SELF SELECTED WALKING SPEEDS ARE ENERGY INEFFICIENT POST-STROKE

Abstract

Purpose/Hypothesis: The purpose of this study was to understand the relationship between walking speed and energy expenditure in persons post-stroke. We hypothesized that the slow self-selected walking speed of stroke survivors would be associated with increased energy expenditure. Increasing walking speed above self-selected speed would lead to a reduction in energy cost to a transition point. Beyond this point, energy cost would increase with increasing speed. Number of Subjects: 8 subjects with chronic post-stroke hemiparesis have been tested to date. Materials/Methods: Subjects walked on a standard treadmill (Parker Treadmill Co., Auburn, AL) at 7 different speeds: self-selected over ground walking speed (SS), 20% slower than SS, their fastest possible speed on the treadmill (FP) and 4 speeds between SS and FP. All subjects wore a safety harness (Biodex Medical Systems, Shirley, New York) without body-weight support. Subjects walked for 5 minutes at each speed while their rate of oxygen consumption (VO2) was recorded (Trueone2400, Parvomedics, Sandy, UT). VO2 was normalized to body mass and energy cost per meter walked was calculated (Cw). Results: Five of the 8 subjects had SS walking speeds well below normal (<;0.7m/s, slow group). The other 3 subjects had walking speeds close to normal (>;0.9m/s, fast group). For subjects in the slow group, the minimum Cw occurred at a speed faster than their SS speed (p<;0.01; SS=0.476±0.056, energy min=0.342±0.042). For subjects in the slow group, with each speed above SS speed, Cw decreased until the speed at which it was at a minimum (p=0.06, 0.02, 0.007, 0.03; SS speed vs. each faster speed, respectively). This minimum occurred at the fastest or second fastest speed. 2 of the 3 subjects in the fast group had a minimum Cw at their SS speed and Cw increased at subsequent faster speeds. For all 8 subjects Cw was greater at the slow speed compared to the SS speed (p<;0.05). Conclusions: In healthy individuals the Cw – speed relationship is U-shaped with higher aerobic demand occurring at speeds faster or slower than the self-selected walking speed. It was previously unclear if the same was true for stroke survivors, that is, if their self-selected speed represented the speed of lowest energy cost or if energy costs could be minimized with faster walking speeds. The results of this study demonstrate that for stroke survivors who have SS speeds well below normal, walking at speeds faster than their SS speed causes them to expend less, not more, energy. However, two stroke survivors with close to normal walking speeds did show a normal Cw – speed relationship. This suggests that by increasing walking speed to close to maximum, stroke survivors with slow walking speeds can increase the energy efficiency of walking. Clinical Relevance: The results of this study preliminarily suggest that for stroke survivors who walk at self-selected speeds that are well below normal, rehabilitation techniques to increase walking speed would make them more energy efficient.