The influence of ankle stiffness, strength, and range of motion, on gait characteristics

The overall purpose of this work was to determine the relationships between plantar flexor muscle stiffness, plantar flexor strength, and dorsiflexion range of motion, and to determine how these variables affect gait characteristics.;Part 1. Deficits in plantar flexor (PF) muscle strength and dorsiflexion (DF) range of motion have been documented in subjects with diabetes and peripheral neuropathy (DM & PN). Stiffness, however, has not been quantified. We compared PF muscle stiffness in subjects with DM & PN and control subjects. Passive PF muscle torque was measured through full ankle range. Stiffness was calculated by taking the slope of the torque v. angle curve through the first and second halves of the range. There was no difference in stiffness between groups, however, subjects with DM & PN had less range of motion (PF excursion and maximal DF angle).;Part 2. We determined the relationships between PF stiffness, strength, and DF range of motion, including the percent contribution of passive torque (stiffness) to total torque. PF stiffness and strength were positively correlated. Stiffness and range of motion were negatively correlated. Strength and range of motion were not correlated. The percent contribution to total torque from passive torque was greater in subjects with DM & PN.;Part 3. We determined the effect of PF strength, stiffness, and DF range of motion on gait kinetic variables (peak ankle moment, power, gait stiffness) and walking speed. When the groups were combined, PF strength contributed positively to all gait variables, and PF stiffness contributed positively to plantar flexor peak moment (PFPM) and walking speed. DF range of motion did not contribute to any gait variable. In DM & PN group only, PF stiffness also contributed to gait stiffness.;Conclusions. Loss of joint motion can occur without an increase in muscle stiffness, a finding that may be indicative of a 'short' v. 'stiff' muscle. PF strength and stiffness are positively related, suggesting that a mechanism to increase stiffness may be to increase strength. PF strength and stiffness are important contributors to gait characteristics. Stiffness may be an even greater contributor in the presence of decreased strength.