STEP LENGTH REDUCTIONS IN ADVANCED AGE - THE ROLE OF ANKLE AND HIP KINETICS

Background. Aging is associated with a reduction in gait velocity, whi ch is due to a shortened step length. This study investigated the rela tionship between joint kinetics and step length. Methods. Three-dimens ional gait kinematics and kinetics were measured during usual pace gai t in 26 older subjects (average age 79) and in 32 young subjects (aver age age 26). Gait measures were obtained at maximal velocity in five o lder subjects. Lower extremity strength was measured in the older subj ects on an isokinetic dynamometer. Results. Older persons had a 10% sh orter step length during usual gait, when corrected for leg length (.6 5 +/- .07, .74 +/- .04/leg length, respectively, p < .001). Older pers ons had reduced ankle plantarflexion during late stance (13 +/- 5 degr ees, 17 +/- 5 degrees, p = .02) and lower ankle plantarflexor power (2 .9 +/- 0.9 W kg(-1), 3.5 +/- 0.9 W kg(-1), respectively, p = .007). An kle strength was associated with plantarflexor power developed during late stance (r = .49, p < .001). When gait kinetics were corrected for step length, the older subjects developed 16% greater hip flexor powe r during late stance than younger subjects (estimate of effect: .15 W kg(-1), p = .002). Older subjects were unable to increase ankle planta rflexor power at maximal pace, but increased hip flexor power 72% (1.1 +/- 0.3 W kg(-1) to 1.9 +/- 1.0 W kg(-1), p = .02). Conclusions. Olde r subjects had lower ankle plantarflexor power during the late stance phase of gait and appeared to compensate for reductions in plantarflex or power by increasing hip flexor power. Appropriate training of ankle plantarflexor muscles may be important in maintaining step length in advanced age.