Physiological and neurological changes with healthy aging cause old adults to alter biomechanical gait strategies. Mechanical plasticity is an ambulatory strategy in which old adults rely on proximal musculature in compensation for decreased distal muscle functioning. Since stride length has been shown to decrease with age, mechanical plasticity may be directly related to the control of stride length. It was hypothesized that old adults rely on hip joint torque and power more than knee or ankle torques and powers when manipulating stride length. It was also hypothesized that young adults rely on even distribution of lower-extremity joint torques and powers when manipulating stride length. The purpose of this study was to identify the relationship between lower extremity joint torques and powers and stride length in old and young adults while walking at an identical velocity.

Healthy young (ages 18-27) and old adults (ages 70-85) were instructed to walk across a level walkway at 1.50 m/sec ± 5%. Twenty strides ranging from each subject’s shortest to longest strides were collected per subject. Stride length was manipulated from trial to trial to ensure that each subject had a relatively even distribution of stride lengths from shortest to longest strides. Ground reaction force and joint kinematics were collected and analyzed with inverse dynamics. Pearson product correlation analyses were used to identify relationships among individual joint torque and power variables and stride length. Stepwise regression analyses were used for a comprehensive view of all lower-extremity joint torques and powers.

Means of preferred and maximal stride lengths were shorter for old adults than young adults. Correlations provided from averaging individual subject correlations within each group resulted in strong predictability of stride length. This method of evaluating how old and young adults manipulate stride length more accurately identified how young and old subjects manipulated stride length. These results indicated that knee and ankle torques and powers were stronger predictors of stride length than hip torque and power. Also, all young adult correlations were stronger than corresponding old adult correlations. For example, young adult knee impulse (r=0.864, r²=0.746, <0.05) had a stronger relationship with stride length than old adult knee impulse (r=0.837, r²=0.701, <0.05). Stepwise regression analyses similarly suggested high predictive power of distal joint function. According to these regressions, hip variables were not predictive of young adult stride lengths while hip impulse, following ankle and knee impulse, was predictive of old adult stride lengths.

This study suggests young and old adults manipulate stride by altering knee and ankle muscle functioning more than by altering hip muscle function. These data did not support the proposed hypotheses. Stronger correlations for young adults suggest these individuals can more accurately control stride length with knee and ankle torques than old adults.