Rearfoot strikes more frequently apply combined knee valgus and tibial internal rotation moments than forefoot strikes in females during the early phase of cutting maneuvers

Key points

1. 01Rearfoot strikes generated the dangerous combined valgus and tibial internal rotation moment pattern in up to 74.3% of trials at foot impact, versus only 27.8% for forefoot strikes.
2. 02The difference was driven by where the ground reaction force acts relative to the tibial rotation axis: rearfoot contact places it posterior, forefoot contact places it anterior, producing opposite tibial rotation directions.
3. 03Both foot strike types produced a similar rapid rise in knee valgus moment after foot contact, but only rearfoot strikes added simultaneous tibial internal rotation.
4. 04The high-risk window was the first 40% (roughly the first 60 ms) of stance, which overlaps with the critical time frame reported for ACL rupture.
5. 05The study used a slow approach speed under controlled conditions, so the magnitude of moments may be higher in real sport situations.

How it was conducted

Design

Controlled laboratory within-subject experiment; each participant performed cutting under both foot strike conditions

Participants

24 healthy female handball players (mean age 21.0 years, mean height 160.4 cm, mean weight 55.6 kg) with no recent lower limb injuries

Task

60-degree cutting maneuver (plant and change of direction) at approach speed less than 2.0 m/s, 10 trials per condition

Measurement

12-camera optical motion capture at 250 Hz and force plate at 1 kHz; knee valgus and tibial rotation moments calculated from ground reaction force and center of pressure

Primary outcome

Occurrence rate of combined knee valgus and tibial internal rotation (VL+IR) moments compared between rearfoot and forefoot strike conditions using chi-squared test (p<0.01)

Statistical approach

Chi-squared test for occurrence rates and statistical parametric mapping paired t-test for time-series moment and CoP data (alpha 0.0125)

What they found

• Maximum occurrence rate of combined VL+IR moments: rearfoot strike 74.3% (158 of 215 trials) at 0% of stance vs. forefoot strike 27.8% (63 of 227 trials) at 4% of stance (p<0.01).
• Rearfoot strike produced significantly higher occurrence rates of combined VL+IR moments throughout the first 40% of the stance phase (p<0.01).
• Tibial rotation moment was significantly different between conditions during the first 0-7% of stance (SPM t-test supra-threshold cluster probability p=0.008), with rearfoot producing internal rotation and forefoot producing external rotation.
• CoP was posterior to the tibial rotation axis in all rearfoot strike trials during the first 10% of stance, and rearfoot CoP remained significantly more posterior than forefoot CoP through the first 63% of stance.
• No significant difference in knee valgus moment time pattern was found between foot strike conditions.
• Approach speed was not significantly different between conditions (rearfoot 1.42 SD 0.14 m/s vs. forefoot 1.43 SD 0.16 m/s; p=0.82).

Limitations

• Slow approach speed (less than 2.0 m/s) does not replicate high-demand sport cuttings, so moment magnitudes may be underestimated; generalization to game speed requires caution.
• Only females were studied; sex-based differences in knee loading mean findings may not apply to male athletes.
• Not all ACL injuries involve the combined VL+IR mechanism, so findings are specific to this injury pathway.
• Shoe conditions varied across participants; although within-subject design controls for this, it may still affect GRF-induced moment magnitudes at impact.

Why it matters

For patients

Female athletes who land on their heel during direction changes may be at higher risk of ACL injury due to a more dangerous knee loading pattern, suggesting that foot strike coaching could matter for injury prevention.

For clinicians

Screening for and correcting rearfoot strike patterns during cutting and deceleration tasks may reduce the frequency of combined valgus and internal rotation loading on the ACL in female athletes.

For readers

This biomechanical study provides a mechanistic explanation for why foot strike pattern matters in ACL injury risk, linking center of pressure position to the direction of tibial rotation moment during sport-specific movement.