Article

Muscle fatigue and dual-task walking (e.g., concurrent performance of
a cognitive interference (CI) while walking) represent major fall risk factors in
young and older adults. Thus, the objectives of this study were to examine the
effects of muscle fatigue on gait characteristics under single and dual-task
conditions in young and older adults and to determine the impact of muscle
fatigue on dual-task costs while walking. METHODS: Thirty-two young (24.3 +/- 1.4
yrs, n = 16) and old (71.9 +/- 5.5 yrs, n = 16) healthy active adults
participated in this study. Fatigue of the knee extensors/flexors was induced by
isokinetic contractions. Subjects were tested pre and post fatigue, as well as
after a 5 min rest. Tests included the assessment of gait velocity, stride
length, and stride length variability during single (walking), and dual
(CI+walking) task walking on an instrumented walkway. Dual-task costs while
walking were additionally computed. RESULTS: Fatigue resulted in significant
decreases in single-task gait velocity and stride length in young adults, and in
significant increases in dual-task gait velocity and stride length in older
adults. Further, muscle fatigue did not affect dual-task costs during walking in
young and older adults. Performance in the CI-task was improved in both age
groups post-fatigue. CONCLUSIONS: Strategic and/or physiologic rationale may
account for the observed differences in young and older adults. In terms of
strategic rationale, older adults may walk faster with longer strides in order to
overcome the feeling of fatigue-induced physical discomfort as quickly as
possible. Alternatively, older adults may have learned how to compensate for
age-related and/or fatigue-induced muscle deficits during walking by increasing
muscle power of synergistic muscle groups (e.g., hip flexors). Further, a
practice and/or learning effect may have occurred from pre to post testing.
Physiologic rationale may comprise motor unit remodeling in old age resulting in
larger proportions of type I fibres and thus higher fatigue-resistance and/or
increased muscle spindle sensitivity following fatigue leading to improved
forward propulsion of the body. These findings are preliminary and have to be
confirmed by future studies.

Langue : ANGLAIS