Research article: Minimizing center of mass vertical movement increases metabolic cost in walking.
Ortega JD, Farley CT. Locomotion Laboratory, Dept. of Integrative Physiology, University of Colorado, Boulder, CO 80309-0354, USA. ortegajd@colorado.edu
J Appl Physiol. 2005 Dec;99(6):2099-107. Epub 2005 Jul 28.
So what is this article’s bottom line ? The premise of the research article was to look at the relationship between vertical movement in gait and its metabolic cost by having human subjects walk normally and with minimal center of mass vertical movement (“flat-trajectory walking”). What the article found was that it costs more to move with a flat trajectory. In other words, dampening the normal vertical oscillations is not a good thing. But we have some concerns.
Not that we have a major problem with this study, but we do have two concerns we think should have been brought up problem.
1- Were these folks in the study assessed for biomechanical compensations ? You have read our discussions on impaired ankle rocker. And one of the major flaws of impaired ankle rocker is the premature heel rise gait, where the person can adopt a rather boucey vertical gait, almost appearing to walk on the ball of their foot. These folks have a very vertical gait.
2- Since the study concluded that the less vertical trajectory gait was seen to be far less metabolically efficient it is a well founded question to ask more about the strategy they employed. In the study they merely added more joint flexion to dampen the vertical trajectory. But, had they been coached to use the core to minimize vertical trajectory and utilize the energy moving forward while still obtaining some of the normal biomechanical components, some of which take advantage of limb extension, would the study have found the same thing ? Once again we find a good study but one that bodes more questions than it answers, such as, did the researchers really know enough about gait biomechanics to give good cues? Furthermore, how much vertical is too much ? How much dampening is too much ?
We still appreciate the study and its findings, but you cannot trust everything you read, at least not without reading the fine print. Here is the full abstract below. Read it yourself and if you are curious enough, get the full study for yourself.
Shawn and Ivo…….keeping you on the edge of the research.
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Journal Abstract
A human walker vaults up and over each stance limb like an inverted pendulum. This similarity suggests that the vertical motion of a walker’s center of mass reduces metabolic cost by providing a mechanism for pendulum-like mechanical energy exchange. Alternatively, some researchers have hypothesized that minimizing vertical movements of the center of mass during walking minimizes the metabolic cost, and this view remains prevalent in clinical gait analysis. We examined the relationship between vertical movement and metabolic cost by having human subjects walk normally and with minimal center of mass vertical movement (“flat-trajectory walking”). In flat-trajectory walking, subjects reduced center of mass vertical displacement by an average of 69% (P = 0.0001) but consumed approximately twice as much metabolic energy over a range of speeds (0.7-1.8 m/s) (P = 0.0001). In flat-trajectory walking, passive pendulum-like mechanical energy exchange provided only a small portion of the energy required to accelerate the center of mass because gravitational potential energy fluctuated minimally. Thus, despite the smaller vertical movements in flat-trajectory walking, the net external mechanical work needed to move the center of mass was similar in both types of walking (P = 0.73). Subjects walked with more flexed stance limbs in flat-trajectory walking (P < 0.001), and the resultant increase in stance limb force generation likely helped cause the doubling in metabolic cost compared with normal walking. Regardless of the cause, these findings clearly demonstrate that human walkers consume substantially more metabolic energy when they minimize vertical motion.
