Passive dorsiflexion stiffness is poorly correlated with passive dorsiflexion range of motion.

OBJECTIVES The purpose of this study was to determine the relationships among passive measures of weight-bearing dorsiflexion range of motion, non-weight-bearing dorsiflexion range of motion and dorsiflexion stiffness, thereby establishing whether they assess similar mechanical characteristics, as each measure has been implicated in injury risk during landings. DESIGN Cross-sectional study. METHODS Passive weight-bearing dorsiflexion range of motion, non-weight-bearing dorsiflexion range of motion and dorsiflexion stiffness were quantified for 42 males (22.8±5.0 years). The relationship between each data set was calculated using Pearson product-moment correlation coefficients. RESULTS Although weight-bearing dorsiflexion range of motion and non-weight-bearing dorsiflexion range of motion were significantly correlated, the strength of the relationship was poor (r(2)=0.18; p=0.004). Weight-bearing dorsiflexion range of motion (mean=43.0±5.0°) was significantly greater than non-weight-bearing dorsiflexion range of motion (29.8±5.9°; p<0.001) and weight-bearing dorsiflexion range of motion and non-weight-bearing dorsiflexion range of motion were also poorly correlated with passive dorsiflexion stiffness (1.48±0.55Nm°(-1); r(2)=0.04 and r(2)=0.14, respectively), despite the latter relationship being significant (p=0.017). CONCLUSIONS Passive dorsiflexion stiffness was not strongly associated with dorsiflexion range of motion, despite the significant correlation in the non-weight-bearing condition. It must be acknowledged that passive dorsiflexion stiffness was weakly associated with dorsiflexion range of motion, although the strength of the association suggests that it may not necessarily determine dorsiflexion range of motion. Furthermore, the functional dorsiflexion limits of the ankle during weight-bearing tasks may be underestimated or misrepresented by non-weight-bearing measures of dorsiflexion range of motion. Therefore, although ankle dorsiflexion range of motion and dorsiflexion stiffness have been implicated in injury risk during weight-bearing tasks such as landings, it may be due to different mechanisms.