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By David Kiefer, MD
Synopsis: This study compared the metabolic cost for walking three different speeds in 30 adults at least 65 years of age, and found that those who ran on a regular basis expended less energy walking than the group that walked exclusively.
Source: Ortega JD, et al. Running for exercise mitigates age-related deterioration of walking economy. PLoS One 2014;9:e113471.
What is the key to staving off the effects of aging and promoting healthy longevity in all of its parameters? There are many facets to this question, one of which pertains to physical morbidity. This article compared walking to running and their effects on "metabolic cost” (explained below), and the result was compelling enough that even the editors of the New York Times featured it in a recent article.
As people age, it becomes more difficult to do physical tasks, including the simple act of walking, and this deterioration correlates with a myriad of health outcomes. One way to measure this difficulty with physical activity, specifically pertaining to walking, is to calculate the metabolic cost for walking, also called the "economy” of walking. Prior studies have found a worsening economy with walking as people age. The authors of this study cite prior research showing a decreased muscular efficiency — perhaps even a greater firing of antagonistic muscles — with walking that may be related to this decline in walking economy. It isn’t too difficult to imagine, then, the connection with activities of daily living such as balance, transfers, and fall risk. Prior studies also show, again as cited by the authors, that older runners have a similar running economy to younger runners, but it is unknown how older runners compare to older walkers when it comes to walking. This, then, speaks to the utility of intensive training regimens to mitigate the decline in walking economy. This trial was designed to shed some light on the physiology of walkers vs runners when it comes to economy of walking.
Thirty volunteers were solicited (see Table 1), all of whom were 65 years of age or older, in line with a median age when a decline in walking economy often occurs. All participants either walked or ran 30 minutes at least three times per week, for at least 6 months before the inception of the study. Study participants attended three sessions, as detailed in Table 2. In short, the metabolic rate for each study participant was measured at rest as well as three walking speeds on a treadmill. The three speeds were 0.75, 1.25, and 1.75 meters per second. As a reference, the middle speed corresponds to 2.8 miles per hour, a relatively brisk walking speed. The metabolic rate was calculated by measuring the rates of oxygen (VO2) and carbon dioxide (VCO2) consumption. Further calculations included ground reaction forces (from settings on the treadmill), metabolic power consumption (from oxygen and carbon dioxide usage, and body weight), and gross metabolic cost of transport (metabolic power consumption divided by speed).
The researchers found runner vs walker differences. For example, gross metabolic cost of transport was 7-10% less in runners across all walking speeds (P = 0.016), even though the standing, resting metabolic rates were similar. Statistics showed that this difference was not due to gender, nor stride variables and kinetics such as stride time and swing time. However, the stride length in runners was 6% less than in walkers (P = 0.33).
The researchers then tapped into a database of similar data encompassing people of different ages, and compared the gross metabolic cost of transport, again the gross metabolic power as a function of speed. They found that older walkers consumed energy at a rate similar to older sedentary adults (P = 0.46), older walkers consumed energy 14.22% faster than young sedentary adults (P < 0.001), older runners consumed energy slower (percentage not supplied) than older sedentary adults (P = 0.016), and older runners consumed energy similar to young sedentary adults (P = 0.237). The authors postulate that these findings show that older walkers are unable to stop the deterioration in metabolic cost of walking because they have the same gross metabolic cost of transport as older sedentary adults.
We are all aware of the epidemic of sedentary lifestyles in the United States and the guidelines that exist to change that. Clinicians have tried the "exercise prescription” and attempted to nudge patients toward the 150 minutes per week of moderate-intensity exercise oft recommended.1 But, is all exercise the same for all people? And, what about for older adults who are particularly at risk for the adverse effects of waning strength and mobility? Some recommendations tailor exercise suggestions for specific demographics, such as for those people trying to lose weight.2 There may also be benefits to more vigorous activity when it comes to overall health and longevity.3
This trial, although small and with important gender differences between the two groups, seems to provide some support that there are benefits to a regular running practice in older adults. Adults older than age 65 years who ran at least 30 minutes three days a week had less metabolic cost for walking than their walking counterparts. This improved metabolic efficiency protected them from the age-related decline in "walking economy,” keeping the runners like young (sedentary) adults, whereas older walkers followed the same downward trend in efficiency as older sedentary adults. The authors tie this research into work showing that intense training in older adults can increase muscular efficiency and stop antagonistic muscle firing, two of the mechanisms that are thought to be related to making runners less metabolic cost for walking. So, it seems, this study showed some quantifiable clinical effects, and there was a plausible mechanism, perhaps enough for clinicians to raise their eyebrows and give this serious consideration.
Of course, as the authors mentioned, this trial should be expanded in size, and its methodology improved (beyond simply a cross-sectional analysis) to definitively change the way we approach exercise recommendations in this demographic. Until then, it is a reminder to continually address this aspect of whole person care; to reiterate the importance of some form of activity for all patients; and to explore that an increased intensity, when it can be safely done, may have some benefits for older adults above and beyond walking.