Puberty is a biomechanical inflection point
For most girls, the years surrounding puberty represent the single largest window of musculoskeletal change they will experience outside of infancy. Bones lengthen rapidly, muscle mass and neuromuscular control struggle to keep pace, and hormonal shifts alter tissue properties. Understanding what specifically changes — and why it matters for ACL and other injury risk — is foundational to any credible prevention program. If you haven't yet read our overview on why girls tear ACLs more often than boys, start there for context before diving into the mechanics below.
What the evidence says
Landmark work by Hewett and colleagues established that neuromuscular control deficits emerging during puberty — not anatomy alone — are strongly associated with increased dynamic knee valgus and ACL injury risk in adolescent female athletes.
The growth spurt problem
During peak height velocity, long bones (particularly the femur and tibia) can grow several centimeters in a matter of months. Muscle-tendon units and the central nervous system's ability to coordinate the newly lengthened limb often lag behind. This mismatch — sometimes called "adolescent awkwardness" — is a normal developmental phase, but in athletes who are simultaneously increasing training loads, it creates a window of relative vulnerability.
Key changes during this window include:
- Limb length increases faster than proprioceptive recalibration
- Relative strength deficits, especially in hip and trunk musculature
- Altered center of mass, requiring new balance strategies
- Changes in tendon stiffness that affect force absorption
Neuromuscular control diverges by sex
Research consistently shows that before puberty, boys and girls display similar landing and cutting mechanics. After puberty, clear divergence emerges. Girls, on average, tend to develop:
- Greater dynamic knee valgus (inward collapse) during landing and cutting
- Reduced hamstring-to-quadriceps activation ratios
- Greater reliance on quadriceps-dominant landing strategies
- Reduced hip and core stabilization during single-leg tasks
This does not mean every female athlete develops "high-risk" mechanics — individual variation is substantial — but population-level trends are consistent enough to inform screening and training priorities.
Hormonal and connective tissue factors
Estrogen and relaxin receptors have been identified in ligamentous tissue, including the ACL, and some research has explored whether fluctuations across the menstrual cycle affect ligament laxity and neuromuscular control. The evidence here is still evolving and should be interpreted cautiously — this is an active area of research, not a settled matter. What is better established is that:
- Females generally exhibit greater generalized joint laxity than males
- The femoral notch (through which the ACL passes) tends to be narrower relative to body size in females
- Q-angle (the angle between the quadriceps and patellar tendon) is often greater due to a wider pelvis, altering force vectors at the knee
Note
None of these anatomical or hormonal factors are modifiable. The good news is that neuromuscular control — the factor most strongly linked to injury risk in the literature — is highly trainable.
A comparison of contributing factors
| Factor | Modifiable? | Strength of evidence | Practical implication |
|---|---|---|---|
| Neuromuscular control (landing/cutting mechanics) | Yes | Strong | Primary target for training programs |
| Hip/core strength | Yes | Strong | Include in every warm-up |
| Growth-spurt timing | No | Strong | Monitor closely during rapid growth |
| Femoral notch width | No | Moderate | Informs risk awareness, not training |
| Menstrual cycle phase | Partially | Emerging | Track symptoms, avoid overreach on claims |
| Q-angle / pelvic width | No | Moderate | Context for movement patterns |
What this means for training design
Programs like the FIFA 11+ and the PEP (Prevent injury, Enhance Performance) protocol were built directly on this biomechanical evidence. They emphasize:
- Strength work for hips, glutes, and hamstrings
- Plyometric training with a focus on landing mechanics
- Balance and proprioceptive drills
- Cutting and deceleration technique coaching
Timing matters too. Because the growth spurt is the period of greatest mismatch between skeletal growth and neuromuscular control, introducing structured prevention training before and during peak height velocity — not after an injury occurs — offers the greatest protective potential. For a detailed breakdown of exercises, see our neuromuscular training guide.
Practical takeaways for coaches and parents
Practice tip
You don't need a sports science degree to apply this research. Watch how an athlete lands from a jump. If the knee caves inward, if the landing is loud and stiff-legged, or if one side looks noticeably weaker than the other, those are visible cues worth addressing with targeted training — not just "core work" in general.
Practical steps include:
- Screen landing mechanics at the start of each season, especially during growth spurts
- Build 10–15 minutes of neuromuscular training into every practice, not as an occasional add-on
- Track growth (height measurements every few months) to flag periods of rapid change
- Educate athletes on normalizing awkwardness during growth without shaming their bodies
Why this matters beyond the knee
While ACL injury is the headline concern, the same neuromuscular deficits are implicated in ankle sprains, patellofemoral pain, and other overuse conditions common in adolescent female athletes. A biomechanically-informed program addresses the whole kinetic chain, not just the knee in isolation.
Understanding these changes is also central to advocacy. When talking to school administrators or budgeting for equipment and coach training, grounding the request in real biomechanical evidence — rather than general "injury prevention is good" language — tends to be far more persuasive to decision-makers who control resources.
Where the science still has open questions
It's worth being honest about the limits of current evidence. Researchers are still working out:
- The precise mechanism by which hormonal fluctuations affect ligament properties in vivo
- Why some athletes with "high-risk" screening profiles never get injured, while some with "low-risk" profiles do
- The optimal dose and timing of neuromuscular training relative to growth velocity
This is why G-MIP treats prevention programming as a living practice, updated as research evolves, rather than a fixed checklist. We track ongoing findings through our research updates and translate them for coaches at our community events.
Sport-specific patterns worth noting
Different sports load the body in different ways, and biomechanical risk factors can manifest differently depending on the demands of the game:
- Soccer involves frequent unanticipated cutting and deceleration, placing high demands on hip and trunk control in reactive, game-like situations.
- Basketball combines repetitive jump-landing with sudden changes of direction, often under fatigue late in games.
- Volleyball features repeated single-leg landings from overhead attacks, stressing similar neuromuscular control systems.
- Gymnastics involves extreme ranges of motion and high-impact landings, requiring sport-specific adaptations of general prevention principles.
Because the underlying neuromuscular deficits are similar across these sports, a shared foundation of hip, core, and landing-mechanics training transfers well — but coaches should still tailor drills to reflect the movement patterns their athletes actually encounter in competition, referenced in more detail on our programs page.
The role of fatigue
Many of the biomechanical changes described above become more pronounced under fatigue. Studies using motion capture have shown that landing mechanics can deteriorate significantly in the second half of a game or after repeated jump-landing cycles, even in athletes who demonstrate excellent mechanics when fresh. This has two practical implications: prevention training should occasionally be practiced under mild fatigue to build resilient patterns, and coaches should be attentive to mechanics late in practices and games, not only during structured warm-ups.
Conclusion
Puberty reshapes the female athlete's body faster than her nervous system can adapt, and that mismatch — not some fixed anatomical destiny — is the primary driver of the sex disparity in ACL injury rates. The encouraging implication is that structured, evidence-based neuromuscular training can meaningfully close that gap. For programs and families looking to act on this evidence, our prevention programs page outlines concrete next steps, and our contact page connects you with a G-MIP educator who can help implement a plan for your team.
References
- Hewett, T.E., et al. "Neuromuscular Risk Factors for Anterior Cruciate Ligament and Knee Injury in Female Athletes." Sports Medicine (various years).
- Myer, G.D., Ford, K.R., Hewett, T.E. "The Effects of Growth on Dynamic Knee Valgus in Female Athletes." Clinical Biomechanics.
- IOC Consensus Statement on Youth Athletic Development.
- Quatman, C.E., Hewett, T.E. "The Anterior Cruciate Ligament Injury Controversy." British Journal of Sports Medicine.