 1,002 athletes, mean age 15.6, 50.4% girls.
Source: Donovan et al., 2020
In youth sport, prevention programmes reduce ankle injuries by roughly 26% (IRR 0.74; 95% CI 0.60-0.91); the programmes with significant results combined strengthening, agility and a multicomponent approach in 15-20 minute sessions twice a week for 3-6 months, with adherence above 62%. Population: 10 randomised studies in athletes aged 13-19, 4 of them in girls only.
Source: Berkey et al., 2024
Low back pain is common in youth sport: estimated 12-month prevalence is 42% (95% CI 29-55%), 3-month prevalence 46% and point prevalence 16%. CAUTION: heterogeneity I² up to 98%, because no shared definition of low back pain in adolescent athletes exists. Population: 80 studies, athletes aged 10-19 of both sexes, 60 sports, 23 countries.
Source: Wall et al., 2022
The cause of back pain in an adolescent who plays sport differs from an adult’s: comparing 100 young athletes aged 12-18 with 100 adults aged 21-77, spondylolysis explained 47% of cases in adolescents against 5% in adults, and disc pain 11 cases against 48. CAUTION: a 1995 retrospective study in specialist clinics — an already selected population, so 47% is NOT the probability that adolescent back pain is spondylolysis.
Source: Micheli e Wood, 1995
In a less selected population the share stays high: of 1,025 NON-elite adolescent athletes presenting to a clinic with low back pain (mean age 15 ± 1.8), 308 — 30% — had spondylolysis. The authors explicitly warn against generalising their sport-by-sport ranking to other settings.
Source: Selhorst et al., 2019
Among adolescent athletes in overhead sports, shoulder problems are common and persistent: of 471 elite handball players aged 15-18 monitored EVERY WEEK for one season, 23% reported substantial shoulder problems and 43% of those had them for at least 3 consecutive weeks; weekly prevalence was 6%. Prevalence was 1.46 times higher in GIRLS (95% CI 1.04-2.06).
Source: Asker et al., 2018
In competitive swimming the highest shoulder-pain rate is recorded in adolescence: 91.3% between 15 and 17, against 20.0% under 15 and 19.4% in masters, coinciding with the highest training volume of the career so far (17.27 ± 5.25 pool hours a week). CAUTION: SELF-REPORTED prevalences of «pain», not diagnoses; association, not cause. Population: systematic review of 12 studies and 1,460 swimmers of both sexes.
Source: Feijen et al., 2020
The shoulder prevention programme with the strongest evidence (OSTRC), performed 3 times a week inside the warm-up for one season, reduced the risk of shoulder problems by 28% (prevalence 17% vs 23%; OR 0.72; 95% CI 0.52-0.98); for substantial problems the estimated reduction was 22% but NOT statistically significant. CAUTION: 45 teams and 660 ADULT elite handball players — not an estimate for athletes aged 13-16.
Source: Andersson et al., 2017
In a still-growing athlete the shoulder has an anatomical weak point: the proximal humeral growth plate provides roughly 80% of the humerus’s growth in length, closes between 18 and 21, and while open is largely cartilaginous, hence mechanically weaker than the surrounding ligaments and tendons. CAUTION: a CLINICAL reference text (StatPearls), not a primary study, with original literature mostly on MALE youth baseball.
Source: Casadei e Kiel, StatPearls, 2023