Falls in the elderly have grave consequences on their quality and length of life. Lower extremity strength deficits have been identified as a risk factor for falls in the elderly. A common extrinsic factor leading to a fall in the elderly is tripping over an obstacle. Yet, little is known regarding how deficits of peak torque and power produced by lower extremity muscles impair an elderly individual's ability to prevent a fall or how elderly individuals with these deficits respond to an obstacle in the gait path. The aim of this study was to determine what differences exist in the gait kinematics and muscular responses, when a sudden obstacle is presented in the gait path, between elderly individuals with and without a lower extremity strength deficit.

To investigate this issue, two distinct groups of elderly subjects were recruited:​ elderly with and without a lower extremity strength deficit. The groups without lower extremity strength deficits (dominant knee strength index at 60°/sec equal to or greater than 220 and 129 Nm, for men and women respectively) and the with lower extremity strength deficits (dominant knee strength index at 60°/sec less than 190 and 117 Nm, for men and women respectively) consisted of fifteen elderly subjects each. Both groups were free of musculoskeletal, neurological or cognitive impairments that would affect their gait and were matched according to age, gender and medication usage. Participation in the study was limited to those individuals who had a body mass index between 20.8 to 31.2.

The differences between the subject groups during obstacle clearing gait were quantified by recording the angular displacements of the hip, knee and ankle joints;​ electromyographic (EMG) activity of the tibialis anterior (TA), lateral head of the gastrocnemius (GAS), lateral head of the biceps femoris (BIC), and the rectus femoris (REC);​ and foot clearance under two walking conditions. The subject groups walked down a 14m gait path. On random trials, a pop up device at a fixed location was activated upon right heel strike, forcing the subject to clear the obstacle during the swing phase of the right lower extremity. Each subject performed five trials of obstacle clearing and non obstacle clearing gait.

Elderly subjects with and without strength deficits exhibited similar obstacle toe clearance (9.7 ± 4.5, 12.2 ± 4.4, 13.7 ± 5.7, and 11.4 ± 4.7 cm for strong and weak, males and females, respectively) and non obstacle toe clearance (9.2 ± 2.2, 13.8 ± 4.7, 8.5 ± 3.3, and 8.7 ± 3.7 cm for strong and weak males and females, respectively). To obtain the necessary obstacle toe clearance, elderly subjects primarily increased the knee joint flexion angle;​ augmenting it with increased hip joint flexion. The mean knee flexion angles (83.7 ± 6.5, 79.± 9, 89.3 ± 11.1, 81.4 ± 9.9 degrees for strong and weak, males and females, respectively) and hip flexion angles (17.2 ± 3.2, 19.4 ± 9.6, 22.9 ± 11.5, 28.9 ± 7.7 degrees for strong and weak, males and females, respectively) and ankle joint angles (-1.8 ± 6.4, 1.7 ± 11.1, 10.3 ± 20.9, 3.5 ± 10.2 degrees for strong and weak, males and females, respectively) at obstacle toe clearance of the subject groups were not significantly (p > .05) different from each other.

Elderly subjects utilized a consistent pattern of increased pre toe clearance EMG activity of the BIC and GAS muscles to accomplish the above kinematic strategy. This pattern of muscle activity was complimented by a variable pattern of increased pre obstacle TA and post obstacle REC EMG activity. No difference in the pattern or timing of the increased EMG activity of the above muscles could be detected visually between the subject groups. There was no significant (p > .05) difference between the subject groups in the integrated individual ensemble averaged subtracted standardized time normalized linear envelopes of the four muscles.

Additionally, the angular velocities of the hip, knee and ankle joints at obstacle toe clearance and the intra subject coefficient of variation of the kinematic and EMG data were not significantly different (p > .05) between the subject groups.