No baseline strength differences between female recreational runners who developed an injury and injury free runners during a 16-week formalized training program

Key points

1. 01No significant differences in hip flexion, extension, abduction, external rotation, or knee flexion and extension strength were found at baseline between injured and uninjured groups.
2. 0254 female recreational runners enrolled; 50 were included in final analysis after 4 exclusions.
3. 03Effect sizes for all six strength measures were small (ES ranging from -0.20 to 0.20) with non-significant P values.
4. 04The study adds prospective evidence that isometric strength screening alone is unlikely to identify female runners at risk of injury before a training program.
5. 05Isometric weakness observed in runners with injuries may develop after, not before, injury onset.

How it was conducted

Design

Prospective cohort study

Participants

50 healthy female recreational runners (age, height, mass reported as group means) enrolled in an 18-week formalized half- or full-marathon training program

Groups

Runners who developed a running-related injury (RRI) vs. those who remained injury-free (INJF)

Strength assessment

Baseline isometric peak torque (Nm/kg*m) of knee flexion and extension, hip flexion and extension, hip abduction, and hip external rotation measured via hand-held dynamometer

Injury definition

Musculoskeletal lower extremity or back injury from running, assessed by a healthcare provider, requiring training modification or substitution for at least one planned day

Follow-up

18-week formalized training program; injury surveillance by a blinded physical therapist twice weekly

What they found

• No significant between-group differences were found for hip flexion (ES = 0.20, 95% CI -0.37 to 0.76; P = 0.48), hip extension (ES = 0.14, 95% CI -0.42 to 0.71; P = 0.62), hip external rotation (ES = -0.11, 95% CI -0.68 to 0.45; P = 0.70), hip abduction (ES = -0.10, 95% CI -0.66 to 0.46; P = 0.73), knee flexion (ES = 0.20, 95% CI -0.37 to 0.76; P = 0.48), or knee extension (ES = -0.06, 95% CI -0.62 to 0.50; P = 0.84).
• No significant differences between groups existed for any demographic variable, history of previous RRI, years of running experience, or weekly mileage prior to the start of the training program.
• Injuries were distributed throughout the 18-week program, with some occurring in weeks 1-4, 5-8, 9-12, and 13-18.
• The within-subject between-limb analysis in the INJF group confirmed no significant limb-to-limb variance in any strength measure.

Limitations

• The injury definition used may undercount overuse injuries if runners continued training through symptoms, as approximately 70% of runners reportedly train through overuse injuries.
• No formal power analysis was conducted to determine required sample size, increasing the risk of a type II error.
• Strength was measured only at baseline; whether weakness developed during training and contributed to injury could not be determined.
• The convenience sample from a single formalized training program limits generalizability; belt-fixation was not used for hand-held dynamometry, which may introduce systematic tester bias.

Why it matters

For patients

Female runners planning a half- or full-marathon program should not assume a normal isometric strength screen guarantees injury protection, as other factors drive injury risk.

For clinicians

Pre-participation isometric hip and knee strength testing does not identify female recreational runners at elevated injury risk; post-injury assessment remains appropriate to guide rehabilitation.

For readers

This prospective cohort challenges the assumption that hip and knee weakness precedes running-related injuries, suggesting the association seen in cross-sectional studies reflects a consequence rather than a cause.