Female athlete health statistics: ACL risk, RED-S, and the sports science research gap

She was 19, a midfielder, and she had not had a period in eight months. Her coach called it "normal for runners." Her athletic trainer was more worried about the knee: the third-degree ACL tear on a noncontact plant-and-cut. The two problems were not unrelated. Low energy availability had thinned her bone density, blunted recovery, and left a body that could not absorb the load her sport demanded. By the time anyone put the pieces together, she had lost a season and part of a growth window she would not get back.

I see versions of this athlete every year. The injuries look different (ACL, bone stress, concussion), but the pattern is familiar. Female athletes carry higher rates of several sport-specific injuries than male peers under the same rules, while the research base that should guide prevention still enrolls women as an afterthought.

This article gathers the primary numbers a reporter or clinician reaches for under deadline: ACL injury rate ratios by sex, RED-S and low energy availability prevalence, bone stress injury rates, concussion incidence and recovery differences, and female representation in sports science research. Every figure is tied to a named source you can open.

Sport classification	Female IR (per 10,000 AEs)	Male IR (per 10,000 AEs)	IRR (F:M)
Contact sports	1.88	0.87	3.00
Fixed-object HIRL (e.g., gymnastics)	4.80	1.75	5.51
Collision sports	2.10	1.12	1.14 (NS)
Limited contact	0.71	0.29	1.21 (NS)
Noncontact	0.36	0.21	1.49 (NS)

Source: Montalvo et al., Journal of Athletic Training, 2019. NS = not statistically significant. HIRL = high-impact rotational landing.

Population	Rate per 100,000 AEs
Women's cross-country	28.59
Women's gymnastics	25.58
Women's outdoor track	22.26
Women, sex-comparable sports	9.13
Men, sex-comparable sports	4.44
All NCAA sports (overall)	5.70

Source: Rizzone et al., Journal of Athletic Training, 2017 (NCAA Injury Surveillance Program, 2004-05 through 2013-14).

The ACL injury rate gap

The ACL statistic that travels farthest in media is usually a range ("two to eight times higher in women"), which is directionally true and almost never pinned to a specific study. The cleaner number for citation is narrower.

In a 2019 systematic review and meta-analysis in the Journal of Athletic Training, Montalvo and colleagues pooled incidence rates by sex and sport classification. For contact sports (basketball and soccer and similar codes with comparable rules), female athletes had an ACL injury incidence of 1.88 per 10,000 athlete-exposures versus 0.87 in males, for an incidence rate ratio of 3.00 (95% CI 2.70-3.34). That is the figure to lift when a story needs one rate ratio with a primary source attached.

The same review found a larger sex disparity in fixed-object, high-impact rotational landing sports such as gymnastics: 4.80 versus 1.75 per 10,000 AEs (IRR 5.51). Collision, limited-contact, and noncontact categories did not show statistically significant sex differences. Absolute rates and relative risk move with how sports are classified and how many women play the highest-collision codes.

A companion meta-analysis by the same group in the British Journal of Sports Medicine framed risk more intuitively. Across 58 studies, the incidence proportion of ACL injury was 3.5% in female athletes (about 1 in 29) and 2.0% in male athletes (about 1 in 50) over windows from one season to 25 years. The female incidence rate was 1.5 per 10,000 athlete-exposures versus 0.9 in males; the season-level incidence rate ratio was 1.7 (95% CI 1.4-2.2). Among amateurs the rate ratio rose to 2.1, so the gap is not confined to elite programs with full medical staffs.

Mechanism remains unsettled. Anatomy, neuromuscular control, landing mechanics, hormonal effects, and training load all appear in the literature. Neuromuscular prevention programs have reduced risk in trials, but implementation is uneven at high school and club levels where many tears occur. The research-participation gap discussed later means much of the prevention evidence still rests on samples that under-enroll the athletes at highest relative risk.

