Do alterations in muscle strength, flexibility, range of motion, and alignment predict lower extremity injury in runners: a systematic review

Key points

1. 01All 7 included prospective studies produced very low quality evidence by GRADE criteria
2. 02No clinical assessment measure was consistently predictive of injury across multiple studies
3. 03Increased hip external-to-internal rotation strength ratio was protective in one study (OR 0.01, 95% CI <0.01 to 0.44)
4. 04Decreased navicular drop was protective in one study but non-significant in two others
5. 05Some findings contradicted clinical expectations, such as stronger hip abductors being associated with more injury in one study
6. 06Clinicians should not rely on any single clinical test to determine running injury risk

How it was conducted

Design

Systematic review of prospective cohort studies (PRISMA + PROSPERO registered, CRD42016020087)

Databases searched

PubMed, CINAHL, Embase, SPORTDiscus, plus hand search up to May 2018

Studies included

7 prospective cohort studies

Participants

Sample sizes ranged from 59 to 326 runners per study; populations included novice, recreational, and high school runners

Clinical assessments

Hip and knee strength, hip and ankle ROM, hip flexibility, hip and ankle alignment (navicular drop, foot posture index, Q-angle, leg length)

Quality assessment

Critical Appraisal Tool (CAT) and GRADE approach; 2 studies rated good quality (>75%), 5 moderate (50-75%)

What they found

• Hip abduction strength: one study found stronger hip abductors significantly associated with injury (OR 5.35, 95% CI 1.46 to 19.53, p <0.01); the other study found no significant association
• Hip external-to-internal rotation strength ratio: one study found a significant protective association (OR 0.01, 95% CI <0.01 to 0.44, p 0.02)
• Hip internal rotation ROM: one study found decreased hip internal rotation protective against medial tibial stress syndrome in females (aOR 0.91, 95% CI 0.85 to 0.99, p 0.02); the other study found no significant association
• Navicular drop: one study found decreased navicular drop protective in females (aHR 0.87, 95% CI 0.77 to 0.98, p 0.01); two other studies found no significant association
• Q-angle: two studies found no significant association with running-related injury (OR 0.9, 95% CI 0.8 to 1.0; cRR 1.26, 95% CI 0.49 to 3.23)
• Ankle dorsiflexion ROM: one study found no significant association (HR 1.00-1.01 for males and females)
• Knee quadriceps and hamstring strength: one study found no significant associations
• Foot posture index: one study found no significant association (cRR 1.65, 95% CI 0.65 to 4.17)
• All clinical assessment alteration categories were downgraded to very low quality of evidence by GRADE

Limitations

• All 7 studies were observational, limiting causal inference; GRADE rated all categories as very low quality
• Majority of studies had sample bias (7/7), inadequate justification of sample size (5/7), and poor reporting of measurement validity and reliability (5/7)
• Heterogeneous populations (novice, high school, recreational), injury definitions, and measurement methods prevented pooling or direct comparison
• Most study samples were small (<300 participants), contributing to imprecision; important confounders such as weekly mileage and injury history were rarely reported

Why it matters

For patients

Runners cannot rely on a single clinical test result such as hip strength or foot arch drop to know whether they are at risk for injury, as no measure has been shown to predict injury consistently.

For clinicians

Clinical musculoskeletal assessments like strength testing, goniometry, and navicular drop currently lack sufficient evidence to be used as standalone predictors of running-related lower extremity injury; multi-factor models and higher-quality prospective studies are needed.

For readers

This review highlights a critical gap: the tests physiotherapists commonly use to screen runners have very low-quality predictive evidence, suggesting that clinical risk assessment in runners requires further research before reliable protocols can be established.