The Effect of Resting Angle on Knee Joint Movement Reaction in Older Adults

Abstract

2114 PURPOSE: To determine the effect of angle on the perception and reaction to knee movement following a gravity-induced perturbation in healthy older adults. METHODS: Twenty-four healthy older adults (23 women, 1 man; mean age = 72.46 ± 7.09 years; height = 162.06 ± 7.25 cm; body mass = 72.86 ± 16.43 kg) were evaluated using a Biodex isokinetic dynamometer. Subjects were seated in an upright position with the lower right leg attached to the resistance arm. The knee was placed in a random starting (resting) angle of 0, 30, or 45 degrees from full extension. Five gravity induced fiexor perturbations were initiated at each angle while the subject was relaxed and blindfolded. Instructions were provided to each subject to catch and hold their leg by contracting the quadriceps femoris muscle as soon as they perceived the movement. The ability to perceive and arrest the perturbation was measured as the absolute change in joint angle from the starting point to maximum knee flexion. The largest and smallest values at each joint angle were excluded from the analysis. RESULTS: The results demonstrated a significant difference in knee movement reaction between the three joint angles (0 deg = 55.71 ± 16.58 deg; 30 deg = 40.43 ± 15.17 deg; 45 deg = 32.93 ± 13.98 deg; F2,46 = 85.0; p< 0.001; ç2 = 0.79). Specifically, the change in angle was greatest at 0 deg flexion, as compared to 30 deg (F1,23 = 58.93, p<0.001, ç2 = 0.72) and 45 deg (F1,23 = 155.74, p<0.001, ç2 = 0.87). The change in knee joint angle was significantly lower at 45 deg than at 30 deg (F1,23 = 25.77, p<0.001, ç2 = 0.53). CONCLUSION: The major findings demonstrated a dependency of the ability to consciously perceive joint movement and to generate a motor response, on resting knee joint angle. The results suggest that increased stiffness of anterior leg structures (quadriceps femoris muscle, anterior knee joint capsule and skin) which occur at a greater knee joint angle, may be a significant mediator underlying voluntary control of sagittal plane lower leg movement in healthy older adults.