Can Shoes Be Worn When Testing Measures Of Passive Ankle Stiffness?

Ankle joint stiffness is a critical variable that influences ankle joint leverage for propulsion during gait and allows for adaptability in different environments. Measures of passive ankle stiffness are typically performed barefoot in an isokinetic dynamometer. However, testing in a barefoot state may pose an injury risk to the foot, particularly in sensory-impaired individuals, such as those with neuropathy. PURPOSE: To identify if shod-based measures of passive ankle stiffness may be used as an alternative to traditional barefoot measurements. METHODS: Able-bodied participants (9 M, 9 F, age = 25.7 ± 2.6 years) were seated upright in an isokinetic dynamometer with the ankle center of rotation aligned with the dynamometer rotation axis and knee locked at 10° flexion with a locking knee brace. For each trial, the dynamometer passively rotated the ankle for 5 repetitions through a full range of ankle plantar- and dorsiflexion motion as the participant remained relaxed. Three trials were performed at 10°/second and 30°/second with (shod) and without (barefoot) shoes. Passive ankle stiffness was calculated as the slope of the torque-angle relationship between 10° plantarflexion and 15° of dorsiflexion (or maximum dorsiflexion if less than 15°). Repetitions 3 and 4 from the third trial were averaged for each condition. Fourteen participants completed two testing days and 4 participants completed 1 testing day for 32 total pairs of data to be analyzed at each speed. Two-way mixed effects model with absolute agreement intraclass correlation coefficients were calculated between shod and barefoot conditions at each speed. RESULTS: Barefoot (15.79 ± 9.03) and shod (15.61 ± 8.37) testing conditions displayed excellent reliability (ICC = 0.922, 95% CI [0.838, 0.962]) at the testing speed of 10°/second. Similarly, at 30°/second, barefoot (24.92 ± 9.97) and shod (26.05 ± 10.96) conditions also showed excellent reliability (ICC = 0.934, 95% CI [0.865, 0.967]). CONCLUSION: The excellent reliability observed between barefoot and shod measures indicates shod measures may be a suitable alternative to barefoot measures of passive ankle stiffness. This is particularly relevant for clinical populations where barefoot testing may not be an ideal testing method. Supported by: NIH NICHD K01HD107295