RED-S and low energy availability

Relative Energy Deficiency in Sport (stylized REDs in current IOC literature, still widely written RED-S) sits under many of the injuries and menstrual disruptions female athletes present with. The core exposure is low energy availability: dietary energy left after exercise expenditure is insufficient for normal physiologic function, often expressed as kilocalories per kilogram of fat-free mass per day.

The 2023 International Olympic Committee consensus statement, led by Mountjoy and colleagues in the British Journal of Sports Medicine, is the current reference. It defines REDs as impaired physiological and/or psychological functioning from problematic (prolonged and/or severe) low energy availability. Systems affected include reproductive function, bone health, immunity, cardiovascular and hematologic systems, metabolism, and performance. The panel reported estimated prevalence of LEA/REDs indicators from 23% to 79.5% in female athletes and 15% to 70% in male athletes, varying by sport, measurement method, and how studies define "at risk."

That range is uncomfortable for a headline, and the authors say so. There is no single definitive diagnostic test. LEA and REDs are sometimes used interchangeably when they should not be. Energy-availability calculations are error-prone. The honest reading is that low energy availability is common enough that every sports medicine clinic should screen for it, and rare enough as a cleanly measured diagnosis that any single prevalence number should be quoted with its method attached.

Between the 2018 and 2023 updates, the IOC panel counted roughly 178 original REDs/LEA publications involving about 23,822 participants, 80% of them female. That is a rare inversion of the broader sports science pattern. The field grew out of the Female Athlete Triad (low energy availability, menstrual dysfunction, and low bone mineral density). REDs expands that model to more body systems and to male athletes without erasing sex-specific reproductive and bone risks in women.

Menstrual disruption is often the first visible sign. Athletes and coaches still normalize "losing your period" as proof of commitment. Clinically it is a hypothalamic response to energy deficit and stress, not a training trophy. Cycle tracking tools such as our period calculator and cycle length calculator help document irregularity, but documentation without restoring energy availability does not protect bone. Related patterns appear in our reviews of eating disorder statistics in women, osteoporosis and bone health, and iron deficiency anemia. These are not separate problems in separate waiting rooms.

Bone stress injuries

Bone stress injuries sit where load, recovery, and energy status meet. When training stress outruns remodeling capacity (often because estrogen is low, calories are short, or both), microdamage progresses from stress reaction to frank fracture.

The largest collegiate dataset still cited is Rizzone and colleagues' analysis of the NCAA Injury Surveillance Program from 2004-05 through 2013-14, published in the Journal of Athletic Training in 2017. Across 25 sports and 11,778,145 athlete-exposures, 671 stress fractures were reported, for an overall rate of 5.70 per 100,000 AEs. Among sex-comparable sports, the rate in women was 9.13 per 100,000 AEs versus 4.44 in men (rate ratio 2.06; 95% CI 1.71-2.47). That is a clean, quotable doubling from a defined surveillance system rather than a single-team series.

Sport-specific rates show where coaches should look hardest. Women's cross-country led at 28.59 per 100,000 AEs, followed by women's gymnastics (25.58) and women's outdoor track (22.26). Metatarsals accounted for 37.9% of stress fractures, the tibia 21.9%, and the lower back/lumbar spine/pelvis 12.1%. Preseason rates exceeded regular-season rates (7.30 vs 5.12 per 100,000 AEs; RR 1.43). About 21.5% of fractures were recurrent, and 20.7% were season-ending. Those percentages turn overuse into a lost year or scholarship.

The link to RED-S is clinical, not theoretical. Chronically low energy availability suppresses reproductive hormones, reduces bone formation, and can leave adolescents with lower peak bone mass they never fully recover. Prevention is unglamorous: adequate fueling, sensible progression of impact volume, and early workup when activity-related pain is progressive. Waiting for a fracture line on MRI is already late.

