| Summary |
Horizontal ground forces are considerably lower than vertical ground forces during normal human locomotion, averaging approximately only -15% of the vertical forces. Despite being much lower in magnitude, the metabolic cost required to produce the horizontal forces is approximately 47% of the total metabolic cost in level walking and 33% of the total metabolic cost in level running. It was hypothesized that the horizontal forces produce 50% of the total external angular impulse on the body during level, incline and decline walking and 33% of the total external angular impulse on the body during level running. The purpose of this study was to compare external angular impulses applied to the body by horizontal and vertical forces during level, incline and decline walking, and level running. Twenty subjects (22.0 ± 1.7 years) were tested in ascending and descending an inclined surface with a 10° slope at a speed of 1.5 m/s. Sixteen of those subjects also participated in a level walking condition at the same speed. Ten subjects (23.2 ± 2.0 years) were tested in a level running condition at 3.83 m/s. Sagittal plane kinematic and ground force data were obtained for each condition. Inverse dynamics were used to calculate segment torques during the stance phases of the movements. The torques were resolved into components due to horizontal and vertical forces and the percentage that each component had on the total angular impulse was calculated. The horizontal ground forces were less than 14% as large as the vertical forces in each movement. These translated into 34% of the total angular impulse for level walking, 25% for ascent, 30% for descent, and 29% in level running. Across all movements the moment arms for the horizontal forces were ~4 fold larger than those for the vertical forces. The data refuted the hypothesis that the horizontal forces produce 50% of the total angular impulse on the body during level, incline and decline walking and 33% of the total external angular impulse on the body during level running. The results did show however that the relatively low horizontal forces account for a proportionally higher percentage of the angular impulses placed on the body segments than the vertical forces in these locomotion tasks. These results partially explain the relatively large metabolic demand of generating relatively low horizontal forces. There do appear to be other factors however involved with the issue of high metabolic cost for low horizontal forces, particularly in walking gaits. |