Concussion rates and recovery

Sex differences in concussion are smaller than the ACL gap but consistent where rules are comparable. Cheng and colleagues' 2019 systematic review and meta-analysis in Sports Health pooled 38 studies of sports-related concussion in males and females age 10 and older. Soccer and basketball showed significantly higher incidence in females: rate ratios of 1.76 (95% CI 1.43-2.16) for soccer and 1.99 (95% CI 1.56-2.54) for basketball. Differences in baseball/softball, ice hockey, lacrosse, swimming/diving, and track and field were not statistically significant. Meta-regression found no significant effect of study design, competition-versus-practice setting, or school level on the rate ratio.

Recovery gaps are measured in days in the best collegiate surveillance. Bretzin and colleagues followed 1,974 sport-related concussions in Ivy League athletes from 2013-14 through 2018-19. Overall median symptom resolution was 9 days. Women had a median of 9 days to symptom resolution versus 8 days in men (P = .03), and 9 days to return to academics versus 7 days in men (P < .001). Median times to limited and full sport return did not differ significantly by sex overall. Within sports, women's lacrosse athletes had longer symptom and academic recovery than men's lacrosse athletes; men's volleyball athletes took longer to return to sport than women's volleyball athletes.

Those medians understate prolonged-recovery cases. Symptom burden, neck strength, reporting culture, and early specialty access all modify trajectories. The safe stance is not that every female athlete will take longer, but that protocols built only on male recovery curves will underserve a meaningful share of women. Same-sport rate differences in soccer and basketball argue for sex-aware surveillance, not for treating concussion as a male football problem women experience only in dilute form.

The sports science research gap

Injury ratios get the headlines. The quieter problem is that the evidence base used to train and rehabilitate athletes still treats the male body as default.

Costello, Bieuzen, and Bleakley quantified the imbalance in 2014 in the European Journal of Sport Science. Across 1,382 articles in three major journals (Medicine & Science in Sports & Exercise, British Journal of Sports Medicine, and American Journal of Sports Medicine), they counted 6,076,580 participants. Only 2,366,968 (39%) were female. The average share of female participants per article sat between 35% and 37%.

Cowley and colleagues updated the picture in 2021 in Women in Sport and Physical Activity Journal. In 5,261 publications totaling more than 12.5 million participants, women were 34% of subjects. Sixty-three percent of publications included both sexes, 31% were male-only, and only 6% were female-only. That 6% is the figure most often quoted as "almost none of the research is about women." It counts exclusive female-only designs, not the share of women inside mixed samples. Both framings matter. Mixed samples that never analyze by sex still leave clinicians without female-specific guidance. We cover a related problem in our article on women in clinical trials and the research funding gap.

A decade after Costello, Ose and colleagues revisited the same three journals for January 2021 through August 2023. Their 2025 analysis in the American Journal of Sports Medicine included 1,441 studies and 40,152,860 participants. Female participants were 17,648,509, or 43.95% of the total. The mean proportion per study was 40.22%. Female-only studies were 7.15%; male-only studies were 18.6%. Only 5.6% of studies included menstrual-status considerations in design. Progress in headcount has not matched progress in study design for female physiology.

Topic-level audits can look worse. Smith and colleagues' 2022 audit in Nutrients of evidence-based performance supplement research found women were only 23% of participants overall, and 16% in studies focused on performance outcomes. Health-focused questions recruited more women; the performance literature, which drives many training-room practices, did not.

Return-to-play criteria, fueling guidelines, and supplement claims often rest on male-dominant samples. Some translate reasonably; many do not, especially where cycle phase, iron status, or energy availability change the response. Closing the gap means funding female-only and adequately powered mixed-sex designs that pre-specify sex analysis.

Audit	Female share of participants	Female-only studies	Male-only studies
Costello et al., 2014 (3 journals)	39%	n/a	n/a
Cowley et al., 2021 (6 journals)	34%	6%	31%
Ose et al., 2025 (3 journals, 2021-23)	43.95%	7.15%	18.6%
Smith et al., 2022 (performance supplements)	23% overall; 16% in performance outcomes	0-8% by supplement	59-77% by supplement

Sources: Costello et al., Eur J Sport Sci 2014; Cowley et al., WSPAJ 2021; Ose et al., Am J Sports Med 2025; Smith et al., Nutrients 2022. Methods and journal sets differ across audits; figures are not directly interchangeable year-to-year trend points.

What clinicians and coaches can do

Screen for energy availability in any female athlete with recurrent injury, stress fracture history, amenorrhea or oligomenorrhea, unexplained fatigue, or progressive performance decline. Ask about dietary restriction, weight targets, and missed meals around training. A missing period for three months in a previously regular athlete is a clinical finding, not a lifestyle note. Referrals to sports dietitians and adolescent gynecology or reproductive endocrinology should be as routine as orthopedic referral after an ACL tear.

Neuromuscular ACL-prevention programs belong in warm-ups for female soccer and basketball and similar contact sports, not just post-injury rehab. Concussion education should cover higher same-sport incidence in women's soccer and basketball and the possibility of longer symptom and academic recovery. Return-to-learn plans need the same formality as return-to-play.

Cycle tools such as the ovulation calculator support self-knowledge, but apps do not diagnose RED-S or replace evaluation when periods stop. Coaches should treat menstrual regularity as a vital sign of load tolerance when injury risk and performance are linked. Researchers and funders have a separate job: stop treating female physiology as a side arm. The Ose audit shows modest gains in participation and stubborn failure to incorporate menstrual status into design. Until that changes, clinicians will keep extrapolating from male data and female athletes will absorb the error.

The midfielder with the torn ACL and eight months of amenorrhea eventually returned, after reconstruction, a season of rehab, bone density evaluation, and a nutrition plan that restored her cycle. The injury was dramatic. The missed periods had been the earlier warning. These statistics exist so the next warning is harder to miss.

Frequently asked questions about female athlete health

How much higher is ACL injury risk in female athletes?

In contact sports, a 2019 meta-analysis by Montalvo et al. found female athletes had three times the ACL injury rate of males (IRR 3.00; 1.88 vs 0.87 per 10,000 athlete-exposures). Across sports and longer windows, the same group's BJSM review put female season incidence about 1.7 times higher, with incidence proportions of 3.5% (about 1 in 29) versus 2.0% (1 in 50) in males.

What is RED-S and how common is it?

Relative Energy Deficiency in Sport (REDs) is impaired health and performance from problematic low energy availability. The 2023 IOC consensus reports estimated prevalence of LEA/REDs indicators from 23% to 79.5% in female athletes, depending on sport and methods. There is no single diagnostic test; ranges reflect screening tools and symptoms plus incomplete energy-availability measurement, not one national survey.

Do female athletes get more stress fractures?

Yes, in NCAA surveillance. Rizzone et al. found stress fracture rates of 9.13 per 100,000 athlete-exposures in women versus 4.44 in men among sex-comparable sports (RR 2.06). Women's cross-country (28.59), gymnastics (25.58), and outdoor track (22.26) had the highest sport-specific rates in that 10-year dataset.

Are concussion rates higher in female athletes?

In sports with comparable rules, often yes. Cheng et al. (2019) reported female-to-male concussion rate ratios of 1.76 in soccer and 1.99 in basketball. Other sports in that meta-analysis did not show statistically significant sex differences. Bretzin et al. found slightly longer median symptom and academic recovery times in collegiate women (9 vs 8 days; 9 vs 7 days) without overall differences in return-to-sport timing.

How underrepresented are women in sports science research?

Cowley et al. (2021) found women were 34% of participants across more than 12.5 million subjects, and only 6% of studies were female-only versus 31% male-only. Ose et al. (2025) reported 43.95% female participants in three leading journals from 2021-2023, with 7.15% female-only studies. Menstrual status was considered in only 5.6% of designs.

When should a female athlete see a doctor about missed periods?

After three months without menses in someone who previously cycled regularly. Sooner if there is weight loss, stress fractures, disordered eating, or performance collapse. Amenorrhea is a medical finding linked to low energy availability and bone risk, not proof of elite fitness. Evaluation should address fueling, training load, bone health, and pregnancy exclusion as indicated.